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Evidence that the key assumption made in discovery of dark energy is in error (phys.org)
486 points by apsec112 on Jan 6, 2020 | hide | past | favorite | 286 comments

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past.

The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of the spectrum: redshift. (Think of the wavelength of a wavy line drawn on a piece of rubber that's then stretched out.) We've known for nearly 100 years that the universe is expanding. (Edit: not just that the objects in it are moving apart but that space itself is expanding.)

The evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do. That means they were moving away from us slower in the past, so something must be accelerating them.

We use the brightness of Type Ia supernovae to measure distance. Even though supernovae aren't identically bright, their brightness follows a curve which lets us calculate their peak brightness (they are standardizable).

This paper argues that the calculations cosmologists use to standardize supernovae brightness fail to take into account the age of the progenitor stars, as far as I can tell. If true, this means our distance measurements are inaccurate and these stars are actually closer than we thought, enough to restore to linear relationship between distance and redshift that one would expect in a universe expanding at a constant rate.

In other words, their redshift is lower not because the expansion rate of space was lower in the past, but because they're not as far away as we thought they were.

Speaking from the pov as a former astrophysicist, that definition of redshift is not quite accurate.

While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity.

The Universe is expanding at every known point at the same time at the same rate. However, this is only an observable effect over > 10 Mpc of distance (e.g. extra-galactic distances). This is far too large to effect a point particle like a photon no matter how far it travels so I'm afraid your analogy of a rubber sheet is incorrect.

The lengthening of said photon's wavelength comes instead from doppler expansion due to the nature of differing relativistic reference frames.

According to our local reference frame, doppler effects of nearby stars and galaxies are only due to local motion such as Andromeda being blue shifted as it approaches us for our eventual merger. However, as you go further and further out from our galaxy the metric expansion of spacetime begins to dominate the relative motion of all bodies, leading to observing progressively redder and redder light curves. A galaxy billions of light years away is perceived to be moving away from our reference frame at a significant percentage of the speed of light!

However, if you were to change our relativistic reference frame to match a distance galaxy's you would not see its photons "stretched out" but in fact they would look completely unshifted despite having traversed nearly all of spacetime, expanding as it went.

> The Universe is expanding at > every known point at the same > time at the same rate

This part I don't get (I am in no way versed in astrophysics).

If I am in a box, and that the box grows 10%, but that at the same time I grow 10%, what has changed?

I mean, if every point in the universe expands at the same rate at the same time, what does it change? Relatively speaking, everything is the same size before and after expanding right?

It feels a bit like expanding a 1 meter line and expanding the meter standard the same rate as the line.

If anyone has an explanation and is willing to spend some time writing it down, I would be most grateful :)

This itches my brain ^^

So, imagine the box is filled with hydrogen gas. The space inside the box gets bigger. But protons don't, they're little packets of quarks that hold each other very powerfully. You'd have to expand space very, very, very fast to rip those quarks apart from each other, and once you did, you would have a bunch of bare quarks, not hydrogen. The quarks aren't getting bigger, since they appear to be indivisible and essentially pointlike, and even if they were made of something smaller, those things will hold tight to each other, too. A nice gentle expansion will just expand the space in between the protons.

This scales up to forces in between atoms, molecules, and bits of matter. It's only at the very large scales (larger than galaxies) that all the forces that are holding the stuff together starts getting overwhelmed by the expansion of space and it starts to pull things apart. The expansion is so gentle that even relatively weak gravity can hold galaxy clusters together even as space grows.

In other words: space gets bigger, but matter doesn't. It more or less stays the same size.

Thanks for this reply. I guess I now understand what people mean by "space is expanding".

If I understand correctly, space is what supports matter? Like a table supports dishes for instance (well, except that space is also "inside" particules) — and so if the table grows, the dishes don't.

I never actually even thought of what "space" means before. I thought that when we talked about space, matter was included in that (in the sense that quarks or whatever is the smallest — known? — particle take some "space" ; they're not points that can't be measured — or are they? ^^').

Anyway, it sparkled back an old interest of mine for astrophysics (well, I read one book from Hubert Reeves when I was a kid — and loved it).

Thanks again :)

(oh, as an added bonus: I guess we have no idea _why_ space is expanding, right? Because, I mean, it's a bit mind boggling...)

Edit: to be a bit clearer; I thought space was just void that "always" existed and extended indefinitely. Like, there was nothing except a small point with all the energy in the universe ; "everywhere" else a bit nothingness. Then, bim, the big bang, and matter was just booming away and making stars and planets and then galaxies and all that was just floating in this void/nothingness that was always there, never changing, still extending indefinitely. And that was why we were saying the universe was expanding — because galaxies were still speeding away from each others due to the big bang ; like an explosion with no friction perpetuing indefinitely. Now I guess I'm really confused about what "space" is...

Quarks and electrons act like they're actually points. Nobody can be totally sure, but the standard math says they are, and nobody has managed to smash them apart into something smaller or measure them as anything other than "smaller than anything we can measure." They might be small loops of energy instead (this is part of string theory), but if they are, they'd be so small it would be beyond known science to prove it. It's easier to prove something has a size (by measuring it) than to prove the opposite. Every instrument has some margin of error, so you'd never be able to exclude there being some size.

The weird thing about the Big Bang is that it's really all of space that banged, and to a first approximation, space and time as we know it didn't exist before a singularity at the beginning of the expansion. It's very possible that's wrong (there may have been a "parent universe" or a "big bounce") but to a first approximation it seems to be that there may not have been a "before" the Big Bang.


Space is filled with virtual particles that are constantly popping into and out of existence. As space expands, do these particles keep appearing in a given volume at the same rate? Or is the density of virtual particles declining as the volume of space increases?

Well so in other words "space" is NOT expanding. It's particles of matter that are moving away from each other. Right?

So fine, but then why would we say that space is expanding, that would seem to imply we know there is some edge of space which is moving away from us, but what evidence do we have that space has such an edge?

Saying that "space is expanding" seems to hold the assumption that space has a (limited) width and height.

No space really is expanding. Think of it this way: You have a rubber band and you pull it apart, if you place two beads on the rubber band the distance between the beads will increase (even though they don't move relative to the rubber). But if you connect the two beads by a strong spring, then their distance will stay the same, despite space expanding. The force of the spring makes them move (relative to the rubber), counteracting the expansion of space between them.

> relative to the rubber

This makes me uneasy about your analogy. It’s like saying “relative to space” which is nonsense. Also, why would space limit itself to only expanding outside a physical body?

It does not. It expands at every point in spacetime. This effect is quite literally negligible on all length scales smaller than far extra-galactic distances.

It is equivalent to asking why a car driving towards me does not turn blue due to doppler shifting. Except even more negligible than that.

I never said it is only expanding outside. Also moving relative to space is not nonsense. Motion is not just relative to other objects in space. This what Newton's bucket thought experiment showed.

Edit: the pearl is made from around bound by electric forces, so you can repeat the same argument for inside the pearl. You can repeat it all the way down until you have to admit that the approximations inherent in the concepts useful to describe the world at distances from nano meters to mega parsec eventually break down.

> Also, why would space limit itself to only expanding outside a physical body?

It doesn't, it's just that the forces within the body (the spring in the analogy) are stronger than the expansion.

The "relative to space" bit is the nonsense part of their analogy, but I'm not sure of a clearer way to describe things than what they did. It's not my field.

Maybe a better way to phrase it would have been moving over the rubber/space? Or through the rubber/space? It really is motion relative to the underlying manifold though. Let's say there was such a thing as a gravitational soliton, that is, a stable ripple in spacetime, then if you are on the same spot as this wrinkle as expansion starts you will move away from it. You move relative to a structure made from spacetime. This was my field for many years. :-)

The mathematically precise statement is that you are not moving on a geodesic. You are therefore experiencing acceleration (the objects that are not bound and have increasing distance are on geodesics and do not experience acceleration).

You can't make an electron bigger, so it can't be stretched out. Other point particles are the same. The forces that hold physical stuff together are much more powerful than the gentle expansion of space, so we don't see people and planets dissolving.

Indeed you can, if you realize that the place occupied by the "point particle" is described by its wavefunction.

I know! But when you poke it, it still acts like a particle and the wavefunction localizes again, right? It doesn't exactly "puff up" like a billiard ball. Electrons don't really get bigger when they are put into states where their position is less localized.

But the expansion of space does "stretch" light- or at least, the wavelength gets longer, so it's not not happening.

Such counteract action will make lot of side effects, which can be measured. For example, trajectories of separating or oscillating bodies will be slightly curved. Do you have any experimental support for this theory?

This isn’t Certhas’s personal theory. It’s part of standard cosmology, called the metric expansion of space. That term should get you pointed in the right direction if you want to learn more about the evidence for it.

It's too complex to explain, I will not understand it. Right?

It's not, but it might take more work than reading a few HN comments.

The effect of the expansion of the universe on bound systems is far to small to be observed. Two objects 1 meter apart would move at a speed of 10^-17 m/s. Utterly unobservable. But we know space is expanding by looking at things that are super far away from us and that are not bound.

Any objects? So it's independent of mass?

It's independent of mass because it's just a little extra space being created everywhere all the time. It's not exactly a force. First, there was 1 meter between them. Now there's 1 meter and a tiny bit more. The amount of space being created is, in theory, the same everywhere. It's not a repulsive force- space is just being created.

It can actually end up making things very far away appear to move faster than light away from us, since there's a lot of space in between.

Yes, any two bound objects will do so, irrespective of their mass or anything else.

We can directly measure distance to stars which are near us, using trigonometry and waiting half of year for Earth to make half of distance around Sun. Distance to thousands of stars is already measured with ±5% precision.[0] Yes, it's true that at least some stars, which are near to us, are moving away from us. However, it can be explained in number of ways, without inventing of Bing Bang or other epic events.

We cannot measure distance to super far away stars directly. Period.

10^-17 m/s is very high speed. Distance to Moon is 0.385E15 mm, and it can be measured at sub-millimeter accuracy, so this effect can be spotted. However, it will violate Conservation of Energy principle: no force applied, but job is done.

0: https://www.youtube.com/watch?v=i6GhsYrU5WQ

What's your point? Do you want me to explain the basics of GR and Cosmology, including the vast amounts of evidence we have for everything in HN comments? Do you think you are pointing out subtle errors in reasoning that none of the tens of thousands of physics students since the early twentieth century spotted?

You don't have the decency to try to learn the basics but presume to lecture me/expect explanations? Take a course. Show a little humility. Even reading Wikipedia thoroughly would have informed you that it's galaxies, not stars that confirm the expansion of the universe. The expansion (not the acceleration of the expansion) is beyond doubt. Conservation of Energy is not a priory defined for the question at hand because in GR you can not just add the energy at different points in space.

Measuring the perturbation to the moon's trajectory from expansion would require knowing all parameters that enter the trajectory to this accuracy, not just the average distance.

This is all basic if you want to learn, but you seem to have a different agenda...

I'm trying to point out, that current evidence can be explained in different way: by kind of Tired Light Theory. TLT plays well with Pilot Wave Theory and it doesn't need epic events in the past just few galactic hours ago. I'm familiar with evidence used by expanding Universe theories and with problems in them.

TLT predicts that value of "Speed of expanse" will be different when measured using different methods or frequencies, and it is: https://en.wikipedia.org/wiki/Hubble%27s_law#Measured_values... .

TLT predicts that there is much more stars, but we cannot see them yet because they are too dim, but more powerful telescopes will be able to pickup them. https://en.wikipedia.org/wiki/Tolman_surface_brightness_test https://www.nasa.gov/feature/goddard/2016/hubble-reveals-obs...

TTL predicts stars and galaxies older than BB (because of no BB), and they are found: https://en.wikipedia.org/wiki/List_of_the_most_distant_astro...

TTL predicts that Cosmic Background Radiation is just radiation of distant objects with Z=1000 .

And so on.

In short, mainstream theories doesn't hold against new data.

Number of red dwarfs is really astonishing: https://youtu.be/LOJ1XmbSKhM?t=1125

Tolman surface brightness test now looks much brighter. ;-)

So yeah, your agenda is not to learn or discuss but to push falsified fringe theories, that were exhaustively discussed until the eighties, when better data ruled them out...

Yep. I was too young in eighties to participate in these discussions, so I can read about them only, and watch some lectures, which is not satisfying enough for my curiosity.

Can we discuss something easier?

Why you think that photon is immortal? Why we have rule of right hand in EM? Why we see star formations older than BB? WTF is "physical vacuum"? What is waved by gravitational waves? What is happen in linear Sagnac interferometer? How photon is formed (it requires FTL to form)? What happens in double slit experiment? And so on.

Have you tried reading the papers from the period? for the rest, enroll in a physics course and try to not fall into the conceptual traps that even many that have studied and taught physics have fallen into.

Nothing is hidden, but it does take time and persistence.

Photons are not "immortal" they can decay if they have enough energy. Rule of right hand is a convention, could be left hand if you define the sign of charge differently. We don't see star formation older than BB but early universe physics is not easy to understand and there are lots of model uncertainties. Physical vacuum is what remains when no excitations are present. Gravitational waves are ripples in space itself. I don't understand what you mean by photons being formed.

You can not expect the concepts and intuitions that you formed by interacting with the macroscopic world to serve you well when thinking about the microscopic and fundamental. People used to think that you need some type of material aether that carries the waves of light. But that turned out not to be concepts that map well to reality. It took decades to learn to unthink these concepts, there is no shortcut to doing so yourself.

If things were moving away from each other, there would have to be something that set them in motion away from each other. What made all far apart galaxies appear to move away from each other?

Expanding space doesn't necessarily imply edge of space. What if your universe isn't flat, what if it's a torus? It could hypothetically have a finite volume but no edge.

There's also no reason an infinite universe couldn't have local expansion everywhere.

Space is expanding but gravitational attraction and other forces are many orders of magnitude stronger on short distance. While the space within the box expands the forces that attract molecules of the box are such that it will not change its shape until the expansion gets much, much stronger.

Think of the changing pressure. If the box is tight and rigid and the pressure outside the box increases, the box will roughly stay the box until the pressure overcomes the the forces between the molecules that build the walls.

Same with space. If you could measure, the increase in the volume of space would put a constant pressure on every molecule to try to rip it from other molecules. The fact that the rate of change of space and the distances between molecules are so small means that it is not evident that it will ever be possible to devise an experiment to show this on very short distances.

We can only see this on very long timescales and between objects that are very far from each other because all other forces on those scales have diminished so much that only then the increase of volume of space can dominate.

Every cosmologist since Hubble who has held that space is expanding, no, they don't assume the universe is finite. The opposite, in fact.

Specific volume is increasing. If space was finite (but still without boundary - think eg surface of a sphere), so would total volume.

Your interpretation of the expansion is incorrect. Basically, it looks like all points are moving away from each other over large distances.

It is easier to understand in 2D: Imagine a deflated balloon with two dots drawn on it. When you inflate the balloon, its 2D surface increases, which results in the two points "moving away" from each other, without either of them actually moving. It‘s just that the surface on which they lie grows. This is also the reason why distant galaxies are getting more distant faster than the speed of light: They are not actually moving, but the space in between us and them grows.

Notice that the farther two points on the surface of the balloon are apart, the faster they will appear to be moving away from each other, which is why the effect is unnoticeable over small (in astronomical terms) distances. Gravity pulls things together much faster than space expansion pulls them apart.

Bringing this back to your example: Imagine "blowing up" the box. Things inside it are growing a little bit (but gravity pulls them back together), but everything seems to be moving away from everything else.

What's still not clear is how I know the other point on the surface of the ballon is moving away from me? I measure it as 9 tick marks away. After inflation it's still nine tick marks.

That is to say, what is my ruler that is untethered to the surface of the balloon?

Your ruler is absolute distances, like the speed of light. You can inflate or deflate the balloon and the number of marks on its surface won't change. But the time required for the light to travel between them will.

Stupid question - How do you know for certain it isn’t just that light is slowing down?

Relativity probably doesn’t work this way at all, but if light did actually slow down, would it be perceived by us as light moving at the same speed across a greater distance?

I asked Ann Nelson (look her up) this when I audited her cosmology class in grad school, thinking I'd come up with a great new idea. She said yes, it's equivalent to the speed of light changing, and then moved on.

Bear in mind that time is not universal. For the speed of light to change over time, it would change at different rates for observers in different reference frames, and this difference would be measurable.

As to the previous question about relative size. If the universe doubled in size, the objects within it such as atoms don’t also double in size. Gravity and the atomic forces don’t change, so eg the size of stable electron orbits or planetary orbits don’t double in size.

Not exactly. Remember, we're not timing the light's transit. We're observing a redshift of it's frequency which could not be caused by c simply decreasing over time.

It's incorrect to think with this analogy. There is no ruler reaching across the universe, growing with it.

It is not the meter that is growing, that's impossible. Instead you must see it as it is, which is that there are more meters continuously appearing in all of space.

I think physical forces (electromagnetism, gravity, strong/weak nuclear) probably become weaker even though your metric (9 ticks) stays the same. I'm just guessing here, that's the only consequence I can think of.

> looks like all points are moving away from each other ...

Do you mean all particles are moving away from each other? I think the question here was what would it mean for "points" to move? What are points anyway?

The analogy was dots on a balloon, and the next sentence used "points" instead of "dots" but meant the same analogy.

A point (in space) is something that could be occupied by an object.

It boils down to this: You take a bowling ball, and put it 1 meter stick away from you at zero velocity compared to you. Assume that at this distance, no forces are exchanged between you and the ball. You wait a billion billion gazillion years, take your meter stick again and measure the distance between you and the ball, and notice it is now 2 meters away. It is the distance between you and the ball that has grown.

Note that the ball has not grown twice its size. The sizes of atoms and molecules have not changed (as they have mechanisms to keep them exactly the size they are, despite space growing). It is only when there are no mechanisms or forces to keep distances between objects fixed, they seem to drift apart very slowly. The question the article addresses, is whether that growth is accelerating or not.

My (limited) understanding is that only space is expanding. Iow there is more space but the space that matter takes up stays constant.

Maybe I'm also confused though

That's basically my lay-person's understanding also. It's because the expansion isn't significant at small scales, so gravity and electromagnetism overpower it. This causes existing objects and clouds to effectively remain the same size [I have to assume that there's an effect, stealing potential energy at very small scales].

Gravity and EM are holding our galaxy, our Laniakea, our Universe. See https://www.youtube.com/watch?v=rENyyRwxpHo .

As I understand it, the forces that keep matter together are strong enough to counteract any expansion.

Unlikely, because expansion of space is equivalent to the slowing of light, as other commenters have mentioned.

Such heuristic explanations are distractions: Locally, gravitational effects (including spatial expansion) manifest as pseudo-forces and hence can be counteracted.

Think about drawing two circles on a balloon, one with radius 1cm, and the other with radius 2cm. the distance between the two perimeters is 1cm, but if we inflate the balloon so that the surfaces double, now the inner circle has a radius of 2, and the outer circle a radius of 4, the distance between the perimeters has grown along side the rest of all the lengths. That's my best understanding of the situation, I mostly do non-linear classical mechanics.

Who pumping the balloon? Where is source of this energy? Can we use this source of energy for our own needs?

We do not know why the balloon is inflating. I think "dark energy" is a form of energy assigned for being responsible for it, but other than the name I don't think we have reached conclusions as to what it actually is.

I am not a physicist.

My understanding is that the fundamental forces are strong enough to resist the local expansion of space.

So the box gets bigger but particles do not get ripped apart or themselves expand. Space is expanding. Not matter. The particles occupy the same space and the fundamental forces keep them together. Space just keeps moving and expanding around them.

This (coupled with the fact that, at least currently, the expansion is happening very slowly) is why the expansion isn't observable unless you're looking at a very large scale.

This makes me wonder whether we would be able to tell the difference between the universe getting larger and matter in the universe getting smaller.

Someone has published that idea a few year ago https://news.ycombinator.com/item?id=19588996

I think it's more a mathematical trick than something deep about the universe. If you tweak the change of the universal "constants" correctly in a universe that doesn't expand, it is equivalent to a universe that expands where the "constants" don't change.

Note that there is some research about the change of the universal constant, but in most models they don't have just the rights values to make the universe look like expanding. https://en.wikipedia.org/wiki/Time-variation_of_fundamental_...

One thing I've never understood is this.

How do we tell the difference between the expansion of space and the dilation of time?

Given that space and time are crudely specking intertwined (spacetime) how do we know that the effect we see -- redshifting -- is due to the spatial expansion at every known "point" and not the temporal expansion (contraction?) at every known moment? Could not the spatial size of the universe be constant and its "clock" be being distorted?

Relativistic frequency shifts can be understood as kinematic effects, namely orientation of photon 4-momentum relative to emitter and absorber 4-velocities.

Now, spacetime geometry might be such that there exists space/time decompositions that allow us to attribute the shift to specific physical effects (relative velocity of emitter and absorber in case of special-relativistic Doppler shift, time dilation in case of gravitational shift in Schwarzschild spacetime, spatial expansion in case of cosmological shift in FLRW spacetime), but from the perspective of spacetime geometry, these are just specific instances of a general mechanism that is agnostic to such attributions.

Don't take this the wrong way.

If you can't explain what's in your head in plain English in answer to a question that was asked in plain English then there's not much point in answering.

I'm not getting the impression that you've answered my question, I'm getting the impression that you don't know how to answer my question.

I'll try again:

General relativity comes with a generic mechanism to compute frequency shifts. We don't need to try to figure out whether or not the effect is due to time dilation or spatial expansion, we can just do the math. But if we're lucky, we can find a way to split up space and time that allow for such intuitive interpretations. However, that's window dressing, so to speak.

All this assumes that the spacetime in question is already known, but that's how it actually happened historically: Friedmann and Lemaitre derived their solutions by imposing certain symmetries on the problem. From that, you can derive observations like redshift (Lemaitre had already done so by 1927, ie two years before Hubble published his paper), which you then compare to observation in order to fix the parameters of your model, or scrap it if it cannot accomodate observation.

As far as I'm aware, at no point in time did a physicist sit down and think "I wonder, what's the best way to incorporate redshift into my model, time dilation or spatial expansion?".

Much better!

Now, if there is a failure to understand your answer the reason why lies with me :)

If this temporal expansion or contraction produces redshift in the exact same way, and you can fit it into Relativity with the appropriate math, well, six of one, half a dozen of the other — until such point as we understand some discrete mechanism underlying the operation of the universe that would be affected by the expansion of one rather than the other: minimum time steps, minimum distances, proceeding from individual bits, increments of information. (Such a thing is theorized, but observing it is on no one's radar today, so good luck.)

(If it doesn't fit, then it's just wrong.)

If this is an accurate conceptual model: https://www.esa.int/Science_Exploration/Space_Science/What_i...

I have this odd notion that the universe has stayed the same "size" (since inception) and that the parameters of the universe and the amount of matter/information has changed over time.

The impression we get (from our perspective) is that of an initial singularity, a period of hyper inflation, and then the expansion we have now.

Probably bollocks but I'd like to know why it's bollocks.

That's the same thing that's always bothered me. That physicists never seem to discuss global time dilation - which also to my layman's eyes seems like a simpler explanation.

Time everywhere is slowing down (speeding up?) Which it's why the expansion of space seems so perfect to neither accelerate nor decelerate.

Thank God there's someone else. I mean, to me, the idea is so moronically obvious (I had the idea about 15 years ago) that there must be some obvious answer why space-boffins insist that it's space that's doing the jiggling rather than time -- even though we've been told that since Einstein we ought to view the dimensions we inhabit as the spacetime (time is just another dimension) continuum.

My gut tells me that the layman's model I have of the universe precludes me from having a handle on why the idea is dumb. I console myself with the knowledge that at least I'm not so dumb that I think the idea is l33t and the whole scientific community are morons. Still, it'd be nice to have an answer.

Seems like a very detailed yet approachable explanation, wondering about your thoughts?


Pretty interesting video. The big takeaway is definitely the end where he talks about the reality of the scientific method.

Unlike math, you can never prove that something is correct and true. You can only prove that reality likely does not fit a given theoretical model to a vanishing probability. The models we have, we only have because they have not been proven to have a vanishingly small likelihood of explaining physical phenomena.

Btw, this is what frustrates everyone about string theory. It's mathematically correct and quite elegant, but extremely difficult to gather any observational data that could prove it unlikely or another theory unlikely compared to it, leaving it in a sort of scientific limbo.

Astrophysics is hard because it is an observational science only. You cannot run your own experiments so you must simply gather as much observational data as possible. It is really, really hard to gather significant data about the universe at the largest scales. The video talked about hundreds of observations, but in a universe with more whole galaxies than grains of sand on earth there are implicitly a huge number of assumptions about how representative any data set is.

The numbers in astrophysics are so mind-meltingly enormous that often unimaginable and unintuitive consequences become regular occurrences.

This new data should obviously not be ignored, but it also shouldn't be interpreted as "disproving" anything. That is journalistic attention grabbing. Rather the results are simply some experimental physicists saying to theoretical ones: "here, look at these interesting new data about important data sources. It reduces our uncertainty about one specific thing. Please incorporate this into your cosmology theories"

> The Universe is expanding at every known point at the same time at the same rate

No, it's not. The (local) metrics sourced by the Earth, Earth-Moon, Sun, solar system, Milky Way, and the Local Group are not at all like FLRW with or without a cosmological constant, while all those metrics are very much like Kerr or LTB, wherein ordinary matter like gas and dust gradually condenses into a point. Conversely, the metric globally is very much like FLRW with a small positive cosmological constant, and very much unlike a spacetime in which matter condenses into a point.

We can use Israel junctions to knit together "stacks" of regions that are well-approximated by a Kerr or LTB metric, and ultimately knit galaxy cluster sized LTB regions into expanding FLRW, representing the LTB regions as dust particles. This matches observations very well, and is called a "swiss cheese" cosmology, the name arising from how gravitational collapse ultimately creates voids -- holes -- in the otherwise homogeneous diluting dusts.

Kolb and others have a decent overview of how an Einstein-de Sitter-Lemaître-Tolman-Bondi swiss cheese universe works (the paper is in the context of the homogeneous-vs-inhomogeneous+backreacting cosmology debate, which is largely about connecting theory with astrophysical observations of a somewhat lumpy real universe especially in the transition from the matter-dominated era to the dark-energy dominated era) : https://www.osti.gov/biblio/21023997-cosmological-observable... ( PDF https://archive-ouverte.unige.ch/files/downloads/0/0/0/3/6/5... ). There's a good textbook treatment in Harwit's _Astrophysical Concepts_ as well (a preview exists at https://books.google.co.uk/books?id=gZfuBwAAQBAJ&pg=PA516&lp... ), and MTW has a (not very easy) overview of Israel-Darmois junctions in §21.13.

Such swiss cheese models match observations so well that it would be surprising (in a cool way) to find that there is any metric expansion at all in our solar system or in any of the galaxies and galaxy clusters we observe on the sky. We don't see that, though. In particular, one should take into account the evidence for accelerated expansion over the past few decades. Given that, one can consider a "fifth-force" (or nth, given Higgs etc.) representable as a field with a density and gradient, rather than the purely geometrical scaling in \Lambda-CDM. (This is at the root of some quintessence projects.) Results usually involve a lot of dynamics to suppress cosmological shear and other "little rip" effects at the margins of clusters with highly-luminous components, and adding several degrees of freedom that lack other physical support seems a lot worse than accepting an Einstein-de Sitter like swiss cheese geometrical model.

> local reference frame

It has nothing to do with reference frames; the metric tensor focuses matter and light one way or another (cf. Raychaudhuri) and within galaxy clusters practically all matter is focused towards a point in the future, whereas globally the same matter, and all other matter, and light, focus towards a point in the past (and the future focus points within galaxy clusters do not themselves focus together in the future). The only requirement is that the manifold is Lorentzian and time-orientable; you can use any system of coordinates that an arbitrary observer carries around with it, and you only need to do that if you care to describe when in the past or future and/or where relative to an observer the focus points lie.

> ... to match a distant galaxy's ...

How do you propose to do that? I think it's worth it for you to think about that a little: does your conception of a frame in which \lambda_{obsv} = \lambda_{emit} (rather than 1 + z = \frac{\lambda_{obsv}}{\lambda_{emit}}) extend into the distant past and distant future? How accelerated is this z-suppressing frame? In this frame what's the expectation for the wavelength of a CMB photon over time, or for galactic and extragalctic H I lines ?

> doppler expansion due to the nature of differing relativistic reference frames

Kinematical interpretations fall apart really spectacularly at high z, and conveniently we have a probe of (6 > z > 1) in the https://en.wikipedia.org/wiki/Lyman-alpha_forest which is a challenge for constructing a sensible z-suppressing frame of reference.

(See also MTW §29.2)

Kinematical interpretations fall apart really spectacularly

I disagree: Relativistic frequency shifts (doppler shift, gravitational shift, cosmological shift,...) can all be understood kinematically:

The invariant quantity you have to consider is photon 4-momentum, with energies at time of emission and absorption given by the projections onto the 4-velocities of the respective observers, so it's all about the relative orientation of some vectors, ie kinematics.

If spacetime is flat, photon momentum is constant, so all that matters is the relationship between emitter and observer frame. However, in curved spacetimes, there's no distance parallelism, and photon momentum at time of emission and absorption will be related by parallel transport along the photon geodesic.

In principle, you could even view the process of parallel transport as a series of infinitesimal Doppler shifts, though I would argue that puts emphasis on the wrong thing (the arbitrary frames chosen along the geodesic).

I'm pretty sure we were talking about the ensemble of redshifts across the sky, rather than one particular photon. (Even in the single-photon case there will be lots of uncertainty about the \lambda_{obsv} vs \lambda_{emit} relationship; think in particular about its interaction with ions along the way. We'd want at least an "ensemble" of photons along the lines of a classical beam equipped with a spectrum).

I'm not sure if you are objecting to approaches like the tetrad formalism in your final sentence, or even to gauge freedom itself. There's no reason an observer -- even an always lightlike one -- can't carry around its own system of coordinates. People from ISS astronauts (LVLH vs ECEF/ITRF) to aerobatic pilots (LVLH/LENU to GPS) to pedestrians looking at map apps on their smart phones do that casually all the time, and nobody expects ensembles of objects to move with respect to each other as one swaps sets of coordinates. Setting a new coordinate system every few steps while navigating on foot through a complicated city core is perfectly fine, and so is setting up a new coordinate frame at every infinitesimal step along an affine-parametrized curve traced out by a photon. IMHO that is the core of relativity.

In arbitrary spacetimes, redshift has to be computed along specific worldlines, ie you tend to treat photons as point particles. I guess in principle, you could solve the Einstein-Maxwell equations (or more likely, the Maxwell equations on a fixed background), but I wouldn't recommend it. There are special cases which are simpler to handle (eg if your spacetime is static and you use adapted coordinates, the time coordinate will be cyclic in the particle Lagrangian, the canonically conjugate energy will be conserved and redshift will be given by the quotient of the roots of the g_{00} components, which formally comes in via normalizing emitter and observer 4-velocities).

I'm not sure if you are objecting to approaches like the tetrad formalism in your final sentence

The final sentence was just a comment on the pedagogy of deriving cosmological redshift via infinitesimal Doppler shifts. There's nothing wrong with it (sections of the frame bundles and all that jazz if you want to get formal), but to me, this feels like putting things on their head: I consider the Doppler shift a special case of the generic relativistic shift, making it circular to then explain the generic case as a series of infinitesimal Doppler shifts integrated along a photon's worldline.

However, if you were to change our relativistic reference frame to match a distance galaxy's [...]

In general, you can't do that: There's no distance parallelism in curved spacetimes...

Well, curved spacetimes only matter when you're dealing with gravitational redshift, which we aren't in this situation.

Why would you think that? FLRW spacetime isn't Minkowski space, thus has nonzero curvature.

> However, as you go further and further out from our galaxy the metric expansion of spacetime begins to dominate the relative motion of all bodies, leading to observing progressively redder and redder light curves. A galaxy billions of light years away is perceived to be moving away from our reference frame at a significant percentage of the speed of light!

Is this not because there is simply more space between things that are farther away and therefore more expanding space? So, more space = more magnitude of expansion?

I think that's exactly the idea. But if space expanded at the same rate everywhere and forever then the relationship would be linear. But it seems that further objects seem to be moving away slower than linear relationship would suggest which might mean that earlier space expanded slower.

But that doesn’t make sense. Here space expands n. Go a distance d away and now you have nd! So if we were to integrate the summation of nd!+V (velocity vector) Spaces, wouldn’t the relationship not be linear? You have an infinite amount of points between A and B. Each point expands at v. Each time point pk+1 is created you are introducing a new expansion that will then add as many expansions as are vector / dimensions at play.

I know my maths is not very accurate and maybe you can help correct my understanding. It just seems adding up each point that creates even more expanding points would never be a linear function.

I’m literally describing creating more flow lines which would cause an exponential growth in acceleration measured without really exceeding certain values.

Don’t understand the downvoted when I asked for more information and said my maths are probably wrong.

I am confused, as a lot of sources (e.g. [1]) make a distinction between doppler and cosmological redshift. When you say "change our relativistic reference frame to match a distant galaxy's", do you mean as that frame was when the photon was emitted, or as it is when it is detected here? (if that is a well-defined distinction under relativity?)

[1] https://calgary.rasc.ca/redshift.htm

So that source draws a line between cosmological redshift and doppler redshift that is so misleading I'd say it's wrong. They are in fact equivalent [1] and basically just depend on your reference frame.

Check out the wikipedia page on Hubble's Law [2] for more.

[1] https://arxiv.org/abs/0808.1081 [2] https://en.wikipedia.org/wiki/Hubble%27s_law

> However, if you were to change our relativistic reference frame to match a distance galaxy's

As a causal science enthusiast I am lost, how does one change our relativistic reference frame?

Consider yourself. Consider a galaxy N million lightyears away that is moving away from you at high speed...

Or is it really? What if it's staying perfectly still, and YOU'RE the one moving?

... How could you even tell?

The principle of Relativity is that you cannot tell any difference, for the laws of physics are the same whether you are moving or the galaxy is moving. The theory of Special Relativity describes which mathematical transformations you need to go from one description to the other (in the absence of gravity, which is a General Relativity concern). Philosophically, the way of unifying these involves mixing up Space and Time, in which various observers cannot agree on a single version of things like speeds and time and energy levels, into a unified Spacetime, which they all can agree on.

"Changing your reference frame" simply means picking something different that you consider to be at rest.

Calculate our speed against CMB. Calculate their speed agains CMB. Compare. It's easy.

... at which point you also get to enjoy your arrival at linguistic metaphysics. If you can identify all material objects that all observers can feasibly see, then you subtract the material objects that one person sees, from the material objects the other person sees in their reference frame, and you end up with... something... that is both a material object, and not a material object at the exact same point in time. So, does that material object actually exist? If so, in what way does that material object exists for the person who cannot feasibly perceive a feasibly perceivable object in any capacity? Kind of like theseus's ship launched into the space-time continuum?

> If you can identify all material objects that all observers can feasibly see, then you subtract the material objects that one person sees, from the material objects the other person sees in their reference frame...

Generally speaking an event is "observable" if some signal (usually light) could reach you from that event. It is generally uninteresting that different observers can see different sets of events at different points in their world-line. If you are lightyears apart, the signals will take time to reach you. This is what "spacelike separation" is all about.

But if you just sit around in one spot, signals can reach you from billions of light-years away. A certain event in your history might have been separated by space, but a point in your future may be separated from it in a timelike manner. You can't get away from events by simply going fast, either: the velocity addition makes signals impossible to outrun. What you need is to employ acceleration.

Consider a modified Zeno's paradox: you are 1 light year away from a signal, and begin accelerating. By the time it has covered 0.5ly, you are now 0.75 ly away. Unlike the original paradox, the math on this one works out: it is the acceleration equivalent of a black hole. (Most gravity and acceleration effects are interchangeable like that).

We could draw this out with a Minkowski diagrams, and find some line beyond which events become truly unobservable. We could call this line the "event horizon" (which, after all, is what the term is about in other contexts, too.)

Clearly it exists to them because it can interact with someone they can interact with.

An unseeable material object does not cease to exist, even though it cannot affect us.

Big rockets. Or something like that.

If I am reading this correctly, in plain English what it seems like they are suggesting is that old Type Ia supernovae worked differently from newer supernovae; e.g. that a Type Ia supernova 5 billion years ago had a different brightness curve than a Type Ia supernova from 50 million years ago.

On its face this seems like an extraordinary claim; I can’t think of how to square it with the (fundamental) assumption that the laws of the universe have not changed during its lifetime.

You're not reading this correctly. It's questioning the assumption that the Supernova are of the same brightness no matter the age of the star. Because the supernovaing stars are on average older now then they were in the early universe, there's a systemic bias in the data making it seem like there is red shift when there is not. No new physics required outside of a new understanding of how Type Ia supernova work.

Do the current models of dark energy not have it changing over time? Or at least allow for the possibility?

The idea that fundamentally, physical law does not change over time, is either a metaphysical or methodological assumption (or a bit of both), but it is certainly not an empirically-derived result, and it clearly does not rule out manifestations of those fundamental laws changing over time.

The issue is much more prosaic than the fundamental laws of physics changing over time. On average, very distant supernovae have a different composition than nearby supernovae. As the universe ages, more light element atoms are fused into heavier element atoms and expelled into space. That material is incorporated into the next generation of stars, so stars begin their lives with less and less hydrogen, as the universe ages. If that influences the light curves of supernovae, then it greatly complicates the use of supernovae as standard candles for distance measurement.

That's what is weird about this: from the paper, "Unlike population age, we find no significant correlation between host metallicity and Hubble residual". So it correlates with age, but not metallicity!

Thanks for the explanation, but I'm stuck on the last sentence of this part:

>evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do.

I think what you mean is "than we'd expect them to."

Right. They have the red shift we would expect to find in more distant objects than they seem to be, just based on how bright their supernovas are. But if the brightness is off, the anomaly might disappear. Or get bigger, all bets are off.

That's how I understand it.

But maybe there are other standardizable objects. The sense I got from TFA is that there aren't.

There are actually. There is a class of star in the "tip of the red giant branch" (TRGB) which have also been used to calibrate luminosities of type Ia supernovae[0] to form a "cosmic distance ladder". I believe they have been used to confirm the accelerated expansion results (though less strongly). I am not super well versed in stellar evolution, but I believe that the TRGB should make this calibration method independent of progenitor age? Hopefully someone could chime in on this. I was formerly a cosmologist and would be very interested to know more about this result from any experts that might be reading this.

[0] There is an explanation of this calibration here: https://aasnova.org/2019/07/26/tldr-the-trgb-gives-us-anothe...

Nope, the link is proposing TRGB-SNIa as an alternative to Cepheid-SNIa, not TRGB as an alternative to SNIa.

Yeah. In my reading, it almost characterized SNIa as fact.

Of course these could have the same, or a related, problem.

>To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us

May be a stupid question but wouldn't this apply only if we knew that the universe is uniformly dense? And we only see a tiny portion of it.

I'm not an astronomer, but "tired light" makes more intuitive sense to me to explain the redshift. In effect, we already know that matter can affect light through gravitational interaction. Since light is travelling so fast and far it seems intuitive thst interstellar matter, as fleeting as it is, could act to slow light down over these great spacetime distances.

Tired light is a very natural and intuitive hypothesis, it just doesn't work when you try to make it match up quantitatively.

This doesn't make much sense to me. The speed of light is a constant, right? Gravitational interactions may change the directional component, but the speed would remain constant, no?

It was expressed clumsily. The idea would be that photons can lose energy over time or space. One problem is that they would all have to lose energy at exactly the same rate as neighboring photons, so be a property of the space they are going through, not the photons themselves.

The speed would remain constant; 'tired light' would shift to longer wavelengths (redden).

Fritz Zwicky proposed the idea in 1929 - didn't work out. In 1933 he 'inferred the existence' of dark matter/energy, after using the averaged speed of a group of galaxies to calculate their mass ... and found they were producing too little light to have that mass. And there it sits a century later. MON Dieu!

C is constant, which is the "speed of light in a vacuum." Light can, and does, travel slower than C, e.g. when traveling through gas or other material.


Scientists have even managed to freeze light for short periods of time.


Constant in a vacuum. Read about https://en.wikipedia.org/wiki/Cherenkov_radiation

No. Gravitational waves are causing fluctuations of speed of light in pure vacuum. (See LIGO/VIRGO experiments). So c is constant in steady physical vacuum only, i.e. it's speed of EM wave in medium. If you will change properties of medium, then c will be changed too.

According to the Wikipedia article, "tired light" has been discredited due to lack of observational evidence and assumptiins about light scattering:


Light scattering assumption is invalid, this is true, so photon losses energy because of an other mechanism.

However, newer telescopes discovers more stars and galaxies than predicted by theories of expanding universe, thus favors Tired Light Theory. Also, discovery of gravitational waves confirmed that (speed of light in pure vacuum) c≠const, so physical vacuum is not an empty space, thus favoring TLT again.

It is hard to overstate how important the resolution of this question is to physics, and in particular to theoretical physics. The “cosmological constant problem”, that is the problem explaining the cosmological acceleration (if it exists), is arguably the most important and hardest question in high energy theoretical physics. Many theoreticians have spent significant effort studying this question, working under the assumption that the empirical evidence is solid. If this is not the case, it changes the landscape of cutting edge physics research.

There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration).

Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.

Do you know if these measurements were possible in the past, and no one thought of doing them? Or are they only recently possible, enabled by new technology?

What's more mind-boggling to me is all these thousands of scientists running around looking at the extreme oddity of multi-dimensional string theory, and nobody bothered to check if the cosmological constant is actually real.

It seems like physics is really being held back by perverse incentives.

And of course my pocket view that string theory will turn out to be the single largest waste of brilliant human minds in history.

I'm not a physicist, but I don't think string theory is a total waste. It agrees with our existing theories and predictions, so it can be viewed as just an alternative mathematical abstraction, and there is value in that.

Whether or not tiny vibrating strings are really at the heart of things is neither here nor there. It's about as relevant to science as god.

The problem with string theory is that there are limitless physics universes you can create within its framework so saying that ours fits in it is not saying a lot. Many universes could be described by it.

Good. Science is meant to be a honest search for facts: data, knowledge and wisdom. Being wrong is a feature. "I don't know" is an acceptable starting point with no shame attached. Being certain means a mountain of data to back it up. Being allowed to be wrong is a requirement. Anyone saying a scientist can't ever be wrong is likely placing oddball limits on progress that will only damage and limit the future[1]. How can you experiment if you can never be wrong?

It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain.

Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example.

Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed.

* not me.

[1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that.

[2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.

Dark matter is definitely not a rounding error [0]. There are multiple evidence for strong gravity effects where we just don't see the required matter the explain the observed phenomenons [1][2]

[0] https://www.forbes.com/sites/briankoberlein/2016/09/23/rotat...

[1] https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to...

[2] http://cosmology.berkeley.edu/Education/CosmologyEssays/Grav...

Briefly, dark matter is very real, it's our knowledge that is dark.

I'm feeling verbose. So here we go.

Dark matter: Maybe something that we'll one day make lunch boxes out of. Maybe also a rounding error. Of some sort. In some way. You haven't got the mountain-of-data yet. A lot-of-data is a good start. This doesn't mean the missing matter isn't some super-energy infused version of something we already know about. For all we know, its simply "ordinary" matter we'd otherwise already have accounted for but seen/detected in distorted ways due to some new phenomena altering our perception. So, its real as opposed to unicorn droppings[0]. But thats only a small part of the story.

Neither dark energy or matter exist as permanent fixtures, or even as just two singulars. They are placeholders while the search for the underlying phenomena continues. The moment the unaccounted matter/energy is discovered due to phenomena A, B, C, D, E, F then those two broad individual placeholders will be replaced with more detailed names, likely in honor of someone famous or otherwise noteworthy feature of the discovery, eg shape, some quantify etc. We'll go from "dark matter" to phenomena A,B,C to something1, something2, somestate3 or whatever.

People like saying dark[1] because it sounds cool, mysterious and edgy. Its the flair for the dramatic. This is fine for awhile as long as it helps. It is a mystery. But today its a big mystery and tomorrow its on someones balance sheet. There's a lot of tomorrows to allow that to happen.

Very important note: Our knowledge is not dark. Knowledge shines light over the unknown so we can see it for what it is. That is the whole point.

[0] I'm asserting for sake of argument that unicorns aren't real. Some could say that horses with a horn were hunted to extinction and we just haven't found a sample. Thats valid as well. I'd still prefer to see some evidence like a skeleton. But for now, I'll just assume for the sake of argument they don't exist and leave the real answer as homework for the interested[2].

[1] Dark. Or transparent. Maybe we are seeing through it instead. Plastic bags in water become "unaccounted for" and can visually disappear due to transparency. Some ocean creature could easily call that bag the equivalent of what we would call dark matter. Its got water in it and around it. Ordinary matter surrounded by something they don't understand. Hydrocarbons. In explaining it we'd mention the multiple processes and atoms responsible for the formation because we know how hydrocarbons are formed. And probably not just one thing. (No I'm not suggesting dark matter is hydrocarbons but I retain the option to ironically laugh if they are a form thereof).

[2] I know an 8 year old who is highly motivated to believe they're real and with enough skills at genetic manipulation she might make it happen. And apparently they eat meat. The small-hill-of-data implies we should be careful out there.

Unicorns are real. They're just call by a different name, Elasmotherium sibiricum [1], a now extinct species of rhinoceros that shortly co-existed with man.

[1] https://www.google.com/search?q=Elasmotherium+sibiricum&tbm=...

I consulted the relevant and qualified[0] unicorn[1] expert who presented evidence[2] to confirm this is all legitimate[3] so it is deemed[4] to be true[5]: Rhinos or mammoths can't be unicorns. There was mention about not being able to ride[6] them but that is not a convincing argument. Domestication of a more horse-like animal was the larger deciding factor.

That said I fully get how a mammoth / rhino could inspire and may actually be the real root of the folk story. While Subject Matter Experts[0] can be wrong the folk story now has its own definition[1] and physical evidence[2].

Sidenote: Now I know why Pratchett likes footnotes.


[0] 8 year old who has read everything about unicorns

[1] reference for the horselike resemblance https://en.wikipedia.org/wiki/Unicorn

[2] relevant toys and pictures presented as proof

[3] like a lot of political "facts"

[4] someone authoritatively says so

[5] or true enough, see [3], to meet perceptual expectations[1].

[6] rhinos can be ridden if you're suitably enthusiastic and are also able to run faster. Mammoths with horns were probably similar. This is logically not much different to how wild unicorns[1] would be so I'd not discount too much. The riding aspect is therefore a weak disqualifier.

I feel like comparing dark energy and dark matter is really disingenuous. Dark energy is a placeholder to explain a really bizarre phenomenon (which is now being questioned). Dark matter is something we can map the distribution of throughout the visible universe via it's gravitational effects. We even have plausible hypotheses for what kind of stuff it might be (WIMPs etc.)

And as soon as we know what it is and the phenomena responsible the naming will change. Especially when we find out its not actually "dark" and is instead x, y or z under a, b, c conditions.

This is one of the most important things I learned from Star Trek. The beginning of wisdom is "I don't know".


> Taken at face values, the luminosity evolution of SN is significant enough to question the very existence of dark energy. When the luminosity evolution of SN is properly taken into account, the team found that the evidence for the existence of dark energy simply goes away

Cosmology is great because there's still so much in flux. There are so many fundamental things that are still in active research. I find it all very exciting.

My exact thought was "Yaye for science!" I love that science has self-correction built into its core.

"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption.""

Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?

The question is moot: it's precisely because we have evidence of things not currently explained (observation does not fit theory) that we must postulate that our theory is wrong, or that there is more to discover, or both.

"Dark energy" is a conventional term to describe some energy of unknown source that has the effect of accelerating space expansion with time. We call "dark energy" the thing that explains this observation, whatever that thing might be (we just assume it's some form of energy since it produces motion, acceleration, in a way seemingly opposed to, and stronger than gravity, but for all we knew it could be fluffy creatures from the 7th dimension, "energy" is just an educated guess).

If you remove the observational discrepancy, then you remove the need for "dark energy" to exist in the first place.

The article precisely suggests that:

- there was no such observational discrepancy, rather errors in calculations following observation

- reality is thus shown to conform to our current equations; it's our interpretation of the pretty pictures we took that was wrong all along; this is now corrected.

If true, it's the end of dark energy as a cause because the consequence is gone.

At no point (before or after it's proven or disproven) does "dark energy" imply a postulate on "what it actually is" — and chances are, when we explain previously unknown phenomena, the finders come up with a new theory and ad hoc terminology. Rarely the word sticks when it's just too good an intuition — e.g. the "atom".

Note that "dark matter" is exactly the same, it's a conventional term to denote some matter-like unknown object that has the effect of giving galaxies their characteristic shapes and interactions forming much larger patterns (structure about as big to individual galaxies as galaxies are to individual stars).

It is my impression that dark energy is generally accepted in cosmology. Whether that counts as "proceeding as if dark energy is well evidenced" is perhaps a different question. If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there. That something should be evidence. Is it enough to count as "well evidenced"? Perhaps not, especially if this new study is correct that one piece of the evidence does not actually support dark energy.

I don't know of any other evidence for dark energy, other than that mathematical physicists think the equations would be prettier with some, although they sort of wish there was more. It is quite embarrassing that the value was so close to zero without being zero, so that might be one embarrassment less.

We already knew there was likely to be something fishy about the most distant supernovas, because we have two divergent values for the Hubble constant, one of them based on these same supernovas.

> I don't know of any other evidence for dark energy, other than that mathematical physicists think the equations would be prettier with some, although they sort of wish there was more.


Hmm. Is this new result in the right direction to solve the Hubble Constant problem?

Haha, it would be fun if we now have three Hubble constants.

my personal favorite value for the Hubble constant is the "c" divided by the age of Universe, it results in 70.8 km/s/Mpc, right in the middle of the other 2 established Hubble constant's values, a very nice coincidence that the objects at the Universe age distance are running away exactly with "c".

A coincidence? I think it might be an identity.

But that would mean that disputes about the value of the Hubble Constant are also disputes about the age of the universe, and vice versa.

Right, and that has been revised a few times recently.

>If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there.

The article stipulates what convinced these people that it was there, namely that they rested their conclusions on an assumption that turned out to be wrong.

This result is based on the assumption that the corrected luminosity of SN Ia through the empirical standardization would not evolve with redshift.

Which is another good reason not to make conclusive judgements based on unproven assumptions (not that everyone that "dark energy" must exist, but many did, and some people still cling to it even if the face of this study). It is also a good example of why one should never give credence to a theory or a supposition based on how many other people give it credence - stick to what you can prove.

As a frequent listener of cosmologists I'd say they regularly frame answers as dark energy were true.

> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?

I thought dark matter and dark energy are simply placeholders for a discrepancy we see between our models of the universe and our observations. No?

No - this article aside, most of the evidence suggests that this is matter that is actually there, not just an error term that we have added to our models.

This article is about dark energy, not dark matter. IANAC, but I think the evidence for the existence of dark matter is stronger than dark energy.

Yes, but the comment I'm replying to mentions dark matter.

it's my understanding that dark matter is another word for the indirect observation of matter that we can't otherwise detect, through gravity. I don't know if calling it a placeholder is the proper parlance.

Dark energy is something predicted by general relativity and iirc it's what is behind the expansion of space (and acceleration of expansion).

> Dark energy is something predicted by general relativity

Not really. GR can accommodate it just fine, but GR did not predict it. In fact, Einstein, who originally introduced the cosmological constant (which was the term then for what we now call "dark energy") in order to allow a static solution to his equation, thereby missed the chance to predict that the universe was expanding, a decade before Hubble's observations showed that it was. Once it became clear that expanding models matched the data, and did not (then) require a cosmological constant to do so, Einstein dropped it, calling it "the biggest blunder of my life". Only in the 1990s, when evidence for accelerating expansion became available, was the cosmological constant (now called "dark energy") put back into the equations so they would match the data.

> it's what is behind the expansion of space (and acceleration of expansion)

The expansion itself, no. The acceleration, yes.

How much would the fate of the universe page on Wikipedia change with linear expansion? Do we have a bit longer before the stretch?

I'm not sure what you mean by "linear expansion". If you mean that the rate of change of the scale factor with respect to time never changes at all, that is not possible except in the edge case of a universe containing zero matter or energy and zero cosmological constant. (This edge case is often called the Milne universe.) Which is obviously not the universe we live in.

If you just mean "no dark energy", i.e., the model that most cosmologists used before the 1990s when accelerating expansion was discovered, it wouldn't change the universe's long term fate very much. It would still expand forever and become more and more diluted; the expansion would just slow down forever instead of accelerating forever. There would be some differences as far as our observable universe--we would not eventually become isolated from all other galaxies and unable to see them--but that's about all.

This doesn't really address your point, but the 2011 physics Nobel [1] said that "What is known is that dark energy constitutes about three quarters of the Universe."

Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least.

1 = https://www.nobelprize.org/prizes/physics/2011/press-release...

The Luminiferous Aether was popular too.

>> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?

As a non-cosmologist just reading HN I would say yes. Not quite as extensively as Dark matter though. I personally think that's a mistake too based on my limited research on the topic. If these are both overturned it will be a huge blow to "scientists" credibility in the eyes of the public. That's how invested they are.

> If these are both overturned it will be a huge blow to "scientists" credibility

This is nonsense. Scientists have been wrong in several occasions, it is just part of the profession. For example, in the years leading to the discovery of relativity, many physicists believed there was something called "ether" that worked to fix the speed of light that they had evidence to be the same in all directions.

Yeah but that was in an age before clickbait and "In this house, we believe science is real" yard signs.

People are too bought into science as a source for truth instead of being a messy, difficult method of discovery.

When chemists were asked, at the end of the 19th century, whether the the atoms in their molecular diagrams were real, they always said, "No, that's just a model we use." It wasn't until Brownian motion needed actual atoms that they began to say atoms had objective reality.

Cosmologists could learn a lot from 19th-century chemists.

I think there were a lot of chemists at that time who were confident that atoms are real, but an influential group of philosophically-minded physicists (Mach, for one) objected to the claim on the basis that the evidence was circumstantial. They gave Boltzmann a good deal of unnecessary grief over the matter (no pun intended).

Yes, all chemists suspected atoms were real, but they were mostly careful not to claim to have evidence for it that they did not, in fact, have -- yet! Nobody but nobody was surprised when we turned out to really have atoms. It was all a relief, but it didn't change much about how chemistry was conducted. It made catalysis easier to understand, and ultimately DNA as a physical basis for life that made biologists generally very uneasy. Many had thought of themselves as studying something divine, and had to get used to being chemists.

You know what they say. Or at least what Lev Landau supposedly said: "Cosmologists are often in error, but never in doubt."

It might be cultural. I think it is. Being unsure or humble is not valued as much as it should be.

It is valued more in more consequential fields. What cosmologists believe never has any legitimate effect on public policy, except to the degree that they command budgets for telescopes, accelerators, and detector arrays.

Generally called aether, believe that ether is a misspelling which has lingered.


If you care what sort of ether you're on about, you say "luminiferous ether".

I believe it's just a regional spelling issue (like paediatriction/pediatriction or encylopaedia/encyclopedia)

Scientist have no idea what dark matter or dark energy is so it’s not like our world would be overturned. If it turns out to be wrong assumptions, that’s fine. Although it would be embarrassing.

It would only be embarrassing if science wasn't so damn hard.

The problem is that these topics get enough press that the general public has heard of them. It's nice that there are no obvious consequences if dark matter or dark energy turn out to be fiction. But the public will hear that "scientists" were wrong about these things they've been talking about for 50 years. Then the public will get another report on a topic like climate change which is also proven by "scientists" albeit different ones. That's an area where the truth of if has real consequences. What are people supposed to think then?

The answer is to properly educate the public on how science works. Science is a series of hypotheses, tested extensively and built upon given the evidence.

It is the fault of our education system and pop culture that people are so terrified of scientists being wrong. People should be thrilled when scientists are shown to be wrong, as it means they are one step closer to understanding what is right.

Our only recourse will be, "Well, you know, cosmologists. They don't behave like real scientists." That will sound suspiciously like "no true Scotsman", but there really is a difference between science with and without consequences.

People were forced to take particle physics seriously, and cosmology slipped in on its coattails.

Cosmologists are behaving like real scientists. There is a gap in our knowledge of physics which appears to be dark matter and dark energy. That's something that needs to be resolved, one way or the other. Currently they are expending a lot of effort looking for dark matter and energy. If it ends up being wasted effort, that would be embarrassing, but it wouldn't have been wrong to look.

Announcing far and wide that the Universe is certainly 96 percent invisible stuff that has never been identified in any way is not what a real scientist would do, if it mattered in any way.

All we really know is that the equations we have don't match the universe we see. Dark-this and dark-that are no better than guesses that seem to bring things back in line with our favored theories, until some actual mechanism is identified.

Do I understand correctly that this is actually saying that accelerating expansion of the universe may be in error? That there is, instead, no accelerating at all, but merely constant expansion?

Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.

There are very few ways to modify Einstein's Equations and still have them make sense. An easy one is to add a constant term. Such a term is known as the Cosmological Constant, and a positive value for it would result in a constant repulsive force between masses regardless of distance. This results in an accelerating expansion of the entire universe, but, with a supremely small value it only becomes noticeable at large scales, where it starts to dominate attractive gravity. This appears to model what we're observed happening with galaxy clusters.

Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. However, the article refers to observational evidence measuring the expansion of the universe, not dark energy. There is no evidence for dark energy as such, and if you listen to colloquia on cosmology, you will hear about the cosmological constant, not dark energy. It is not necessary to hypothesize the existence of negative energy particles to model what we've observed, and you'll only really hear the term used in the popular press because it sounds sexy.

> Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field.

No, that's not what dark energy is. "Dark energy" is just a general term for "anything that acts like a cosmological constant in the Einstein Field Equation". It could be an actual physical constant, just an inherent property of spacetime, or it could be some kind of energy field. We don't know. (Btw, the energy associated with dark energy is positive, not negative; the pressure is what's negative.)

Thank you for the correction

Well, actually there are infinite ways of modifying the equations and still have them compatible with current observations. Check out for instance https://en.wikipedia.org/wiki/F(R)_gravity but there are many more examples with additional fields.

There is a standard cosmological model called LCDM model, Lambda Cold Dark Matter model, which is basically the minimal thing you can use to fit cosmological observations, it contains a cosmological constant and cold dark matter, that is dark matter that is heavy enough that it is cold in the present universe. From the cosmic microwave background and Baryon Acoustic Oscillations (BAO), that is basically the distribution of galaxies, you can measure values for your favorite cosmological model. There are additionally for the dark matter density galactic rotation curves and for the cosmological constant super nova data.

Now dark energy is basically another name for the cosmological constant. (In general relativity the cosmological constant gives you the curvature of empty space, and dark energy is the same term moved to the right hand side.) However, the philosophical difference is, that sufficiently funny particles, like for example the Higgs, can easily mimic the effect of an cosmological constant. So there is an industry of people who calculate the effects of different extensions of the standard model on LCDM cosmology.

Now, above I said that CMB, BAO and SN data all agree in cosmological observations on the value of the cosmological constant. So for it to be wrong, it needs to either evolve, or several different measurements need to conspire to mask the effect of an constant. So my assumption is, either their non standard evolution is compatible with LCDM cosmology, or there is something wrong with the analysis.

Sabine Hossenfelder comments on this paper:

Dark Energy might not exist after all


Amusingly, this video is about entirely different work that also calls into question the basis for claims about dark energy.

Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.

Ah, that is funny - I just assumed i didn't understand the different descriptions because I'm not an expert. That they are different explains my puzzlement.

* indeed this is the same result as https://www.quantamagazine.org/no-dark-energy-no-chance-cosm... which is different from the OP paper

It sounds like the earlier article is pretty flawed and doesn't control for things like redshift associated with the motion of the solar system, so I very much doubt that the observations in that paper will end up "stacking" with those in this one. I'm no expert, but it seems like this more recent paper presents a much more serious challenge to the existence of dark energy.

negative dark energy. sounds sexy.

So these guys criticize SN-!a as standard candles, and then rely on other results criticizing BAO and CMB measurements also indicating accelerating expansions. However, why all these measurement would err in the wrong direction is not clear. I'm not convinced yet.

Haha, called it!

Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable.

In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but there is no reason to assume it is the only one. We just don't get to study any young-universe stars that haven't blown up.

Did anybody even discuss metallicity and possible effects on brightness of t1a sn's, when DE was first proclaimed? If not, why not?

> Haha, called it!

One or two years from now I invite you to take a look back at this comment and see if you still feel so smug. This is a relatively recent paper, give it some time to be chewed up and spit out by the cosmological community before hailing it as the deathknell of a decades old tricky problem.

I will happily eat crow if they find reliable independent corroboration of the actual distance of these events. That will not be easy. The universe has many ways to adjust the relative brightness of photons at different wavelengths on a common path, and many ways to vary the relative brightness when they are emitted.

Does this have any affect on the search for dark matter? Are the two interconnected at all?

No. Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies. Dark energy is/was assumed to exist in anomalous expansion of the universe based on redshifts.

>Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies.

That's what initiated Zwicky's notion in the '30s. It is far from being the only, or even the main, evidence for dark matter (which can be read as "mass effects we can detect not associated with matter we can currently detect").

More accurately: motion dynamics not compatible with both General Relativity and the mass we can see and reasonably infer. There is of course a stupendously huge amount of mostly invisible "interstellar medium", and even more "intergalactic medium", mostly ions of loose atoms and small molecules, and we use estimates of how much of that there must be. If its motion has anything to do with plasma fluid dynamics, all bets are off, because those equations are what mathematicians call intractable, and physicists would call career-limiting.

They will happily declare 3x more unknowable Dark Matter than normal stuff before allowing plasma dynamics to have any effect on anything. Can hardly blame them.

This finding would not cast any doubt on the existence of dark matter.

Even if this paper is correct, there is still overwhelming evidence for dark energy provided by other observations, in particular those of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO). This article provides some details on why Dark Energy is in no danger of being called in question: https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...

As far as I can tell, Quanta Magazine article does mention the original post findings. Additionally, the Quanta article and the findings preprint were published just a week apart. Not enough time to formulate a good response:

* Quanta Magazine article: 17 Dec 2019

* Arxiv preprint: 10 Dec 2019 [1]

CMB and BAO are mentioned in the original post too:

> Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely.

[1]: https://arxiv.org/abs/1912.04903

Correction: "Quanta Magazine article does NOT mention the original post findings"

Late to the party but does anybody know if this is connected to the findings a few weeks ago that this Quanta article is replying to? (https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...)

I know they are proposing different mechanisms for the error in calculation but it gives a sense of a 'moment' shifting against dark energy. Coincidence?

Can someone eli5 why if space itself is expanding, how can an observer detect that if they too are expanding at the same rate?

Spatial expansion is a great heuristic explanation, but it can be misleading: Locally, the cosmological constant will manifest as just another pseudo-force, easily overcome by nuclear and electromagnetic forces holding us together.

As I understand it:

We are not expanding. Size of e.g. a hydrogen atom is not changing.

And we are not expanding because other forces are stronger at short range. Similar to how the electroweak force is preventing you from falling through your chair, even though the gravity of the entire earth is pulling you.

Dark energy, as we thought before this paper at least, would overcome gravity only on the grandest scales, between galaxies.

When dark energy was first accepted, it seemed to me, as an outsider, that it happened very quickly, without, apparently, any time as a possibly-contentious, 'could this be so?' hypothesis in the way that, for example, dark matter did (and, to some extent, still is.) That surprised me because, up to that point, there seemed to be a problem with the cosmological distance ladder, with different methods getting different results, and with there being stars that seemed older than the universe supposedly was.

In comparison, when superluminal neutrinos were tentatively announced a few years ago, there was a lot of justified skepticism about there being experimental error (admittedly, overthrowing special relativity is an even more extraordinary claim than dark energy.)

Not so fast. See [1] and [2] for an explanation. There are good reasons to suspect that there are errors made in this analysis.

[1]: https://arxiv.org/abs/1912.02191

[2]: https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...

Hold up, this is a different thing than what [1] and [2] are responding to.

Yes, I'm totally lost. Was there accidental confusion here? Or is the new paper (by completely different authors) somehow building on those other papers and flick is implying it suffers from the same criticisms?

Would love to know if this is genuinely newsworthy or not.

It would be pretty impressive indeed if [1] countered this article, since the Arxiv preprint came online 6 days later.

Thanks! It’s a little disingenuous/irresponsible on part of the phys.org article to not even mention the Rubin+Heitlauf rebuttal and the ensuing discussion, even though they’re from a month ago. EDIT: No wait, this OP is about a different paper from a week later... Hmm.... interesting times.

Are galaxies in old universe more densely packed than in our neighbourhood?

Can expansion be seen not in redshift but in angular distances of galaxies? I'm asking in general not in relationship to the article. It wouldn't help for the problem raised by this article.

Do you know any good source where I could follow through the whole argument that universe is expanding and the expansion accelerates? Without handweaving.

So... Big Rip is postponed indefinitely?

I thought there was little reason to expect a big rip, because it requires assumptions about an increasing cosmological constant, which there’s no evidence for.

What do you mean? There's lots of evidence that the expansion of the universe is accelerating and that's the whole reason we believe that dark energy exists. Most cosmologists do believe we're heading for a big rip.

No, "big rip" and "accelerating expansion" are not the same thing. A big rip would require that the density of dark energy in the universe is increasing with time. We have no evidence that it is, and most cosmologists do not believe we are heading for a big rip.


No, most cosmologists believe we're heading for the Big Freeze.

The Big Rip would require something called "phantom energy", a special form of dark energy. While not entirely ruled out, our observations disfavor it and it would be problematic from a theoretic standpoint.

I can recommend this podcast on possible fates of the universe: https://www.preposterousuniverse.com/podcast/2019/10/28/70-k...

According to TFA, it's the "most direct and strongest evidence for the accelerating universe" that's now possibly an artifact. As I understand it, "dark energy" is fundamentally just another way to say "accelerating expansion".

The big rip would imply that eventually, all points in space are accelerating away from one another faster than the speed of light, which would tear apart atoms, subatomic particles, and everything down to the smallest divisible units of matter and energy. The accelerating expansion doesn't imply this at all, and would instead leave big dense things like galaxies intact to burn out and fade away.

Acceleration comes from the cosmological constant - more volume means more dark energy, which means more velocity (acceleration). Only if the cosmological constant isn't constant would we expect a big rip.

Now, we're questioning the acceleration part also apparently.

The existence of a cosmological constant is different from it's ever increasing value.

The evidences for the later are non-existent.

radiation spreads and matter clumps. in this universe matter was allowed to form but radiation dominates. island chains swallowed up by a rising ocean.

if you look at the magnetic soup we call matter, or maybe electromagnetism is a better term, is dark matter / dark energy / anti-matter (&anti energy??) just the same thing of a higher frequency

say if matter / observables go from 0hz - 30+ Zhz.. is dark energy from 30+Zhz to ???Zhz and perhaps anti matter / energy from ???Zhz to ???????Zhz? (more question marks being higher ? :D )

or is this completely invalid and a dumb thought?

Electromagnetism is only one of a number of fundamental forces [1]. See [0] if you are curious about EM radiation at different frequencies. Radio and microwaves, infrared and visible light, ultraviolet light up to x-rays and gammarays are all part of the EM spectrum.

[0] https://en.wikipedia.org/wiki/Electromagnetic_spectrum [1] https://en.wikipedia.org/wiki/Standard_Model

https://xkcd.com/955/ comes to mind.

I am going to wait to get excited about this until it is replicated by others.

Ya, I should have placed bets that dark energy would turn out to be illusory.

One less thing to worry about.

the science is settled! the science is settled!


Read more about the Primer Fields.

Why should we?

No, really. Rather than tell us to go read something (just a term, not even a link) that has a name that might, just possibly, be relevant to the topic at hand (or might be some obscure abstract mathematical thing, or something about painting), maybe you could tell us why you think we should read more about them, and where you recommend we go to do so.

After a bit of looking at it, I agree: It looks very much like a quack.

If you find things like this interesting I suggest you look on youtube for videos on the electric universe.

The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.

It should be noted that among cosmologists, electric universe is widely considered to be bunk science.

And Plasma Physicists think that "dark matter", "dark energy", & the assertion of gravity (ignoring plasma) being the dominant force in the Univese is mathematics without physical evidence. Thus "pathological science". Irving Langmuir, discoverer of the double layer effect in plasmas & coined the term "plasma" physics, came up with the definition of "Pathological Science". He was also around during the birth of the "Standard Model".


They may feel that way, but the difference is that standard cosmology is a highly-successful predictive model consistent with all popular physical theories, while plasma cosmology is proposing physically unlikely phenomena that have never been observed, interpreting prehistoric art for 'observations', and fails to account for many modern observations. It's perhaps not as bad as the so-called electric universe, but it is certainly a much more likely example of pathological science than standard cosmology is.

Good luck finding physical evidence of "dark matter" & "dark energy" then. How many more billions will need to be spent chasing windmills?

We already have the equations from Oliver Heaviside & James Maxwell, btw. But have fun playing math games with no physically reproducible experiments.

Maxwell's equations won't help you understand how time works, so you can't run a successful GPS, for example. They also don't explain why stars introduce le sing effects.

Perhaps dark matter and dark energy are indeed a wrong conclusion - Sabine Hofstadter, to take a mainstream scientist, thinks so as well, and proposes some explanations that don't throw the baby out with the bath water.

Either way, physics thrives when we have observations which don't match our theories, and the only thing we can do to bring them closer is to experiment.

If a paradigm shift turns out to be necessary, then it should happen once the new paradigm is actually capable of explaining at least most (if not all) of the currently understood phenomena. For example, special relativity was perfectly in line with Newtonian mechanics, and could be used to derive the same conclusions for planet motion that Newton had painstakingly measured 400 years ago. If it hadn't been consistent with those (and with Maxwell's equations) than it would have never been accepted. And in fact, it wasn't entirely accepted until one of its more outlandish predictions - gravitational lensing - was observed experimentally, not just in general lines, but down to the actual measurement predicted by the maths.

Or the lensing is explainable using standard optics...


Here's the EU critique:


The thing is there were mulitiple ways of interpreting phenomona & through certain cultural choices, a certain orthodoxy was created. The problem we are seeing with modern astrophysics is that in order to explain the working of the universe using only Gravity, theories require esoteric mathematics that are by nature not observable.

Instead of putting all of our eggs in one basket, we should look at each of the foundational assertions of modern cosmology with skeptism & reevaluate our positions, particularly when there are non-observable mathematical artifacts. We have better technology & instruments now. We don't need to double down on the same religious beliefs using ever more esoteric math that is increasingly not falsifiable...

From the definition of "pathological science". Looks more like it applies to the Standard Model from these points...

* The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.

* The effect is of a magnitude that remains close to the limit of detectability, or many measurements are necessary because of the very low statistical significance of the results.

* There are claims of great accuracy.

* Fantastic theories contrary to experience are suggested.

* Criticisms are met by ad hoc excuses.

* The ratio of supporters to critics rises and then falls gradually to oblivion.

When you look at pictures like [1] it's very hard to accept a kind of galactic-cluster level atmosphere that would produce that type of lensing.

You're also ignoring the observed clock differences between clocks in LEO and clocks on the ground - which happen to have the exact values predicted by GR.

And these are just some of the more neatly observable consequences of GR. There are many others that are more sophisticated to notice, but that an EU theory would have to explain rigorously before it could even be seen as an alternative theory, not to mention hoping to be accepted.

Mind you, it is very likely that GR has some holes, as does QM - after all, we do know that they are not compatible with one another. We also have dark matter and the positive cosmological constant which are iffy. We also see that the maths of GR have a singularity when analyzing what would happen in the center of a black hole, and since we know that these objects exist, it's likely that there are unknown effects that the math doesn't predict and that would prevent the mathematical singularity from forming.

But noting that a theory which has made highly successful and precise predictions has some limitations as well is by no means a reason to throw it out and start from scratch. It's much more likely, just as happened with Newtonian Mechanics, that we will find some extension of GR and QM that can successfully account for the discrepancies. Perhaps dark matter will actually be observed directly, perhaps extending the Standard Model of particle physics. Perhaps some unexpected limits similar to the speed of light will be found that can explain what happens inside a black hole. Perhaps dark energy is simply an artifact of the linear approximations we are using to solve the non-linear equations of GR [2].

[1] https://en.wikipedia.org/wiki/Gravitational_lens#/media/File...

[2] http://backreaction.blogspot.com/2019/10/dark-matter-nightma...

To your point about throwing out the baby with the bathwater, here is the strength of the EU argument:

"The EU community is a challenger to the standard gravitational model, believing space-time to be a misinterpretation of the Universe. The things we see in the Universe – from large scale filamentary structures connecting galactic clusters, to Earth’s climate and meteorology – are plasma phenomena driven by electromagnetic forces."

Note that it's still in an early phase & the physics is being figured out. This includes a heavy reliance on reproducible physical experimentation & unified models from small to large. Existing classical physical models are preferred. Custom math may come later, as one can create a Hamiltonian to model the phenomona, but the equation does not bring understanding of what is occurring without an underlying physical explanation.

> When you look at pictures like [1] it's very hard to accept a kind of galactic-cluster level atmosphere that would produce that type of lensing.

It's also difficult to accept that space-time is warped, especially without physically reproducible experiments, however we somehow trained ourselves to think this is the orthodox opinion. It was also once difficult to imagine the Earth not being at the center of the Universe.

The EU critique is that plasma is ubiquitous in space & the phenomenon has not been explored. It's only recently that we have discovered the onmipresence of plasma throughout space, which is something that Einstein did not account for in his models.



QM does have a connection with Maxwell's Equations as QEM.


Plasma Physics offers a way to, with physically reproducible experimentation, create a bridge with astrophysics.

There's even multiple hypothesis to explain the nature of Gravity.

Black Holes have not been directly observed & the Plasma Physics/EU explanation is that Quasars are a z-pinch in a galactic Birkeland Current.


How do we know that the Atomic clock frequency itself is not be affected by gravity? It seems like a simpler explination than "space-time" being affected by gravity while the Atomic clock frequency remains consistent in the reference frame.

The problem I have with assuming plasma is pervasive in the void of space is that, unlike the hypothesised dark matter, plasma should be hot and visible. As I understand it, there is mainstream acceptance that there is a possibility that some regions of space, such as the galactic center, could contain plasma (though the preferred explanation is that they contain matter pulled apart by a supermassive black hole), and some other regions such as nebulae do contain plasma, but the picture I linked earlier doesn't show any kind of hot visible substance that could refract light to produce that lensing effect.

If gravity affected the atomic clock frequency, we would need to understand how. Either way, we know from observations of the speed of light being constant in any reference frame that time dilation must exist when moving at high speeds. GR incorporates acceleration and gravity here.

Note that rejecting GR doesn't get rid of space-time (perhaps at best, it gets rid of curved space-time). We know from very good observations that the speed of light is a physical constant, so at least special relativity must be true (or we need some other theory to explain this physical phenomenon).

However, if we got rid of GR we would also need a new explanation for a very old problem: why is an object's inertial mass (the amount that it opposes motion) equal to its gravitational mass (the amount that it is attracted by the earth through Newton's formula)? GR has a beautiful unification of these two masses, making acceleration equivalent to gravity (which also happens to match how we feel, by the way).

Now, if I understand correctly, Plasma Cosmology does not discount GR, but simply proposes that plasma physics is more important in some galactic structures, especially the large-scale structure of the universe. There seem to be some technical limitations (related to implications for the state of the early universe vs observed current state), but perhaps they are resolvable.

Electric Universe starts from there essentially and seems to go much farther, getting rid of gravity and GR (and Special Relativity?) and hits all of the issues I mentioned above.

To your point re: supplementing experimentally backed systems (i.e. Newtonian Mechanics):

"...what is really wanted for a truly Natural Philosophy is a supplement to Newtonian mechanics...and introducing the additional facts, chiefly electrical - especially the fact of variable inertia - discovered since his time..."

"...it may be that when the structure of an electron is understood, we shall see that an 'even-powered' stress in the surrounding aether is necessarily involved. What I do feel instinctively is that this is the direction for discovery, and what is needed is something internal and intrinsic, and that all attempts to explain gravitation as due to the action of some external agency, whether flying particles or impinging waves, are doomed to failure..."

-- Sir Oliver Lodge - Nature, Feb 17, 1921

I'm not sure what this quote is meant to illustrate. The structure of the Electron is now understood in QM (it is structure-less, an elementary particle), the luminiferous aether is disproven, and gravity is understood as equivalent to acceleration, essentially through E=mc2, instead of being carried by particle or wave (though it can cause waves, as recently detected). On the other hand, other fields, such as the electrical field, are shown to reduce to particles flying around (photons, for the electric field), so if the quote was meant to say that electrical charge could replace a graviton, that has proven wrong.

Unfortunately, electric universe can't explain anything, as it is not a mathematical model, and it doesn't account for the vast majority of observations successfully predicted by relativity - especially gravitational le sing and time dilation.

Despite the similar name, dark matter really has very little to do with dark energy, and the lines of evidence for them are totally different. AFAIK there is fairly overwhelming evidence for the existence of dark matter at this point, and it's mostly a question of what exactly it is rather than whether the effect is real.

Dr. Anthony Perat, protege of Hannes Alfven, has a cosmological model based on plasma, which is observable & subject to physically reproducible experiments & replaces the need for both Dark Matter & Dark Energy as mathematical artifacts.


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