4 ms·

Gravity is traveling at the speed of light. Space is expanding. Objects far apart are traveling away from each faster than the speed of light. Or more that t

Gravity is traveling at the speed of light. Space is expanding. Objects far apart are traveling away from each faster than the speed of light. Or more that the space between them is expanding faster then the speed of light. So those objects will never have any sort of interaction. Only ways around this if space itself start contracting. (No known way for this to happen). Or somehow the universe is a big circle, and going far enough brings you back to the starting point. Negative curvature. We don’t have any good theories on this. Some highly interesting ones that move the problem up a level. For Example one theory is our entire universe is inside a black hole created from the remains of a four dimensional hyper star. The math seems to work. Soo cool. But then where does the hyper star come from? It’s “turtles all the way down”, is the thought to lot of the best theories. Or everything is a simulation, again math kind of works. No direct evidence, but neat idea. But who’s hosting the sever that’s running the universe. Something from nothing problem is a real trouble maker.

Johnjonjoan 6y ago
Objects far apart may be traveling faster than the speed of light but once the universe reaches equilibrium won't there be intermediate masses that gravity will be able to travel through? I was also under the impression that an expansion of space would just reduce the gradient of the gravity along that space and not inhibit its propagation. If like a bubble space has some form of surface tension then would there be a point that it can no longer expand? Gravity could then become dominant and force the contraction. -edit-> I guess that wouldn't contract the space though just the matter? I promise I'm not being pedantic or contrarian for the sake of it but to further my knowledge, thanks for your input!
- fhars 6y ago
  There is no "equilibrium" the universe is moving towards, it is just expanding, and the "intermediate masses" are getting more spread out the more the universe expands. The expansion doesn't inhibit the propagation of gravity, it just makes the attraction between masses weaker and weaker the further they are apart, until they are so far apart that the space between them expands faster than the speed of light, at which moment they will no longer be able to interact with another, neither by light nor by gravity, and the contracting effect of gravity becomes weaker and weaker the larger the universe becomes. According to out current best cosmological model, Lambda-CDM (which, admittedly, is mostly a phenomenological model for things we only half understand, but still describes our current observations better than any competing model), gravity used to be the dominant force in the universe when it was smaller so that the masses were closer together until quite recently. But now it looks like the expansion, the "Lambda" term in "Lambda-CDM", the cosmological constant of general relativity, has become the dominant force in the universe, and the universe is slated to expand ever faster. It could start to contract if Lambda were closer to zero, but it currently doesn't look like it might move there. But then we don't know why Lambda it there at all and what causes it not to be zero in the first place, as everyone expected it to be until about two decades ago (Einstein himself thought of the introduction of the term into his theory as a blunder, as it would obviously be zero in any sane universe.)
  - deleted 6y ago
    [deleted]
aspaviento 6y ago
> Only ways around this if space itself start contracting. (No known way for this to happen). Maybe at the border of the universe there's a crunchy layer of mass that at some point gravity force will win over expansion.
- treeman79 6y ago
  Current estimate is that there is no border. It goes on forever. Space is infinite and increasing. Matter is fixed and static. So a bigger infinity divided by a smaller infinity. Which means density is heading towards 0. This is heat death of universe. Now since dividing infinity by infinity is nonsense, this a sign our understanding is incomplete
vokep 6y ago
>Or everything is a simulation, again math kind of works. No direct evidence, but neat idea. But who’s hosting the sever that’s running the universe. Its programmers all the way up! But really, awhile ago I settled on the belief that its very possible we're in a natural simulation. Natural, as in, the same way that plants are simulations of L-Systems or in particular the same way my GPU once spat out cellular-automata-like behavior in a glitch. If we are in a simulation, we've got no prior on what the world "above" us might be like. Oftentimes I see the theory shot down with "Our universe is too big and complex, theres no way any computer could be big enough to simulate it!" which is valid if assuming scale and physics anything like ours. But that's not a reasonable assumption here. It could be that the computational power of a cheap smartphone in the above world is similar to what a supercomputer the size of Jupiter or even Sun or any scale really for all we know. But that still assumes a programmer. If computing is done a lot in the above world at that sort of scale, our universe could be the result of a hardware glitch. That specific scenario may be quite unlikely, its just the extension of the GPU creating cellular automata by chance that I mentioned earlier. There's many other ways for algorithms of simulation to naturally emerge from reality just existing and things within it creating new sub-systems, which from within such a system, appear to be "something from nothing". So in a sense, it seems most likely that whatever the case is we are likely not one the "first layer" of reality, we are "simulated" within sub-layers. So then the interesting question is not how did this particular something come from nothing, but how can anything come from nothing, in the very first place, ever, at all? Once something exists, while scientifically we'd want an answer for how to get from there to here, its just a matter of what exact process that is.

Johnjonjoan 6y ago

Objects far apart may be traveling faster than the speed of light but once the universe reaches equilibrium won't there be intermediate masses that gravity will be able to travel through? I was also under the impression that an expansion of space would just reduce the gradient of the gravity along that space and not inhibit its propagation. If like a bubble space has some form of surface tension then would there be a point that it can no longer expand? Gravity could then become dominant and force the contraction. -edit-> I guess that wouldn't contract the space though just the matter? I promise I'm not being pedantic or contrarian for the sake of it but to further my knowledge, thanks for your input!

fhars 6y ago
There is no "equilibrium" the universe is moving towards, it is just expanding, and the "intermediate masses" are getting more spread out the more the universe expands. The expansion doesn't inhibit the propagation of gravity, it just makes the attraction between masses weaker and weaker the further they are apart, until they are so far apart that the space between them expands faster than the speed of light, at which moment they will no longer be able to interact with another, neither by light nor by gravity, and the contracting effect of gravity becomes weaker and weaker the larger the universe becomes. According to out current best cosmological model, Lambda-CDM (which, admittedly, is mostly a phenomenological model for things we only half understand, but still describes our current observations better than any competing model), gravity used to be the dominant force in the universe when it was smaller so that the masses were closer together until quite recently. But now it looks like the expansion, the "Lambda" term in "Lambda-CDM", the cosmological constant of general relativity, has become the dominant force in the universe, and the universe is slated to expand ever faster. It could start to contract if Lambda were closer to zero, but it currently doesn't look like it might move there. But then we don't know why Lambda it there at all and what causes it not to be zero in the first place, as everyone expected it to be until about two decades ago (Einstein himself thought of the introduction of the term into his theory as a blunder, as it would obviously be zero in any sane universe.)
- deleted 6y ago
  [deleted]

aspaviento 6y ago

> Only ways around this if space itself start contracting. (No known way for this to happen). Maybe at the border of the universe there's a crunchy layer of mass that at some point gravity force will win over expansion.

treeman79 6y ago
Current estimate is that there is no border. It goes on forever. Space is infinite and increasing. Matter is fixed and static. So a bigger infinity divided by a smaller infinity. Which means density is heading towards 0. This is heat death of universe. Now since dividing infinity by infinity is nonsense, this a sign our understanding is incomplete

vokep 6y ago

>Or everything is a simulation, again math kind of works. No direct evidence, but neat idea. But who’s hosting the sever that’s running the universe. Its programmers all the way up! But really, awhile ago I settled on the belief that its very possible we're in a natural simulation. Natural, as in, the same way that plants are simulations of L-Systems or in particular the same way my GPU once spat out cellular-automata-like behavior in a glitch. If we are in a simulation, we've got no prior on what the world "above" us might be like. Oftentimes I see the theory shot down with "Our universe is too big and complex, theres no way any computer could be big enough to simulate it!" which is valid if assuming scale and physics anything like ours. But that's not a reasonable assumption here. It could be that the computational power of a cheap smartphone in the above world is similar to what a supercomputer the size of Jupiter or even Sun or any scale really for all we know. But that still assumes a programmer. If computing is done a lot in the above world at that sort of scale, our universe could be the result of a hardware glitch. That specific scenario may be quite unlikely, its just the extension of the GPU creating cellular automata by chance that I mentioned earlier. There's many other ways for algorithms of simulation to naturally emerge from reality just existing and things within it creating new sub-systems, which from within such a system, appear to be "something from nothing". So in a sense, it seems most likely that whatever the case is we are likely not one the "first layer" of reality, we are "simulated" within sub-layers. So then the interesting question is not how did this particular something come from nothing, but how can anything come from nothing, in the very first place, ever, at all? Once something exists, while scientifically we'd want an answer for how to get from there to here, its just a matter of what exact process that is.