
Physicists simulate critical 'reheating' period that kickstarted the Big Bang - dnetesn
https://phys.org/news/2019-10-physicists-simulate-critical-reheating-period.html
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mhartl
The article appears to be confusingly written, making reference to a time
“before” the Big Bang:

 _Just before the Big Bang launched the universe onto its ever-expanding
course, physicists believe, there was another, more explosive phase of the
early universe at play: cosmic inflation, which lasted less than a trillionth
of a second._

But cosmic inflation was _part_ of the Big Bang, not something that happened
“before” it. According to the current understanding, the Big Bang included the
beginning of time itself—in more technical terms, the Universe has no boundary
in time (or space)—so asking what happened “before” the Big Bang is akin to
asking what’s north of the North Pole.

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jschwartzi
Isn't the Big Bang only observable as the Cosmic Microwave Background? The Big
Bang is the oldest event we can observe, but that doesn't mean nothing was
happening before it. It just means we can't observe what was happening.

The travel time for light from that event doesn't seem to tell us very much
about how old the Universe is as an n-dimensional space. It only tells us how
far back we can observe. We can choose t_0 to be the point in time at which
that farthest emitted light was emitted. That doesn't mean there isn't a t_-1,
it only means that our axis of positive time starts there because that's all
we can observe right now. We know some event happened and before that event we
can make no observations, while after that event we can make observations. So
everything observable follows from that event. But absence of observations is
not evidence of absence.

It's actually sensible to ask what's north of the North Pole because it
reveals something about the geometry of the coordinate space. You're
considering the North Pole as a fixed boundary where all lines end, whereas
the asker considers it as a point that all lines pass through(this is a more
correct interpretation). In our polar coordinate system going to that point
would result in being somewhere south of north but on the other half of the
semicircle. Whether it's sensible to ask that about the universe seems like an
open question to me.

The sensible thing to me is to wonder at the question while recognizing that
we aren't currently able to answer it sensibly. Maybe we never do.

~~~
saagarjha
We can’t observe things before recombination, a couple hundred thousand years
after the Big Bang, when electrons bound to nuclei and photons stopped being
constantly scattered.

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sunstone
I believe there's some hope they may be able to see past this point using the
new gravitational astronomy.

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AnimalMuppet
> The team found this extreme transformation would have been even faster and
> more efficient if quantum effects modified the way that matter responded to
> gravity at very high energies, deviating from the way Einstein's theory of
> general relativity predicts matter and gravity should interact.

> all with known physics

Um... I'd like to see their "known" theory of quantum-modified general
relativity...

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QuesnayJr
Isn't there a linearized gravity that you can quantize? Like in these lecture
notes:
[http://www.staff.science.uu.nl/~hooft101/lectures/erice02.pd...](http://www.staff.science.uu.nl/~hooft101/lectures/erice02.pdf)?

~~~
AnimalMuppet
I think so. But can you (validly) linearize gravity in the circumstances that
were thought to exist at the time we're talking about?

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QuesnayJr
I tried looking at the paper and some of its references, and answering this
question is well outside my area of competence.

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ivalm
There is a bit of conflation of "observable universe" with "universe". The
"observable universe" (as observed now) would be absolutely tiny, but the
overall universe may be large even pre inflation, we simply don't see anything
outside our tiny cone.

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Thorentis
The more we learn about the Big Bang and the way it may have happened, the
less intriguing, or put another way, the less satisfying a theory it becomes
for me. It just makes me more curious about what happened before the Big Bang,
or at least, it makes what happened before the Big Bang seem more important to
understanding the origins of the universe.

~~~
sysbin
One possibility is infinite Big Bangs. Universe expands until it reaches a
point where it begins retracting, then reaches point where big bang happens
and then it repeats all over again for infinity. Basically can result in our
lives being repeated for infinity. All the events reoccur to make earth
exactly as before and where all forces proceed forward the same as before.
Similar the forces could occur slightly different but if this is happening for
infinity. I'm assuming irritations would repeat.

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reading-at-work
This activates my existential dread pretty hard. The idea of never existing
again after I die and there being no afterlife is pretty scary by itself, but
the idea of this life repeating infinitely is somehow even worse. Though I
guess each individual experience in the infinite continuum would be isolated
so it's not like I'm remembering all of my past lives, in which case I guess
it doesn't matter either way. It's a weird mental rabbit hole to go down.

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imtringued
I've thought about these things a lot. There are so many logical problems with
an afterlife. Heaven/Utopia doesn't make sense because it would have to be
based on your current life. (do you arrive old or young in heaven etc)
Reincarnation is problematic because you would have to stand in a queue while
waiting for your soul to be assigned to a new body. My theory with the least
amount of logical flaws is assuming that there is a global soul which is
reading the "standard input" from all philosophical zombies simultaneously or
it only selects one philosophical zombie.

None of this really matters because only depressed people worry about the
"meaning" of life, primarily because they have been denied all other sources
of "meaning" and therefore cling to the one thing everyone (including
themselves) has: a life. It's only human to grow attached to things and our
lives are our most priced possessions after all.

~~~
sysbin
> My theory with the least amount of logical flaws is assuming that there is a
> global soul which is reading the "standard input" from all philosophical
> zombies simultaneously or it only selects one philosophical zombie.

Can you expand on the only selects one philosophical zombie? I don't really
understand what you're attempting to express.

I think all people "think" about existence at some point. Maybe sad people
think about it more than others.

