[ExI] Expansion of the Universe

BillK pharos at gmail.com
Sat Dec 29 09:19:01 UTC 2012

Ethan Seigel has done another interesting post.

Because of the expanding Universe, the farther away a galaxy is, the
faster it appears to be moving away from us, or the more redshifted
its light is. This image — from a section of the Hubble Ultra Deep
Field — shows the highest redshift galaxies ever discovered. And yet,
you don’t need to be this extreme to already be out of reach: any
galaxy with a redshift of 1.8 or more, or that’s more than about 16
billion light years distant right now, is already beyond our reach.

Not even if we had a relativistic spaceship, not even if we could
travel at the speed of light ourselves could we reach it. Our first
radio broadcast will never be received by those galaxies, and in fact
nothing we do from now on can ever affect them. They’re already gone.
In fact, the part that is presently within our reach encapsulates just
4% of the volume of the presently observable Universe!

And it’s only going to get worse over time; as the Universe’s clock
ticks by, the objects closer to that edge continue to expand away,
receding progressively faster from us. While we might be able to reach
the Virgo cluster now, in 100 billion years, it too will be gone. In
100 billion years, I should clarify, this will be all that’s left.
The local group. Ourselves, Andromeda, and our mutual satellite
galaxies. That’s it.

So much for humanity expanding throughout the universe.
If humanity is ever able to reach another galaxy, we'll only get to
the nearest few out of 200 billion galaxies.


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