Question about the big bang singularity

[JuneSpring25]

TL;DR Summary

A question about the beginning of the universe and the original singularity

In big bang theories where our universe begins from a singularity (ignoring other theories just now), what would happen if the universe didn't begin as a single point but rather began as energy in an uneven shape? Would we be able to tell from the way the universe is now? Do we know that if the universe began in a big bang, it had to start as a single point? If so, why?

Thanks for any answers! I'm super aware of how clumsy my layman's questions are but any attempted answers appreciated.

 

[PeroK]

In big bang theories where our universe begins from a singularity

A singularity is a breakdown in the mathematics, not a single point.

Do we know that if the universe began in a big bang, it had to start as a single point? If so, why?

It didn't. Your question is based on a misunderstanding.

 

[berkeman]

TL;DR Summary: A question about the beginning of the universe and the original singularity

Do we know that if the universe began in a big bang, it had to start as a single point?

You may like this Insights article, which contains some useful info about the Big Bang (scroll down about half-way through the article): https://www.physicsforums.com/insights/big-bang-infinities/#-About-the-Big-Bang

 

[JuneSpring25]

TL;DR Summary: A question about the beginning of the universe and the original singularity

In big bang theories where our universe begins from a singularity (ignoring other theories just now), what would happen if the universe didn't begin as a single point but rather began as energy in an uneven shape? Would we be able to tell from the way the universe is now? Do we know that if the universe began in a big bang, it had to start as a single point? If so, why?

Thanks for any answers! I'm super aware of how clumsy my layman's questions are but any attempted answers appreciated.

A singularity is a breakdown in the mathematics, not a single point.

It didn't. Your question is based on a misunderstanding.

Oh thank you. Does the energy need to be uniform at the start of the big bang? Could it be in some way unevenly distributed?

 

[Vanadium 50]

Could it be

Maybe it could be, but it isn't. It is very, very uniform.

 

[Ibix]

Oh thank you. Does the energy need to be uniform at the start of the big bang? Could it be in some way unevenly distributed?

In order to get the universe we see today the initial conditions have to have been uniform, so uniform that we had to develop new models of the early universe to explain how that could even happen. There were only tiny and very small-scale deviations from perfect uniformity, which eventually grew into the stars and galaxies we see.

 

[JuneSpring25]

In order to get the universe we see today the initial conditions have to have been uniform, so uniform that we had to develop new models of the early universe to explain how that could even happen. There were only tiny and very small-scale deviations from perfect uniformity, which eventually grew into the stars and galaxies we see.

Thank you for the answers.

Do we know that the tiny differentiations we see that create galaxies etc, are caused by quantum mechanics?

Could there have been a small amount of unevenness in the original energy state that created differences in in the way the universe 'unfolded' or did the early states have to be uniform?

 

[Ibix]

Do we know that the tiny differentiations we see that create galaxies etc, are caused by quantum mechanics?

I don't think "know" is the right word. It's more that a naive model shouldn't make such a uniform space as we see - it's very very surprising that the CMB has such an even temperature. So we develop inflation theory to explain the large-scale uniformity, and QM uncertainty naturally provides small fluctuations and GR says the fluctuations grow after inflation ends. So given that we've got a mechanism that forces uniformity and another that breaks that uniformity, why would you need to propose another mechanism? And why wouldn't it get steam-rollered by inflation anyway?

So it's not that the fluctuations must be quantum mechanical in origin. It's that there's no need to propose anything else, and you'd have to figure out how any such mechanism worked alongside inflation.

Could there have been a small amount of unevenness in the original energy state that created differences in in the way the universe 'unfolded' or did the early states have to be uniform?

If you mean, can you describe a universe where that is so, sure. But if you want to talk about our universe, no, not unless there's physics going on that we haven't got a sniff of yet.

 

[HomesliceMMA]

In order to get the universe we see today the initial conditions have to have been uniform, so uniform that we had to develop new models of the early universe to explain how that could even happen. There were only tiny and very small-scale deviations from perfect uniformity, which eventually grew into the stars and galaxies we see.

I believe, but I could be wrong, that it had to have apparently been so uniform that such conditions only had a 1 over [insert big number here, like in the trillions] possibility of happening. Does that sound right? Could be confusing things. Thanks.

 

[timmdeeg]

Not really. It is believed that the patch of the universe which represents the universe as we see it today has been in thermal equilibrium (means homogeneous) in the very beginning. And that this patch has been blown up tremendously (search "horizon problem" and "inflation" for details) such that we see the microwave background almost homogeneous.

 

[BIGphysician]

TL;DR Summary: A question about the beginning of the universe and the original singularity

In big bang theories where our universe begins from a singularity (ignoring other theories just now), what would happen if the universe didn't begin as a single point but rather began as energy in an uneven shape? Would we be able to tell from the way the universe is now? Do we know that if the universe began in a big bang, it had to start as a single point? If so, why?

Thanks for any answers! I'm super aware of how clumsy my layman's questions are but any attempted answers appreciated.

I assume because of conservation of energy and to balance the equation at t=0 and infinity? But it depends your perspective, maybe it's okay if it's uneven like you're saying and black holes act as something like a pressure release valve that balances the overall equation at any particular moment.

 

[Ibix]

I assume because of conservation of energy and to balance the equation at t=0 and infinity?

Energy is not conserved in FLRW spacetimes.

But it depends your perspective, maybe it's okay if it's uneven like you're saying and black holes act as something like a pressure release valve that balances the overall equation at any particular moment.

Do you have a reference for this, or is it something you came up with?

 

[phinds]

I assume because of conservation of energy and to balance the equation at t=0 and infinity?

There is no "t=0" in the Big Bang Theory, which describes the evolution of the universe AFTER the period of inflation** and is silent on any creation event prior to that.

** the Inflation Period, posited by Alan Guth when he was a young physicist at Cornel, is not itself proven, but is fairly widely assumed correct (but not by all physicists) because of the problems it solves (the Flatness Problem, the Horizon Problem, and the Monopole Problem).

 

[Klystron]

There is no "t=0" in the Big Bang Theory, which describes the evolution of the universe AFTER the period of inflation** and is silent on any creation event prior to that.

** the Inflation Period, posited by Alan Guth when he was a young physicist at Cornel, is not itself proven, but is fairly widely assumed correct (but not by all physicists) because of the problems it solves (the Flatness Problem, the Horizon Problem, and the Monopole Problem).

I have always found Alan Guth's publications readable and instructive. This linked PDF may help basic understanding,

Guth, Alan (Fall 2002). "Inflation and the New Era of High-Precision Cosmology" (PDF). physics@mit. MIT Department of Physics.