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At some point, given the universe's expansion, galaxies will be moving away so fast that the observable universe will be just one galaxy. Already, the effective

At some point, given the universe's expansion, galaxies will be moving away so fast that the observable universe will be just one galaxy. Already, the effective rate from galaxies far away is actually faster than the speed of light. Even at light speeds, we cannot reach 94% of them as we would never catch up if we left today. In cosmic scales of many billions of years, observers on every galaxy will eventually think that their galaxy is the only one that has ever existed. Large distance and time scales are rather gloomy.

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dumpsterdiver 2y ago
Indeed, the only hint they would have that they were not alone would be the "weak" gravitational effects of all other existing matter pulling at the fringes of their visible universe. Perhaps they'll refer to this phenomenon as "dark energy".
mr_toad 2y ago
The galaxies in our local group are gravitationally bound.
- deleted 2y ago
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- 0xfae 2y ago
  Right, but isn't the expansion increasing? So if they don't merge into one big galaxy at some point the expansion would out run gravity?
arbuge 2y ago
> In cosmic scales of many billions of years, observers on every galaxy will eventually think that their galaxy is the only one that has ever existed. Unless of course some of them manage to find ways to preserve information and keep records over those billions of years. The lost galaxies will be known from that.
- saulpw 2y ago
  But the information would still be forever locked away in its own galactic island. Even transmitting at the speed of light, the information could never reach any other galaxy. So no, in this far future, a galaxy would only be able to know itself.
  - arbuge 2y ago
    We have records of other galaxies right now. Assuming we manage to preserve those and humanity over these kinds of time scales, our descendants would be able to access those records and learn that other galaxies once existed that are beyond their cosmic horizon now.

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dumpsterdiver 2y ago

Indeed, the only hint they would have that they were not alone would be the "weak" gravitational effects of all other existing matter pulling at the fringes of their visible universe. Perhaps they'll refer to this phenomenon as "dark energy".

mr_toad 2y ago

The galaxies in our local group are gravitationally bound.

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0xfae 2y ago
Right, but isn't the expansion increasing? So if they don't merge into one big galaxy at some point the expansion would out run gravity?

arbuge 2y ago

> In cosmic scales of many billions of years, observers on every galaxy will eventually think that their galaxy is the only one that has ever existed. Unless of course some of them manage to find ways to preserve information and keep records over those billions of years. The lost galaxies will be known from that.

saulpw 2y ago
But the information would still be forever locked away in its own galactic island. Even transmitting at the speed of light, the information could never reach any other galaxy. So no, in this far future, a galaxy would only be able to know itself.
- arbuge 2y ago
  We have records of other galaxies right now. Assuming we manage to preserve those and humanity over these kinds of time scales, our descendants would be able to access those records and learn that other galaxies once existed that are beyond their cosmic horizon now.