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More bad news for controversial 20-year-old claim of dark matter detection (arstechnica.com)
100 points by furcyd 14 days ago | hide | past | web | favorite | 54 comments



[flagged]


You have not read the article or you have not understood it. For your interest, the article is about how a specific explanation to dark matter is put into question, not whether dark matter exists or not. If you want to discard dark matter you have to propose a better model of physics that also matches all our observations.

The poster you're referring to is a troll account which already has several dead comments with almost the same content.

Don't engage with them, especially in a thread like this, where they tend to come out of the woodwork. Flag and move on.


This does beg the question that what if we as a collective also encounter these sort of defects.

For example on a macro scale based on our vantage point from our planet we only have a visible and limited line of sight to specific areas of the galaxy and the visible universe. The same could be same for the atomicverse.

What if we are incorrectly making assumptions about things because we don’t see the full picture of how things actually are conceived, embarrassingly so. On the magnitude of way far off.


> What if we are incorrectly making assumptions about things because we don’t see the full picture of how things actually are conceived, embarrassingly so.

This could be true, but I wouldn't call it "embarrassing" to come to flawed conclusions based on inabilities to gather evidence. That's how science works: we do the best with what we have, and continuously try to gather more evidence and refine our theories in response.


There are many instances in history of “embarrassingly,”:

• The theory that the earth is not the center of the universe - people persecuted sometimes killed for different assumptions. • Spontaneous generation, the idea that life just arises out of nothing, at the time period this was accepted and other ideas disregarded which led to many lives lost due to disease. • Mental illness assumptions in the past led people to view people with mental illness as possessed by demons, etc. leading to cruel and unusual confinement for these individuals • Lots of other examples

I would also propose that when observing our primate ape cousins even the smartest monkey to us appears to be “embarrassingly” putting together a coherent picture of actual reality.

Then that proposes an interesting thought experiment. If we encountered an alien species with as much intellectual distance from us as we are to the monkeys, then how would our most innovative theories fare against theirs? I would imagine we would be seen as “embarrassingly,” able to put even a fraction of the puzzle together.

We have our senses, and therefore we design our materials and probes to match our senses. Sometimes we can imagine high dimensionality in say the form of a tensor? Sure. Maybe we don’t have a complete picture so we build and optimize tools only related to our own sense processing. What if there are more than our senses, and we are incapable of seeing a deeper image of reality? What if have the senses of a snail as a comparison to an even more advanced species.


> If we encountered an alien species with as much intellectual distance from us as we are to the monkeys, then how would our most innovative theories fare against theirs?

That depends on how far you are willing to suspend disbelief in your concept of what such an alien might look like.

Are they made of atoms? If so, then they are overwhelmingly like to have senses very similar to ours. This is because our senses are fundamentally rooted in the physics of atoms, and there just aren't that many fundamentally different things that atoms can do. They can absorb and emit photons, they can stick together and be pried apart, they can emit alpha and beta particles, and they can fuse and fission. That's about it. And with those fundamental building blocks there is only so much you can do. You can imagine, say, aliens that can natively detect different parts of the E-M spectrum than we do, but that's not going to lead them to new physics that we haven't discovered.

On the other hand, if these aliens are made of dark matter then all bets are off. But given how hard it is for us to detect dark matter at all it's hard to imagine how we would get to the point where we would even recognize a life form made of it, let alone figure out how to communicate with it.


> our senses are fundamentally rooted in the physics of atoms, and there just aren't that many fundamentally different things that atoms can do. They can absorb and emit photons, they can stick together and be pried apart, they can emit alpha and beta particles, and they can fuse and fission. That's about it. And with those fundamental building blocks there is only so much you can do.

Our traditional physical senses:

- Sight. Based on interacting with photons.

- Sound. This is based on atoms physically colliding with each other. However, we process it using a complex apparatus that essentially performs a Fourier transform on the raw air-pressure data, extracting the frequencies of the wave pattern that reaches our ears on the assumption that a wave pattern is what we will get.

- Touch. This is based on atoms colliding with each other. It is set up more for the detection of large-scale structural characteristics. (e.g. hard / soft / liquid)

- Smell. This is based on atoms colliding with each other. It is totally unlike touch in that the sense of smell processes molecules based on their molecular shape -- the specific way in which they interact with dedicated sensors -- rather than on their physical characteristics. At this level, you're interacting with a molecule more than with a substance.

- Taste. From a physics perspective, this is basically just the same thing as smell. From a biology perspective, it's pretty different.

I don't see this as good evidence that the set of possible senses is meaningfully limited by a simplistic view of how atoms can physically interact with other atoms.

We have many other senses that are less obviously based in simple physical interactions, like the sense of time.

Some people have had magnets implanted, leveraging their existing sense of touch into a sense of magnetic fields. This is something humans don't ordinarily have, and is actually not allowed for by your list of the capabilities of atoms -- you forgot that atoms can hold an electric charge -- but is analogous to some other animals' ability to sense electric fields.

I'm curious how you think "emitting an alpha particle" differs from "being pried apart" or "fissioning".


> many other senses

Yeah? Like what? You've listed two. Two is not "many".

You don't need to have a magnet implanted to feel a magnetic field. All you have to do is hold two magnets close to each other.

As for our "sense" of time, this arises from the fact that our brains perform data processing at a characteristic speed, and that in turn is an emergent property of atoms.

> I'm curious how you think "emitting an alpha particle" differs from "being pried apart" or "fissioning".

Alpha-decay is spontaneous, fissioning generally needs to initiated by neutron bombardment. "Being pried apart" was intended to refer to chemical reactions, not nuclear ones.


> Yeah? Like what?

Most people try to support an argument with something stronger than "I don't know very much".

You can sense acceleration.

You can sense temperature.

You can sense the position of the various parts of your own body. ("proprioception")

You can sense whether you need to eat, and what you should eat. ("hunger")

Note that from a physical perspective, hunger appears identical to taste and smell. That is to say, it is implemented by special receptors that bind to a particular molecular shape. But unlike those two, it is not general-purpose -- it is a computational artifact, the specialized means by which your digestive system sends messages to your nervous system. But it is no less of a sense than your others. A sense is a means of receiving input. This should tell you that the number of senses you may experience is not limited by the number of interactions one atom may have with another atom; it is at least as large as the number of different types of computation you might want to do.

If you're really interested in a catalog of senses, I suggest checking out the psychology literature. And whether you're interested or not, I suggest trying to base your arguments on something more than bluster.

Believing that humans have five senses has all the scientific backing of believing in the tongue map.


I think 'lisper wasn't interested in a catalog of senses, but whether they're "going to lead them to new physics that we haven't discovered". Once you listed are less about physics/external world and more about internal status of the body.

I don't think asserting that there's nothing more for us to discover is a good method of determining whether we might discover something new.

If an alien sense relying on physics unknown to us were to come to our attention, it seems likely to me that it would indeed lead us to discover that new physics. But since we don't know whether physics like that exists or not, we can't say whether such a sense could exist either. lisper has very clearly claimed that such a sense cannot exist because there is no such physics; I don't see how he could be interested in the question you state.

> Ones you listed are less about physics/external world and more about internal status of the body.

I'd say temperature, time, touch, hearing, sight, and smell are primarily about the external world and proprioception, taste, and hunger are primarily about the internal status of the body. That's really what distinguishes taste from smell. Acceleration seems like a gray area.


> If an alien sense relying on physics unknown to us were to come to our attention, it seems likely to me that it would indeed lead us to discover that new physics. But since we don't know whether physics like that exists or not, we can't say whether such a sense could exist either.

But we do know enough physics already to explain everything we can observe that surrounds us, not with our senses alone but with the measurement devices that we can construct.

The only physics that we can't measure and completely explain is that one that is anyway inadequately reachable not only to us with out human senses but to our measurement devices which already can measure changes in length 1000 times the size of the proton, which happen on the 4 km length (see LIGO).

The only physics that remains to be known better are the effects that happen on the galactic and intergalactic scales or inside of the black holes and during the first picoseconds of the existence of the universe, or with the particles that exist too short or interact too little to influence anything we can observe:

http://www.preposterousuniverse.com/blog/2010/09/23/the-laws...

"The Laws Underlying The Physics of Everyday Life Are Completely Understood"

"there’s no question that the human goal of figuring out the basic rules by which the easily observable world works was one that was achieved once and for all in the twentieth century."

"You might question the “once and for all” part of that formulation, but it’s solid. Of course revolutions can always happen, but there’s every reason to believe that our current understanding is complete within the everyday realm. Using the framework of quantum field theory — which we have no reason to doubt in this regime — we can classify the kinds of new particles and forces that could conceivably exist, and go look for them. It’s absolutely possible that such particles and forces do exist, but they must be hidden from us somehow: either the particles are too massive to be produced, or decay too quickly to be detected, or interact too weakly to influence ordinary matter; and the forces are either too weak or too short-range to be noticed. In any of those cases, if they can’t be found by our current techniques, they are also unable to influence what we see in our everyday lives."


There’s a ton of things we have no explanation for — superconductors, how protons collide, a ton of things about material science, we’re still not great at non-local effects, etc. That’s setting aside the doozy of “gravity and particle physics say wildly incompatible things, and we’re not sure how to fix that”.

And when I say “how protons collide”, I mean numbers from existing accelerators don’t match predictions and they’re having to change models — and all the fixes they can come up with (eg, elaborate swarms of virtual quarks) still don’t fix the collision numbers.

There’s still a pretty poor understanding of 4D topology, and the effects and possible knotting states play in non-local interactions. Microsoft for instance theorizes that you can have 4D anyons, but no one is sure how to build them. And it comes into play in more mundane ways when talking about plasma physics or fluid dynamics, since the same mathematics governs stability there.

You seem to be wildly overstating the success of science.


And then I'd claim you wildly understating the success, of course. Superconductivity is not an effect that involves any "new physics" in the sense of the necessity of changing the underlying theories: it's the typical "emergent" property, and we know that modeling many of the "emergent" properties is far away from our possibilities. Ditto with the material science, or any other observations where "too many of the stuff known to us interacts at the same time." It's not "we don't know" in the sense that the basics will have to change it's "we don't know because there's too much to model at once" like we can't reliably predict the weather 2 weeks in advance, even if we understand the nature of the particles that produce the weather.

Edit: to answer your response below this post:

It's a [Citation needed] for you that the fundamentally "new physics" is needed instead of reaching the limits of our instruments or the modeling capability.

The second you mention is not something that contradicts what we measure, it just that naively trying to combine the provably successful models that match our measurements to produce "something more" outside of their domain really doesn't work: and that of course doesn't have to work to claim that the models do work for the things that they actually model, and which independently correspond to the things we can "observe" (where "observe" includes using our best measuring devices).


I disagree: I don’t think we know what features of the underlying model lead to the emergence of things like superconductivity, and having to account for that explicitly will demonstrate a new paradigm for analyzing the base mechanics — which is likely to lead to a new interpretation and “new physics”.

I’ll also note you didn’t reply to two big ones:

They can’t predict proton on proton collisions in a hyper controlled tube accurately.

They can’t predict how the two most established theories, each boasting dozens of orders of magnitude of accuracy, interact.


Since we're talking about hypotheticals:

Imagine a lifeform that experiences entanglement directly.

Or one that senses gravity waves. (It would have to be very, very, very big. But even so.)

Or one that is just as good at making maps of social and political configurations as it is at mapping its physical surroundings.

Or one that has evolved with an intuitive understanding of the patterns that define how knowledge is structured, rather than learning low-cost approximations for essentials and off-loading high-cost speculation to external media and low-threat contexts, like humans do.

"There are only so many ways for atoms to do stuff" is true, but that doesn't mean we have the first clue what all of those ways are.


> that doesn't mean we have the first clue what all of those ways are

Actually we know a few constraints that they have to meet:

1. They have to provide an evolutionary advantage in some environment

2. They have to be Turing-computable

3. They have to realizable in hardware made of atoms (unless you want to consider dark-matter aliens)

So:

> a lifeform that experiences entanglement directly

I don't know what you meant by this. You do experience entanglement directly. The entire classical world is made of entanglements. Your very existence is a massive network of entanglements.

> one that senses gravity waves

> It would have to be very, very, very big

This is actually conceivable for a dark-matter alien, but then we have all the aforementioned problems of detecting and communicating with it. For an alien made of ordinary matter this is inconceivable because #1 above.

> just as good at making maps of social and political configurations as it is at mapping its physical surroundings.

Humans are actually pretty good at this in their ancestral environment where there are at most 100-200 individuals to deal with.

But this is actually the most likely avenue IMO, an alien that can "natively" handle communities of millions or billions of individuals where everyone knows everyone else.


> Some people have had magnets implanted, leveraging their existing sense of touch into a sense of magnetic fields.

Touch is an EM forces interaction, not very different from magnets.

https://www.youtube.com/watch?v=MO0r930Sn_8


Apes use very similar senses, but our brain gives us the advantage of deriving more from those same senses. Similarly, aliens might be able to process the data better, or gather and process more data than we can.

In a sense, we are alien compared to our ancestors of hundreds of years ago. Our technology extended our natural sensors and we started to learn more about our place in the solar system, galaxy, super cluster and so on. We learned more about physics too. I suspect there is more to the story and more advanced aliens would have some surprising things to say about the nature of our universe. We might have difficulty understanding it if there is a large knowledge gap though.


We really have only one significant evolutionary advantage over apes and that is our ability to reason symbolically, i.e. to use language and math. We got that hundreds of thousands of years ago, and that, plus the invention of writing, turned us into Turing machines. That's as far as you can go in this universe unless you can somehow evolve a quantum computer, but that seems exceedingly unlikely. It's hard to imagine an environment where there would be an evolutionary advantage to being able to factor large primes.

Aliens might have made significant scientific and social progress over us (most likely) but we will have no trouble coming up to speed if we get access to their libraries. It's a lot harder to figure something out for the first time than it is to learn it once someone else has figured it out.


None of those examples you mentioned had a lack of evidence, which is why we changed our perspective on how those things worked. The opposition to them was not scientific.


What's interesting to me is while we have no reference for how close we are to understanding ultimate reality, you are nevertheless sure enough in your beliefs to call ancestral knowledge and other species 'embarassing'.

To all your "embarassing" examples: what would have been the plausible alternative?

"people would have understood mental illness like we do today" and "people would have had a better understanding of abiogenesis" is emphatically not a possibility.

People saw mental illness, were afraid of it, and put it into the very best system with explanatory power they had at their disposal.

I can't see anything qwrong with that, and certainly don't see why you should laugh at them.


On the point of mental illness, Foucault is well known for his view on it (quoting from SEP):

>But, according to Foucault, the new idea that the mad were merely sick (“mentally” ill) and in need of medical treatment was not at all a clear improvement on earlier conceptions (e.g., the Renaissance idea that the mad were in contact with the mysterious forces of cosmic tragedy or the seventeenth-eighteenth-century view of madness as a renouncing of reason). Moreover, he argued that the alleged scientific neutrality of modern medical treatments of insanity are in fact covers for controlling challenges to conventional bourgeois morality. In short, Foucault argued that what was presented as an objective, incontrovertible scientific discovery (that madness is mental illness) was in fact the product of eminently questionable social and ethical commitments.


I think that the scientific community at large is so frightened of the shame of being wrong that they cling to obviously flawed concepts like dark matter (how come I never got to just add in a chunk of invisible theoretical force whenever my equations were unbalanced in school, eh?).

The fear of embarrassment is a large part of the inertia against scientific revolutions. Furthermore, men hold an inordinate amount of their masculine confidence in their correctness, further exacerbating their ability to admit to being wrong.


If your equations don’t balance because of a lack of a coherent and falsifiable theory for why they don’t, I guess you’ve stumbled across one of the big open questions in science. Which is fine, it just means there’s still white spots on the map. Granted, they’re enormous. Still better than jusf giving up and attributing it to a deity.


Our own optimism drives us to stay evolutionary fit. Which is great for us. I just wish I could see the full picture one day.

It’s mind boggling to think everyone who has lived on this planet died with an incomplete picture and understanding about the true nature of the universe.


Okay now get back to work.


Who said anything about a deity? My only point is that hubris and embarrassment play a huge role in holding back the evolution of human understanding.

This is a fine opinion to hold in general, but if you're going to tie that to the failings of a particular theory (dark matter), you better be able to be specific about what those failings are and how hubris and embarrassment have led to those failings.

Just claiming something is "obviously flawed" does nothing to advance science, hubris or not.


Dark matter is obviously flawed because it is clearly a patch on a broken paradigm. The hubris is related to the inability of scientists to even discuss that maybe, jut maybe, gravity is not the only organizing force in the cosmos (you know, we create plasma in labs with electricity, not gravity right? But let’s just ignore that completely because there can’t be electricity in space because hysterical raisins).

Or how about the discrepancy around quasars and red shift implying that maybe the doepler effect is not 100% transferable to space? Nope, don’t try that if you want a job or credibility.

The book that proves these dynamics historically is called The Structure of Scientific Revolutions.


Kuhn is interesting reading, but he does not give any guideline to predict or create the next paradigm. For every paradigm shift there is probably thousands of theories which just turns out to be useless blind alleys.

You allude to some alternative theory, but you are pretty vague about it.


Dark matter is a supersolid that fills 'empty' space, strongly interacts with ordinary matter and is displaced by ordinary matter. What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the supersolid dark matter. The state of displacement of the supersolid dark matter is gravity.

The supersolid dark matter displaced by a galaxy pushes back, causing the stars in the outer arms of the galaxy to orbit the galactic center at the rate in which they do.

Displaced supersolid dark matter is curved spacetime.


Nah I didn't intend to accuse you of that, just that science is the successor model to religion as a way to understanding the world. I guess I don't agree about science 'clinging' to dark energy / dark matter - they're basically placeholders until a more coherent theory comes around, and so far that hasn't happened. I don't think a majority of physicists would bat an eye to wave goodbye to those concepts if it became clear how to do it.

Now, that's not saying there isn't a whole lot of dogma in science that should be gotten rid of, I even think that the Kopenhagen interpretation has gotten to a dogmatic point - I just don't think that it applies to cosmology. Plenty of influencial astrophycists have open discussions on this, see e.g. R. Penrose.


> they're basically placeholders until a more coherent theory comes around

No.

https://medium.com/starts-with-a-bang/theres-a-debate-raging...


Nobody seems to have a good idea for what we are dealing with other than we have a mysterious extra "force" show up in our observations, so there's no real "shame" in being wrong here because nobody's gotten it right.


Sorry, but when the fundamental equations of your cosmological worldview require elaborate “empty patches” and tons of “oh inventing this would really balance the equations” but you refuse to question the underlying assumptions (gravity as the only organizing force, despite being the weakest one we know), then you are not conducting honest science. And that dishonesty runs rampant through every scientific revolution.

It’s not a gender thing. Although, it’s a mental issue —> narcissism, pride, ego.

These traits exist in each and everyone to some scale of a degree.

But I agree, as someone who used to be super passionate about research. I would say seeing highly regarded individuals fabricate data and assume wrong assumptions, in order to appear respected and important, did dissuade me and me think of the research industry in a different light, one of a business.

There are many smart scientists, and they are working hard. The ones that have the resources and means to influence academic papers, experiments and grants are able to influence particular theories and experiments over others.

️ that can lead some theories, your example dark matter is a perfect example to be more accepted than questioned.


From Lou Cixin’s ‘The Three-Body Problem’ the “Shooter and Farmer” metaphor seems relevant here.

“In the shooter hypothesis, a good marksman shoots at a target, creating a hole every ten centimeters. Now suppose the surface of the target is inhabited by intelligent, two-dimensional creatures. Their scientists, after observing the universe, discover a great law: “There exists a hole in the universe every ten centimeters.” They have mistaken the result of the marksman’s momentary whim for an unalterable law of the universe. The farmer hypothesis, on the other hand, has the flavor of a horror story: Every morning on a turkey farm, the farmer comes to feed the turkeys. A scientist turkey, having observed this pattern to hold without change for almost a year, makes the following discovery: “Every morning at eleven, food arrives.” On the morning of Thanksgiving, the scientist announces this law to the other turkeys. But that morning at eleven, food doesn’t arrive; instead, the farmer comes and kills the entire flock.”

A counterpoint to such an observation is that ideally, scientists understand that they’re working with imperfect and incomplete information. It’s still hard to see the universe from a perspective you don’t inhabit though.


what is dark matter? is it the opposite of matter? how can it be called matter when it doesn't exist?

or are these objects from higher dimensions as Michio Kaku postulates? that galaxies are essentially in a bubble of dark matter preventing it from hurling in every direction.

as well as the presence of dark matter in orbits, could it not be the space-time curvature from the mass itself but from the encapsulating dark matter around it?

I no very little of this subject so I can only ponder and fantasize.


Via Wikipedia[0]

    Dark matter is a hypothetical form of matter that is thought 
    to account for approximately 85% of the matter in the universe, 
    and about a quarter of its total energy density. 

    (...)

    Its presence is implied in a variety of astrophysical 
    observations, including gravitational effects that 
    cannot be explained unless more matter is present 
    than can be seen. 
Also, since it will inevitably come up as it always does in threads about dark matter or dark energy , here is an article[1] and related[2] HN thread arguing the theoretical justifications behind the existence of dark matter, what is known or can be inferred about its properties and why chances are no one missed whatever simple solution you can think of, like "maybe it's just normal matter but they can't see it because it's far away" or "maybe it's just black holes" and why it's also not entirely hubris or ignorance on the part of the scientific community.

[0]https://en.wikipedia.org/wiki/Dark_matter

[1]https://medium.com/starts-with-a-bang/this-is-the-real-reaso...

[2]https://news.ycombinator.com/item?id=18207276


The article you link there does not mention the SISSA discovery of 2016 [1]. In particular in mini-spiral galaxies there seems to be an unexpected, and inexplicable, interaction between dark and visible matter. This falsifies the primary prediction put forth in that medium article. And in general this issue is one that poses a critical problem for dark matter largely because it cannot just be massaged into the model.

And that last point is really the problem with model based physics. They are really really hard to falsify which can provide certainty through inertia. For instance take the heliocentric vs geocentric earth. The geocentric view (that the Earth was the center upon which everything rotated) was based upon a model. It started out fairly simple and intuitive. But then we kept coming upon ever more issues. For instance if everything else rotates around Earth then that must mean other planets travel in sort of 'swirly' type patterns that we see nowhere else in physics. Well, okay - why not. Hmm it also turns out that some planets, such as Mercury, need to just magically stop in their orbit and start going backwards at some point. Again, it's a model that we can't really falsify so okay - why not.

And it absorbs really bizarre observation after another. The only way to refute it was ultimately to be able to see 'through the eyes of god' that geocentricism was wrong. This was not hubris or ignorance on part of the scientific community. It was inertia. Hundreds of years scientific study was built upon the assumption of a geocentric Earth. Astrology was a scholarly pursuit, at least as reputable as psychology is today, developed over centuries. And it was 100% dependent upon the geocentric model. We've rewritten history to blame geocentricism on the church alone, but there was far more in play there. Going against the geocentric model meant having the arrogance to call numerous well reputed fields completely wrong, to completely discredit and repudiate the work of the most brilliant minds of the times, and to basically say you somehow know better than hundreds of years of work and pretty much everybody else.

No, it's certainly not hubris that drives inertia. It's the lack thereof. Einstein's theory of relativity sounds absolutely insane. It took the sort of man who would go on to condescendingly mock quantum entanglement as "spooky action at a distance" to have the sort of ego and self confidence, bordering on hubris, to be able to not only consider such possibilities but to spend years of countless effort refining and developing it. Much of this done when he, unable to find a professorial position, was working in a patent office - no less! Indeed if we have any bias in play, I'd expect it's rather a contagion of humility driven by the exponential growth in complexity.

If anything, the arrogance would come in the form of an aggressive disregard for alternatives. See the practically militant response to things such as MOND [2] hypotheses. It still suffers many problems, as does dark matter, but remains a viable alternative hypothesis which remains rather unexplored. Of course there is a practical issue there. Since nobody expects things such as MOND to be correct, which it probably is not, then spending years proving that is effectively wasted. By contrast as most people expect dark matter to be correct, proving it right or wrong would be an achievement worthy of a trip to Stockholm. It means pursuing MOND (or other alternatives) is a very difficult choice, in terms of career progression and prospects. Scientific inertia is a problem with no clear solution.

[1] - https://phys.org/news/2016-12-unexpected-interaction-dark-or...

[2] - https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics


> what is dark matter? is it the opposite of matter? how can it be called matter when it doesn't exist?

Dark matter is what we call the discrepancy between our observations of how galaxies and galaxy clusters move, and how our theories tell us they should move based on our best estimates for how much normal matter is in those galaxies.

We call it "dark matter" because our formulas give the right prediction if we add a lot of mass where we see none, that is, if we assume there is some matter there that does not emit or interact with light.

AFAIK, the difference between general relativity with 3 spatial dimensions and one with additional spatial dimensions show up on the small scale, and not large scale like galaxies[1].

> could it not be the space-time curvature from the mass itself but from the encapsulating dark matter around it

If dark matter is indeed some kind of matter, then it would indeed affect the space-time curvature. That's in fact the entire point behind calling it dark _matter_, as mentioned above.

Of course there is the possibility that our theories needs to change. There have been proposed alternatives that does not require additional matter in the form of new particles. The problem is that it's very difficult to get the theories to match non-dark matter observations, all the "normal stuff", as well as dark matter observations.

[1]: https://www.forbes.com/sites/briankoberlein/2016/04/26/looki...


>We call it "dark matter" because our formulas give the right prediction if we add a lot of mass where we see none, that is, if we assume there is some matter there that does not emit or interact with light.

I'm not a physics expert so forgive me if this is a naive take, but could black holes just sitting around, too far from other objects to have a visible effect, account for this unaccounted mass? IIRC they're small in size but incredibly heavy, and if space is infinite then they could just be sitting around taking up mass.


Someone has thought of this, mainly involving primordial black holes. IIRC the idea is that right after the big bang, when the subtle density differences in the gas permeating the entire universe caused pockets of gas to contract and eventually form stars, some pockets would collapse into black holes directly.

edit: I should add that they can't be regular black holes formed from stars, because then they'd have the same distribution of the stars in the galaxy they formed. While the the stars in a galaxy are most numerous near the center and get less numerous away from the center, the mass we have to insert in the form of dark matter to make the equations add up has to be evenly spread from the center and far beyond the visible edge of the galaxy.

The problem with this primordial black hole idea is that having lots of such black holes about would leave a very tell-tale signature thanks to gravitational lensing, which would be very strong near the event horizon. So far, no searches have found this.

Here's one news article describing the results of a recent search: https://physicsworld.com/a/supernovae-reveal-that-primordial...

See also https://en.wikipedia.org/wiki/Primordial_black_hole


It makes me feel good I came up with a similar theory to what a trained physicist did, even if it's likely wrong...

Thanks for the links, I'm on a wikipedia binge now :)


You're welcome!

I think part of the issue with dark matter and similar is that the main stream mostly hears about the theories that are the best candidates, and not about all the alternative explanations physicists have thought about but discarded due to some more or less obvious issues. Most won't even make it to arXiv, since they'll be eliminated by some rudimentary cross checks.

So the public might get the impression that physicists don't even try to come up with alternatives, but that couldn't be further from the truth.


Dark matter is the hole in the formulas, the dark spot were no lights shines yet. We don't really know whether it exists or not, we only know that our models of the universe have this strange corner were things don't work as they should work. And because all the others corners work so well, we assume that there must be something else.

Its called dark matter because the strange corner is in the models regarding matter. Thre is also dark energy, a strange corner in our models of energy.


Why is every single comment here being downvoted? I think many of them raise valid points and discussions; I, too, have always been suspicious of "dark matter" and have always looked at other possible explanations, such as "it appears there is matter/gravity there from our vantage point, but with a broader perspective/more complete picture we might see that { space time curves differently at the local, galaxy, intergalaxy scale (for example)}".

You make it sound like physicists haven't tried looking for alternative explanations.

Faced with our many, varied observations there are two choices: either general relativity is wrong at larger scales, or there's some stuff out there that doesn't interact with light or much of anything else.

Maybe it's a combination of both, but to begin with it's usually a good idea assume the simpler alternative that it's just one of them.

Some physicists are looking at changing general relativity. MOND[1] is just a modification of Newton's law, so while it does reproduce the galaxy rotation curve observations it doesn't really explain anything in the same way GR does, and it's also non-relativistic which is pretty much a showstopper. There are efforts to make a relativistic MOND-like theory, such as TeVeS[2], but so far nothing has stood up. Some have considered that maybe quantum gravitational effects[3] reproduce the dark matter observations, but that approach also seem to have problems.

Your example implies a modification of GR. It appears to be very difficult to modify GR at large scales while conforming to all the observations which validate plain GR. So a good alternative guess is that there's something matter-like out there we can't see. Doing so, physicists have considered MACHOs[4], and they're currently searching for WIMPs[5], sterile neutrinos[6] and axions[7] to name a few candidate particles.

If some new theory comes along which supersedes GR, explains all the things plain GR can while also explaining the dark matter observations, then it would be welcomed and embraced by the physics community. Until then, physicists are looking in the direction they feel is the most promising one.

[1]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics [2]: https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93... [3]: https://en.wikipedia.org/wiki/Entropic_gravity [4]: https://en.wikipedia.org/wiki/Massive_compact_halo_object [5]: https://en.wikipedia.org/wiki/Weakly_interacting_massive_par... [6]: https://en.wikipedia.org/wiki/Sterile_neutrino [7]: https://en.wikipedia.org/wiki/Axion


IMO, nothing is certain until we arrive at the boundary of universe creation/expansion. This is where all of the real stuff is taking place. Until then, it will be mostly theories and opinions.

Conflating theory and opinion is a bad category error. You're going to have to learn to accept that nothing outside the realm of mathematical proof is certain. Not even Cell Theory is certain.

There’s no boundary. If you live on the surface of an expanding balloon, where’s the boundary of expansion/creation? There isn’t one. It’s expanding uniformly at every point.

but how can you put a start and finish to something that is eternal and infinite?

god knows how many iteration of terrestrial universes we have gone through already.

alls I'm saying is we ask these questions like asking Google and expect clear cut answers when reality itself is uncertain, until it is observed.




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