High School How is the Big Bang compatible with an infinite universe?

[jerromyjon]

or i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce.

Yeah, that's what I am talking about! I'm too beat to get any further into this tonight. Thanks for the links!

 

[NickAtNight]

Correct, the Big Bang implies that the Universe had a beginning and thus is finite.

My understanding is that the Universe is not infinite in size. The size of the Universe is sphere approximately 13.8 billion light years in radius.

The competing model for an infinite Universe (Steady State Theory) is currently out of favor based on current evidence.

The fate of the Universe could be:
1) Big Crunch - Collapsing back to a singularity (currently out of favor)
2) Steady State -
3) Continued Expansion - Resulting in a slow cold death. Currently in favor

 

[phinds]

Correct, the Big Bang implies that the Universe had a beginning and thus is finite.

No, the Big Bang Theory is silent on the origins. If you follow the math backwards to "t=0" you get an unphysical result, so the consensus is that we don't know what was going on at that time. The BB Theory ASSUMES there was nothing before t=0 because it is purely a discussion of what happened after about one Plank time after "t=0" [see note 1]

My understanding is that the Universe is not infinite in size. The size of the Universe is sphere approximately 13.8 billion light years in radius.

That is a deeply flawed understanding. The OBSERVABLE universe is that size the universe is bigger and might be infinite (or might not, but estimates of its size if it is not generally run to many orders of magnitude greater than the observable universe.

EDIT: note 1: I should add that because there is currently no known way to tell from any empirical evidence that there was anything prior to t=0, it is common to say that there was nothing and that space and time started with the singularity. There ARE theories (speculative, unproven and perhaps not provable) that there was something before t=0 but if there was it is not addressed in the BB Theory, which as I said starts at one Plank time.

 

[NickAtNight]

Dr. Michael S. Turner
The Dark Side of the Universe.

 

[NickAtNight]

Incorrect.

The Big Bang theory was not silent as to its origin.

Georges Lemaitre, posited that the Universe started from a single 'particle' at a definite point in time.

"http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_lemaitre.html , the expansion of the observable universe began with the explosion of a single particle at a definite point in time. This startling idea first appeared in scientific form in 1931, in a paper by Georges Lemaître, a Belgian cosmologist and Catholic priest. The theory, accepted by nearly all astronomers today, was a radical departure from scientific orthodoxy in the 1930s. Many astronomers at the time were still uncomfortable with the idea that the universe is expanding. That the entire observable universe of galaxies began with a bang seemed preposterous."

The point that the math collapses as T reaches 0 is not relevant. That argument is best left to models beyond the Big Bang model.

 

[Mordred]

Incorrect.

The Big Bang theory was not silent as to its origin.

Georges Lemaitre, posited that the Universe started from a single 'particle' at a definite point in time.

"http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_lemaitre.html , the expansion of the observable universe began with the explosion of a single particle at a definite point in time. This startling idea first appeared in scientific form in 1931, in a paper by Georges Lemaître, a Belgian cosmologist and Catholic priest. The theory, accepted by nearly all astronomers today, was a radical departure from scientific orthodoxy in the 1930s. Many astronomers at the time were still uncomfortable with the idea that the universe is expanding. That the entire observable universe of galaxies began with a bang seemed preposterous."

The point that the math collapses as T reaches 0 is not relevant. That argument is best left to models beyond the Big Bang model.

He's referring to the region of causality of our observable universe. Not the entire universe.

 

[NickAtNight]

I do not believe that you stated that correctly.

That is a deeply flawed understanding. The OBSERVABLE universe is that size the universe is bigger and might be infinite (or might not, but estimates of its size if it is not generally run to many orders of magnitude greater than the observable universe.

Based on current observations, the Observable universe is only about 4% of the total universe.

Then we have about 25% Dark Matter.

and the rest, about 75% is Dark Energy.

We have not identified what Dark Matter and Dark Energy are yet.

However, these do not necessarily increase the size of the Universe beyond the boundaries set by the Big Bang.

 

[Mordred]

I do stated that correctly.

Based on current observations, the Observable universe is only about 4% of the total universe.

Then we have about 25% Dark Matter.

and the rest, about 75% is Dark Energy.

We have not identified what Dark Matter and Dark Energy are yet.

However, these do not necessarily increase the size of the Universe beyond the boundaries set by the Big Bang.

The 4% is the amount of baryonic matter. All the % above is the cosmic inventory of our observable universe

 

[phinds]

I do not believe that you stated that correctly.

Based on current observations, the Observable universe is only about 4% of the total universe.

Then we have about 25% Dark Matter.

and the rest, about 75% is Dark Energy.

We have not identified what Dark Matter and Dark Energy are yet.

However, these do not necessarily increase the size of the Universe beyond the boundaries set by the Big Bang.

You completely misunderstand. You appeared to be talking about the SIZE of the "universe" which you stated in size units, but you stated it as the size of "the universe" when the number you gave is the size of the OBSERVABLE universe which as I said is not the size of the universe. Now you are talking about the relationships among the constituents of the universe which has zero to do with the size of the universe.

Also, if we are going to be completely correct here, the observable universe is NOT 13+ light years in diameter. It is 13+billion years old and about 95 billion light years in diameter.

Before you post further, I suggest you study some basic cosmology.

 

[PeterDonis]

Incorrect.

You should not be making authoritative statements if you don't have the knowledge to back them up.

The Big Bang theory was not silent as to its origin.

Georges Lemaitre, posited that the Universe started from a single 'particle' at a definite point in time.

Lemaitre's statement is not the Big Bang theory as it exists today; the theory as it exists today has undergone a lot of development since Lemaitre. The term "Big Bang" as it is used in our best current theory does not refer to the "initial singularity" at t = 0; it refers to the hot, dense, rapidly expanding state of the universe at the end of inflation. The theory does not include any statement about how the universe came into existence; that is still being investigated and we don't have a definite answer to it.

The point that the math collapses as T reaches 0 is not relevant. That argument is best left to models beyond the Big Bang model.

Do you realize you are contradicting yourself here? First you say the Big Bang theory says the universe began at a definite point in time; then you say that issue is "best left to models beyond the Big Bang model" (which, as I have just noted, is more or less correct--the Big Bang model does not include any statement about how the universe came into existence).

 

[guywithdoubts]

As a layman, the idea that the Big Bang "happened everywhere at once" is probably the most confusing (and on occasion, misleading) thing I've ever had to think about, and it has never helped me get the right scenario. In my humble opinion, it might be better to stop using it among non-physicists.

If you go backwards in time all galaxies get closer and closer together until you reach this point in time where everything is so hot and dense that our math doesn't work anymore. That's the Big Bang. No matter where you are in this Universe, everything gets closer and closer together. That's probably what it means for it to "happen everywhere at once", but it's not very helpful, because, after all, it doesn't "happen". It's just a moment in time.

 

[phinds]

As a layman, the idea that the Big Bang "happened everywhere at once" is probably the most confusing (and on occasion, misleading) thing I've ever had to think about, and it has never helped me get the right scenario. In my humble opinion, it might be better to stop using it among non-physicists.

If you go backwards in time all galaxies get closer and closer together until you reach this point in time where everything is so hot and dense that our math doesn't work anymore. That's the Big Bang. No matter where you are in this Universe, everything gets closer and closer together. That's probably what it means for it to "happen everywhere at once", but it's not very helpful, because, after all, it doesn't "happen". It's just a moment in time.

I agree w/ you to some extent, and I certainly had some of the same confusion when I started out, but the problem is that it is necessary to counter the wide-spread and COMPLETELY wrong statement that it happened at a point. What would you suggest as an alternative to "everywhere at once" ?

 

[Mordred]

The reason we use that is there is the common misconception that the BB can be seen in a certain direction. Which is false, the BB encompasses the entire Observable universe when you extrapolate backwards. As such there is no specific point or location of the BB. Every point and location of the Observable universe was at one time part of the BB

 

[guywithdoubts]

What would you suggest as an alternative to "everywhere at once" ?

I would simply explain the "go backwards in time" scenario from the very point of view of the layman. In your eyes everything gets closer, brighter; provided that you survive, eventually all that can be seen around is bright light (which is the absolute opposite of what pop science depicts) until you get to this point you don't know what happens beyond, and that's all we know. I don't mean the expression "everywhere at once" is a bad one, it's the only way you can explain inflation or dark energy, but it's definitely misleading for the BB.

 

[jerromyjon]

it is necessary to counter the wide-spread and COMPLETELY wrong statement that it happened at a point

I think if you assume infinite space, and behold the power of infinity, choose any point, anywhere, and that is all we need of infinite space that is relevant to the BB. If time ended for a "previous universe" at t=0 or before the BB isn't even relevant, and whatever happens outside our causal "sphere" of space isn't relevant.

 

[phinds]

I think if you assume infinite space, and behold the power of infinity, choose any point, anywhere, and that is all we need of infinite space that is relevant to the BB. If time ended for a "previous universe" at t=0 or before the BB isn't even relevant, and whatever happens outside our causal "sphere" of space isn't relevant.

I have no idea what this means.

 

[jerromyjon]

I have no idea what this means.

Take any "chunk" of infinity and call it finite. Would it matter where you select your sample from and would it look any different from a finite model?

 

[phinds]

Take any "chunk" of infinity and call it finite. Would it matter where you select your sample from

not on cosmological scales

and would it look any different from a finite model?

Maybe, maybe not, depending on the exact values but it's still not OK to say they are the same.

 

[Promytius]

An event, referred to as the Big Bang, that happened in our past was not the beginning, but a local beginning; after requires a before. It's a theory, not a fact; it's an elegant, incomplete notion to help us mentally wrestle with things of which we are not yet capable of insightful and complete penetration. So at one point in one point one thing happened and we gave it a name, but it is just one of an infinite number of events, some of which may be quite the same; for in an infinite universe or an infinite multiverse, all things exist.
Space - the rest of everything - has to be infinite, because an inside requires an outside, and an outside would define not-an-end and require a further container.

 

[rootone]

Space - the rest of everything - has to be infinite, because an inside requires an outside, and an outside would define not-an-end and require a further container.

Not necessarily. Topology can be strange.
Can you imagine a piece of paper which has only one side.
https://en.wikipedia.org/wiki/Möbius_strip
or a bottle whose inside is also the outside.
https://en.wikipedia.org/wiki/Klein_bottle

 

[PAllen]

An event, referred to as the Big Bang, that happened in our past was not the beginning, but a local beginning; after requires a before. It's a theory, not a fact; it's an elegant, incomplete notion to help us mentally wrestle with things of which we are not yet capable of insightful and complete penetration. So at one point in one point one thing happened and we gave it a name, but it is just one of an infinite number of events, some of which may be quite the same; for in an infinite universe or an infinite multiverse, all things exist.
Space - the rest of everything - has to be infinite, because an inside requires an outside, and an outside would define not-an-end and require a further container.

Consider the argument that for any position, there must be left an right, therefore unless 'chopped' any surface is infinite. Then consider the surface of a ball (2-sphere). Your argument is assuming Newtonian time & space in a scenario where all evidence suggest they are wholly inaccurate.

 

[jerromyjon]

Then consider the surface of a ball (2-sphere)

Then consider the torus it swipes out of space, then twist it for 1/2 a loop and you are almost there.

 

[phinds]

So at one point in one point one thing happened and we gave it a name, but it is just one of an infinite number of events, some of which may be quite the same

I found your whole post incoherent, but this sentence in particular is just weird.

; for in an infinite universe or an infinite multiverse, all things exist.

No, all things do NOT exist. There are lots of things that are physically impossible and none of them exist

Space - the rest of everything - has to be infinite, because an inside requires an outside, and an outside would define not-an-end and require a further container.

Again, you are not making sense. I realize that you think this makes sense but it does not follow. The universe does not have to be infinite.

Perhaps if you could address your points one at a time rather than in a jumble, we could address them.

 

[PeterDonis]

This thread has run its course and is now closed.