
Dark matter may be older than the Big Bang - howard941
https://www.sciencedaily.com/releases/2019/08/190807190816.htm
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saagarjha
Previous discussion:
[https://news.ycombinator.com/item?id=20654625](https://news.ycombinator.com/item?id=20654625)

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FreeFull
Saying that it happened before the Big Bang is super misleading. Most readers
would assume that the inflationary period is part of the Big Bang.

~~~
Simon_says
Agreed. I wonder what the authors think “Big Bang” refers to if it occurred
after inflation.

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mirimir
That's what I was going to ask.

But from
[https://news.ycombinator.com/item?id=20666140](https://news.ycombinator.com/item?id=20666140),
cited by sls:

> They're using "Big Bang" to mean the hot, dense, rapidly expanding state
> that is the earliest state of the universe for which we have good evidence.
> In models with inflation, this state occurs at the end of inflation, when
> "reheating" transfers all the energy stored in the inflaton field to the
> Standard Model fields (quarks, leptons, and radiation).'

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r10tAct
The scientific discussions of Dark Matter seem to be the scientific version of
political doublespeak which boil down to- "We aren't really sure what is going
on but since you have questions, we should have answers..." I'm about to check
the previous article and comments and kudos for krastonov for the suggested
reading.

Still trying to make sense of this dark matter subject besides the usual, no
one is really sure...

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loblollyboy
This article says that 'mathematically' it could have happened before but
leaves it at that. Does anyone know what kind of math? And the prerequisite
knowledge I might need to know (subjects, bonus points for good textbooks). I
myself have a pretty firm knowledge of undergrad and some grad level physics.
But I find myself recently interested in (big time/spacial scale) cosmology
and also quantum phys, but I don't really know where to begin.

~~~
parsimo2010
This pretty much all falls under the umbrella of mathematical physics- any
mathematician will tell you it's not "real" math. Don't let that stop you from
studying it if you're interested, but it's not for the faint of heart and most
people require a mentor (aka an advisor and PhD program)- many self proclaimed
"autodidacts" stall out once there are no longer online tutorials and they
have to slog through textbooks written by physicists and mathematicians who
seem to enjoy making a subject hard to understand.

Starting with analysis, measure theory, and I suppose the obligatory linear
algebra should first if you don't already have those. Spectral theory and
maybe group theory are probably next steps to having enough background to do
the quantum and relativistic stuff. I glanced at the abstract for the source
material for the HN post
([https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.061302)),
and it almost certainly requires spectral theory.

I'm not an expert in this area, so a mathematical (or theoretical)
astrophysicist might chime in and fill in the gaps.

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sak5sk
Could someone explain to a layman what is our best theory as to the limits of
the universe as it pertains to the start of the big bang? How do we know the
big bang is not just a tiny spec in the middle of a giant ocean (similar to a
supernova, but on a larger scale) that's part of something much much bigger? I
am guessing it's just beyond our knowledge to figure out what lies beyond the
big bang, but if that were true, wouldn't dark matter truly exist way before
any big bang(s) took place?

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philipov
> _How do we know the big bang is not just a tiny spec in the middle of a
> giant ocean_

This is referred to as the Cosmic Landscape, or, Eternal Inflation. In eternal
inflation, the cosmological constant becomes a field in its own right, the
Inflaton field, and our universe is a pocket of spacetime where that field has
randomly adopted a value allowing nontrivial structure to form.

[https://en.wikipedia.org/wiki/Eternal_inflation](https://en.wikipedia.org/wiki/Eternal_inflation)

The big problem is that science is based on repeatable experiments, and it's
very difficult to make a theory of what happens outside the observable
universe that can be tested even in principle. If a theory doesn't make
falsifiable predictions, then it isn't science. Until someone comes up with a
prediction that can be tested, one might as well ask, "How do we know the
world wasn't created by God?"

There are infinitely many things we don't know, the challenge is coming up
with something we _can_ know.

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hprotagonist
no debates from me here.

i will add though that from “it’s not science” it does not necessarily follow
that “and therefore it’s not useful.”

the obvious example is that the idea of falsifiability as a criterion for what
is and is not science is itself unfalsifiable — but very useful!

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faissaloo
I still feel like MOND would make alot more sense than all this weird dark
matter stuff
[https://en.m.wikipedia.org/wiki/Modified_Newtonian_dynamics](https://en.m.wikipedia.org/wiki/Modified_Newtonian_dynamics)

~~~
dwaltrip
Dark matter doesn't necessarily need to be viewed as this super weird thing.
It seems to be simply some unknown substance that exerts gravitational force
while not interacting or only very weakly interacting with most other forms of
matter / energy.

We have seen somewhat similar things before. Neutrinos interact very weakly
with matter. A single neutrino needs to pass through a stack of lead that is
an entire _light year_ in length just to have a 50% chance of hitting a single
atom (yes, 1 actual light year).

And we have certainly have encountered unknown substances and particles
before.

My layman's understanding is that no variation of MOND has managed to get that
close to the comprehensive and robust scope of explanation provided by general
relativity.

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tengbretson
If your friend talked to you about a topic and spoke about it in the same
manner that scientists talk about dark matter you would call them an idiot and
change the subject.

~~~
mikhailfranco
_' Dark Matter'_ is physicist code for _' gravitating stuff that we cannot
see'_.

 _' Dark Energy'_ is physicist code for _' anti-gravitating non-stuff vacuum
that we cannot see'_.

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snitko
I feel like this is all insane and doesn't make any sense. At least to the
general public. What difference does it make? It doesn't even improve our
understanding of reality in any meaningful way, it doesn't impact us in any
way. We might have as well been where we are now technology wise without
knowing about Bing Bang at all. What is it even? Because when you actually ask
that question - where did it come from - it's a question you can't really
answer within the framework of our consciousness. And if you can't answer that
question, yet another layer above Big Bang doesn't really matter.

~~~
mturmon
Dark matter seems to comprise about a quarter of the mass-energy of the
Universe, and we don't know what it is.

It seems worth investigating.

