
Black holes ruled out as universe’s missing dark matter - myinnerbanjo
http://news.berkeley.edu/2018/10/02/black-holes-ruled-out-as-universes-missing-dark-matter/
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sulam
This spawned a question for me that seems like it must be nonsensical but I
don’t know the answer.

Why did the Big Bang not just produce a Big Hole? IOW, if all the current mass
of the universe was in a small volume wouldn’t it have promptly created a
black hole?

I’m assuming the answer has something to do with mass not actually existing in
its current form until the universe expanded enough. However I don’t have any
mental framework to understand why that would be true. If someone reading this
knows the answer and can point me at it, I’d be grateful. TIA!

~~~
DougWebb
I'm absolutely not an expert, but I believe there wasn't any mass at first; it
was all energy. It had to slow down to become mass, at which point it was
spread out enough. Or something along those lines.

Another possibility is that black holes are places where lots of mass
accumulates in the same place in space, while the big bang was a rapid
expansion of space itself. Even if there was enough mass in one spot to be
what we'd consider a black hole, the space it occupied expanded, dragged the
mass along with it, and ripped the black hole apart.

~~~
InclinedPlane
"Mass" is just another name for "rest-energy".

A single photon cannot have mass because it has zero energy in the reference
frame where it is at rest (zero net momentum). But a pair of non-parallel
photons can have rest-mass, and indeed the mass of the photons inside a star
is considerable, for example.

~~~
pdonis
_> "Mass" is just another name for "rest-energy"._

Not if you're talking about what the source of gravity (spacetime curvature)
is. Massless particles still have energy and still cause spacetime curvature.

~~~
InclinedPlane
The "source" of gravity is the stress-energy tensor. "Mass" (rest-energy) is a
simplification that is useful for approximations and conceptualizations.

~~~
pdonis
_> "Mass" (rest-energy) is a simplification that is useful for approximations
and conceptualizations._

Yes, but not in a context where radiation is present, since radiation can have
energy but has no rest mass (rest energy).

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prmph
One question I have: is it not possible that the big bang occurred an infinite
time ago? If the expansion of the universe is accelerating with time, does it
not indicate that, if we reverse the time, the deceleration is asymptotic?

In that case the big bang is compatible with a universe that has always
existed and did not have a beginning

~~~
gpderetta
Even a car constantly accelerating for a long time was still at t0.

~~~
smithmayowa
A big bang event could explain the reason why the universe expanded in the
first place, but it does not explain the accelerating expansion of the
universe currently, forgive me for my ignorance if any, but in physics I was
taught that any object which moves or is in constant motion was acted upon by
a force, and so if the big bang created an expansion it will be a constant
expansion and not an accelerating expansion as is obtained presently, as there
is a requirement for a kind of force to cause an accelerating expansion which
is not explained by a singular big bang but by a continuous big bang, which
could as well be infinite in nature.

~~~
gpderetta
Again IANAP (and I'm sure any actual physicist will be horrified by my
explanation), but the big bang is not an explosion that a time 0 set some mass
in motion. But you are, in a way, right: the big bang is not over, is
literally still happening right now. General relativity still predict that the
process started a finite amount of time ago; wether the process will continue
indefinitely or not is still an open question.

The expansion is an expected behaviour of space time, and is predicted by
general relativity given a certain parametrization of the density of matter an
energy of the universe. To explain the acceleration, though, a large energy
parameter is required, which has not been yet identified with any known
process, although many theories exhist; as placeholder the parameter is known
as dark energy. It is of course possible, but generally considered unlikely,
that general relativity is incomplete and another theory could explain the
acceleration without dark energy.

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GarrisonPrime
Isn’t “dark matter” just a way to account for an unexplained behavior? It
bothers me that its existence is treated as a given, when it could be a case
of mistaken assumptions. If calculations say the universe is acting as if it
contained much more mass than we observe, we should also consider the
possibility that our method of calculation may be flawed.

I’m not claiming dark matter doesn’t exist, only that I fear the human
tendency to run with a hypothesis too eagerly and discard alternate options.

Similar to how everyone seems to speak as if Hawking radiation is a given
fact, when it is thus far completely unproven and nothing more than a
suggested idea.

~~~
cdumler
Yes, Dark Matter is a statement about the premise that something appears to be
operating gravitationally while have no (or perhaps so little that we don't
recognize it) interaction with other matter; however, it is not without
reason.

The primary focus on matter as the candidate is that if you don't believe that
some form of matter is responsible, you begin having to explain how a lot of
our Laws are incorrect. Dark Matter is really a problem that we have a notion
how our Laws should work at the cosmic scale, yet they don't. And yet, we
don't see any obvious reason why they shouldn't give how thoroughly we've
tests these Laws.

For instance, if you say that our equations for gravity is off, why is it
completely consistent for everything in our solar system? Why is consistent
down to the most precise test for gravitational frame pulling? It seems to be
only different when you talk about very large masses creating gravity on
objects tugged at very long distances. Why does it just cut over to different
behavior?

If you say that gravity is emergent, then how do you explain the standard
model's place for the graviton? Granted, it's not testable (gravity is so weak
it's beyond direct testing), but it seems to be fit right in to a spin-2
tensor where we would expect a gravity-like particle to be. Why would you
expect that to not be true?

That said, Dark Matter matter candidates are getting weeded out pretty
quickly, these days. No new types of particles are being discovered, and Dark
Matter observatories are largely coming up empty. But, that's science: got an
idea? Test it and let the results speak.

As an aside, I think one thing to remember is: just because science doesn't
know the answer to something, it often knows what can't be the right answer.
Look into the theory's and their criticisms.

~~~
ziftface
Is it possible that it's something other than gravity? A force we don't know
about because of how weak it is but has an effect on a large scale?

I'm completely ignorant of the subject so I don't know how crazy that might
sound.

~~~
cdumler
No, that is a perfectly valid question. The answer is: science has no idea
what gravity _is_. What we do know is:

The Newton/Einstein definition is that it is an effect by mass on space/time.
Mass always travels in a straight line (unless acted on), but mass causes
space/time to curve. So, what we see as gravitation attraction is a fake
force. No different than being "pushed" into the back of your seat when a car
accelerates. You are staying still, the car is moving forwards. The
Newton/Einstein definition does not specify any mechanism. The description,
however, is highly specific, and so far every test for the most subtle effects
have been validated. Well, except for cosmic structures.

Quantum mechanics says that particles emit/receive interactions via the
graviton carrier, and that it can be quantized and transmitted via waves. In
the last few years, we have detected gravitational waves. It fits perfectly
and exactly as we would expect over cosmic distances. Unfortunately, the
amount of energy necessary to detect an actual graviton is beyond anything we
can expect to be able to produce for the forceable future and likely will
never have the resources. So that is out. Also, it makes no claim on how it
can affect space/time.

So, just like we original argued over whether or not it was particles or
waves, I think this paradox strongly suggests that we're just not looking at
gravity correctly. I suspect that the real problem is "What is time?" Why do
things experience different rates of time? It seems obvious to me that
gravity, time, and entanglement are related. Gravity is very likely to be Dark
Matter: a stand-in name until we can grasp the fundamentals.

~~~
oAlbe
> Unfortunately, the amount of energy necessary to detect an actual graviton
> is beyond anything we can expect to be able to produce for the forceable
> future and likely will never have the resources.

Sorry for the late reply. Why is that? What determines the amount of energy
needed to detect a given particle?

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chopin
One thing I do not understand: If a black hole in line-of-sight increases
intensity, the intensity for other view points must decrease (the total number
of emitted photons needs to stay constant). If black holes make up a
substantial part of the dark matter, there should be (statistically) few in
the line-of-sight and many more slightly off. Therefore I'd expect that this
cancels out. Does anyone know how it is accounted for this?

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brink
Sorry if this question is naive or ignorant or just doesn't make sense; but
could this dark matter be influence from higher "spatial" dimensions that we
can't see? I mean - doesn't string theory demand something like 10 dimensions
in total?

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swframe2
Since, we can only see "the observable universe", how do we know how much mass
is beyond our view? If we don't know what is there, why do we think there is
missing mass?

~~~
mort96
When we measure the amount of mass in a galaxy, we see that the galaxy's
rotation is way faster than the amount of mass would indicate.

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andrewflnr
Assuming this pans out, is there anything left but WIMPs?

~~~
erik_landerholm
AXIONS

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nautilus12
Does this mean that black holes possibly might not even exist? Aren't there
examples of them being directly observed?

~~~
sulam
We have observed their x-ray jets directly and have observed their creation
(recently). Pretty sure they exist. :)

~~~
oldandtired
Let's change this a little bit.

We have observed specific phenomena but not that which created such phenomena.

As far as "Black Holes" as per theoretical descriptions are concerned, they
cannot exist in a finite time universe as far as we (the observers) are
concerned. The theoretical models used all have as a basic assumption that
increasing gravity (whatever that may be) will cause a slow down in time as
observed at distances away from such increase. As such, all phenomena involved
in the creation of such entities will slow to a complete stop as far as we are
concerned.

Hence, if the universe is of any finite duration, we will not have seen the
creation of even 1 black hole of any kind. On the other hand, if the universe
has existed eternally, it is still likely that these entities are still in the
process of formation and not yet in existence.

I don't doubt we are seeing some interesting phenomena, but not the entities
called "Black Holes". The argument for the creation involves changing
perspective to some observer who is falling into or through the event horizon
(choose which one of these you want, as there are apparently a couple of
choices here in the theoretical models). Since we are not such observers, that
perspective is actually irrelevant to us. What is relevant is what we observe
in the universe at large.

The basic problems (irrespective of mathematical assumptions) with the
processes of "Black Hole" generation relate to non-uniformity of compression,
time dilation and other basic assumptions for the "Black Hole" models.

I find the reasoning used for the existence of "Black Holes" in our universe
to be lacking in logical rigour and appears to have a lot of hand-waviness to
it.

I am currently reading the documentation for the Metamath system and there are
some quite enlightening comments in that about mathematics and those who study
it. Especially as it relates to us who are not mathematicians as our career.
One of these relates to the amount of "faith" we have to exhibit when trusting
that specific "proofs" are in point of fact true. Even mathematicians who are
not in that specific speciality do not have the necessary background to verify
any proof outside of their own mathematical area.

Mathematics is a profoundly useful tool but as we have seen in the past and we
will see in the future, it has problems (like all areas).

~~~
InclinedPlane
We have observed matter falling into a black hole. We've watched "hot spots"
in orbit of a black hole in the accretion disk shine their light at us as they
orbited the black hole. We've watched as the orbit got tighter and tighter and
the light was dimmed by gravitational red shifting, then we've watched the
light blink out and disappear as the blob of gas fell below the event horizon.

The evidence for the existence of black holes is incredibly strong at the
moment. In fact in some ways it's stronger than the evidence for the existence
of atoms about a century ago. Nobody except cranks or extreme contrarians
seriously disputes the theory these days.

~~~
oldandtired
No. Incorrect. Wildly inaccurate.

We have made certain observations that are assumed to be the result of matter
falling into a "Black Hole". We do not have any observations that show us this
as a fact. Read the observational material very carefully.

Go back over the last few decades and see how many times it is declared "we
have seen x for the first time", where x is the is the same entity each time,
in this particlualr case "Black Holes".

Men (women, children) want to believe that they have a certain handle on the
truth and reality. What is very unpleasant to most is not having that
certainty. This applies to all people across the board and even more so to
those whose expertise is dependent on their being right. Many scientists are
in this category.

It is often difficult to sit in the place of recognising that we just don't
know. We have some ideas which, on the evidence, give a handle to investigate
further, but we should understand that our understanding can be turned on its
head.

The evidence for the existence of something is there, yes. But, is it a "Black
Hole" of the theory presented, hmmm, that is unknown and for the time being,
unknowable. As we cannot get out there and actually do the appropriate
experiments to test this. We can only do remote observations and these can be
easily misinterpreted.

>>Nobody except cranks or extreme contrarians seriously disputes the theory
these days.

The problem here with this view is that it has been "cranks" and "extreme
contrarians" who have brought about the biggest changes in science. There are
Nobel Prize winners amongst them. All views about the nature of our universe
should have those who dispute it. This should spur on our investigations into
the nature of the universe. If we are unable to handle someone disputing our
models and theories of the universe, then what are we doing? We are not
serious about expanding our knowledge, we are serious about our reputations
and being right.

The biggest problem for science today is that people don't trust it because it
keeps getting things wrong, yet all the while saying that it is the only
source of truth.

Science is one of a group of tools we can and should use to investigate the
universe around. It has its limitations as does all the other tools we have
and we need to recognise that though this tool is helpful in understanding, it
is not the tool that gives us the truth.

~~~
SiempreViernes
You had like, a _slim_ case before GW150914. Now you just have to either
accept that black holes (in the sense of the external metric predicted by GR)
do exist, or go make friends with the climate change deniers.

The science discussion about the existence is _settled_ , as evidenced by your
complete lack of any concrete objection to the interpretations. (Just saying
"measuring is ambiguous, maybe we didn't understand it properly" like it is an
objection is typical cranking)

~~~
oldandtired
You really need to read the information provided about GW150914. There is no
direct observation of the event, irrespective of what LIGO might say about the
matter, LIGO is an indirect methodology.

I have no doubt that something was observed, but what that was will take far
more research and repeated events that can be backed up by other observational
means before we have any real evidence before us.

The science is only settled for those who want certainty in their models and
theories. For practical uses, one can believe that electrons exist and act in
particular ways and we build "technology" based on those "beliefs". Yet, we
still do not have any real handle on what these particular entities are.

I used to believe in "black holes" and other assorted entities. I had no
problems with these things, until I started noticing the discrepancies. It
made me take a longer look and I realised that we know far less than we think
and we understand far less than we think we do.

I live country that experiences climate change, yet, what I find interesting
is that if you have questions about whether or not it is anthropogenic, you
are immediately classified as a denier. The same goes for many different areas
in science. If you don't accept the dogma you have to be a "crank".

What science needs is a higher level of scepticism than what it currently has.

Too many of the "settled" things are not "settled" at all. We have barely
scratched the surface of the universe around us and the major failing we have
is this desire to be certain. There are huge amounts of experimental
observations that are showing that we really have no clue and an enormous
number of new models are being developed as the years go by.

~~~
SiempreViernes
Look, to do science you have to believe the world outside your head can be
observed; and if you are ready to trust the rickety and convoluted stack that
encodes pulses from a keyboard into photons from a screen to accurately convey
information, then gravity waves have been observed and match predictions for
black holes _exactly_.

If you want to stick to reading Gorgias of Leontini that is fine, but please
don't bother the rest of us that do accept the world outside as real.

~~~
oldandtired
You miss the point of what I am saying. Observations are being made, but is
the given explanation actually meaningful? The universe is real. This does not
mean that our explanations or interpretations are "truth". The problem I have
with the current mindset is that it trends to treating others with a different
viewpoint, model or theory as being unworthy of consideration, to be treated
as pariahs, imbeciles, crackpots, heretics, to be hunted down and
assassinated.

We should be accepting that our models and theories are both incomplete and
wrong, irrespective of how useful they are. Every model and theory has its
points of failure. That should be expected and is not a problem. Starting from
that basis, we keep investigating to get better models or theories that help
us gain a better insight into the universe around us. If that means giving up
one model for something completely else, then what's the problem. Our universe
is beautiful, complex, a place of incredible wonder that we can have an
exciting time exploring and discovery.

There is a vast difference between the reality of the universe and what our
models and theories are. The first is the territory, the second is only a map
and maps can be notoriously faulty.

In regards to your reference to Gorgias of Leontini, I had to look that up. I
chuckled. Is it possible that some of the "superstars" of science today are
modern students of him?

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jngreenlee
I can't wait for the n-gate synopsis of this one.

Get back to social mining you minions, you.

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mpc755
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.

~~~
ravar
what are you talking about dude, could you point to something on the arxiv?

~~~
mpc755
Another way to think of this is that spacetime has mass. Spacetime and dark
matter are both referring to the same 'stuff'. The stuff is a supersolid that
is displaced by ordinary matter.

The Earth displaces the 'stuff'. The displaced 'stuff' pushes back. The
displaced 'stuff' pushing back is gravity.

Curved spacetime = Geometrical representation of gravity.

Displaced supersolid dark matter = Physical representation of gravity.

