common designer vs common descent?

KerrMetric · Mar 6, 2006

Remus said:
I have a lot of respect for physicists. I think yall have a good bead on things. *tips hat*

I'm surprised to hear you say that as a YEC according to your profile. And my field of physics directly impinges on that belief.

Remus · Mar 6, 2006

This sounds interesting. Which field would that be?

KerrMetric · Mar 6, 2006

Remus said:
This sounds interesting. Which field would that be?

I work in planetary science - specifically modelling giant planet/dwarf star formation and planetary/dwarf star atmospheric physics.

Remus · Mar 6, 2006

Impressive. I have some questions about the big bang. Would you be able/willing to answer them?

KerrMetric · Mar 6, 2006

Remus said:
Impressive. I have some questions about the big bang. Would you be able/willing to answer them?

Yes. I have taught classes on it.

Remus · Mar 6, 2006

KerrMetric said:
Yes. I have taught classes on it.

Thanks.

Have you read about this:
http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/28/full/

It talks about a very large and very young galaxy that is about 16 billion light years away. They are saying that we are seeing it about 800 million years after the big bang. My first question is:
How big was the universe 800 million years after the big bang?

KerrMetric · Mar 6, 2006

Remus said:
Thanks.

Have you read about this:
http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/28/full/

It talks about a very large and very young galaxy that is about 16 billion light years away. They are saying that we are seeing it about 800 million years after the big bang. My first question is:
How big was the universe 800 million years after the big bang?

At about 800 mllion years after the observable Universe was about 1/7 th of its current size.

Remus · Mar 6, 2006

KerrMetric said:
At about 800 mllion years after the observable Universe was about 1/7 th of its current size.

Is there any way to figure out how big the physical universe was at this time?

KerrMetric · Mar 6, 2006

Remus said:
Is there any way to figure out how big the physical universe was at this time?

As far as you are concerned the size of the observable is what you require.

The true size of the Universe is an unknown since we don't know if it is infinite or not. This isn't particularly important from a physics standpoint as we can only ask questions about what we can observe.

Remus · Mar 6, 2006

I'm afraid that my understanding (or lack thereof) of the big bang model is getting in the way. Let me try this a different way. If we are seeing this galaxy at only 800 million light years old, how can we see it at 16 billion light years away? Wouldn't that mean that this galaxy traveled faster than the speed of light (from our reference frame) to get to where it is ... or rather where it was?

I'm sure there is a flaw in my understanding, but I don't know what it is.

Willtor · Mar 6, 2006

Remus said:
I'm afraid that my understanding (or lack thereof) of the big bang model is getting in the way. Let me try this a different way. If we are seeing this galaxy at only 800 million light years old, how can we see it at 16 billion light years away? Wouldn't that mean that this galaxy traveled faster than the speed of light (from our reference frame) to get to where it is ... or rather where it was?

I'm sure there is a flaw in my understanding, but I don't know what it is.

Yeah, I had the same question, once. The thing is that light is traveling towards us, but the space between things is expanding. Thus, light from something 1 light year away takes more than a year to reach us.

KerrMetric · Mar 6, 2006

Remus said:
I'm afraid that my understanding (or lack thereof) of the big bang model is getting in the way. Let me try this a different way. If we are seeing this galaxy at only 800 million light years old, how can we see it at 16 billion light years away? Wouldn't that mean that this galaxy traveled faster than the speed of light (from our reference frame) to get to where it is ... or rather where it was?

I'm sure there is a flaw in my understanding, but I don't know what it is.

800 million years after the Big Bang implies 12.9 billion years ago. So at first look this implies faster than light travel since 16 billion is greater than 12.9 billion.

This is your problem, correct?

But the expansion of the universe is not a special relativistic effect. It is true that nothing can travel faster than light in its own local frame of reference but there is nothing in general relativity that prevents this when comparing different reference frames. It is only faster than light if you attempt to use our coordinate system (reference frame) to measure things in that distant galaxies frame.

The fact is that since the universal expansion has changed over time and is currently accelerating the distance is greater than the light travel time distance a simplistic application gives. ie. 16 billion is greater than 12.9.

Remus · Mar 6, 2006

Okay. I think this:

But the expansion of the universe is not a special relativistic effect

is the part that I was missing. I'm going to have to let this soak in a bit. Thanks for your time.

KerrMetric · Mar 6, 2006

Remus said:
Okay. I think this:

is the part that I was missing. I'm going to have to let this soak in a bit. Thanks for your time.

Special relativity applies only to a local frame of a static flat spacetime. The problem on cosmological distance scales is that you are in a realm where general relativity applies and the static assumption (and possibly though it seems not the flat assumption) certainly does not apply i.e. the expansion.

If you were near the distant galaxy the laws of special relativity would seem to hold just as they do locally here. But you cannot use observations of that frame and couch them in coordinates of our frame.

common designer vs common descent?

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Not just any Willtor... The Mighty Willtor

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