How Can We See Light from the Early Universe?

[DevilsAvocado]

... You never leave a photon sphere ...

But the photons leave us, don’t they? (Otherwise, where is the 'freeze button'? )

Edit: And now things get complicated. Check out the link for 'photon sphere' – "A photon sphere is a spherical surface round a non-rotating black hole"... Mamma Mia!

 

[Chalnoth]

Thanks Chalnoth, for the elegant clarification.

And from this we can derive that 'working overtime' won’t do it if 'Albert Laymanstein' is not using his brain – the inflation (of course) must have happen between BB and Recombination to get the uniform CMB (like stretching a wrinkled sheet), right...?

The big bang theory, without inflation, correctly predicts the amount of light elements that we measure. This means that it's basically correct, without modification, to very early times. Inflation proposes some changes to what happens at even earlier times.

It's not useful, I don't think, to talk about the "big bang" as if it were a singular event that spawned our universe, because that just adds confusion to the fact that the big bang theory describes what happens at later times, and has nothing at all to say about what happened at the earliest of times (or rather, it has some things in the theory, but we know they're completely wrong).

Instead, what we know is this: when we look at the past of our universe, the big bang theory describes things correctly back to a certain point. Before that, inflation describes things correctly. But we don't know how inflation started (other than it had to begin somehow). Perhaps if we discover precisely what inflation was, that theory will automatically come along with a method of generating an inflating patch, but we don't yet know.

One thing still puzzles me: How can Saul Perlmutter and the other guys at the http://en.wikipedia.org/wiki/Supernova_Cosmology_Project" prove that the (DE) expansion is accelerating now, when the information is ~13 billion years old...? I get that is proven from the redshift, but how can one say it’s starting 'now', and not x billion years ago?

Because the expansion since then affects the relationship between redshift and brightness. Basically, distant supernovae are too dim compared to their redshifts.

 

[Chalnoth]

That’s what excited me in post #43. There are 'signs' in the current CMB of 'things' outside the observable universe, or?

Very very indirectly. Basically we expect that any sort of boundary can't be sudden: there's going to be some effects going on near the edge that would be detectable. So in a way, the fact that we see no significant deviations from smoothness and uniformity out to the limits of our vision (the CMB), we know that this smoothness and uniformity must continue for a while beyond the limits of our vision.

 

[DevilsAvocado]

It's not useful, I don't think, to talk about the "big bang" as if it were a singular event that spawned our universe, because that just adds confusion to the fact that the big bang theory describes what happens at later times, and has nothing at all to say about what happened at the earliest of times (or rather, it has some things in the theory, but we know they're completely wrong).

I read somewhere that the expression "Big Bang" actually came from one of the "steady state” proponents (Fred Hoyle?), as a 'patronizing' joke... and then it became the official name of the theory. A more describing name is perhaps The Universe Evolution Theory...

Instead, what we know is this: when we look at the past of our universe, the big bang theory describes things correctly back to a certain point. Before that, inflation describes things correctly. But we don't know how inflation started (other than it had to begin somehow). Perhaps if we discover precisely what inflation was, that theory will automatically come along with a method of generating an inflating patch, but we don't yet know.

Interesting, I watched Sean Carroll (Caltech) & Mark Trodden (UPenn) on Bloggingheads.tv, and in one section http://bloggingheads.tv/diavlogs/21709?in=23:39&out=40:25". At 27:00 Sean state – "You’re attempted to explain why the early universe is so special, by imagine it started out even more special …!"

There’s clearly 'some' work to do...

Because the expansion since then affects the relationship between redshift and brightness. Basically, distant supernovae are too dim compared to their redshifts.

Thanks, for the explanation. I read that the photons actually arrive at a 'lower rate' (like a machinegun slowing down) due to the expansion of space. I guess this is causing the 'dusky effect'...

Thanks for taking the time.

 

[DevilsAvocado]

... there's going to be some effects going on near the edge that would be detectable ...

Fantastic. And I guess that Planck will 'reveal' even more on this topic. (I’m not lurking for 'insider info'! )

 

[Chalnoth]

I read somewhere that the expression "Big Bang" actually came from one of the "steady state” proponents (Fred Hoyle?), as a 'patronizing' joke... and then it became the official name of the theory. A more describing name is perhaps The Universe Evolution Theory...

Yes, basically. It was a derogatory term for the theory. I don't really like "Universe Evolution" either, as Evolution is too closely associated with biological evolution, which is a completely unrelated process.

Perhaps "uniform expansion theory" or simply go by the names of the people that came up with the metric: "Friedman-Walker-Robinson theory," or FRW theory for short.

Interesting, I watched Sean Carroll (Caltech) & Mark Trodden (UPenn) on Bloggingheads.tv, and in one section http://bloggingheads.tv/diavlogs/21709?in=23:39&out=40:25". At 27:00 Sean state – "You’re attempted to explain why the early universe is so special, by imagine it started out even more special …!"

There’s clearly 'some' work to do...

Most definitely. The fact that the earliest stage of our universe had such vastly lower entropy than our current stage really needs explaining. Sean's got some really good popular articles that go into why this is, such as this one:
http://www.scientificamerican.com/article.cfm?id=the-cosmic-origins-of-times-arrow

Thanks, for the explanation. I read that the photons actually arrive at a 'lower rate' (like a machinegun slowing down) due to the expansion of space. I guess this is causing the 'dusky effect'...

Thanks for taking the time.

Well, another aspect of the redshift is time dilation. Basically, if it takes twice as long for the next peak of the electromagnetic wave to arrive, then it also takes twice as long for the next photon to arrive.

 

[S.Vasojevic]

Most of the stuff we see out there (stuff at very roughly redshift greater than one) is now and always has been receding faster than the speed of light, according to the simplest definition of recession velocity (the definition of recession velocity is actually rather arbitrary).

What is the simplest definition of recession velocity, and how it yields recession faster than light for z > 1, and why is Marcus saying that it is safer to say that it is true for z > 1.7 ?

 

[Chalnoth]

What is the simplest definition of recession velocity, and how it yields recession faster than light for z > 1, and why is Marcus saying that it is safer to say that it is true for z > 1.7 ?

First, you construct a distance by imagining what would happen if we froze the universe's expansion right now, and timed some light signals between different places. Then you ask how rapidly this distance changes with time. That gives you a relative velocity.

And Marcus is just plugging in the numbers and showing that it's really only true for things around that far away. I was just pulling a number off the top of my head because I didn't remember exactly and didn't feel like looking it up.

 

[S.Vasojevic]

Thanks Chalnoth.