Do ‘bouncing universes’ have a beginning?
In trying to understand the nature of the cosmos, some theorists propose that the universe expands and contracts in endless cycles.
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How can a cyclic universe expand infinitely in each cycle.?
Tau.Neutrino said:
Do ‘bouncing universes’ have a beginning?In trying to understand the nature of the cosmos, some theorists propose that the universe expands and contracts in endless cycles.
more…
I think the laws prevent perpetual motion.
So the universe will eventually run out of energy.
But God might make us another one.
What other possibilities for a bouncing universe might there be?
Cyclic universe with no beginning and no end.
Cyclic universe with a beginning and an end.
A cyclic universe with a beginning that came out of nothing.
A cyclic universe with a beginning that came out of something.
Tau.Neutrino said:
Do ‘bouncing universes’ have a beginning?In trying to understand the nature of the cosmos, some theorists propose that the universe expands and contracts in endless cycles.
more…
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When did time begin?, is one of the most profound questions of all time.
We have two solutions,
1 t=0
2 infinite universes
3 it is hard to explain that time is infinite
Time doesn’t need to be infinite in a theoretically measurable sense in order to produce a cosmos in which what we see as “beginnings and ends” take place ad infinitum.
There could be epochs of measurable time emerging from more reduced states in which such time comes and goes.
Tau.Neutrino said:
What other possibilities for a bouncing universe might there be?Cyclic universe with no beginning and no end.
Cyclic universe with a beginning and an end.
A cyclic universe with a beginning that came out of nothing.
A cyclic universe with a beginning that came out of something.
> How can a cyclic universe expand infinitely in each cycle.?
I do know the answer to that, actually two answers.
1) The universe has a beginning and an end without expanding infinitely.
The mass of the Higgs particle tells us that the universe is metastable. Eventually, in finite time, an event will occur to make the entire universe explode with unimaginable force. The time coordinate can remain the same, but space has to be reset so that the start of the new explosion is mapped back to a single point. Since there is no way the next universe can communicate back with this one, due to randomisation over all space, the start of the next universe is essentially pointlike.
2) The universe has a beginning and and end while still expanding infinitely.
This won’t happen, because of the Higgs mass, but is the solution from General Relativity.
To see the answer, you need to look at Penrose Diagrams. In Penrose diagrams, space and time are mapped differently, the constant is the speed of light, which is drawn as straight lines at 45 degrees. Curves of constant space and constant time (for an inertial observer) are drawn as hyperbolas. And infinite time and infinite space are mapped back to points on a square. General Relativity tells us that we can do this mapping, map space-rime onto a different coordinate system. The result is the diagram drawn below.
Now a feature of the diamond is that we can tile the plane with it. So we can put another square next to it, this is a second universe. If we put the second universe with its “distant past” at the same point as our “timelike infinity” then we get a straightforward cyclic universe.
More interesting, though, is that we can place the second universe next to ours with edges touching. This is shown in the next diagram
Penrose coordinates also come in useful for mapping black holes. One possibility is that matter falling into one of our black holes comes out as one (or two, because as you have seen there are two ways in which to put a second universe next to ours) other universes, randomised to that it appears to come from a big bang.
Are you wondering how to map infinite time and space back to points on a square? That’s Penrose coordinates. The equations are a bit tricky, see https://arxiv.org/pdf/1802.02263.pdf is you really want to know what they are.