@Patrice: I still don’t see where you get that decohering (say, without free will, with a larger object) is irreversible. Nonlocality doesn’t make a difference to reversibility; in principle, the Schrodinger equation is perfectly reversible, and decoherence is supposed to follow (with some assumptions about system size) from the Schrodinger equation.
When you say that entanglement “can only arise via interactions,” you are making an assumption – in particular, you are restricting the “allowed” initial conditions to those which are disentangled. In a local experiment, this is entirely unjustified, which is my primary point; your remark about the Aspect experiment is the only example (to my knowledge) of particles which could never have had an interaction (according to current theories). I am not saying that it is impossible (or even unlikely) that the initial conditions of the universe have everything disentangled; I would not make a physical claim such as that without the grounds of something like the Aspect experiment. Instead, I am simply saying that a disentangled initial state is an assumption you make when you set up a particular problem, and saying “a quantum system starts out disentangled” is just as helpful as “the problem starts with a low-entropy state” – as most standard responses to the question do, it avoids time-reversal symmetry by explictly putting a time-irreversible element of the problem in (the initial condition restriction) which does not occur in the end.
Let’s simplify the discussion, though. Quantum mechanics has very few axioms. Setting aside the measurement postulate, all axioms are explicitly time-symmetric; the only one which even mentions time is the Schrodinger equation, which is explicitly time-reversible. In order to derive a time-asymmetry, it therefore requires something additional – your “things at the start of the universe are completely disentangled” is one such example, unless you add a “things at the end of the universe are completely disentangled” as well.
I don’t think the wave discussion is particularly relevant anymore, but I will say that I don’t think the generality of the wave idea is a benefit – quite the opposite, I think as a physical formulation it makes it (after a fashion) a weakness, because it allows you to speak vaguely (“waves”) of things that are precise (“solutions to the KG/wave/Dirac/KdV equation”), whereas that is impossible with precise terms (“eigenstates”)… but that’s more a terminological distinction than anything else, and has nothing to do with the time-reversability of the theory, so I’m not going to continue along this line of discussion due to off-topic-ness.
Robin
And finally, given that my mind is just information processing, and there are infinitely many ways that information could be processed, most of which would be vastly simpler that the way it is ostensibly being processed – how can I claim to know what the laws of physics are at all? Since something that could process this information would not have to be situated in the physical environment we ostensibly observe?
Haruki Chou says:”Patrice Ayme says: “..how to get an arrow of time in a universe governed by time-symmetric underlying laws.”
But don’t we already know that the underlying laws are not time-symmetric?
(CPT is a symmetry, but T alone is not).”
That’s an excellent point, Haruki Chou (and I did not understand Magnema’s objection to it, although I meditated it).
We know, from direct experimental evidence, that CP is violated (by the weak interaction: nuclear decay happens in some peculiar directions sometimes).
But CPT is conserved (there is such a theorem, which Feynman found so complicated to prove that one could not claim it was fully understood).
Thus T is violated.
What I try to present is why T is obviously violated by all and any Quantum process.
To rephrase my reasoning: all Quantum processes, as they proceed, build up a space, and an order in this space (which then create the Quantum probabilities). Thus, one way in time, one starts with one or several waves, and create a space and an order. To go the other way, one cannot start with one or several waves, and just invert, because one is stuck with a space and an order, to start with.
A proper Quantum Initial Condition is for a set of waves. And the Quantum process always terminates with a space and an order, a completely different machinery, so the situation is intrinsically time-asymmetric.
(BTW, I agree with HC’s point that the easiest way to a brain is to create supernovas, and stars from those, etc.)
Magnema
@Robin: That last one is what I take to be the biggest question. If our brains are characterized by information (a “computationalist” theory of mind), and if information does not require instantiation to exist (Platonism), then… where does this leave us? There’s not really a good answer, unless you want Lewis/Tegmark’s Modal Realism/Mathematical Universe…
Magnema
@Patrice: To the point of CPT: That T is not a symmetry is true, but CPT is, and my argument is that that is sufficient. In particular: note that reversing T is the same as reversing CP. However, I do not think most people believe that reversing CP would reverse the macroscopic appearance of the arrow of time – i.e., reversing CP would not invert the second law of thermodynamics. I suppose that’s more of an appeal to intuition than an argument, but I think it’s a valid one – the kind of reasoning by which people usually derive the second law of thermodynamics from fundamental physics has equal difficulty with T as a symmetry and CPT as a symmetry.
As for your interpretation: I’m trying to follow, since I’ve mostly studied QM from a linear-algebraic perspective. When you speak of waves developing a space, what space are you referring to? Are you referring to quantum gravitational waves generating/being spacetime, or the Hilbert space in which quantum particles interact? And what “order” are you referring to, precisely – something with measurement?
I think in practice, experimentalist are much more likely to use the term “vacuum fluctuations” to refer to literal measurement outcomes. (When referring only to the mathematical fact that there is a non-zero spread of an unmeasured vacuum state with respect to some operator, they would use “vacuum uncertainty” instead.) If so, then “vacuum fluctuations” are just a certain king of quantum fluctuation, where the later is what happens anytime a system is amplified (measured) in a basis besides the one that diagonalizes it.
“Nothing actually “fluctuates” in vacuum fluctuations!
The system can be perfectly static. ”
Sean,
Will be grateful if you kindly tease out the above two sentences in layman terms.
Thanks and regards,
John Barrett
I was under the impression that these Boltzmann Brains were supposed to actually mimic consciousness. Is the term “brains” used more metaphorically speaking? I ask, because some of the descriptions you give about quantum fluctuations doesn’t seem like they would allow for some type of consciousness. If someone believed in a higher consciousness or some sort of deity, then wouldn’t that put them against the many worlds interpretation, since Boltzmann Brains cannot come into existence in this interpretation of quantum mechanics? Maybe an explanation for the less gifted is needed here, or am I just way off about this whole Boltzmann Brain theory?
i often hear / read (in fairly informal discussions) that the density fluctuations in the early universe (and, therefore, also in this here cheese sandwich) are due to quantum fluctuations that happened while inflation was going on, and which get ‘stuck’ because of the shrinking horizon.
so, provided the above is even a partially correct reading of the commonly accepted narrative, which of sean’s three classes of fluctuation do they fit into?
Hi Sean, I think H.D. Zeh deserves more credit when talking about “Many Worlds” and “Decoherence”. For example I just read his paper http://arxiv.org/abs/0809.2904 where he also makes the point that nothing is fluctuating. But this is a general impression: Zeh discovered decoherence and produced lots of seminal and pioneering work in the understanding of quantum mechanics but is often neglected – for example when your wife sugested Zurek as a worthy Nobel Prize candidate.
Mark S.
Sean or anyone else, please check out this video on something called “Hydrinos.” Investor meeting on new SunCell tech:
Interesting paper! I find it odd in the way he describes decoherence and recoherence as if the other states actually still exist after the act of observation. Then I buy into the Copenhagen Interpretation. He makes it sound like energy is able to leave a system in Schrodinger’s Paradox, like a dead cat would leave our universe (God knows, we could do without one more dead cat!). I guess the same could be said about the MWI, where you end up with the same cat you started with and a dead cat with a whole extra universe of energy! Then I find it surprising that he would support Hawking Radiation, considering the drastic lengths gone to the conservation of energy in developing that theory.
I found the main argument against action at a distance and quantum teleportation to be rather weak. He seems to be implying that the actual action or mechanism behind action at a distance is due to bringing the results of both ends of the experiment back together. Then he implies that the mechanism behind quantum teleportation comes from the experiment starting at the same location. I think these ideas would be inconsistent in trying to pin down the same underlying mechanism, as it would be difficult to explain both with the same underlying principal from the interaction coming before and after the fact.
Other than that, note to self; derive a non-local theory of relativity and correlate the observational differences in systems from two differing reference frames in Minkowski spacetime.
Bogdan Barbu
Sorry for the being a little off-topic but I really have no idea where else to ask. There seems to be some evidence that time is emerges from entanglement. But if there is no time, how do can such correlations be dynamic?
Analogously, Lawrence Krauss often talks abou how spacetime might have come into existence because of quantum fluctuations (my understanding of “virtual particles going in and out of existence on a time scale so short you can’t measure them”). If there is no spacetime, what is the medium in which this occurs?
I can imagine two explanations, possibly simultaneously true:
1. Ambiguous language.
2. A global/background spacetime against which we measure everything.
Sorry for asking such layman questions but I would really appreciate some clarifications.
@John B:
I think there are some misunderstandings about the so-called “MWI”. Zeh’s point is that if you use only quantum mechanics (as described by the Schrödinger equation) and nothing else, you can describe the measurement process by decoherence. Then everything is unitary and deterministic, there are no dead cats disppearing and no extra Universes of energy.
It is rather the Copenhagen collapse interpretation which would imply unitarity violation and information loss.
You arrive at essentially the same picture Everett had in mind, though the name “Many Worlds” is misleading, as it is not the Universe that splits, but only the observer (Zeh likes to call it “Many-Minds Interpretation”) who defines a macrostate by ignoring information which leads to suppression of intereference between the different branches of the wave function (cat dead versus cat alive) which have existed before the measurement as they do after the measurement.
This view is perfectly consistent and gets rid of a lot of quantum paradoxes, you only have to accept that our classical world is not fundemental but emergent.
@Bogdan:
I’m no expert in this but I think the point is that you start with a bunch of possible solutions to the Wheeler-DeWitt equation and average out some degrees of freedom (e.g. gravitational), this defines a macrostate so you have entropy (typically related to the cosmological scale factor). Then you can use entropy as an order parameter which you call time.
Again, there is a paper by Zeh about this: http://www.rzuser.uni-heidelberg.de/~as3/PLA86.pdf
as well as a book:
H.D. Zeh: The Physical Basis of The Direction of Time (The Frontiers Collection, Springer 2007)
@Sean: By the way, if your adherence to Many Worlds is consistent, then (again compare Zeh http://www.rzuser.uni-heidelberg.de/~as3/no-quantum-jumps.pdf) there are also no particles (and no void) so on the most fundamental level your motto (a Democritus quote?) does not really make sense. Do you agree?
rebelscum
In Quantum phase transitions they talk about “Quantum fluctuations”. Do they mean vacuum fluctuations?
This is clearly not a ‘many worlds’ interpretation, but I believe it is an EPR-complete account of the world we observe — and, somewhat ironically, fully in the spirit of Democritus, as found in the more complete quotation:
By convention there is color,
By convention sweetness,
By convention bitterness,
But in reality there are
atoms and space.
The Senses:
Poor intellect, do you hope to defeat us
while from us you borrow your evidence?
Your victory is your defeat.
@Patrice: I still don’t see where you get that decohering (say, without free will, with a larger object) is irreversible. Nonlocality doesn’t make a difference to reversibility; in principle, the Schrodinger equation is perfectly reversible, and decoherence is supposed to follow (with some assumptions about system size) from the Schrodinger equation.
When you say that entanglement “can only arise via interactions,” you are making an assumption – in particular, you are restricting the “allowed” initial conditions to those which are disentangled. In a local experiment, this is entirely unjustified, which is my primary point; your remark about the Aspect experiment is the only example (to my knowledge) of particles which could never have had an interaction (according to current theories). I am not saying that it is impossible (or even unlikely) that the initial conditions of the universe have everything disentangled; I would not make a physical claim such as that without the grounds of something like the Aspect experiment. Instead, I am simply saying that a disentangled initial state is an assumption you make when you set up a particular problem, and saying “a quantum system starts out disentangled” is just as helpful as “the problem starts with a low-entropy state” – as most standard responses to the question do, it avoids time-reversal symmetry by explictly putting a time-irreversible element of the problem in (the initial condition restriction) which does not occur in the end.
Let’s simplify the discussion, though. Quantum mechanics has very few axioms. Setting aside the measurement postulate, all axioms are explicitly time-symmetric; the only one which even mentions time is the Schrodinger equation, which is explicitly time-reversible. In order to derive a time-asymmetry, it therefore requires something additional – your “things at the start of the universe are completely disentangled” is one such example, unless you add a “things at the end of the universe are completely disentangled” as well.
I don’t think the wave discussion is particularly relevant anymore, but I will say that I don’t think the generality of the wave idea is a benefit – quite the opposite, I think as a physical formulation it makes it (after a fashion) a weakness, because it allows you to speak vaguely (“waves”) of things that are precise (“solutions to the KG/wave/Dirac/KdV equation”), whereas that is impossible with precise terms (“eigenstates”)… but that’s more a terminological distinction than anything else, and has nothing to do with the time-reversability of the theory, so I’m not going to continue along this line of discussion due to off-topic-ness.
And finally, given that my mind is just information processing, and there are infinitely many ways that information could be processed, most of which would be vastly simpler that the way it is ostensibly being processed – how can I claim to know what the laws of physics are at all? Since something that could process this information would not have to be situated in the physical environment we ostensibly observe?
Haruki Chou says:”Patrice Ayme says: “..how to get an arrow of time in a universe governed by time-symmetric underlying laws.”
But don’t we already know that the underlying laws are not time-symmetric?
(CPT is a symmetry, but T alone is not).”
That’s an excellent point, Haruki Chou (and I did not understand Magnema’s objection to it, although I meditated it).
We know, from direct experimental evidence, that CP is violated (by the weak interaction: nuclear decay happens in some peculiar directions sometimes).
But CPT is conserved (there is such a theorem, which Feynman found so complicated to prove that one could not claim it was fully understood).
Thus T is violated.
What I try to present is why T is obviously violated by all and any Quantum process.
To rephrase my reasoning: all Quantum processes, as they proceed, build up a space, and an order in this space (which then create the Quantum probabilities). Thus, one way in time, one starts with one or several waves, and create a space and an order. To go the other way, one cannot start with one or several waves, and just invert, because one is stuck with a space and an order, to start with.
A proper Quantum Initial Condition is for a set of waves. And the Quantum process always terminates with a space and an order, a completely different machinery, so the situation is intrinsically time-asymmetric.
(BTW, I agree with HC’s point that the easiest way to a brain is to create supernovas, and stars from those, etc.)
@Robin: That last one is what I take to be the biggest question. If our brains are characterized by information (a “computationalist” theory of mind), and if information does not require instantiation to exist (Platonism), then… where does this leave us? There’s not really a good answer, unless you want Lewis/Tegmark’s Modal Realism/Mathematical Universe…
@Patrice: To the point of CPT: That T is not a symmetry is true, but CPT is, and my argument is that that is sufficient. In particular: note that reversing T is the same as reversing CP. However, I do not think most people believe that reversing CP would reverse the macroscopic appearance of the arrow of time – i.e., reversing CP would not invert the second law of thermodynamics. I suppose that’s more of an appeal to intuition than an argument, but I think it’s a valid one – the kind of reasoning by which people usually derive the second law of thermodynamics from fundamental physics has equal difficulty with T as a symmetry and CPT as a symmetry.
As for your interpretation: I’m trying to follow, since I’ve mostly studied QM from a linear-algebraic perspective. When you speak of waves developing a space, what space are you referring to? Are you referring to quantum gravitational waves generating/being spacetime, or the Hilbert space in which quantum particles interact? And what “order” are you referring to, precisely – something with measurement?
I think in practice, experimentalist are much more likely to use the term “vacuum fluctuations” to refer to literal measurement outcomes. (When referring only to the mathematical fact that there is a non-zero spread of an unmeasured vacuum state with respect to some operator, they would use “vacuum uncertainty” instead.) If so, then “vacuum fluctuations” are just a certain king of quantum fluctuation, where the later is what happens anytime a system is amplified (measured) in a basis besides the one that diagonalizes it.
“Nothing actually “fluctuates” in vacuum fluctuations!
The system can be perfectly static. ”
Sean,
Will be grateful if you kindly tease out the above two sentences in layman terms.
Thanks and regards,
I was under the impression that these Boltzmann Brains were supposed to actually mimic consciousness. Is the term “brains” used more metaphorically speaking? I ask, because some of the descriptions you give about quantum fluctuations doesn’t seem like they would allow for some type of consciousness. If someone believed in a higher consciousness or some sort of deity, then wouldn’t that put them against the many worlds interpretation, since Boltzmann Brains cannot come into existence in this interpretation of quantum mechanics? Maybe an explanation for the less gifted is needed here, or am I just way off about this whole Boltzmann Brain theory?
naive observational astronomer question coming up!
i often hear / read (in fairly informal discussions) that the density fluctuations in the early universe (and, therefore, also in this here cheese sandwich) are due to quantum fluctuations that happened while inflation was going on, and which get ‘stuck’ because of the shrinking horizon.
so, provided the above is even a partially correct reading of the commonly accepted narrative, which of sean’s three classes of fluctuation do they fit into?
Hi Sean, I think H.D. Zeh deserves more credit when talking about “Many Worlds” and “Decoherence”. For example I just read his paper http://arxiv.org/abs/0809.2904 where he also makes the point that nothing is fluctuating. But this is a general impression: Zeh discovered decoherence and produced lots of seminal and pioneering work in the understanding of quantum mechanics but is often neglected – for example when your wife sugested Zurek as a worthy Nobel Prize candidate.
Sean or anyone else, please check out this video on something called “Hydrinos.” Investor meeting on new SunCell tech:
https://youtu.be/R0PYe-4090g
Comments?
@Heinrich
Interesting paper! I find it odd in the way he describes decoherence and recoherence as if the other states actually still exist after the act of observation. Then I buy into the Copenhagen Interpretation. He makes it sound like energy is able to leave a system in Schrodinger’s Paradox, like a dead cat would leave our universe (God knows, we could do without one more dead cat!). I guess the same could be said about the MWI, where you end up with the same cat you started with and a dead cat with a whole extra universe of energy! Then I find it surprising that he would support Hawking Radiation, considering the drastic lengths gone to the conservation of energy in developing that theory.
I found the main argument against action at a distance and quantum teleportation to be rather weak. He seems to be implying that the actual action or mechanism behind action at a distance is due to bringing the results of both ends of the experiment back together. Then he implies that the mechanism behind quantum teleportation comes from the experiment starting at the same location. I think these ideas would be inconsistent in trying to pin down the same underlying mechanism, as it would be difficult to explain both with the same underlying principal from the interaction coming before and after the fact.
Other than that, note to self; derive a non-local theory of relativity and correlate the observational differences in systems from two differing reference frames in Minkowski spacetime.
Sorry for the being a little off-topic but I really have no idea where else to ask. There seems to be some evidence that time is emerges from entanglement. But if there is no time, how do can such correlations be dynamic?
Analogously, Lawrence Krauss often talks abou how spacetime might have come into existence because of quantum fluctuations (my understanding of “virtual particles going in and out of existence on a time scale so short you can’t measure them”). If there is no spacetime, what is the medium in which this occurs?
I can imagine two explanations, possibly simultaneously true:
1. Ambiguous language.
2. A global/background spacetime against which we measure everything.
Sorry for asking such layman questions but I would really appreciate some clarifications.
@John B:
I think there are some misunderstandings about the so-called “MWI”. Zeh’s point is that if you use only quantum mechanics (as described by the Schrödinger equation) and nothing else, you can describe the measurement process by decoherence. Then everything is unitary and deterministic, there are no dead cats disppearing and no extra Universes of energy.
It is rather the Copenhagen collapse interpretation which would imply unitarity violation and information loss.
You arrive at essentially the same picture Everett had in mind, though the name “Many Worlds” is misleading, as it is not the Universe that splits, but only the observer (Zeh likes to call it “Many-Minds Interpretation”) who defines a macrostate by ignoring information which leads to suppression of intereference between the different branches of the wave function (cat dead versus cat alive) which have existed before the measurement as they do after the measurement.
This view is perfectly consistent and gets rid of a lot of quantum paradoxes, you only have to accept that our classical world is not fundemental but emergent.
@Bogdan:
I’m no expert in this but I think the point is that you start with a bunch of possible solutions to the Wheeler-DeWitt equation and average out some degrees of freedom (e.g. gravitational), this defines a macrostate so you have entropy (typically related to the cosmological scale factor). Then you can use entropy as an order parameter which you call time.
Again, there is a paper by Zeh about this:
http://www.rzuser.uni-heidelberg.de/~as3/PLA86.pdf
as well as a book:
H.D. Zeh: The Physical Basis of The Direction of Time (The Frontiers Collection, Springer 2007)
@Sean: By the way, if your adherence to Many Worlds is consistent, then (again compare Zeh http://www.rzuser.uni-heidelberg.de/~as3/no-quantum-jumps.pdf) there are also no particles (and no void) so on the most fundamental level your motto (a Democritus quote?) does not really make sense. Do you agree?
In Quantum phase transitions they talk about “Quantum fluctuations”. Do they mean vacuum fluctuations?
In regard to QFT and the brain, I was happily surprised to see Frank Wilczek echoing my thoughts on vision, spectra, action, symmetry and manifolds:
http://bit.ly/1PJvneX
This is clearly not a ‘many worlds’ interpretation, but I believe it is an EPR-complete account of the world we observe — and, somewhat ironically, fully in the spirit of Democritus, as found in the more complete quotation:
By convention there is color,
By convention sweetness,
By convention bitterness,
But in reality there are
atoms and space.
The Senses:
Poor intellect, do you hope to defeat us
while from us you borrow your evidence?
Your victory is your defeat.