Cosmology Has Some Big Problems

https://blogs.scientificamerican.com/observations/cosmology-has-some-big-problems/

by LinuxBender • 7 years ago

64 72 7 years ago

blogs.scientificamerican.com

michaelsbradley• 7 years ago

https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pd...

eaim11• 7 years ago

Yes! Thanks for this

stcredzero• 7 years ago

It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe.

Is it really? Have people formulated specific break downs, then gone to look for evidence?

fhars2• 7 years ago

A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248). That does indeed refute the assumpion that dark matter is everywhere, but that is not an assumption anyone makes and is not part of any relevant theory of dark matter. On the contrary, the existence of galaxies like that is generally seen as one of the strongest arguments for the existence of dark matter as an independent, if elusive physical entity.

nabnob• 7 years ago

Couldn't it just as easily mean that our predictions based on general relativity are wrong?

Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or

2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out.

It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?

czbond• 7 years ago

Not necessarily. This great video from PBS Spacetime is a fairly detailed, but good for a 'nearly' layman on the findings in depth. https://www.youtube.com/watch?v=5t0jaE--l0Y

A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy

AnimalMuppet6• 7 years ago

Well... assuming that the local rules are the same as the rules billions of light-years away is an assumption, based on a philosophical presupposition that the rules are uniform. What probability should we assign to that assumption? 100% in the absence of evidence to the contrary? Or should we reserve some skepticism, remembering that it is an assumption?

Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.

jerf3• 7 years ago

"Have people formulated specific breakdowns, and goon looking?"

They have. Considerable effort has been expended trying to detect changes in various constants related to light, including speed but also some other things. It is expected that if constants were changing, spectra would change as well. So far as I know, all those results have been negative, but it's not for lack of trying. Similar arguments can be deployed for the nuclear forces as well w.r.t. spectrum, rates of fusion, various things you'd be able to observe in certain types of supernovae, etc.

One of the things I don't like about this genre of articles is that it's typically quite mistaken, if not outright disingenuous, about the current state of cosmology. From what I could see, the idea that cosmologists are all stodgy old fogies brought up in a paradigm of the Big Bang and who won't entertain any other thoughts is diametrically opposed to the truth. To my eyes, the field is a bubbling cauldron of various exotic ideas and attempts to resolve all these issues. There's no lack of theories in cosmology and attempts to resolve these issues, including many quite radical ones (the holographic principle, changing constants over time, heck even "Dark Energy" is quite radical in many ways even if it is also the accepted theory at the moment).

What we lack are theories that explain all the observations. Dark matter is favored not because it's the only idea that anyone has come up with, but because it's still the one that best fits the facts. (As PBS Space Time pointed out last week, ironically, the galaxies recently discovered to not contain dark matter are themselves quite strong evidence dark matter must exist: https://www.youtube.com/watch?v=5t0jaE--l0Y , because almost all other theories to explain galactic rotations are based on characteristics that can not vary by galaxy like matter distributions can. "MOND", for instance, is not "MOND, except in these two galaxies".)

If you can solve all these problems, as near as I can tell, you'll be celebrated, not shut down by the old fogerati. But be prepared for your theory to need to cover a lot of existing observations; we're centuries past "Well, what if gravity just worked differently?" or "What if the constants aren't constant?" You're going to need a great deal more detail than that.

rgrieselhuber• 7 years ago

Biggest takeaway from this is how many underlying presuppositions appear to be assumptions.

eaim11• 7 years ago

Yes.

shrimp_emoji• 7 years ago

It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe?
To explain observations of galaxies inconsistent with general relativity, the existence of dark matter was posited as an unknown and invisible form of matter calculated to make up more than a quarter of all mass-energy content in the universe

Food for thought: the best current evidence of dark matter is the Bullet Cluster[0]. In particular, look at this picture: https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_s...

At first, these were two blobs of dark matter and gas. They collided. That resulted in what we see now: the dark matter portions (purple, measured by gravity lensing) magically went through each other (because dark matter is weird like that) while the gas portions (pink) actually collided and formed a shockwave (like normal matter behaves), with much of the gas remaining in the middle.

The tone in the article quotes there makes it seem like dark matter is some esoteric rounding error, but that seems like pretty "solid" evidence for... the anomalous mass readings we call dark matter.

0: https://en.wikipedia.org/wiki/Bullet_Cluster

calebgilbert• 7 years ago

To be fair, I bet most, if not all, cosmologists would agree that they know far less than they don't know. The title of the article is a bit sensationalistic from that point of view, but then I guess "Cosmology has some big details to work on" isn't nearly as catchy.

hhs6• 7 years ago

Interesting view. Near the end, it says:

“The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.”

Empiricism is based on sense observations. And a lot of science has been confined to human senses. I’m curious if tapping into more basic science research by analyzing different types of senses, for instance, available to animals, may offer breakthroughs down the line. For instance, fish employ the lateral line system to detect pressure gradients in the environment.

wilg• 7 years ago

What kind of senses available to animals are there that we should be using for science?

Also I'm not entirely sure what you mean that we're confined to "the 5 senses". First, humans have way more senses. Second, I don't think it's confining ourself to build technology that converts something we can't sense (like gravitational waves) into something we can (like a spreadsheet).

dfischer2• 7 years ago

What aren’t we using from the animal kingdom? We create sensors that are extra human. Infrared etc...

Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.

hhs6• 7 years ago

Indeed, I agree with your point, “Maybe this is an unknown unknown problem.”

I’m not sure why my comment is being downvoted, is there something I said that’s in bad taste?

chongli• 7 years ago

We have no better access to the sense data of the Ampullae of Lorenzini in a shark than we do to the signals recorded by a radio telescope. Arguably, our access is worse for the shark than for the telescope.

Ultimately, no matter what we use to record the data (animal or instrument), we can only access the results through our 5 senses.

gerbilly• 7 years ago

One way to think of scientific instruments: like telescopes, microscopes, voltmeters is that they are extensions of our senses.

hhs6• 7 years ago

I agree, thanks for the note.

JackFr2• 7 years ago

But the reality of them is that they are not extensions of our senses, so much as compressors of experience. That is they map a broader reality into our limited sensate experience. When we use them we have to remember that the map is not the territory, and we have to be especially careful about artifacts they may introduce.

jerf3• 7 years ago

When it comes to cosmology, our observations have been using light, because that's what has traveled in space. It is pretty obviously not that useful to ask a dog to sniff the sky or a homing pidgeon to navigate to Alpha Centauri, or something. We've obviously long since passed using only the visible spectrum.

We also recently added gravitational wave detection to our repertoire. I seriously doubt any animals out there are detecting gravitational waves.

I'm not sure how a science based on observing every wavelength of light we can get our hands on, the vast majority of which no animal on Earth can detect or use, and also gravitational waves, is "confined to human senses".

hhs6• 7 years ago

Makes sense, and agree with the last point, “I'm not sure how a science based on observing every wavelength of light we can get our hands on, the vast majority of which no animal on Earth can detect or use, and also gravitational waves, is "confined to human senses"”. Thanks for the explanation.

lkrubner• 7 years ago

About this:

"It is pretty obviously not that useful to ask a dog to sniff the sky or a homing pidgeon to navigate to Alpha Centauri, or something."

That example might be bad, but there are others that are valid. For instance, in healthy human women, the menstruation cycle seems to be the exact length of the moon's orbit. Is that a coincidence, or do human bodies have a way of gaining data from the moon? If so, what is that data? Maybe the mechanism is as simple as a springy protein that can absorb tidal forces and convert it to an information signal. Or perhaps something novel is going on.

There are potentially a lot we can learn about the universe by making simple observations here on Earth.

AnimalMuppet6• 7 years ago

Yes and no. Yes, we're seeing gravity waves and radio waves and gamma rays and near infrared and millimeter wave and neutrinos, and maybe a few others that I forget. We're way past human senses, or any animals.

And yet I keep thinking of a deaf species that runs across Beethoven's Ninth Symphony. They can put an oscilloscope on the pressure waves in the air, so they can "see" what's going on. They can study the different frequencies of vibrations, and they can find patters in the time variation of those frequencies.

But they can't hear it. Hearing Beethoven's Ninth is really different from studying the frequencies with an oscilloscope. They could even hook up a brain scanner to a human listening to it, watch the brain start lighting up, and they still wouldn't understand.

We can gather data via all these different frequencies and modes. And yet I wonder how much we're not getting, not because we don't have the data, but because we don't have the right... something. (I can't even figure out what words to use for that something. The music analogy is the best I can do.)

jcroll• 7 years ago

Ethan Siegel write up on this problem: https://www.forbes.com/sites/startswithabang/2018/06/22/why-...

acqq2• 7 years ago

But also about other claims from the Ekeberg's article (who, as I see, is a "a philosopher of science"):

https://www.forbes.com/sites/startswithabang/2018/07/26/ther...

"There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating"

Careful reader of Ekeberg's article can both recognize that the article claims are inspired by the claims of the "cheating" side but also that where he writes his own he completely fails on physics. I.e. if one side is cheating, he'd be a third side, the one that's completely unscientific: even the physicists that develop theories that compete with dark matter would not write what Ekeberg wrote: "Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. But according to the latest measurements, it is not, suggesting the theory needs to be reexamined." It's plain nonsense. The reason:

https://www.forbes.com/sites/startswithabang/2019/01/16/myst...

"Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible."

We even have the pictures where the galaxies and dark matter aren't at the same place, totally the opposite of Ekeberg's "everywhere" strawman claim, and exactly that opposite was always treated as the biggest support for dark matter:

https://www.forbes.com/sites/startswithabang/2017/11/09/the-...

Once I've reached that strawman claim, I've checked what the profession of Ekeberg is. I openly admit his uncritical bias just confirmed my own bias about that profession.

astro1233• 7 years ago

I'm a grad student working on cosmology, and while I agree there is a lot of work still to do (we don't know what 95% of the matter that makes up the universe is!), I disagree with a lot of what the author says.

Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere.

We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve

For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm

Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.

Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited.

Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity

It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model

This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang.

Today's space telescopes provide no direct view of anything

I have no idea what that means. They literally observe the sky...

There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...

scrozart• 7 years ago

> Today's space telescopes provide no direct view of anything
I have no idea what that means. They literally observe the sky...

Seriously! At this point they're just spitballing.

astro1233• 7 years ago

I was maybe a bit too cavalier here. I think I understand what the author means - the data that they gather is understood in the context of the model that we think is best.

But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen...

People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.

astro1233• 7 years ago

For some reason edits are silently failing, but an addendum to

Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.

Admittedly the DE from Einstein is for very different reasons than the DE today, but we again had the big bang and no DE from the 60s until the 90s (observations from https://en.wikipedia.org/wiki/Supernova_Cosmology_Project) so they don't go hand in hand.

petschge2• 7 years ago

The fact that SOME galaxies are inconsistent with the theory of Dark Matter actually strengthens that theory.

If the difference in rotation curves, the usual signature of dark matter at the galaxy level, from what GR predicts based on the mass of luminous objects was due to a modification in the way gravity works, then that should apply to ALL galaxies. Modified Newtowian Dynamics (MOND) (or the relativistic TeVeS models) should work the same for all galaxies, at least all of roughly same mass and same depth of the gravitational potential.

The fact that we can find similar sized and aged galaxies that behave like they have different amounts of dark matter is therefore NOT caused by the way gravity works. The next best explanation is that most galaxies contain dark matter, but some loose it through their evolution history, e.g. due to interaction with other galaxies.

whatshisface• 7 years ago

To be clear, they're not inconsistent with the theory of dark matter, they're inconsistent with those galaxies specifically having dark matter. The author was wording that in a confusing way.

scott_s• 7 years ago

I found the authors' points about reports from the past several months disingenuous, since he's advertising a book that was clearly written and edited well before those announcements. It's valid to talk about those points in the context of arguments from the book, but leading with those points implies those arguments are a result of those points.

mnl• 7 years ago

I've rarely seen more spectacular agreements with a theory than those of a Lambda-CDM fit of Planck's 2015 data. That can't be wrong (but as I've never worked on it, this statement is just some guy's personal impression based on his physics instinct). What's your take on those results?

ccvannorman• 7 years ago

I've never been a fan of Dark Matter. Not all galaxies have dark matter, but only incredibly diffuse galaxies don't have it[0]. Doesn't that mean that the density of matter in a galaxy is what gives rise to "faster rotations/more gravity", and not just the total matter irrespective of its galactic density?

Furthermore, the "Bullet Cluster" example is telling. Apparently, the extra mass stuck around the more dense part of the galaxy, and not in the less dense gas cloud that resulted from the collision. Again, only the dense parts of this cluster exhibit "faster rotations/more gravity".

So to me, this is terribly un-compelling. So there's a magic invisible matter that just so happens to only coalesce around dense galaxies/galactic areas and never around sparse ones.

[0] http://www.astronomy.com/news/2019/03/ghostly-galaxy-without...

edit: s/no matter/irrespective of (poor use of the homonym "matter")

eaim11• 7 years ago

@astro123

There’s a tautology in your critique. You’re attempting to suggest that there is evidence for dark matter. There isn’t. Dark matter is a theory, one that has not yet produced empirical evidence to support it (& perhaps cannot ever do so.)

mkl• 7 years ago

If you want to reply to a comment, please click the "reply" button below that comment, rather than starting a new comment thread. @<username> doesn't do anything here.

eaim11• 7 years ago

Ah, understood, thanks. Sorry about that.

eaim11• 7 years ago

@astro123 Sorry my comment uploaded before I was done. It is an error to state that there is evidence for dark matter. There is no evidence for it other than that as a hypothesis it adds support to a larger cosmological theory; that of the so-called Big Bang. But that is basically a circle in the proof. A tautology.

ephimetheus• 7 years ago

What about the Bullet Cluster?

eaim11• 7 years ago

If the Bullet Cluster had offered not hypothetical but empirical, incontrovertible evidence for Dark Matter, at this juncture we wouldn’t even be calling it Dark Matter anymore.

eaim11• 7 years ago

@astro123

The following excerpt is the crux of the author’s argument regarding DM, & it points to the dark elephant in the room that a lot of physicists are bothered by but don’t want to discuss:

“It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? The answer lies in a peculiar feature of cosmological physics that is not often remarked. For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm, is not to describe known empirical phenomena but rather to maintain the mathematical coherence of the framework itself while accounting for discrepant observations. Fundamentally, they are names for something that must exist insofar as the framework is assumed to be universally valid.”

eaim11• 7 years ago

All said and done, the current state of cosmology (whether one falls in with mainstream theories or not) is a mess. It has so many addendums, codicils & caveats that one has to be almost a type of lawyer of physics to be able to navigate it. We await our new Einstein. Our new Heisenberg. Our elegant theory of everything; or as one science writer put it: The universe on a T-shirt.

eaim11• 7 years ago

Here’s an article from Rob Sheldon, who worked on ROSETTA. He is less timid than Ekeberg:

https://uncommondescent.com/intelligent-design/rob-sheldon-t...

Cosmology Has Some Big Problems

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