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You're right of course but I find the cyclic version so much more intuitive. The force from the big bang was imparted in an instant yet gravity is a constant f

You're right of course but I find the cyclic version so much more intuitive. The force from the big bang was imparted in an instant yet gravity is a constant force. IANAP but surely at some point the accumulative force of billions/trillions/... of years of gravity overcomes the force imparted by the big bang and the universe compresses into a singularity again? I'd really appreciate someone explaining why this isn't obviously the case.

coldcode 6y ago
I'm not sure we can ever tell the difference between the two models. Given the assumption that both produce a "boring" universe, and that models are never completely verifiable, it could be that either pathway appears the same to us at this point in time.
tyfon 6y ago
The issue with this view is that in the universe we see today the gravitational force is not strong enough to do what you describe here. There is acceleration of the expansion i.e. energy is added to the system (in the form of vacuum energy possibly). To say it in another way, the energy used to expand the universe today is not only the initial force imparted by the big bang but is added to as part of quantum processes in empty space. However as the universe expands, the amount of matter (dark + luminous) does not increase so the proportion of gravity/matter to dark energy (the force that accelerates the expansion) is getting lower and we get an acceleration. These observations exclude the possibility of a "big crunch". Disclaimer: I am a statistician not a cosmologist but this is how I have understood it.
- Johnjonjoan 6y ago
  Cheers, I now understand why it's not such a clear case. I fear I may have many more harder to answer questions now though - Thanks none the less!
  - GioM 6y ago
    Take the idea a little further, to the end of the universe, and the rate of acceleration of expansion of space increases so much that stars become isolated from each other, then planets from stars, then molecules from each other, then atoms, and then quarks, the constituents of matter itself, and then.... An interesting thing happens. When you tear a quark away from it's antiquark, you get two quarks. The energy is equal to that required to bring another quark into existence. At this point, the rate of expansion is so vast that every quark in the universe has been forever isolated from one another, and then each bursts into a sea of high-energy quark-gluon plasma. The massive energy of expansion is rapidly consumed generating these quarks, and then the expansion slows, never stopping, but continues at a much slower rate. Wait... we've seen this before. A quark-gluon plasma, rapidly expanding from a single point, in a universe isolated from all others. Only expansion is required to generate new universes, forever.
    - deleted 6y ago
      [deleted]
treeman79 6y ago
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.)
hacknat 6y ago
The Universe can be infinite without being cyclic.

coldcode 6y ago

I'm not sure we can ever tell the difference between the two models. Given the assumption that both produce a "boring" universe, and that models are never completely verifiable, it could be that either pathway appears the same to us at this point in time.

tyfon 6y ago

The issue with this view is that in the universe we see today the gravitational force is not strong enough to do what you describe here. There is acceleration of the expansion i.e. energy is added to the system (in the form of vacuum energy possibly). To say it in another way, the energy used to expand the universe today is not only the initial force imparted by the big bang but is added to as part of quantum processes in empty space. However as the universe expands, the amount of matter (dark + luminous) does not increase so the proportion of gravity/matter to dark energy (the force that accelerates the expansion) is getting lower and we get an acceleration. These observations exclude the possibility of a "big crunch". Disclaimer: I am a statistician not a cosmologist but this is how I have understood it.

Johnjonjoan 6y ago
Cheers, I now understand why it's not such a clear case. I fear I may have many more harder to answer questions now though - Thanks none the less!
- GioM 6y ago
  Take the idea a little further, to the end of the universe, and the rate of acceleration of expansion of space increases so much that stars become isolated from each other, then planets from stars, then molecules from each other, then atoms, and then quarks, the constituents of matter itself, and then.... An interesting thing happens. When you tear a quark away from it's antiquark, you get two quarks. The energy is equal to that required to bring another quark into existence. At this point, the rate of expansion is so vast that every quark in the universe has been forever isolated from one another, and then each bursts into a sea of high-energy quark-gluon plasma. The massive energy of expansion is rapidly consumed generating these quarks, and then the expansion slows, never stopping, but continues at a much slower rate. Wait... we've seen this before. A quark-gluon plasma, rapidly expanding from a single point, in a universe isolated from all others. Only expansion is required to generate new universes, forever.
  - deleted 6y ago
    [deleted]

treeman79 6y ago

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.)

hacknat 6y ago

The Universe can be infinite without being cyclic.