4 ms·

> FTL should be possible because the universe expands [EXP] at speeds greater than that of light. The universe isn't expanding faster than the speed of light,

by cmsj 3y ago

> FTL should be possible because the universe expands [EXP] at speeds greater than that of light. The universe isn't expanding faster than the speed of light, it seems to be expanding everywhere at the same rate. Galaxies beyond a particular distance from us are receding at/above the speed of light only because all of the expansion between us and them stacks up and is pushing them away from us at faster than the speed of light. They are not being pushed through space though, space itself is expanding. Furthermore, since the speed of light is really more accurately the speed of causality, once these distant objects are receding faster than the speed of light, no further information (which in practice means EM radiation, but in theory means any/all causality) from them can ever reach us. So, I'm not sure how it follows that because universal expansion exists and is being driven by something, it should therefore be possible for us to harness it. The universe seems to be extremely clear that causality is not allowed to happen faster than c.

fnordpiglet 3y ago
More specifically expansion isn’t movement per se, it just appears to be movement. It’s actually the expansion of distance between points without energy applied. There may be a time when expansion makes things appear to move faster than the speed of light away from each other, but that time will mean we can never observe anything and the universe has effectively ripped itself apart. As has been noted this can already be observed at large distances as the expansion accumulating between us and those distant points creates the appearance of faster than light travel. [0] That happens only in certain situations for certain constant assumptions and certain mathematics and physics assumptions, which can be totally overturned and we are in no way sure expansion is accelerating, slowing, going at the same rate, or even our empirical observations that support expansion aren’t caused by some as of now unknown physical process. [0] https://en.m.wikipedia.org/wiki/Hubble_volume https://en.m.wikipedia.org/wiki/Hubble_volume
- ithkuil 3y ago
  > without energy being applied I'm confused. Why is the cosmological constant then also called dark energy if it's not equivalent to there being some energy in empty space?
  - fnordpiglet 3y ago
    Dark energy isn’t energy in a conventional sense (hence its disclaimer). In fact it isn’t known to actually exist and is more a placeholder explanation of the apparent expansion effects and ascribing some universal energy that can account for the expansion and the resistance to expansion gravity seems to exert. No energy is expended or moved to cause expansion as dark energy is constant and universal.

by cmsj 3y ago

fnordpiglet 3y ago

More specifically expansion isn’t movement per se, it just appears to be movement. It’s actually the expansion of distance between points without energy applied. There may be a time when expansion makes things appear to move faster than the speed of light away from each other, but that time will mean we can never observe anything and the universe has effectively ripped itself apart. As has been noted this can already be observed at large distances as the expansion accumulating between us and those distant points creates the appearance of faster than light travel. [0] That happens only in certain situations for certain constant assumptions and certain mathematics and physics assumptions, which can be totally overturned and we are in no way sure expansion is accelerating, slowing, going at the same rate, or even our empirical observations that support expansion aren’t caused by some as of now unknown physical process. [0] https://en.m.wikipedia.org/wiki/Hubble_volume https://en.m.wikipedia.org/wiki/Hubble_volume

ithkuil 3y ago
> without energy being applied I'm confused. Why is the cosmological constant then also called dark energy if it's not equivalent to there being some energy in empty space?
- fnordpiglet 3y ago
  Dark energy isn’t energy in a conventional sense (hence its disclaimer). In fact it isn’t known to actually exist and is more a placeholder explanation of the apparent expansion effects and ascribing some universal energy that can account for the expansion and the resistance to expansion gravity seems to exert. No energy is expended or moved to cause expansion as dark energy is constant and universal.