
Big Bounce Simulations Challenge the Big Bang - SirLJ
https://www.quantamagazine.org/big-bounce-simulations-challenge-the-big-bang-20200804/
======
Zamicol
I despise the big bounce because it's dogmatic in origin. "It makes sense that
the universe just bounces instead of 'coming from nowhere'!"

Every time cosmologists looked, the universe got bigger and suggested growth.
The big bounce at no point in history ever looked right. Moreover, the big
bounce kicks the bucket down the road. It ultimately has the same metaphysical
issues.

I find the reasoning poor as well. "I don't like inflation" != "The universe
ends in contraction". Yes, it's proven difficult to explain CMB smoothness,
but this doesn't mean the big bounce is a better candidate than other non-
empirical ideas.

I'm confident truth will be far stranger than big bounce fiction.

~~~
mytailorisrich
The metaphysical issues are unavoidable because whatever the theory we come up
with or, I think, whatever the reality is, it can only fall within 2
possibilities:

\- Infinity: There is no beginning and something always precedes the 'current'
step (e.g. the Big Bang occurred out of something)

\- Discontinuity: There is a beginning. Everything suddenly started out of
nothing.

While both options are hard to grasp for the human mind, the second one, which
is the standard Big Bang also sits very uncomfortably with Physics' concepts
and is the more 'disturbing' of the two. I think that's why people have been
looking for alternatives to the standard Big Bang theory.

Infinity, is still unfathomable but at least it is easier to fit Maths and
Physics around.

Even adding God to the mix still leads to these 2 options, because if the
Universe was created by 'God' it implies that the Big Bang is not the
beginning and that something (God) pre-existed. The idea that we might be in a
simulation is equivalent to a creator God, just more hi-tech.

It really seems to me that these alternatives, infinity or discontinuity, are
inescapable.

~~~
simonh
Well, there's the Marvin Minsky answer. He believed that there is no
difference between a possible universe and a real universe. Think of the
difference between an algorithm that only exists in theory and running the
algorithm on a computer. What do we add to the result by running it? We don't
change the result, or grant it any greater validity in a metaphysical sense.
The answer was always going to be the same and always will be the same. Minsky
thought that our world is simply a possible world, but to suppose it is 'real'
or not doesn't change anything and more than doing a calculation makes the
result correct. It simply is.

It's similar in some ways to the concept of block time, in which there is no
progression of time. The universe simply exists and the perception of the
'present' is an illusion. Similarly for Minsky the perception of reality or
existence is an illusion.

~~~
ardy42
> It's similar in some ways to the concept of block time, in which there is no
> progression of time. The universe simply exists and the perception of the
> 'present' is an illusion. Similarly for Minsky the perception of reality or
> existence is an illusion.

Labeling something an "illusion" like that seems like a massive cop-out, made
by a mapmaker to avoid confronting the fact that their maps don't fully
represent the territory. Fossils weren't illusions, and I don't think the
present or existence are illusions either.

~~~
colordrops
If a surgeon pokes your brain in the right place, that desk in front of you
will disappear. You aren't experiencing reality directly, as per Plato's Cave.
Reality seems precisely to be an illusion.

~~~
testrun
The desk is still there, as confirmed by outside observers. If you are blind,
is everything you touch non-existent?

~~~
colordrops
How do you know about "outside observers" other than through a model you
formed in your mind by data received through your senses? "Objective reality"
is just another shadow on Plato's wall that can be extinguished.

~~~
vlovich123
Nihilism is neat until you realize it makes not testable predictions. So sure,
everything could be totally an illusion and your brain is hooked up to a
computer somewhere (or it is a computer). That’s a metaphysical claim that’s
not falsifiable and doesn’t even make any useful predictions.

That’s not particularly relevant to a discussion about science and the Big
Bang. In science we assume that multiple measurements by multiple people of
the same phenomena gives us a good idea of the behavior and whether it matches
our models. Our models will likely forever be incomplete but throwing our
hands up in the air and trying to say “yes, but do we _really_ know that”
doesn’t seem helpful.

------
runxel
Both theories are somewhat incomprehensible for normal human beings. The idea,
that everythinw we know _just came into existence_ at some point is as
shocking as trying to think of something that has no beginning and no end. We
humans are inherently bad in dealing with these terms.

~~~
onion2k
_The idea, that everythinw we know just came into existence at some point is
as shocking as trying to think of something that has no beginning and no end._

It's only an issue if you think about space and time as separate things. I
find it makes (a little) more sense when you understand that time is a
function of spacetime. Therefore if you're happy with space not existing prior
to the big bang (which people do seem to be OK with) then _automatically_ time
didn't exist either, and hence 'before the big bang' ceases to be a problem.

~~~
istjohn
This is what gets me. I can imagine no space and no time. But in a reality
without space and time, by definition, nothing happens. There is nothing to
act or be acted on. There is no timeline by which to order cause and effect.
But the Big Bang posits that, in fact, something did happen: space and time
began. The most incredible event imaginable occurred in the most impossible
circumstance. It just doesn't compute for me. It's much easier for me to
imagine that time is just turtles all the way down.

~~~
yetihehe
> The most incredible event imaginable occurred in the most impossible
> circumstance.

Think of time as "it prevents everything happening at once". Before there was
time, nothing prevented everything happening at once, without space nothing
prevented everything happening in the same place, so everything happened at
once and in the same place. That everything happening made so much noise that
it created space and time in a very big bang.

~~~
appstateguy
What is that "something" that is happening all at once? In my naive
understanding of cosmological theories is they seem to end in probabilities
(e.g., eternal inflation) that emerge from a kind of (oxymoronic) "chaotic
static", but what does that mean for this to "happen all at once"? That
statement seems to imply there's no degree of freedom through which something
can occur (at least casually).

I suppose the question comes to, what is time? I imagine "time" to be a degree
of freedom through which something can change. I understand some see time to
be related to entropy, and that it's an emergent property of this
thermodynamic property but this seems too limiting. It would seem entropy is
more-so an explanation for the arrow of time, but not time itself.

If time is defined as the dimension through which something can change then
should time not be fundamental to any cosmological theories that extends
beyond the Big Bang?

~~~
yetihehe
> What is that "something" that is happening all at once?

Not "something". Everything. Like "What is possible to happen? Everything is
possible". If you can't divide that possibility by time period, everything
possible will happen with probability of 1. How improbable is that universe
will happen during 1 trillion years? Very improbable. But if you can't tell in
how many years universe will happen, it just will exist.

> but what does that mean for this to "happen all at once"

If you don't have time to make difference between two things happening one
after another, they will happen both at the same exact "time".

> If time is defined as the dimension through which something can change then
> should time not be fundamental to any cosmological theories that extends
> beyond the Big Bang?

The problem is, time depends on local state of space. More energy/matter in a
chunk of space means time is slower relative to other chunks of space. So when
you try to go into past with mass in chunk of space increasing into infinity,
that time notion breaks.

------
monktastic1
Many comments here address an important issue: the human mind has a hard time
making sense of both an eternally existing universe, as well as something-
from-nothing. But most of the issues stem from presupposing physicalism. It's
understood even by staunch physicalists that choosing this metaphysics is
ultimately arbitrary[1].

There's another way to approach all this. Start by asking: _what 's the one
thing I know for certain?_ It's hard to say any more than _it certainly seems
like something is happening._ Investigate this sheer fact of "seeming." See
what the seeming is like _before_ you apply any metaphysics on top of it. What
happens when you do this extremely precisely?

Suppose that the _correct_ metaphysics is that you are ultimately the
primordial ground of being, that (paradoxically) weaves itself into apparent
realities. What we think of as _physical reality_ is just one instance. It
transcends parameters like time and causality, but can give rise to them of
its own will. Being the primordial ground of being, nothing logically prevents
you from knowing this ultimate truth directly and unequivocally (unlike if you
were really just a human).

As it so happens, the preceding paragraph describes _how_ you would (re)arrive
at this knowing. Or at least, that's what's suggested by various mystical
traditions. As far as I can tell, there's definitely something to it.

[1] "There is no way to distinguish between the scenarios by collecting new
data. What we’re left with is our choice of prior credences. We’re allowed to
pick priors however we want. [...] We have every right to give high credence
to views of the world that are productive and fruitful." —Sean Carroll, The
Big Picture (p.91)

------
caiobegotti
I have never heard about Big Bounce before, honestly, but the illustration at
the top of the article basically made sense in a heart beat and I'm impressed
how simple yet how much of the idea it conveys, apparently, correctly. Kudos
to the visual artist, usually these scientific illustrations used to explain a
weird or novel idea are over the top.

~~~
alchemism
I vaguely recall hearing of this from a different field of study.

[https://www.cs.ubc.ca/~goyal/age_of_universe.php](https://www.cs.ubc.ca/~goyal/age_of_universe.php)

------
blocked_again
Anyone else when they think about the origin of Universe for a long time,
start to wonder how the hell do we even exist and get a feeling like a panic
attack? I don't really know how to accurately describe the feeling. Its a very
weird sensation. It only happens when I think about the origin of Universe.
And its very very hard to arrive at that state. Requires a lot of
concentration. I must have experienced it like less than 5 or 6 times in my
life so far.

~~~
maze-le
It is called existential anxiety, it shows that you are able to contemplate
about your own insignificance in contrast to the grand scheme of things
(universe, all of existence, etc.). We all have it on one level or another, I
used to have it when looking into a dark cloudless night, realizing that all
of the little dots I can see out there could technically be orbited by another
planet that bears life, inhabited by millions or billions of other lifeforms
that could be able to feel and think.

Usually it is nothing to worry about, except when you get obsessed by it and
it starts to control aspects of your life because you build a worldview around
it or try hard to avoid it or explain it away: then it is called an
existential crisis. But what it really means is that the mind gets overwhelmed
by the fact that the universe is orders of magnitudes more complex than what
the self has ever encountered in our daily lifes. Our brains have evolved so
that bipedal apes that migrated from forests into the steppes can survive and
cooperate in groups. It was never meant to be confronted by questions of this
dimension, but yet here we are.

You can make your peace with it, and embrace it. It can also be a source of
endless curiosity, spirituality and creativity.

~~~
russellbeattie
I remember learning the term "existential crisis" long before I ever
experienced it. Then after floundering mentally for a long time, I suddenly
connected the two, and the realization that so many other people throughout
history have had the same exact feeling - so much so that there's a term for
it which is almost a cliche - made me feel a lot better for some reason.

I decided to accept the Douglas Adams perspective: In an infinite universe, an
infinite number of seemingly improbable things will inevitably happen,
including a random number of particles ejected from astronomical explosions
collecting together in one spot in such a way and for just enough time to
create life as we know it, and for some of that life to think, "Why am I
here?", before entropy rips all of it apart again a cosmic blink later. We
exist because in an infinite universe, all things that can happen will happen,
including you. There's even a universe in which a god did in fact create
everything... which is an interesting question: How do we know if we're in
that universe or not?

~~~
perl4ever
Have you heard of these somewhat disturbing concepts:

[https://en.wikipedia.org/wiki/Boltzmann_brain](https://en.wikipedia.org/wiki/Boltzmann_brain)
and
[https://en.wikipedia.org/wiki/Quantum_suicide_and_immortalit...](https://en.wikipedia.org/wiki/Quantum_suicide_and_immortality)
?

~~~
russellbeattie
"Theoretically, over an extremely large but not infinite amount of time, by
sheer chance atoms in a void could spontaneously come together in such a way
as to assemble a functioning human brain."

That's fantastic.

------
oxymoran
The universe always having always existed makes slightly more sense to me than
it just popping out of nowhere. Sure, from the Big Bang onwards the inflation
theory seemed to make sense but it didn’t explain how everything could
magically erupt out of nothing or what caused said eruption when nothing
existed prior to it. For all the crap that religions get for believing in
nonsense, I always felt the Big Bang was a scientific parallel.

~~~
scarmig
That's just our own minds applying their own adaptive heuristics to the
universe, though. We're used to dealing with systems that have a history,
because that's what allows us to avoid the tiger lurking in the dark. But
there's no particular reason to think that kind of evolved thinking should be
scale free, through time and space.

Why is a universe that has always been in existence, cycling through different
states, any more sensible than one that pops into existence only to ultimately
fizzle out? Both require the presupposition of some kind of uncaused system.
Gathering evidence pointing toward one or the other is key.

I do think that the Big Bang maps better to Western religious cosmogony
(matter was created ex nihilo) and Big Bounce to philosophical materialism
(matter is the fundamental substrate of the world), but that shouldn't bias a
scientist against the Big Bang.

~~~
throwawayhacka
In this territory, a lot of arguments of the form "This does seem to be the
obvious conclusion based on our human thought ,but that is a mere
delusion/illusion" \- the implication is that someone has an ultra-insightful
way to see through the illusion. They don't ; they just seek a little bit of
self-edification and ego-stroking by suggesting as much. Arguments of that
style are incredibly weak "It only VERY POWERFULLY SEEMS SO" is actually an
admission that an unbiased person would reach the conclusion being rejected.
The scientific community clung to the steady-state model of cosmology for
nearly a century before embracing Big-Bang theory - this was due to
philosophical attachments rather than any sort of evidence - these sorts of
motivations are still at play today. They mocked and derided those who
advanced alternatives until the evidence became so overwhelming that it could
no longer be denied.

------
JadoJodo
Sir Roger Penrose and Dr William Lane Craig had an interesting discussion[0]
that included him talking about the Big Bounce (around the 50-minute mark).

[0] [https://youtu.be/9wLtCqm72-Y](https://youtu.be/9wLtCqm72-Y)

------
catmistake
As I have long suspected, though computer science is a subset of mathematics,
cosmology is actually a subset of computer science.

~~~
Johnjonjoan
They're both variations on information theory.

------
breakbread
This seems at least superficially similar to Roger Penrose's Conformal Cyclic
Cosmology theory.

Anyone here able to weigh in on that?

------
cloudking
There's some interesting theories about what was happening before the big bang
in the Joe Rogan interview with Brian Greene
[https://youtu.be/FHAA_1Guxlo](https://youtu.be/FHAA_1Guxlo)

------
Santosh83
It is also worth nothing that cyclic cosmogony was envisioned more than two
millennia ago in Hinduism.

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

------
Razengan
Most human questions about the origin of things assume that the default state
must be Nothing.

Why can't it be Everything?

i.e., instead of imagining the Universe as a white dot on a black canvas, how
about thinking of it as a black dot on a white background?

------
sliken
My biggest problem with the big bang is why didn't the incredible density of
energy (it hadn't cooled enough for matter) just turn into a black hole?

The big bounce avoids this particular problem.

~~~
JesseMeyer
Inflationary theory. Someone more educated on the topic can pine in, but my
lay understanding is that the output of some form of primeval radioactive
decay (Big Bang) caused a phenomenal rate of spacial expansion, which caused
space to expand faster than the rate of gravitational collapse in those first
moments.

~~~
sliken
It's not the rate of gravitational collapse you have to beat, it's the speed
of light.

Although I guess that makes sense. After all it's spacetime, not space. So if
the expansion rate is higher than the speed of light, then you don't have the
black hole problem.

------
mellosouls
TL:DR; despite the title, mostly the theory challenges inflation (which itself
was originally partly an attempt to answer predictive flaws with earlier
cyclic theories) - the big bang itself is countered in so far as a "single
point" state is not required.

With this continuous (eternal?) contraction and expansion, I'm reminded eerily
of a heart beating, or _something_ breathing...

------
ralfd
I thought the universe is too big as to contract again?

~~~
mabbo
The results don't necessarily tell us about the future- but that there may
have been a bounce in the past.

As far as being too big, that's not quite it. Everything is moving away from
each other because of the big bang, but astronomers realized that hey, gravity
should be slowing that down. So they tried to measure the deceleration of the
expansion of the universe. Instead they found it's accelerating.

There's a lot of theories as to why, but right now it's just called "Dark
Energy" because no one really has a full understanding of it. Space itself
seems to be stretching out, becoming larger.

Will the acceleration of expansion continue forever? Maybe someday it will
slow and reverse? No one is sure yet.

------
OneGuy123
The bing bang is way too accepted in the mainststream: in reality there is no
concrete proof for it.

Therefore we can either: a) Fit the models to fit the data. b) Invent more
physical phenomena to make it fit the data (quasi particles in physics).

There is nothing wrong in doing that, but there is severe arrogance of saying
that "the bing bang happened" where in reality we just have a hypothesis.

And even "the most widely accepted by CONSENSUS" hyptothesis doesn't make mean
is actually TRUE.

It's perfectly fine to make new theories, but at the end of the day we simply
don't know enough: and yet the mainstream/every kid believes in the the bing
bang to the extend as religous people believe in God.

~~~
joshvm
There was very much a prediction of the Big Bang, before it was strongly
supported by experimental evidence. This is what Penzias and Wilson got the
Nobel prize for. Their accidental detection of the Cosmic Microwave Background
matched a prediction by Gamow, and others previously, and it was also used as
evidence to rule out solid state theory. Does that mean it's the whole story?
Of course not necessarily, and the Big Bounce isn't necessarily incompatible
with these observations. However, I don't think the idea that the universe
rapidly expanded at some point in the past is under any doubt.

So this wasn't a model fitting the data. In fact it was an _accidental_
observation which agreed with a model that had been suggested much earlier.
The fact Penzias and Wilson weren't even looking for it makes it even more
unbiased. Wilson, I believe, was also a solid state person (as were many
prominent physicists in the 20s and 30s).

~~~
whatshisface
Do you mean "solid state" or "steady-state?"

~~~
joshvm
Oops, yes, I meant steady-state! :)

