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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.




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