Quote:
Originally Posted by sman
So this particular galaxy has put 16.4 billion light years between us in 15 billion years? This kinda throws up a flag for me.
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Sorry, I didn't see this question before. Yes, you're spot on. In fact, the furthest thing we can see is the cosmic microwave background which is *currently* about 46 billion lightyears from us (that is to say, the comoving distance between us and it is 46 billion lightyears).
This means, as you correctly infer, that the hot condensed plasma which eventually become the milky way and the hot condensed plasma which eventually became some other galaxy put 46 billion lightyears between each other in 13.6 billion years. This also means it is currently expanding away from us at faster than the speed of light.
The question is: how can we see something that is expanding away from us at faster than the speed of light? In fact, we cannot; we are not seeing the thing that is expanding away from us at that speed. We are *not* seeing the galaxy as it exists today—nor can we. We see it as it existed in the very young universe. Back when the light was emitted it was not expanding away from us as fast as it is today.
Galaxies which have a light travel time distance less than 13.7 billion lightyears with a comoving distance greater than 13.7 billion lightyears started out inside our cosmic horizon but have subsequently moved out of our horizon. So we can't see how they exist today—nor will we ever be able to no matter how long we wait. We can only see how they used to be when they were inside our past light cone.
~modest
