View Full Version : Changing scenery at the edge of the observable universe.

2010-Feb-13, 12:45 PM
I was wondering about this and hoping someone could answer.

We are limited to what we can see in the observable universe as is presented to us by photons leaving a scource that lies within our light horizon. That is, if the scource was moving away from us at greater than c (as occurred during the inflationary phase of the universes expansion) then the light from that scource is unable to reach us.

As our ability to peer further and further into the farthest reaches of the universes increases, it is theoretically possible to image objects at the light horizon, but no further.

We now know that the universe is expanding at an accelerating rate and the further an object is away from us the faster it is accelerating away from us due to the increasing spped of the expansion of space itself.
As the expansion of space is not limited to sub c speed, does that mean that objects that we currently see at the extreme edge of the observable universe will "wink out" as the speed at which space is expanding at that distance away from us exceeds c and therefore moves the distant object beyond the light horizon?

Andrew D
2010-Feb-13, 04:04 PM
Yes, they will "wink out". If I'm not mistaken, an object moving across the 'light horizon' would look the same to us as if it were crossing the event horizon of a black hole. In fact, one can think of us (with a grain of salt) as living at the center of a giant, inside out black hole (It's worth noting that every point appears, to itself, to be at the center of a sphere with the same radius). So, the object just starts moving slower and slower, getting dimmer as the wavelength of its light reaching us is stretched infinately. Eventually, it effectively dissapears, though we could never actually observe it crossing the horizon.

Jeff Root
2010-Feb-13, 09:37 PM
I think that the most distant galaxies will simply redshift more and more,
and become dimmer and dimmer. But the distance at which a galaxy of a
given absolute brightness redshifts and dims to practical invisibility will
continually decrease as the expansion accelerates.

-- Jeff, in Minneapolis