
Cosmology Has Some Big Problems - LinuxBender
https://blogs.scientificamerican.com/observations/cosmology-has-some-big-problems/
======
astro123
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](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](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...

~~~
petschge
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
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.

~~~
slowmovintarget
To be even more clear, "dark matter" isn't a theory. It is a name for
something we need theories about.

I wish the article had made that apparent.

~~~
eaim
Sorry but that’s an intellectual dodge. A verbal fiddle. Saying it is a “name
for something” doesn’t make the fact that it’s a hypothesis disappear. One is
simply positing the need for more “Russian dolls” inside the Russian doll one
has hypothesised to begin with.

------
shrimp_emoji
>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...](https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_scale.jpg)

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](https://en.wikipedia.org/wiki/Bullet_Cluster)

------
ccvannorman
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...](http://www.astronomy.com/news/2019/03/ghostly-galaxy-without-dark-
matter-confirmed)

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

------
jcroll
Ethan Siegel write up on this problem:
[https://www.forbes.com/sites/startswithabang/2018/06/22/why-...](https://www.forbes.com/sites/startswithabang/2018/06/22/why-
cosmologys-expanding-universe-controversy-is-an-even-bigger-problem-than-you-
realize/#3587f0422381)

~~~
acqq
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...](https://www.forbes.com/sites/startswithabang/2018/07/26/theres-
a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating/)

"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...](https://www.forbes.com/sites/startswithabang/2019/01/16/mysterious-
galaxy-measured-exquisitely-and-contains-no-dark-matter-at-all/)

"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-...](https://www.forbes.com/sites/startswithabang/2017/11/09/the-
bullet-cluster-proves-dark-matter-exists-but-not-for-the-reason-most-
physicists-think/)

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.

------
eaim
@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
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.

~~~
eaim
Ah, understood, thanks. Sorry about that.

------
eaim
@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.”

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

~~~
eaim
Yes.

------
calebgilbert
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.

------
hhs
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.

~~~
jerf
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".

~~~
AnimalMuppet
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.)

~~~
jerf
I actually think there's a bit of an answer to that, in the No Free Lunch
theorem. To "experience" Beethoven's 9th Symphony, you need cognitive biases
that it can tickle in the way that Beethoven intended. An alien missing those
biases won't "get it", but then they'll get things we won't. But there's no
solution to having the right biases for everything. All we can do is throw a
lot of things at it and hope for the best, and what's more, that's the best we
or any alien in the physical universe could do.

(Heck, you don't even need a deaf species. There's a lot of reason to believe
that birds don't experience music the way we do, and they're not even strictly
speaking "aliens".)

So there's no particular gain to worrying about being limited to "human"
senses, because there is no actionable way to "transcend" them in that sense
other than by being something other than what you are. It's certain to be
true, there's nothing to be done about it that we aren't already doing, and
thus, it isn't really an interesting criticism to vaguely suggest that we
should somehow be something other than ourselves.

~~~
AnimalMuppet
I wasn't suggesting that we should be other than ourselves - just that, by
being ourselves, there are things that we don't "get", even when we can see
the data.

------
eaim
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.

------
eaim
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...](https://uncommondescent.com/intelligent-design/rob-sheldon-the-
real-reason-there-is-a-crisis-in-cosmology/)

------
eaim
@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
What about the Bullet Cluster?

~~~
eaim
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.

------
michaelsbradley
[https://www.nobelprize.org/uploads/2018/06/alfven-
lecture.pd...](https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pdf)

~~~
eaim
Yes! Thanks for this

------
stcredzero
_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?

~~~
fhars
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](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
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?

~~~
darkmighty
It's not that simple. It's not like a) Some galaxies fit predictions, b) Some
do not, and we add unknown dark matter.

It's that when they do not fit predictions, there is a single parameter (the
mass of dark matter) that does explain its behavior, whose model is that of a
weakly interacting gas halo. So dark matter tries to fix things in a very
precise way, it's not an arbitrary curve fitting exercise.

Now whether there is really weakly interacting matter out there or some other
explanation is valid is still an open question afaik; but the evidence is
quite strong so far.

~~~
astrobe_
> Now whether there is really weakly interacting matter out there

Not "out there". It's supposed to be >80% of the matter of the universe. We
supposedly are eating some every day.

~~~
pdonis
_> It's supposed to be >80% of the matter of the universe. We supposedly are
eating some every day._

It's >80% of the _average density_ of the matter in the universe. But that's
an average over all of the universe. On the scale of our planet, or of the
solar system, that density is negligible--as in "30 orders of magnitude
smaller than the density of the stuff you eat" negligible.

