Question about speed of light and information

[Omega0]

For example, from examining what General Relativity says about the interior of a black hole, we can be certain that General Relativity is incorrect. Exactly where it breaks down is uncertain. If there exists a theory which describes the interior of a black hole and has no singularities or other inconsistencies, then that theory has a chance of being correct. Then, if we're lucky, that theory will have observational consequences outside of a black hole that we can test.
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More than that, a lot of theorists just find this kind of question interesting, even as they realize that it may be unsolvable.

I completely agree. For me it has the bad taste of ruling out nature. The constant hope to circumvent the speed of light. As mentioned before, I think this has to do with the problem of the end of our existence. Call it resignation, I call it realism - which helped physics a lot.

 

[Omega0]

Quantum entanglement is ended by decoherence. ...
But it's going to be really difficult to ever observe that entanglement precisely because those particles don't interact much with photons.

I agree, that's why I wrote, from a very therotical point of view. I am thinking about "the end" of our universe. What will happen if space expands more and more?
What if the decoherence will be seldom? If there is no photon doing this?

 

[Chalnoth]

I agree, that's why I wrote, from a very therotical point of view. I am thinking about "the end" of our universe. What will happen if space expands more and more?

The universe will become empty.

What if the decoherence will be seldom? If there is no photon doing this?

If there are no particles around, then there's nothing to set up any sort of entanglement. But as long as there are particles that interact with photons, there will also be photons.

 

[Chalnoth]

I completely agree. For me it has the bad taste of ruling out nature. The constant hope to circumvent the speed of light. As mentioned before, I think this has to do with the problem of the end of our existence. Call it resignation, I call it realism - which helped physics a lot.

I don't understand what you're trying to say. Determining what various models say about the interior of a black hole doesn't violate the speed of light. It's just a thought experiment. Different people find different things interesting, and that is ultimately very important for the progress of science. The fact of the matter is that we just can't know what avenues of investigation are going to be fruitless before pursuing them, so it's important for people to pursue a diversity of directions for future research.

 

[Omega0]

The same way quantum entanglement is preserved between any set of spacelike separated events.
No. Why would it?

How does for example the Dirac propagator look like if you have 2 particles where one has v > c? Wouldn't you say it makes no sense to couple two particles if they have no exchange of information?

 

[Omega0]

The universe will become empty.
If there are no particles around, then there's nothing to set up any sort of entanglement. But as long as there are particles that interact with photons, there will also be photons.

I don't want to set up any sort of entanglement, I just say that it is impossible to have entanglement if there is no more connection. This is something fundamental.

 

[Chalnoth]

I don't want to set up any sort of entanglement, I just say that it is impossible to have entanglement if there is no more connection. This is something fundamental.

You're trying to say that entanglement is impossible across an event horizon?

The answer to that is no. Entanglement is certainly possible. It just doesn't have much of any meaning any longer.

The reason is that entanglement is just a requirement of consistency. If particle A and B are in a state with zero total angular momentum, then the angular momentum of A must be opposite to the angular momentum of B. This will remain true until either particle undergoes an interaction that changes its angular momentum. But if you can only ever measure particle B because particle A has traveled past a horizon, then the entanglement has largely lost its meaning.

Note that there is no superluminal transfer of information here. The information lay in the initial entangled state with zero angular momentum. That previous state informs the fate of both particles, and neither particle travels faster than light.

 

[Omega0]

I don't understand what you're trying to say. Determining what various models say about the interior of a black hole doesn't violate the speed of light. It's just a thought experiment. Different people find different things interesting, and that is ultimately very important for the progress of science. The fact of the matter is that we just can't know what avenues of investigation are going to be fruitless before pursuing them, so it's important for people to pursue a diversity of directions for future research.

Okay. Your opinion. I think it's waste of time to think about something which we can't measure by definition. Just my opinion. I think it's better to measure something, see the "dark path" we are on meanwhile - and afterwarsds to think about it.

 

[Chalnoth]

Okay. Your opinion. I think it's waste of time to think about something which we can't measure by definition. Just my opinion. I think it's better to measure something, see the "dark path" we are on meanwhile - and afterwarsds to think about it.

If you think it's a waste of time to think about it, then don't think about it.

 

[Omega0]

You're trying to say that entanglement is impossible across an event horizon?

The answer to that is no. Entanglement is certainly possible. It just doesn't have much of any meaning any longer.
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But if you can only ever measure particle B because particle A has traveled past a horizon, then the entanglement has largely lost its meaning.

What is the difference between "possible" and "lost its meaning"? If the link is gone it's gone. The decoherence here is something not described in our current theory.

Note that there is no superluminal transfer of information here. The information lay in the initial entangled state with zero angular momentum. That previous state informs the fate of both particles, and neither particle travels faster than light.

I didn't write this.

 

[Omega0]

If you think it's a waste of time to think about it, then don't think about it.

Thanks for your hint but I think that thinking should be focused to the really issues - and not speculation.

 

[anorlunda]

You're trying to say that entanglement is impossible across an event horizon?

The answer to that is no. Entanglement is certainly possible. It just doesn't have much of any meaning any longer.

Leonard Susskind's recent lectures ER=EPR are highly entertaining and informative on precisely the subjects discussed in this thread. Of course it is about the cutting edge of informed specuation on quantum gravity; not hard science yet. ER stands for Einstein-Rosen bridges (wormholes connecting black holes predicted by solutions of GR). EPR stands for Einstein–Podolsky–Rosen quantum entanglement. The = refers to the idea that these might be aspects of the same thing. Pretty eyebrow raising IMO.

 

[Chalnoth]

What is the difference between "possible" and "lost its meaning"? If the link is gone it's gone.

There is no link. Entanglement is just a result of consistency of the theory.

Essentially, after particle A and B interact with one another, each particle contains information about the properties of that interaction. If either particle interacts with something, that information gets diluted into the environment.

If you want to know why some theorists talk about the black hole information paradox at all, the answer is that the paradox arises due to a fundamental inconsistency between General Relativity and Quantum Mechanics. In GR, there are no-hair theorems which prove that the only quantities that can describe a black hole are mass, charge, and angular momentum. If a proton enters the event horizon, then the charge of the black hole will increase by the charge of the proton, and the mass will increase as the proton's mass, and the angular momentum will change depending upon the trajectory of the proton. But the information that it was a proton that entered the black hole is destroyed forever. Never mind entanglement: all of the information contained in the makeup and configuration of the infalling matter is destroyed and can never be recovered in the context of General Relativity.

This is a paradox because quantum mechanics is unitary: unitary physical laws are always reversible, in that if you have the exact state of a system at one time, then you can in principle reconstruct the exact state at any other time. But a black hole as described by General Relativity won't let you do that: because the black hole only contains information about mass, charge, and angular momentum, it is impossible to extrapolate from the configuration of the black hole in order to figure out what matter fell into said black hole. So one of these two perspectives must be false. Either physics is unitary and black holes preserve information, or physics is not unitary and information is destroyed upon entering the black hole.

Typically theorists who propose that physics is unitary claim that the event horizon is only an apparent horizon, and that if we could discover the full quantum nature of a black hole we would see that the horizon is just an approximation of the microscopic behavior.

The decoherence here is something not described in our current theory.

Which decoherence? Decoherence in general is well-described by current theories of quantum mechanics.

 

[PeterDonis]

How does for example the Dirac propagator look like if you have 2 particles where one has v > c?

Saying "one has v > c" is misleading. You're talking about a curved spacetime, so you can't compare velocities at spatially separated points. The Dirac propagator in curved spacetime is perfectly well-defined, but you can't carry over all your intuitions from flat spacetime.

Wouldn't you say it makes no sense to couple two particles if they have no exchange of information?

Entanglement between particles is not a matter of them "exchanging information", at least not in any classical sense where "information exchange" is restricted to the speed of light. It's fair to say that we don't completely understand what's going on with entanglement, but that's just as true of ordinary cases of spacelike separated experiments in flat spacetime; there's nothing about curved spacetime or an expanding universe or cosmological horizons that adds any new difficulties.

 

[PeterDonis]

Thanks for your hint but I think that thinking should be focused to the really issues - and not speculation.

You've stated and re-stated this opinion of yours. There's no point in continuing to state it. What counts as "really issues" vs. "speculation" is a subjective judgment. Please try to keep focused on mainstream science and what its theories say, not on your opinions (or indeed anyone's opinions) about what's worth talking about. If you think something isn't worth talking about, then, as Chalnoth has already advised you, just don't talk about it. Don't keep posting that you don't think it's worth talking about; that adds nothing useful to the discussion.

 

[stedwards]

Which decoherence? Decoherence in general is well-described by current theories of quantum mechanics.

I might point out that "decoherence" is selective bookkeeping. It's another example of making the subjective choice between system and environment. Coherence between Particles A and B is destroyed when one of them interacts with particle C. But the coherence of the ABC system is preserved.

 

[Chalnoth]

I might point out that "decoherence" is selective bookkeeping. It's another example of making the subjective choice between system and environment. Coherence between Particles A and B is destroyed when one of them interacts with particle C. But the coherence of the ABC system is preserved.

Each additional particle you add to the mix increases the oscillation time of the system as a whole. It doesn't take very many particles before the oscillation time is longer than the age of the universe. When the oscillation time becomes much longer than the time allotted for the experiment, the existence of other components of the wavefunction becomes hidden.

 

[Jimster41]

There is no link. Entanglement is just a result of consistency of the theory.

Essentially, after particle A and B interact with one another, each particle contains information about the properties of that interaction. If either particle interacts with something, that information gets diluted into the environment.

If you want to know why some theorists talk about the black hole information paradox at all, the answer is that the paradox arises due to a fundamental inconsistency between General Relativity and Quantum Mechanics. In GR, there are no-hair theorems which prove that the only quantities that can describe a black hole are mass, charge, and angular momentum. If a proton enters the event horizon, then the charge of the black hole will increase by the charge of the proton, and the mass will increase as the proton's mass, and the angular momentum will change depending upon the trajectory of the proton. But the information that it was a proton that entered the black hole is destroyed forever. Never mind entanglement: all of the information contained in the makeup and configuration of the infalling matter is destroyed and can never be recovered in the context of General Relativity.

This is a paradox because quantum mechanics is unitary: unitary physical laws are always reversible, in that if you have the exact state of a system at one time, then you can in principle reconstruct the exact state at any other time. But a black hole as described by General Relativity won't let you do that: because the black hole only contains information about mass, charge, and angular momentum, it is impossible to extrapolate from the configuration of the black hole in order to figure out what matter fell into said black hole. So one of these two perspectives must be false. Either physics is unitary and black holes preserve information, or physics is not unitary and information is destroyed upon entering the black hole.

Typically theorists who propose that physics is unitary claim that the event horizon is only an apparent horizon, and that if we could discover the full quantum nature of a black hole we would see that the horizon is just an approximation of the microscopic behavior.Which decoherence? Decoherence in general is well-described by current theories of quantum mechanics.

It's also possible both could be wrong, right?

One thing that keeps bothering me about decoherence - it always seems to get used to describe the end of entanglement, and the irrelevance of entanglement to observed classical phenomenon. But isn't enanglement always happening also? Aren't all things traversing the strange path of of entanglement, superselection rules, decoherence, re-entanglement, from one instant to the next. The surface of the future has always seemed to me like a veil of seething entanglement and decoherence.

 

[Jimster41]

Each additional particle you add to the mix increases the oscillation time of the system as a whole. It doesn't take very many particles before the oscillation time is longer than the age of the universe. When the oscillation time becomes much longer than the time allotted for the experiment, the existence of other components of the wavefunction becomes hidden.

I wouldn't mind if you expanded on that a bit. Seems important, and I'm not quite getting it.

 

[Omega0]

There is no link. Entanglement is just a result of consistency of the theory.
...
Which decoherence? Decoherence in general is well-described by current theories of quantum mechanics.

How would you set up an Hamiltonion if the distance variable makes no sense?

 

[Chalnoth]

I wouldn't mind if you expanded on that a bit. Seems important, and I'm not quite getting it.

The way that we observe interactions of the pre-collapse wavefunction is by looking at interference patterns. In order for two wavefunctions to interfere, they have to oscillate in a coherent manner. That is, the total oscillation time of the system of interfering wavefunctions must be small. But when one or both of the two wavefunctions becomes coupled to a larger system, the oscillation time blows up, and the interference pattern disappears.

Does that help?

 

[Omega0]

You've stated and re-stated this opinion of yours. There's no point in continuing to state it. What counts as "really issues" vs. "speculation" is a subjective judgment. Please try to keep focused on mainstream science and what its theories say, not on your opinions (or indeed anyone's opinions) about what's worth talking about. If you think something isn't worth talking about, then, as Chalnoth has already advised you, just don't talk about it. Don't keep posting that you don't think it's worth talking about; that adds nothing useful to the discussion.

I am just thinking. For me it is quite natural to discuss about my thoughts. If any thoughts apart of some mainstream tracks are not welcome, please let me know in which track my thinking exactly have to be. It might be wrong from my assumptions that physics is a free place to talk with others.

 

[Omega0]

The way that we observe interactions of the pre-collapse wavefunction is by looking at interference patterns. In order for two wavefunctions to interfere, they have to oscillate in a coherent manner. That is, the total oscillation time of the system of interfering wavefunctions must be small. But when one or both of the two wavefunctions becomes coupled to a larger system, the oscillation time blows up, and the interference pattern disappears.

Does that help?

This for example is a statement which says that decoherence is a natural thing which finally does not allow coherence on a cosmic scale. I find this very natural but is this true?

 

[Jimster41]

The way that we observe interactions of the pre-collapse wavefunction is by looking at interference patterns. In order for two wavefunctions to interfere, they have to oscillate in a coherent manner. That is, the total oscillation time of the system of interfering wavefunctions must be small. But when one or both of the two wavefunctions becomes coupled to a larger system, the oscillation time blows up, and the interference pattern disappears.

Does that help?

Yes, thanks. I get wild questions about what does and doesn't qualify as an interference pattern, at what scales and due to what causes, do they stop at a certain point really, or carry on while we just call them something else, like particles, molecules, compounds, plants, animals, people, civilizations etc etc? But I was getting your drift. I just wasn't sure.

 

[Chronos]

A classical view can be refreshing. Decoherence is synonymous with fuzziness - or out of focus.

 

[Chalnoth]

This for example is a statement which says that decoherence is a natural thing which finally does not allow coherence on a cosmic scale. I find this very natural but is this true?

There may be rare situations with particles that don't interact much with anything achieving cosmic scale coherence, but for the most part, no, this isn't possible.

 

[Jimster41]

A classical view can be refreshing. Decoherence is synonymous with fuzziness - or out of focus.

I thought decoherence was exactly the opposite . I thought it meant the "collapse of the wave function" or whatever metaphor for classical-making-measurement-of-superposition one is most comfortable with.

So in a volume of isolated space with one kind of stuff, some specific gas or concrete or whatever, what is the ratio of entanglement and coherence at any given time? What if two different kinds of stuff are mixed, like light and gas or gas and concrete, or light and concrete? Does that change the ratio? Is it mass that dictates the degree of entanglement?

 

[Weinsyein]

Speculations about events that we cannot yet know about are useful for they tell us where we want to go. And who knows when we will get there. Hmm, I've left physics for philosophy (sorry).

 

[Weinsyein]

As light leaves a star (gravity hole) it loses energy -- is red shifted. Ever wonder if the "Black Holes" are really infrared holes? Maybe the light undergoes a severe red shift. Just a thought.

 

[PeterDonis]

Ever wonder if the "Black Holes" are really infrared holes? Maybe the light undergoes a severe red shift.

Light coming from just above the horizon of a black hole does undergo a large red shift. But the redshift is an effect, not a cause; it doesn't explain what a black hole is, it's just a consequence of what a black hole is.