Something out of Nothing

[SpeedFreek]

You have that last part backwards. The light horizon defines age of the universe. It is because we can only see to our "light horizon" that we know the universe has a finite age.

Really? I thought it was due to the rapid inflation, and that we can only see about 13.7 billion light-years because the light from much further than that will never have time to reach us. Otherwise, would we not be able to see all the way back to the bang itself?

That is how we know the universe has a finite age. If it had an infinite age, the light would have had time to reach us.

The assumption is that we would see more of the universe in that direction (more galaxies etc), but would only be able to see as far as the Milky Way in this direction. Our Milky Way is on the edge of the observable universe for an object that is on the edge of ours.

There, you see? The observable universe. Brian Greene, in his Fabric of the Cosmos, mentions on pps. 292-293:

In inflationary cosmology, space was stretched by such a colossal factor that the observable universe, the part we can see, is but a small patch in a gigantic cosmos (that we can't see). And so, even if the entire universe were curved, the observable universe would be very nearly flat.

At least, inflationary cosmology predicts this. I take it that you accept most of what inflationary cosmology says about the predicted critical density and all of that that led to inferences about dark matter and dark energy.

Yes, of course, but that has nothing to do with the age of the universe.

And, from "All About Science- Big Bang Theory, An Overview:"

(This is just a webpage I googled. I'm not normally a "google scholar", but I thought I'd include this.)

Big Bang Theory- The Premise

Discoveries in astronomy and physics have shown beyond a reasonable doubt that our Universe did in fact have a beginning. Prior to that moment, there was NOTHING; during and after that moment there was SOMETHING: our Universe.

And no one knows for sure what a singularity is, or where it comes from.

Where did it come from?

We don't know.

Why did it appear?

We don't know.

Yup, that is a popular, but misleading, description of the Big Bang. A lot of people say there was NOTHING before the Big Bang, but they are not actually reflecting what Big Bang theory actually says.

 

[ZenGalacticore]

You have that last part backwards. The light horizon defines age of the universe. It is because we can only see to our "light horizon" that we know the universe has a finite age.

Really? I thought it was due to the rapid inflation, and that we can only see about 13.7 billion light-years because the light from much further than that will never have time to reach us. Otherwise, would we not be able to see all the way back to the bang itself?

That is how we know the universe has a finite age. If it had an infinite age, the light would have had time to reach us.

Not if the overall expansion of space is faster than light. (I know, nothing inside the Universe can exceed the speed of light, but, according to some of what I've read, the expansion itself can.)

 

[SpeedFreek]

Really? I thought it was due to the rapid inflation, and that we can only see about 13.7 billion light-years because the light from much further than that will never have time to reach us. Otherwise, would we not be able to see all the way back to the bang itself?

That is how we know the universe has a finite age. If it had an infinite age, the light would have had time to reach us.

Not if the overall expansion of space is faster than light. (I know, nothing inside the Universe can exceed the speed of light, but, according to some of what I've read, the expansion itself can.)

Superluminal expansion has no impact on the age of the universe, even the exponential superluminal expansion theorised during the inflationary epoch. Do you know why?

Additionally, you are using a mechanism (inflation) that is proposed to have occurred during the first second of the history of the universe, and erroneously concluding that the mechanism might allow the universe to have been more than one second old when inflation occurred!? Why do you think inflation is theorised to have happened during the first second?

 

[ZenGalacticore]

Superluminal expansion has no impact on the age of the universe, even the exponential superluminal expansion theorised during the inflationary epoch. Do you know why?

I have no idea, and I'm sure you will educate me.

Btw, I'm quite flattered that you are very into this discussion. I followed the entire thread (I think there may have been more than one, IIRC) between you and HarryCostas about ultimate cosmology. It was very entertaining, and sometimes informative. No offense to Harry, but the informative parts largely came from you, Speedy.

Additionally, you are using a mechanism (inflation) that is proposed to have occurred during the first second of the history of the universe, and erroneously concluding that the mechanism might allow the universe to have been more than one second old when inflation occurred!? Why do you think inflation is theorised to have happened during the first second?

[/quote]

First 'second' ? My understanding is that the rapid inflation happened in the first Planck second or some such thing. Something like the first 10 to the negative 88 seconds or some such incomprehensible length of time.

Can't remember if I'm getting my terms right. I know about the Planck length, but I'm not sure I've got the whatever-its-called measurement of time right. But something like a googolplex of them happen in the time it takes me to punch the period key to end this sentence. :lol:

 

[SpeedFreek]

Additionally, you are using a mechanism (inflation) that is proposed to have occurred during the first second of the history of the universe, and erroneously concluding that the mechanism might allow the universe to have been more than one second old when inflation occurred!? Why do you think inflation is theorised to have happened during the first second?

First 'second' ? My understanding is that the rapid inflation happened in the first Planck second or some such thing. Something like the first 10 to the negative 88 seconds or some such incomprehensible length of time.

Can't remember if I'm getting my terms right. I know about the Planck length, but I'm not sure I've got the whatever-its-called measurement of time right. But something like a googolplex of them happen in the time it takes me to punch the period key to end this sentence. :lol:

Yes, quite correct, and that is what I meant even if I didn't put it into words very well! I should have said "during a very small part of the first second" or something similar. But the point I was trying to make was that it happened before the universe was a second old. So why would it have any bearing on our current estimate for the age of the universe if we (think we) know when it happened?

 

[earle]

I'm reading George Smoot's "Wrinkles In Time". On page 85, in explaining the presence of radiation everywhere equally in all directions, he states.."The classical Big Bang didn't happen at specific place within an infinate void; rather. it happened everywhere because it was everything. There was "nothing"---not even empty space--outside of it."

But on page 180, in discussing the initial inflation (10 -35 sec) he says..."after the first moment of creation, all the potential mass and radiation of our part of the universe was subsumed in a primal soup of energy, parcelled within a tiny region a trillionth th size of a proton..."

Is this contradictory? Or am I missunder standing him?

BTW..I am a new member of this community and am reallly enjoying the posts I've read today. Thank you for them.

Earle

 

[csmyth3025]

I'm reading George Smoot's "Wrinkles In Time". On page 85, in explaining the presence of radiation everywhere equally in all directions, he states.."The classical Big Bang didn't happen at specific place within an infinate void; rather. it happened everywhere because it was everything. There was "nothing"---not even empty space--outside of it."

But on page 180, in discussing the initial inflation (10 -35 sec) he says..."after the first moment of creation, all the potential mass and radiation of our part of the universe was subsumed in a primal soup of energy, parcelled within a tiny region a trillionth th size of a proton..."

Is this contradictory? Or am I missunder standing him?

BTW..I am a new member of this community and am reallly enjoying the posts I've read today. Thank you for them.

Earle

I don't think the two passages are contradictory. I think the author used the phrase "...parcelled within a tiny region a trillionth the size of a proton..." for dramatic effect. The "tiny region" he's referring to is the same region the universe occupies today - which is to say, everything we can see and beyond. The author, I believe, is trying to put emphasis on the idea that the vast distances that the universe covers today were once very small distances. To illustrate this concept, I'll repost my previous comment in this thread:

As I understand it, if we "run the clock backwards" 13.7 billion years, all the galaxies in our observable universe will contract until they come to a central point (where we are). This doesn't mean that we're at the center of the universe.

If someone living in a galaxy at the edge of our observable universe simultaneously "runs the clock backwards" 13.7 billion years, all the galaxies in their observable universe will contract until they come to a central point (where they are). That doesn't mean that they're at the center of the universe either.

If someone living at the far edge (away from us) of our "neighbor's" observable universe simultaneously "runs the clock backwards" 13.7 billion years, all the galaxies in their observable universe will contract until they come to a central point (where they are). But again, they're not at the center of the universe either.

As you can see, we could, in theory, repeat this same scenario almost forever for each observer in each galaxy on the far edge of the next observable universe progressively farther away from us (if the universe is almost infinite). In the end, all of these central points would wind up being the same central point (the Big Bang).

All of this is based on our assumption that the universe is homogenous and isotropic (on the large scale). That is to say that we don't live in a priviledged location in the universe and that anyone else living anywhere else in the universe will pretty much see what we see (on the large scale).

Chris

 

[earle]

Thank you Chris. As a non-astrophysicist with a layman's interest in the subject, I find it easier to accept the larger viewpoint of what the pre-universe was before the BB. Smoot's comments are that the pre-universe was not empty open "space" with nothing in it but a super condensed point to later explode, but seems to have been a soupy cloud of developing synthesis that at some point released itself into a burst of energy.
I'm sure this has all be covered in several threads here already and I have been reading them, but...well..it's like the National Library....it takes awhile. :lol:

Earle