Accelerating expansion of universe is an illusion

[bohm2]

I'm not sure how strong the evidence is for this but I found it interesting:

"Now, a new theory suggests that the accelerating expansion of the universe is merely an illusion, akin to a mirage in the desert. The false impression results from the way our particular region of the cosmos is drifting through the rest of space, said Christos Tsagas, a cosmologist at Aristotle University of Thessaloniki in Greece. Our relative motion makes it look like the universe as a whole is expanding faster and faster, while in actuality, its expansion is slowing down — just as would be expected from what we know about gravity.

If Tsagas' theory is correct, it would rid cosmology of its biggest headache, dark energy, and it might also save the universe from its harrowing fate: the Big Rip. Instead of ripping it to bits, the universe as Tsagas space-time envisions it would just roll to a standstill, then slowly start shrinking."

http://www.astro.auth.gr/~tsagas/Publications/Journals/PRD/PRD14.pdf
http://www.msnbc.msn.com/id/44690771/ns/technology_and_science-science/

 

[Chronos]

The author made good points favoring a dark flow interpretation, but, there remains plenty of observational work to confirm this is a viable alternative to dark energy. The basis for including a cosmological constant [dark energy] in GR is mathematically sound. QM provides a mechanism. The real puzzle is why it is so weak.

 

[Chalnoth]

I'm not sure how strong the evidence is for this but I found it interesting:

"Now, a new theory suggests that the accelerating expansion of the universe is merely an illusion, akin to a mirage in the desert. The false impression results from the way our particular region of the cosmos is drifting through the rest of space, said Christos Tsagas, a cosmologist at Aristotle University of Thessaloniki in Greece. Our relative motion makes it look like the universe as a whole is expanding faster and faster, while in actuality, its expansion is slowing down — just as would be expected from what we know about gravity.

If Tsagas' theory is correct, it would rid cosmology of its biggest headache, dark energy, and it might also save the universe from its harrowing fate: the Big Rip. Instead of ripping it to bits, the universe as Tsagas space-time envisions it would just roll to a standstill, then slowly start shrinking."

http://www.astro.auth.gr/~tsagas/Publications/Journals/PRD/PRD14.pdf
http://www.msnbc.msn.com/id/44690771/ns/technology_and_science-science/

I have a really really hard time buying that this could both explain the acceleration and be consistent with our current observations of the isotropy of our universe.

 

[RUTA]

I have a really really hard time buying that this could both explain the acceleration and be consistent with our current observations of the isotropy of our universe.

You need a lot of coincidences to be fooled in this fashion. If the universe has conspired against our best science to the extent that we can't figure out what's really going on, we might as well give up trying.

 

[DevilsAvocado]

... Now, a new theory suggests that the accelerating expansion of the universe is merely an illusion, akin to a mirage in the desert.

https://www.physicsforums.com/showthread.php?t=536522"


(Hi RUTA, nice to have you back!)

 

[RUTA]

https://www.physicsforums.com/showthread.php?t=536522"


(Hi RUTA, nice to have you back!)

I was away while I was working on this very problem, actually. I bailed on all discussion forums during this time to focus on the problem at hand. I do believe the Nobel citation should not have stated "for the discovery of the accelerating expansion of the Universe," since that conclusion follows from their data only in the context of a particular theory of cosmology. They certainly deserve the prize, but the citation should have said something like, "for observational techniques associated with type Ia supernovae." Then, the Nobel committee doesn't have to worry about changes to our theoretical cosmology that change the interpretation of the data.

 

[DevilsAvocado]

I was away while I was working on this very problem, actually. I bailed on all discussion forums during this time to focus on the problem at hand. I do believe the Nobel citation should not have stated "for the discovery of the accelerating expansion of the Universe," since that conclusion follows from their data only in the context of a particular theory of cosmology. They certainly deserve the prize, but the citation should have said something like, "for observational techniques associated with type Ia supernovae." Then, the Nobel committee doesn't have to worry about changes to our theoretical cosmology that change the interpretation of the data.

Cool, I had some remorse about not recapturing the discussion on simplices manifold/non-separability/RBW... a lot of 'messy things' in world politics got between, and then you were gone...

Anyhow, I’m glad you’re back, and maybe sometime we could continue... I have bunch of 'topics' in pipeline that I’ll try to get posted... but maybe later?

The comment on the Nobel citation is interesting. It’s not the first time those Nobel guys made a "mistake", and of course – not one single human has seen DE, or know what it is, or how it works.

But as you said - they certainly deserve the prize – they proved the accelerating expansion beyond any doubts, even if we don’t know the 'mechanism'.

 

[RUTA]

Cool, I had some remorse about not recapturing the discussion on simplices manifold/non-separability/RBW... a lot of 'messy things' in world politics got between, and then you were gone...

Anyhow, I’m glad you’re back, and maybe sometime we could continue... I have bunch of 'topics' in pipeline that I’ll try to get posted... but maybe later?

The comment on the Nobel citation is interesting. It’s not the first time those Nobel guys made a "mistake", and of course – not one single human has seen DE, or know what it is, or how it works.

But as you said - they certainly deserve the prize – they proved the accelerating expansion beyond any doubts, even if we don’t know the 'mechanism'.

Thanks, I'm glad to be done with this last calculation. It was nasty

To clarify on this topic, what everyone agrees these guys did was obtain distance moduli (μ) out to redshift z ~ 1.5 using type Ia supernovae. Whether or not this data provides evidence that the universe is expanding depends on your cosmology model. Using inhomogeneous spacetime models, for example, the data does not show accelerating expansion (arXiv:gr-qc/0605088v2). Likewise, the PRD paper that started this conversation shows the accelerated expansion could be an illusion. However, no one is disputing the validity of the μ versus z data these Nobel recipients obtained, and that process took them years to perfect and employ.

 

[HarryWertM]

Begging patience for an imbecile...

If a supernova far, far away is moving very, very fast does that mean the universe long, long ago was moving faster than today?

 

[RUTA]

Begging patience for an imbecile...

If a supernova far, far away is moving very, very fast does that mean the universe long, long ago was moving faster than today?

Consider the relationship between the Milky Way and a galaxy that is far away today, for example. In the flat, matter-dominated (pressureless dust) GR cosmology model (Einstein-deSitter, EdS for short) that galaxy was moving away from us at time of emission at a much faster speed than it is today (time of reception). The rate of recession between the two galaxies will continue to diminish, slowing to v = 0 at t = ∞. In the Lambda CDM model (EdS + cosmological constant), the recession rate slowed at first, but then started to speed up again (when cosmological constant outward pressure started to dominate attraction of matter). But, in both models, the galaxies today are still not receding faster than they were at time of emission, although eventually in LCDM they will be.

 

[DevilsAvocado]

Thanks, I'm glad to be done with this last calculation. It was nasty

Congrats!

To clarify on this topic, what everyone agrees these guys did was obtain distance moduli (μ) out to redshift z ~ 1.5 using type Ia supernovae. Whether or not this data provides evidence that the universe is expanding depends on your cosmology model. Using inhomogeneous spacetime models, for example, the data does not show accelerating expansion (arXiv:gr-qc/0605088v2). Likewise, the PRD paper that started this conversation shows the accelerated expansion could be an illusion.

Oops... I took it for granted this was some 'cranky solution'...

A lot of questions arise:

• How could a contracting universe look like an expanding universe? We will not get the same 'setup', playing 'the movie' backwards, right?
  
  
• How could we observe the (extreme) red-shift in the CMB?
  
  
• Why do we observe red-shift at all?
  
  
• When did the universe swap 'direction'? BB did happen, right?
  
  
• Are all data from Type II Supernovae wrong?

 

[DevilsAvocado]

Begging patience for an imbecile...

If a supernova far, far away is moving very, very fast does that mean the universe long, long ago was moving faster than today?

According to the Lambda-CDM model the answer is: At early inflation, yes, later, no.

 

[RUTA]

Oops, I'm sorry, I've given the wrong impression. The universe is expanding, no one disputes that. It's just a question of whether or not the expansion is speeding up or slowing down. In LCDM it was slowing down until the cosmological constant started dominating the matter density at which point it started speeding up. This demarcation occurs in the data at about z = 0.752 (arXiv:1105.3470).

 

[DevilsAvocado]

Oops, I'm sorry, I've given the wrong impression. ...

Phew, big relief!

Thanks

()

 

[petm1]

How could a contracting universe look like an expanding universe? We will not get the same 'setup', playing 'the movie' backwards, right?

If you think of space and time as opposite directions, you would know that looking out in space is looking back in time to the same point.

 

[DevilsAvocado]

If you think of space and time as opposite directions, you would know that looking out in space is looking back in time to the same point.

Thanks, I understand, but I was thinking more on the second law of thermodynamics, the entropy of the universe, and the arrow of time.

AFAICT, you will not end up with an "exact copy" of the early universe, if you tried to reverse the current expansion for 13.75 billion years...

 

[Chalnoth]

Thanks, I understand, but I was thinking more on the second law of thermodynamics, the entropy of the universe, and the arrow of time.

AFAICT, you will not end up with an "exact copy" of the early universe, if you tried to reverse the current expansion for 13.75 billion years...

Why not? If you have the current configuration of our universe exactly, then in running the clock backward it will necessarily reach an identical state.

 

[RUTA]

How could a contracting universe look like an expanding universe?

As an aside, in answer to this question, it is possible in theory to see increased redshift with increased distance in a collapsing universe. The reason is that the redshift only tells you the universe scale factor is bigger at reception than at emission. Thus, z is independent of what happens dynamically between emission and reception. So, if a photon is emitted during an expanding phase and received shortly after the collapsing phase begins, as in the closed model, then you will see increased redshift with increased distance even though the universe is now collapsing. I explained this in a paper some years ago (“Kinematics between Comoving, Photon Exchangers in the Closed Matter-dominated Universe,” W.M. Stuckey, American Journal of Physics 60, No. 6, 554 - 560 (1992)).

 

[Chalnoth]

As an aside, in answer to this question, it is possible in theory to see increased redshift with increased distance in a collapsing universe. The reason is that the redshift only tells you the universe scale factor is bigger at reception than at emission. Thus, z is independent of what happens dynamically between emission and reception. So, if a photon is emitted during an expanding phase and received shortly after the collapsing phase begins, as in the closed model, then you will see increased redshift with increased distance even though the universe is now collapsing. I explained this in a paper some years ago (“Kinematics between Comoving, Photon Exchangers in the Closed Matter-dominated Universe,” W.M. Stuckey, American Journal of Physics 60, No. 6, 554 - 560 (1992)).

Well, that's not really a contracting universe looking like an expanding one, though. The redshift combined with a distance measure still captures accurately the expansion history. The recent start of the collapse would also be captured in the relationship between redshift and distance (though if the collapse was recent enough it could only be extrapolated).

 

[DevilsAvocado]

Why not? If you have the current configuration of our universe exactly, then in running the clock backward it will necessarily reach an identical state.

True, but it would be a terrible bad "illusion", because of the change of the direction of time; watching the omelet jumping out of the pan to 'regenerate' into 4 complete eggs... we would just know that there’s something 'fishy' going on...

Or?

 

[RUTA]

Well, that's not really a contracting universe looking like an expanding one, though. The redshift combined with a distance measure still captures accurately the expansion history. The recent start of the collapse would also be captured in the relationship between redshift and distance (though if the collapse was recent enough it could only be extrapolated).

Except that at the shortest distances we don't see expansion regardless, we see collapse (gravity overcomes cosmological expansion within Local Group), so very close to the onset of collapse you would see only increasing redshift with increasing distance once you ignore the smallest z (which are negative). But, you're right, you should be able to fit the overall curve to see where you're at in the evolution.

 

[DevilsAvocado]

As an aside, in answer to this question, it is possible in theory to see increased redshift with increased distance in a collapsing universe. The reason is that the redshift only tells you the universe scale factor is bigger at reception than at emission. Thus, z is independent of what happens dynamically between emission and reception. So, if a photon is emitted during an expanding phase and received shortly after the collapsing phase begins, as in the closed model, then you will see increased redshift with increased distance even though the universe is now collapsing. I explained this in a paper some years ago (“Kinematics between Comoving, Photon Exchangers in the Closed Matter-dominated Universe,” W.M. Stuckey, American Journal of Physics 60, No. 6, 554 - 560 (1992)).

I buy this, no problem. But something ought to happen to the CMB when we are collapsing (a strange mix of red-shift and "blue-shift"?), unless we assume the collapse just started...?

Or is this just a dumb guess... (<-- probably yes)

 

[Chalnoth]

True, but it would be a terrible bad "illusion", because of the change of the direction of time; watching the omelet jumping out of the pan to 'regenerate' into 4 complete eggs... we would just know that there’s something 'fishy' going on...

Or?

Well, we'd be running back in time too, so we wouldn't see anything at all out of the ordinary :)

 

[Chalnoth]

Except that at the shortest distances we don't see expansion regardless, we see collapse (gravity overcomes cosmological expansion within Local Group), so very close to the onset of collapse you would see only increasing redshift with increasing distance once you ignore the smallest z (which are negative). But, you're right, you should be able to fit the overall curve to see where you're at in the evolution.

Yeah, that's why I said that you'd have to extrapolate if the transition to collapse was near enough. The peculiar velocities just make the measurement too noisy in the local area.

 

[DevilsAvocado]

Well, we'd be running back in time too, so we wouldn't see anything at all out of the ordinary :)

Agreed!

): yranidro eht fo tuo lla ta gnihtyna ees t'ndluow ew os ,oot emit ni kcab gninnur eb d'ew ,lleW

 

[RUTA]

I buy this, no problem. But something ought to happen to the CMB when we are collapsing (a strange mix of red-shift and "blue-shift"?), unless we assume the collapse just started...?

Or is this just a dumb guess... (<-- probably yes)

As time went on you would see all the redshifts diminish, passing from redshifts to blueshifts. The point at which blueshifts turn to redshifts would (over eons) creep out to what is now the largest z, i.e., the CMB.

 

[Chronos]

I doubt you could predict the state of the universe by running it backwards due to the HUP. Similarly, the current state of the universe is not predictable by running the numbers forward from any given set of initial conditions. QM is probabilistic, not deterministic.

 

[Chalnoth]

I doubt you could predict the state of the universe by running it backwards due to the HUP. Similarly, the current state of the universe is not predictable by running the numbers forward from any given set of initial conditions. QM is probabilistic, not deterministic.

If you want to get into the quantum details, you just need to know the full wavefunction of the universe at anyone point in time, and you can perfectly-predict that wavefunction at any other point in time. There is no non-determinism to be found there: the wavefunction simply evolves.

 

[Chronos]

Agreed, the wave function evolves - just not predictably.

 

[Chalnoth]

Agreed, the wave function evolves - just not predictably.

No, exactly predictably. That's what quantum mechanics says. There is an appearance of probabilistic collapse only because are also quantum-mechanical.

 

[Chronos]

So, HUP predicts a pencil balanced on its point can only remain in balance for a few seconds, yet, has deterministic predictive powers for the future [or past] of the universe over the course of billions of years? I doubt that.

 

[Chalnoth]

So, HUP predicts a pencil balanced on its point can only remain in balance for a few seconds, yet, has deterministic predictive powers for the future [or past] of the universe over the course of billions of years? I doubt that.

The Heisenberg Uncertainty Principle only talks about the accuracy of specific sorts of measurements. One way of thinking about it is that the wavefunction can (in principle) be determined precisely, but the wavefunction can only give precise information about either position or momentum, not both. This is, fundamentally, because once you have fully-defined the wavefunction in terms of position (for example), the wavefunction is completely determined. You can simply calculate the wavefunction as a function of momentum from the wavefunction as a function of position. This relationship, the fact that the position-space wavefunction and the momentum-space wavefunction are really the same exact thing represented differently, is what gives you the Heisenberg Uncertainty Principle.

But the principle itself says nothing whatsoever about what happens when you just deal with the dynamics in a purely quantum-mechanical sense, just talking about how the wavefunction evolves in time. In that case, it's all purely deterministic.

 

[Skolon]

But the principle itself says nothing whatsoever about what happens when you just deal with the dynamics in a purely quantum-mechanical sense, just talking about how the wavefunction evolves in time. In that case, it's all purely deterministic.

Yes, it is, but just mathematically.

You make a wrong physical assumption: "just need to know the full wavefunction of the universe at anyone point in time". This is a physical impossibility, I'm sorry. So, for us the Universe will be forever non-deterministically.

 

[Chalnoth]

Yes, it is, but just mathematically.

You make a wrong physical assumption: "just need to know the full wavefunction of the universe at anyone point in time". This is a physical impossibility, I'm sorry. So, for us the Universe will be forever non-deterministically.

Well, yes. But that is as much true classically as it is quantum-mechanically. This is a practical limitation, not a fundamental one.

Edit: Actually, let me amend that slightly. It is a fundamental limitation in the sense that the information needed to contain the full state of the universe would require a computer more complex than the entire universe. So in that sense it is a fundamental limitation. But what I'm trying to say here is that quantum mechanics doesn't change anything, at least not as far as this is concerned.

 

[netdragon]

I was away while I was working on this very problem, actually. I bailed on all discussion forums during this time to focus on the problem at hand. I do believe the Nobel citation should not have stated "for the discovery of the accelerating expansion of the Universe," since that conclusion follows from their data only in the context of a particular theory of cosmology. They certainly deserve the prize, but the citation should have said something like, "for observational techniques associated with type Ia supernovae." Then, the Nobel committee doesn't have to worry about changes to our theoretical cosmology that change the interpretation of the data.

I agree, because even after it's proven wrong, using type 1A supernova will still be useful, and we'll just need to consider an extra variable of our local dark flow or whatever else is causing our relative acceleration. However, the average person wouldn't understand what the big deal with type 1A supernova is, so I can understand the naming the Nobel committee used.

I also can see why they picked to honor it now because of the threat of evidence mounting against universal acceleration of expansion. Good science is good science, even if they are eventually shown to be "wrong" because they missed some detail. Newton was eventually shown to be "wrong", for instance, however Newtonian physics still accurately describe specific macro-phenomena like how two billiard balls will interact at the macro level when we don't need to be so precise to consider the minute relativistic and quantum level effects. Einstein may be shown to be "wrong", especially if we can't refute the CERN neutrino results (if this doesn't turn out to be some experimental error). But then it will probably be some edge case / exception, and not the general rule. So "right" or "wrong" isn't the best way to look at it, but instead experimental and mathematical results add conditions to previously accepted theories. Most theories are eventually found to be incomplete, but if they stood the test of time for a while then they are at least correct in some limited scope. So in that light, the men being honored still did a good job.

AFAICT, you will not end up with an "exact copy" of the early universe, if you tried to reverse the current expansion for 13.75 billion years...

Doesn't the "no cloning" theorem prevent that? Or is it allowed as long as the "exact copy" doesn't exist simultaneously as the original?

Edit: No, in both Copenhagen and revised Everett interpretations, ways around "no cloning" exist for this discussion as long as no exact copy is made but instead separate measurements are made on the same quantum wave function. Instead, quantum decoherence is the issue. QC is reversible but wave function collapse isn't. See later.

True, but it would be a terrible bad "illusion", because of the change of the direction of time; watching the omelet jumping out of the pan to 'regenerate' into 4 complete eggs... we would just know that there’s something 'fishy' going on...

Or?

That would be interesting and I've thought about this quite a bit. I think our view of causality is biased and people who were experiencing everything backwards would just be used to it.

Edit:

Well, yes. But that is as much true classically as it is quantum-mechanically. This is a practical limitation, not a fundamental one.

Edit: Actually, let me amend that slightly. It is a fundamental limitation in the sense that the information needed to contain the full state of the universe would require a computer more complex than the entire universe. So in that sense it is a fundamental limitation. But what I'm trying to say here is that quantum mechanics doesn't change anything, at least not as far as this is concerned.

I agree more with your Edit better than your first statement but complexity of the computer is irrelevant when no computer is powerful enough to solve a problem. You seemed to have taken a "hidden variable" interpretation and believe there is actually a deterministic state versus a probabilistic one and that we can fully "know" the state if we crunch hard enough and have a complex enough computer. I can't read for sure if that's your viewpoint, or if you were just using terms that have different meanings in Computer Science. It's a common misconception that since you can describe the entire universe as a wave function, that you can deterministically describe its state. I'm a Computer Scientist and have also studied quantum computing and the mathematics behind it (which sadly isn't required study yet at most universities). It is useful when having these discussions to refer to theories of both classical and quantum computation and just view the universe as a giant quantum computer with some gates that perform a measurement to break superposition and create classical states (through decoherence). First of all, we do not know yet whether a classical computer can be as powerful as a quantum computer, and the general consensus is "no". Nevertheless, even if a classical computer could do everything a quantum computer can do, and therefore an ideal turing machine (the most powerful classical computer possible) could model the universe's classical states and superpositional states, then you still have another fundamental blocker: You can crunch all you'd like, even with an ideal turing machine -or- a quantum computer for that matter, and you'll never be able to deterministically "calculate" the "the universe" in a way you could predict 100% what the next state was going to be. This has been shown mathematically using a combination of the undecidable halting problem and Godel's incompleteness proof to show a T.O.E. can never completely describe the universe in a predictive way. The best you can do is an approximation, a probabilistic result!
This is a lot more than a practical limitation, it is a fundamental blocker. http://adsabs.harvard.edu/abs/2008PhyD..237.1257W"

However, all that is irrelevant since unitary quantum calculations are reversible, and therefore every part of the universe that's in quantum superposition is reversible. Of course, the classical states are reversible. What isn't reversible, unfortunately, are the wave function collapses "due to measurement" (really due to quantum decoherence). Therefore, at best, the universe could have a certain probability of reversing into the same state it was before. However, to say that it is 100% likely to reverse into the same state is not something we can acertain unless the universe had a completely known state which is not possible.