B Expanding Universe -- What is it expanding into?

[jwaldo]

TL;DR Summary

Do you believe in the Big Bang?

I believe in the Big Bang but I struggle with something. If the Big Bang happened and universe is expanding there has to be something (or really nothing) there for the universe to be expanding into. Any thoughts?

 

[Vanadium 50]

That's nor what the Big Bang theory says. It is an expansion of space not an expansion into a preexisting space.

 

[PeterDonis]

there has to be something (or really nothing) there for the universe to be expanding into.

No, there doesn't. As @Vanadium 50 says, the Big Bang model does not say this.

 

[Ibix]

The universe is not a finite region expanding into a larger region. It is literally everything there is. We describe it as expanding because the things we can see in it are all getting further apart in a "centerless" way - which is to say that wherever you are in the universe, distant galaxies are all moving away from you with a speed that increases with distance. It is not because we can see the whole thing and can see its edges moving away - indeed it doesn't have edges as far as we're aware.

 

[jwaldo]

No, there doesn't. As @Vanadium 50 says, the Big Bang model does not say this.

Doesn’t it make sense though? If you take a firecracker and compress it on all sides it will not blow up but if there is something for it to explode into it will explode and expand.

 

[jwaldo]

The universe is not a finite region expanding into a larger region. It is literally everything there is. We describe it as expanding because the things we can see in it are all getting further apart in a "centerless" way - which is to say that wherever you are in the universe, distant galaxies are all moving away from you with a speed that increases with distance. It is not because we can see the whole thing and can see its edges moving away - indeed it doesn't have edges as far as we're aware.

I am simply saying there has to have been something to the Big Bang to explode into

 

[Ibix]

I am simply saying there has to have been something to the Big Bang to explode into

No, there doesn't. You are thinking of the Big Bang as an explosion from a point in space. That model is not consistent with the universe we see. The Big Bang happened everywhere at once, and the initial "explosion" is the start of spacetime as a thing. It doesn't need a pre-existing background to work with.

 

[PeterDonis]

Doesn’t it make sense though?

Not if you actually understand the Big Bang model, no.

If you take a firecracker

The Big Bang is nothing like a firecracker, or any ordinary explosion.

 

[Ibix]

If you take a firecracker

Just a general note, reasoning from analogy is extremely dangerous. You really need to understand where your analogy differs from whatever you are analogising, and that's what's biting you here. A firecracker is very little like the Big Bang. I wouldn't even call the Big Bang an explosion if I could think of a less inappropriate word. There was no pile of explosives sitting there waiting to go off. There was no place where it all started - it started everywhere.

(Side note: Hoyle coined the term "Big Bang" as an insult to a theory he really didn't like. It wasn't meant as a good description and it isn't really, and it's kind of unfortunate that it caught on.)

 

[PeroK]

Doesn’t it make sense though? If you take a firecracker and compress it on all sides it will not blow up but if there is something for it to explode into it will explode and expand.

The universe is not a fire cracker. It's a four dimensional spacetime geometry.

 

[diogenesNY]

This might be a good starting point. An article by Charles Lineweaver and Tamara Davis entitled Misconceptions about the Big Bang. This is an article originally published in _Scientific American_ magazine by two astonishingly credible researchers who have managed to pack a whole lot of science into a very readable article.

https://www.scientificamerican.com/article/misconceptions-about-the-2005-03/

If you have paywall problems, here is another, albeit differently formatted version:

https://ia904500.us.archive.org/35/items/lineweaver-davis-inflation-expansion/LINEWEAVER DAVIS INFLATION EXPANSION ++++ .pdf

Okay, maybe this is even the best one, with the original SciAm illustrations and pagination:

http://pages.erau.edu/~reynodb2/LineweaverDavis_BigBang_SciAm_March05p36.pdf

Hope this helps and is the beginning of a fun intellectual adventure for you.

 

[Vanadium 50]

I am simply saying

Are you asking us or telling us?

 

[phinds]

Doesn’t it make sense though?

Only if you refuse to learn any actual physics.

 

[Junak]

No, there doesn't. You are thinking of the Big Bang as an explosion from a point in space. That model is not consistent with the universe we see. The Big Bang happened everywhere at once, and the initial "explosion" is the start of spacetime as a thing. It doesn't need a pre-existing background to work with.

But, we know something can't happen in its own. There need to be something to cause the big bang. And also energy can neither be created nor be destroyed. So the energy released in the big bang had some forms before the big bang. So where or in what form these vast amount of energy exist if there was nothing before big bang. In other words what is energy..? From where or how energy came for the first time in the universe..? These are just my thoughts. Apologizes if there is any mistakes in it.

 

[phinds]

And also energy can neither be created nor be destroyed.

Just so you know, that statement is only true locally. It does not hold for cosmological distances. Light that is emitted with a certain amount of energy has less energy if/when it arrives at a cosmologically receding detector. Some of its energy has just disappeared due to accelerating cosmological expansion.

energy is not conserved

it’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity.

 

[phinds]

There need to be something to cause the big bang.

What you are talking about is the singularity that is sometimes called the Big Bang Singularity or, in popular (and ignorant) teminology, The Big Bang. The current model of cosmology, the "Big Bang Theory" is silent on any such creation event. If you find the answer to your question I guarantee you a Nobel Prize.

As Michio Kaku is found of saying "We don't know what banged, we don't know why it banged, and we don't know how it banged."

 

[phinds]

But, we know something can't happen in its own

No. We don't.

 

[PeterDonis]

we know something can't happen in its own. There need to be something to cause the big bang.

No, we do not know this. Some models (such as eternal inflation) have events extending infinitely far back into the past; others do not. All of the models are consistent with our best current understanding of physical laws.

energy can neither be created nor be destroyed.

This is a property of the Einstein Field Equation, yes. And the EFE applies at every event in the spacetime manifold. But the Big Bang initial singularity (in models where there is one) is not part of the spacetime manifold, and the EFE is not well-defined there. (A more detailed discussion of this point would go well beyond the "B" level.) So this property of the EFE cannot be used to argue the point you are trying to argue.

 

[Vanadium 50]

It seems you have moved away from asking questions, and more towards telling us your opinion. Sure that's what you want to be doing?

 

[Ibix]

But, we know something can't happen in its own

No we don't.

Formally, we can point out that just because (so far) we have never seen things happening without cause doesn't mean that we cannot find a counter example tomorrow. The laws of physics as we understand them predict that we will not, but you never know.

But if we use those same laws of physics to run our model of the world backwards then we get a singularity. That is, the laws of physics as we understand them lead to a region where they don't work. We therefore know that our understanding of the laws isn't completely correct, and "nothing happens without a cause" is most definitely up for question.

And also energy can neither be created nor be destroyed.

This is not true in general. There are local conservation laws in general relativity, so it does predict that you can't get free energy schemes. But you can only define a global conservation law in some spacetimes, and cosmological spacetimes are not of that type. So energy conservation isn't a particularly plausible argument in terms of origin of the universe.

So where or in what form these vast amount of energy exist if there was nothing before big bang.

You're assuming global conservation of energy. You are also assuming that "before" makes sense when you are talking about something that is not part of spacetime, but "before" is a notion about events in spacetime. You first need to justify using those concepts (i.e., come up with a good mathematical framework that includes them, make predictions with it and show that those predictions are consistent with at least some experimental data) before you can take the question seriously.

 

[gmax137]

This might be a good starting point. An article by Charles Lineweaver and Tamara Davis entitled Misconceptions about the Big Bang. This is an article originally published in _Scientific American_ magazine by two astonishingly credible researchers who have managed to pack a whole lot of science into a very readable article.

https://www.scientificamerican.com/article/misconceptions-about-the-2005-03/

If you have paywall problems, here is another, albeit differently formatted version:

https://ia904500.us.archive.org/35/items/lineweaver-davis-inflation-expansion/LINEWEAVER DAVIS INFLATION EXPANSION ++++ .pdf

Okay, maybe this is even the best one, with the original SciAm illustrations and pagination:

http://pages.erau.edu/~reynodb2/LineweaverDavis_BigBang_SciAm_March05p36.pdf

Hope this helps and is the beginning of a fun intellectual adventure for you.

I hope the OP, @Junak , has read the linked article. I never studied cosmology, but I have read a few popular articles and books. These left me with questions and ideas similar to @Junak 's. The Sci Am article does a pretty good job addressing these questions.