[Airthumbs (OP)]

If the Universe eventually slows down and then starts to contract, resulting in cyclic bangs, would this not leave any kind of evidence such as multiple layers of CMBR? 

[Æthelwulf]

According to Penrose I believe, there is evidence in the form of ''Cosmic Bruising.''

[MikeS]

If the universe were truly cyclic then between consecutive universe cycles there must be an information barrier.  Were this not so the universe could be considered to be continuous. Time in some sense must cease to exist between universe cycles or it would be continuous.  Continuous time implies a continuous universe.  So there can only be one CMBR the present one.  Unless, there are multiple big bangs 'within' the present universe.  I believe entropy forbids this.

We can certainly theorize on the universe being cyclic.  I think it is but we can never prove it.

[Don_1]

I agree with Mike, the collapse of the universe would be total, leaving a complete void in which nothing, not even so much as an echo would exist. When the Big Bang happens again, all information would be new, with no trace of what had preceded it, so there can be no possibility of proving a cyclic universe. The only hint that such is the case would be if the universe were to begin to contract and that might be in many 10's, 100's or 1000's of billions of years to come, most likely long after our solar system has ceased to exist.

[MikeS]

I personally think the Universe is cyclic for various reasons but for one very simple one in particular.

Mainstream believes the Universe expansion to be accelerating.  Acceleration implies an input of energy.  Assuming the Universe to be finite then that energy will eventually run out.  The acceleration will stop and gravity will make the Universe contract.

[imatfaal]

I personally think the Universe is cyclic for various reasons but for one very simple one in particular.

Mainstream believes the Universe expansion to be accelerating.  Acceleration implies an input of energy.  Assuming the Universe to be finite then that energy will eventually run out.  The acceleration will stop and gravity will make the Universe contract.

Agree with acceleration bit - that's why we have used dark energy as a place-holder until the source can be identified. The lack of energy does not imply collapse though!  Escape velocity is calculated to a theoretical infinite point - stuff with escape velocity does not fall back

[CliffordK]

Would it be possible that only 99% of the matter in the universe would collapse in on itself.  And, 1% would remain at the time of a second "big bang".  So, there would be waves of truly ancient stellar remnants that would get pushed out further along the edge of the universe. 

The problem is that if we are not near an edge, if such an edge exists, then we may never be able to see them.  And, if all of the fusionable matter is used up, and they have been cooling for an eternity, then such matter would be nearly impossible to see.

[Airthumbs (OP)]

MikeS, if the universe contracted faster then the speed of light then would it be possible that an information barrier could not exists between bangs.  Maybe some of the Universe is radiated away after each bang in the form of light?  That might explain why there is a difference of temperature in the CMBR.  The Universe has to be expanding into something so that something is your information reserve.  Unless of course you believe in the possibility that absolutely nothing can exist. 

[MikeS]

MikeS, if the universe contracted faster then the speed of light then would it be possible that an information barrier could not exists between bangs.  Maybe some of the Universe is radiated away after each bang in the form of light?  That might explain why there is a difference of temperature in the CMBR.  The Universe has to be expanding into something so that something is your information reserve.  Unless of course you believe in the possibility that absolutely nothing can exist. 

If it contracted faster than the speed of light it would mean matter travelling faster than the speed of light which is forbidden.  Or are you proposing the illimination of space (the opposite of what is now being proposed as the creation of space)?
How can some of it be radiated away in the form of light, radiated to where?

[Bill S]

...are you proposing the illimination of space (the opposite of what is now being proposed as the creation of space)?

If space is being created as the Universe expands, if it is not being illiminated, and if the cycles are infinite, then there must already be infinite space.

If there is infinite space, then there is nowhere where there is no space.  This would imply that our present Universe must be expanding into pre-existing space, which we are told it is not.

If there is infinite space, how could more be created?  Surely it is not possible to have more than an infinite amount of anything.

[MikeS]

I personally think the Universe is cyclic for various reasons but for one very simple one in particular.

Mainstream believes the Universe expansion to be accelerating.  Acceleration implies an input of energy.  Assuming the Universe to be finite then that energy will eventually run out.  The acceleration will stop and gravity will make the Universe contract.

Agree with acceleration bit - that's why we have used dark energy as a place-holder until the source can be identified. The lack of energy does not imply collapse though!  Escape velocity is calculated to a theoretical infinite point - stuff with escape velocity does not fall back

I agree "stuff with escape velocity does not fall back."

The problem is in analysing whether or not escape velocity is reached near to the end of the Universe.  Velocity becomes a messy subject depending upon time, direction and distance.

Time.
When the matter/energy density in the Universe is very low the temperature will approach absolute zero and time tend towards ultimate dilation.  One second in that time will last much, much longer than one of our seconds.  If a second becomes longer then the Universe travels further in that second than it would in our second.  This is acceleration.  Acceleration implies an input of energy but here isn't an input of energy.  Also it takes more energy to do anything when it is cold just the same as it takes more energy to do anything in a strong gravitational potential (not to be confused with GPE).
There seems to be a paradox but that paradox is overcome by velocity decreasing. Decreasing from the perspective of our time frame, remaining constant from the perspective of the 'local' time frame.
If the universe were expanding but time infinately dilated (stopped) this makes no sense as it implies action outside of time.

Gravity becomes weaker with distance.  Time dilates with distance as the mass/energy density/temperature drops.  If time dilation progresses faster than the weakening of gravity then velocity will continually decrease.  Eventually there will be no further expansion and gravity will be free to make the universe contract.

It is believed that the universe is expanding and that expansion is accelerating.  The velocity is approaching but cannot exceed the speed of light.  This implies the input of an almost infinite amount of energy.  Towards the end of the Universe there can be no new energy, in fact there is precious little energy available. The energy that is available is in the form of inertia, kinetic and GPE. This would seem to indicate the expansion loosing velocity.

The other two ingredients of velocity are direction and distance.  Without the passage of time they become fairly meaningless concepts.  For example velocity is measured in relation to  something else.  At what point does space-time become so dilute that measurements can no longer be taken or be a meaningful concept?

Assuming the Universe to be finite.  It contains a finite amount of mass/energy.  This manifests itself in gravity.  For the Universe to exceed its escape velocity would seem to imply, to me, that it would have to an excess of energy over and above what it contains.  That makes no sense.

So, can the Universe exceed its escape velocity at the end of the Universe?

[MikeS]

...are you proposing the illimination of space (the opposite of what is now being proposed as the creation of space)?

If space is being created as the Universe expands, if it is not being illiminated, and if the cycles are infinite, then there must already be infinite space.

If there is infinite space, then there is nowhere where there is no space.  This would imply that our present Universe must be expanding into pre-existing space, which we are told it is not.

If there is infinite space, how could more be created? Surely it is not possible to have more than an infinite amount of anything.

If you consider the speed of light in a vacuum to be infinite (from its reference frame if it had one) then it explains why in an inertial reference frame both approaching photons and receding photons travel at the same speed.

Infinite does not seem to be a fixed quantity.  You can't put a finite value on something that is infinite.  Infinity plus one is a meaningless concept.

[JP]

If you consider the speed of light in a vacuum to be infinite (from its reference frame if it had one) then it explains why in an inertial reference frame both approaching photons and receding photons travel at the same speed.

No, it doesn't explain that at all since photons don't have a reference frame, so you can't consider them to have one!

[yor_on]

The theory of relativity, as well as Maxwells ideas, define the speed of light in a vacuum as 'c', constant in all (non accelerating) frames of reference. And the fact that your clocks will tell you differently in a accelerated frame is explained by accelerations equivalence to 'gravity'. And gravitational 'time dilations' of clocks have been proved on Earth by NIST.

So light has a 'speed' for us. In its own frame of reference? That one is impossible to define to me. I like to wonder about that too, but what we have is 'time less', 'mass less' propagation according to cosmology. We do not see 'tired light' in any experiment I know of.

And if photons are 'time less' but with a 'speed' then maybe the arrow should be the answer?

[Airthumbs (OP)]

MikeS, if the universe contracted faster then the speed of light then would it be possible that an information barrier could not exists between bangs.  Maybe some of the Universe is radiated away after each bang in the form of light?  That might explain why there is a difference of temperature in the CMBR.  The Universe has to be expanding into something so that something is your information reserve.  Unless of course you believe in the possibility that absolutely nothing can exist. 

If it contracted faster than the speed of light it would mean matter travelling faster than the speed of light which is forbidden.  Or are you proposing the illimination of space (the opposite of what is now being proposed as the creation of space)?
How can some of it be radiated away in the form of light, radiated to where?

If space can expand faster then the speed of light then the opposite must also be true.  If whatever mechanism involved in the current expansion was reversed then this is what I meant by the Universe contracting faster then the speed of light.  If the Universe expands faster then the speed of light does that mean matter travels faster then light also?  Me thinks not...   so we have a problem, what I am proposing is that matter cannot travel faster then the speed of light therefore if the Universe does contract the same way as it expands then there must be stuff leftover that cannot keep up with the contraction and that is what I refer to as the reserve.  And I have no idea what this leftover stuff would be radiated into but I don't think it's nothing...   I hope I am making sense here!  Sounds like illimination, yep that be what I is proposing...