Source
r/askscience•
Amicus22

Is the observable universe getting smaller or larger?

Basis of my question:

The observable universe is considered the age of the universe multiplied by the speed of light. This would mean the observable universe is expanding.

However:

The universe is expanding in such a way that distant object will appear to be moving away from us at faster than the speed of light. Would the light from these objects never reach us? Or would it just be red-shifted? Can light be red-shifted to the point where that light is no longer theoretically "observable"?

Assuming the rate of the expansion of the universe is increasing could there be objects we can observe today that we will not be able to observe in the future?

Posted Jan 31, 2011, 3:28 AM UTC

74
iorgfeflkdCondensed matter | Biophysics | Relativity•

Google a Lawrence Krauss lecture; he talks about this. I believe that currently's it getting bigger, but it's projected that in a trillion years it will only consist of the milky way.

7
djcrazyarmz•

Just the lecture I had in mind.

Basically, the universe is expanding, and at an accelerating rate. Krauss points out that this acceleration will eventually cause the observables to move away from us (the future observers, rather) faster than the speed of light (which is allowed in GR), so that information would never make it to the people of the future and they would only be able to see what is a part of our own galaxy. http://www.youtube.com/watch?feature=player_detailpage&v=7ImvlS8PLIo#t=3051s

1
Acglaphotis•

This is the lecture iorgfeflkd is talking about.

3
RobotRollCall•

It's technically getting smaller. But it's important to remember that it's really an academic question. It's not like distant galaxies are vanishing from our telescopes or anything.

Look at it this way. When the light that makes up the cosmic microwave background was emitted, about 300,000 years after the start of the Big Bang, it was blackbody radiation corresponding to a temperature of about 3,000 K. Today it's been redshifted by a factor of a thousand, and it's still easily detectable as microwave radiation. By contrast, the most distant object ever observed — unless there's a new one found since last week — has a redshift of about ten. That's a hundred times less than the cosmic microwave background.

We've got a long way to go before we reach the limit of the observable universe.

1