Thread: Another 'age of the universe' 'size of the universe' question thread

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May 2006
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Another 'age of the universe' 'size of the universe' question thread

Started reading this thread but it seemed to get hijacked by someone 'silly' who objected to language.

So.

Some questions:
1. Are the oldest objects we can see also the farthest away?
2. If the farthest away object we can see is the oldest,
a. is the size of the universe 2x that distance? (i.e. if it took light from some distant quasar / galaxy 13 billion years to get here, presumably its light has also been travelling the same time and distance in the opposite direction, right?), or is it,
b. (the object's speed away from us x 13 billion years) + "a". (see above: 13 billion years x 2) -
3. If our solar system is 4.6 billion years old, and the universe is only 13 billion years old, given the present theory that heavy element formation requires several stars to form and supernovae to seed the star/planetary disk with heavier elements - can enough stars form and supernovae in the first 2/3 of time since the big bang to create sufficient raw materials for our solar system to have formed in the last 1/3?

2. Originally Posted by DyerWolf
Started reading this thread but it seemed to get hijacked by someone 'silly' who objected to language.

So.

Some questions:
1. Are the oldest objects we can see also the farthest away?
2. If the farthest away object we can see is the oldest,
a. is the size of the universe 2x that distance? (i.e. if it took light from some distant quasar / galaxy 13 billion years to get here, presumably its light has also been travelling the same time and distance in the opposite direction, right?), or is it,
b. (the object's speed away from us x 13 billion years) + "a". (see above: 13 billion years x 2) -
3. If our solar system is 4.6 billion years old, and the universe is only 13 billion years old, given the present theory that heavy element formation requires several stars to form and supernovae to seed the star/planetary disk with heavier elements - can enough stars form and supernovae in the first 2/3 of time since the big bang to create sufficient raw materials for our solar system to have formed in the last 1/3?
It will be easier to answer if we constrain the questions a bit.

Are the oldest objects we can see the most distant? Perhaps. There are some very old stars -- the ages of which we gauge by comparing models of stellar evolution to the properties of the stars -- in the Milky Way's globular clusters, and a few passing through the disk of the Milky Way. Models suggest that some of these stars might be around 12-15 billion years old.

The most distant galaxies and quasars whose spectra we can observe have redshifts which, together with a good deal of other cosmological information, indicate that we are seeing light they emitted something like 10-13 billion years ago.

It is not straightforward to convert the redshift of a distant object into an "age" -- it depends a great deal on which cosmological parameters you choose, and also on exactly what you mean by "age". A good place to go for this sort of question is Ned Wright's cosmology calculator:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

Finally, yes, it is possible to fit several cycles of star formation into the period between the time when the first stars in the Milky Way formed, and the time when the solar system formed.

- Evidence suggests that the universe is much bigger than we can see.
- The Sun is a comparatively long-lived star. Large stars (the ones that go supernova) have much shorter lifetimes than stars like our Sun.

4. http://www.astro.ucla.edu/~wright/CosmoCalc.html
Ooh, great; a calculator! I love playing around with them. Excuse me while I experiment (tell me if I'm getting this all wrong, by the way).

If you leave all the values at the default setting but set the redshift (z) to 1248, you get a snapshot of what the Universe looks like at the decoupling era (when the universe was 300,000 years old). (assuming all the other numbers are correct).

The light emitted at the Decoupling era has travelled for 13.665 gigayears before reaching our instruments; but because the universe is expanding, the point of emission is now 45.737 gigalightyears away.
The point of emission is fleeing away in the opposite direction very fast; I find that this little image helps me to visualise that effect.
http://www.atlasoftheuniverse.com/expansion.gif

When the light was emitted, the point of emission was much closer to us than it is now, no more than 36.613 million light years away; this is the angular size distance.

Finally the luminosity distance is a measure of how much the light has become dimmed by the expansion of the universe; this is the largest measure of distance of all, and comes out to a whopping 57116.356 gigalightyears. No wonder the Cosmic Microwave background is so dim...

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