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This might be obvious to most, but at first it wasn't clear to me why in 150 billion years the vast majority of the known universe will be unreachable. The answ
by __blockcipher__ 5y ago
This might be obvious to most, but at first it wasn't clear to me why in 150 billion years the vast majority of the known universe will be unreachable. The answer is in the acceleration of expansion (which the blogpost mentioned but I didn't connect the dots on at first); eventually the rate of expansion ("velocity") will greater than the speed of light.
- tobmlt 5y agoParsing this, I’d like to match it up with the Hubble horizon, at least for your stated condition that the velocity of expansion is greater than the speed of light: That already holds for us relative to points across the Hubble horizon. Their “past-emitted” light is still reaching us, meanwhile their “presently emitted” light never will. I need to check the proper definitions but that’s the gist. Kinda erie!
- amelius 5y ago> eventually the rate of expansion ("velocity") will greater than the speed of light. What will that do to the speed of light as measured on Earth? And will this affect, say, the correct operation of computers?
- WillySchu 5y agoThe speed of light ought to remain constant (for inertial observers). So nothing would be different locally as far as I'm aware.
- raattgift 5y agoThe speed of light (in vacuum) is constant for accelerated observers too. :-) The dipole anisotropy of the Cosmic Microwave Background will continue to be a good tool to see the constancy of the speed of light for all observers into the practically infinite future, assuming the infinite future looks a lot like de Sitter space (which is essentially what the standard cosmology predicts). http://www.astro.ucla.edu/~wright/CMB-dipole-history.html http://www.astro.ucla.edu/~wright/CMB-dipole-history.html The far future of the universe will still have generally covariant physics, as does its far past, sharpening up your second sentence.
- krapp 5y agoAt that point in time (assuming time has any meaning in that reference frame,) everything will be moving away from everything else faster than any force, even information, could possibly travel between them. There won't be computers. There won't even be atoms to make matter to make computers with.
- amelius 5y agoI'm still wondering if the change would be instantaneous or gradual. Will the speed of light be constant and then suddenly impossible to measure?
- WillySchu 5y agoI'm not precisely sure what you're referring to as "the change" here. The rate of expansion is increasing continuously though, if that's what you're asking. As far as the measurability of the speed of light, I don't think anything changes in principle. It should remain measurable and constant. However, it gets a lot more complicated in practice, since it's pretty unclear who or what would actually be doing the measuring and how they might go about it.
- agumonkey 5y agoessentially it's similar to a black hole.. nothingness
- rendall 5y agoNo. The expansion of the universe does not mean that atoms themselves will fly apart
- simonh 5y agoDistant regions of the universe already are receding from us faster than light. Due to the accelerating rate of expansion, that horizon beyond which this is true is shrinking inwards towards us, so that in 150 bn years even galaxies outside our local group will be beyond that horizon. Hurry up Elon, we're running out of time!