Temporal symmetry solves all quantum paradoxes?

[TheAlkemist]

Excerpted from an article by U. of Hawaii Physics Professor, Victor J. Stenger:


"As has been known for seventy years, quantum phenomena depend not only on the initial conditions of an experimental setup but also on the final conditions. This observation already signals that the quantum world is time-symmetrical. Quantum phenomena do not distinguish between "initial" and "final." These are commonsense designations that can be interchanged without making any changes in the basic theory...

...All the alleged paradoxes of quantum mechanics result from the unnecessary use at the quantum scale of the singular time direction of common experience. No doubt the arrow of time we all experience in our lives is an objective reality. But it can be shown to be a consequence of the statistical behavior of systems of large numbers of particles. The probabilistic behavior observed on large scales does not apply for the small numbers of particles involved in quantum phenomena."

Source:http://www.colorado.edu/philosophy/vstenger/Timeless/nowhen.html

But if our common sense experience of the world is time asymmetric (I know we remember the past and wonder about the future) in the way we perceive causality, what sense does it make to talk about an objective reality where time is symmetric?

What are your thoughts on this?

Thanks.

 

[DrChinese]

Could be. You may want to take a look at some of the time symmetric interpretations of Quantum Mechanics, as there are several. Generally, these do not assign a preferred direction to time - although they each handle things a bit differently. I think one of the more interesting is Relational Blockworld:

http://arxiv.org/abs/0903.2642

 

[TheAlkemist]

Could be. You may want to take a look at some of the time symmetric interpretations of Quantum Mechanics, as there are several. Generally, these do not assign a preferred direction to time - although they each handle things a bit differently. I think one of the more interesting is Relational Blockworld:

http://arxiv.org/abs/0903.2642

Thanks.

 

[DevilsAvocado]

... what sense does it make to talk about an objective reality where time is symmetric?

Good question. I have a slight feeling that Professor Victor J. Stenger may have 'overlooked' that fact that the universe started with low http://en.wikipedia.org/wiki/Entropy" (a nearly uniform gas) and developed towards higher entropy.

It’s true that a single QM particle doesn’t 'care' if it goes this way or that way. But for bigger systems, like our universe, the http://en.wikipedia.org/wiki/Second_law_of_thermodynamics" is a fact. Therefore it could be 'problematic' to talk about objectivity vs. subjectivity, when talking about the universe as whole...

That’s why you never see 1 omelet randomly transform into 4 eggs!

Sean M. Carroll has written a very good article around entropy and the arrow of time for http://www.scientificamerican.com/article.cfm?id=the-cosmic-origins-of-times-arrow".

Does Time Run Backward in Other Universes?

(P.S. Google "Does Time Run Backward in Other Universes?" there’s a 'back-up copy' out there somewhere... )

 

[TheAlkemist]

Good question. I have a slight feeling that Professor Victor J. Stenger may have 'overlooked' that fact that the universe started with low http://en.wikipedia.org/wiki/Entropy" (a nearly uniform gas) and developed towards higher entropy.

It’s true that a single QM particle doesn’t 'care' if it goes this way or that way. But for bigger systems, like our universe, the http://en.wikipedia.org/wiki/Second_law_of_thermodynamics" is a fact. Therefore it could be 'problematic' to talk about objectivity vs. subjectivity, when talking about the universe as whole...

That’s why you never see 1 omelet randomly transform into 4 eggs!

Sean M. Carroll has written a very good article around entropy and the arrow of time for http://www.scientificamerican.com/article.cfm?id=the-cosmic-origins-of-times-arrow".

Does Time Run Backward in Other Universes?

(P.S. Google "Does Time Run Backward in Other Universes?" there’s a 'back-up copy' out there somewhere... )

Ah! Makes sense. Thanks for the article ref.

"But for bigger systems, like our universe, the http://en.wikipedia.org/wiki/Second_law_of_thermodynamics" is a fact."

Is this because of decoherence?

 

[DevilsAvocado]

Is this because of decoherence?

Well, I don’t think so... (Disclaimer: I’m just a layman)

It’s just the simple fact that everything strives towards http://en.wikipedia.org/wiki/Thermodynamic_equilibrium" . Like the simple fact that when you pour milk in your coffee, if you just leave it like that, it will finally mix completely (due to the fact that the molecules are constantly colliding with each other and the wall of the cup).

And there are always many more ways for a "system" to "organize" in high entropy than low entropy, like coffee with milk, or an egg:

[URL]http://www.scientificamerican.com/media/inline/AB230924-FA4D-9EAC-5E5E8D5152C227B1_3.jpg[/URL]

Now, the really weird thing is that our universe started as a "fresh egg", so to speak, and then everything has gone "down the hill"...

To make things even more complex: Gravity plays a major role when deciding what high/low entropy is. And negative gravity (expanding space) is a competitor to gravity. The key point is equilibrium, in respect of +/- gravity:

[URL]http://www.scientificamerican.com/media/inline/AB230924-FA4D-9EAC-5E5E8D5152C227B1_4.jpg[/URL]

I think we could summarize it like this: Since our universe started as a "fresh egg", we are now experience the "egg" being "broken" – and our time is running in the same direction as the "degeneration" of the "egg". I think...

The big question is: If our universe started as a "broken egg" – would we then experience time running in the other direction?

I have no idea...

All we can be sure of is that if "living creatures" where possible in such a universe – it would be the most terrible horror movie ever! People would crawl up from the ground, as they start their life. And walk backwards for 75-85 years, to finally "disappear" as babies!? ()


P.S. QM particles will always run in any direction they want, regardless if the "egg" is broken or fresh.

 

[haael]

The big question is: If our universe started as a "broken egg" – would we then experience time running in the other direction?

No, it will just last for eternity in thermodynamical equilibrium. Random fluctuations will still be possible, though. Maybe our part of universe is just such a gigantic statistical fluctuation...

However, I suspect that we have macroscopic time because of spacetime expansion. If the volume is constantly increasing, the gas filling the universe will never reach equilibrium.

 

[DevilsAvocado]

No, it will just last for eternity in thermodynamical equilibrium.

I’ll guess you’re right. Sean M. Carroll also speculates around this, and draws the conclusion that "we" would interpret a "backward universe" as backward, but "they" wouldn’t notice any difference at all...

But what if the laws of nature also where different? So that "systems" strived away from equilibrium? What would happen then??

However, I suspect that we have macroscopic time because of spacetime expansion. If the volume is constantly increasing, the gas filling the universe will never reach equilibrium.

Could be, but I think we can be pretty sure that in a collapsing universe – time is not running backwards.

 

[Tomsk]

No doubt the arrow of time we all experience in our lives is an objective reality. But it can be shown to be a consequence of the statistical behavior of systems of large numbers of particles.

I don't think that is accurate. Certainly, if a system in a thermodynamic state A evolves unitarily to a state B, then the entropy of B is greater than the entropy of A. But there is no reason at all why B should be at a later time than A, since the in-between evolution is time symmetric!

I don't like the big bang explanation for this. Even if there was a good reason for the entropy of the universe to be very low at the BB, why should that affect us? I don't like the idea that something on a cosmological scale can affect our every day scale - ice cubes and eggs and things. Surely the entropy of the universe is completely dominated by black holes, in which case who cares about broken eggs, we should see entropy increase in both directions in time almost equally!

 

[stone1]

Surely the entropy of the universe is completely dominated by black holes, in which case who cares about broken eggs, we should see entropy increase in both directions in time almost equally!

Not if time is only in our minds and if "increasing entropy" and "time" are the same thing (the second law is as much about "increasing entropy" as it is about "time"). Saying that entropy should increase in both directions of time is like saying that time should flow into the future both when time flows into the future and when it flows into the past.

 

[JesseM]

I don't like the big bang explanation for this. Even if there was a good reason for the entropy of the universe to be very low at the BB, why should that affect us? I don't like the idea that something on a cosmological scale can affect our every day scale - ice cubes and eggs and things. Surely the entropy of the universe is completely dominated by black holes, in which case who cares about broken eggs, we should see entropy increase in both directions in time almost equally!

Given an isolated low-entropy system around today, you don't need any cosmological considerations to derive the fact that its entropy is likely to increase in the future as long as it stays isolated, you can derive it with statistical mechanics alone. The problem is that because of time-symmetry, you can use the same laws of physics to "retrodict" what the state of a system was in the past if you know the state now, and exactly the same statistical derivation implies the entropy should have been higher in the past--which for most low-entropy systems is not the case! In fact if we trace the history of a typical low-entropy system backwards, we usually find that the low entropy is a consequence of its interaction with some even lower-entropy system in the past, and this chain of decreasing entropy does go all the way back to the Big Bang. Here's a discussion from Roger Penrose, starting on p. 317 of his book The Emperor's New Mind:

We shall try to understand where this 'amazing' low entropy comes from in the actual world that we inhabit. Let us start with ourselves. If we can understand where our own low entropy came from, then we should be able to see where the low entropy in the gas held by the partition came from--or in the water glass on the table, or in the egg held above the frying pan, or the lump of sugar held over the coffee cup. In each case a person or collection of people (or perhaps a chicken!) was directly or indirectly responsible. It was, to a large extent, some small part of the low entropy state in ourselves which was actually made use of in setting up these other low-entropy states. Additional factors might have been involved. Perhaps a vacuum pump was used to suck the gas to the corner of the box behind the partition. If the pump was not operated manually, then it may have been that some 'fossil fuel' (e.g. oil) was burnt in order to provide the necessary low-entropy energy for its operation. Perhaps the pump was electrically operated, and relied, to some extent, on the low-entropy energy stored in the uranium fuel of a nuclear power station. I shall return to these other low-entrop sources later, but let us first just consider the low entropy in ourselves.

Where indeed does our own low entropy come from? The organization in our bodies comes from the food that we eat and the oxygen that we breathe. Often one hears it stated that we obtain energy from our intake of food and oxygen, but there is a clear sense in which that is not really correct. It is true that the food we consume does combine with this oxygen that we take into our bodies, and that this provides us with energy. But, for the most part, this energy leaves our bodies again, mainly in the form of heat. Since energy is conserved, and since the actual energy content of our bodies remains more-or-less constant throughout our adult lives, there is no need simply to add to the energy content of our bodies. We do not need more energy within ourselves than we already have. In fact we do add to our energy content when we put on weight--but that is not usually considered desirable! Also, as we grow up from childhood we increase our energy content considerably as we build up our bodies; that is not what I am concerned about here. The question is how we keep ourselves alive throughout our normal (mainly adult) lives. For that, we do not need to add to our energy content.

However, we do need to replace the energy that we continually lose in the form of heat. Indeed, the more 'energetic' that we are, the more energy we actually lose in this form. All this energy must be replaced. heat is the most disordered form of energy that there is, i.e. it is the highest-entropy form of energy. We take in energy in a low-entropy form (food and oxygen) and we discard it in a high-entropy form (heat, carbon dioxide, excreta). We do not need to gain energy from our environment, since energy is conserved. But we are continually fighting against the second law of thermodynamics. Entropy is not conserved; it is increasing all the time. To keep ourselves alive, we need to keep lowering the entropy that is within ourselves. We do this by feeding on the low-entropy combination of food and atmospheric oxygen, combining them within our bodies, and discarding the energy, that we would otherwise have gained, in high-entropy form. In this way, we can keep the entropy in our bodies from rising, and we can maintain (and even increase) our internal organization. (See Schrodinger 1967.)

Where does this supply of low entropy come from? If the food that we are eating happens to be meat (or mushrooms!), then it, like us, would have relied on a further external low-entropy source to provide and maintain its low-entropy structure. That merely pushes the problem of the origin of the external low entropy to somewhere else. So let us suppose that we (or the animal or mushroom) are consuming a plant. We must all be supremely grateful to the green plants--either directly or indirectly--for their cleverness: taking atmospheric carbon dioxide, separating the oxygen from the carbon, and using that carbon to build up their own substance. This procedure, photosynthesis, effects a large reduction in the entropy. We ourselves make use of this low-entropy separation by, in effect, simply recombining the oxygen and carbon within our own bodies. How is it that the green plants are able to achieve this entropy-reducing magic? They do it by making use of sunlight. The light from the sun brings energy to the Earth in a comparatively low-entropy form, namely in the photons of visible light. The earth, including its inhabitants, does not retain this energy, but (after some while) re-radiates it all back into space. However, the re-radiated energy is in a high-entropy form, namely what is called 'radiant heat'--which means infrared photons. Contrary to a common impression, the Earth (together with its inhabitants) does not gain energy from the sun! What the Earth does is to take the energy in a low-entropy form, and then spew it all back again into space, but in a high-entropy form. What the sun has done for us is to supply us with a huge source of low entropy. We (via the plants' cleverness), make use of this, ultimately extracting some tiny part of this low entropy and converting it into the remarkable and intricately organized structures that are ourselves.

He goes on to explain why the visible light photons coming in have lower entropy than the infrared ones radiated back out (basically just because the infrared ones have lower energy so there must be more of them, which means the energy is spread out over more 'degrees of freedom' when it goes out than when it came in, which implies higher entropy). He also explains that the low entropy of the sun must be due to the contraction of an even lower-entropy nebula, and that ultimately the existence of diffuse collections of gas such as nebulas can be traced back to the initial smoothness of the distribution of matter and energy shortly after the Big Bang.

 

[Tomsk]

I am kind of familiar with Penrose's argument from The Road to Reality, but I don't really buy it. The 2nd law is so utterly unquestionable from a statistical point of view that I feel like the time asymmetry we see needs a much stronger argument than one that just looks back in time like that. So what if we seem to have fairly low entropy now from the sun or whatever, there is still nothing stopping entropy from getting even lower in the future!

The idea that time itself is the same thing as increasing entropy is nicer but it doesn't really have a good theoretical underpinning, since time seems to be completely symmetric at a fundamental level.

There was an interesting paper recently by Lorenzo Maccone that tried to explain this. He said that any process that decreases entropy is necessarily decoupled from any observer, in such a way that the observer has no record of the higher-entropy-in-the-past state. I think it relied on quantum effects so I'm not sure it works completely on the classical scale. I prefer the idea that time asymmetry comes from some fundamental rule like that though.

 

[DevilsAvocado]

... The problem is that because of time-symmetry, you can use the same laws of physics to "retrodict" what the state of a system was in the past if you know the state now, and exactly the same statistical derivation implies the entropy should have been higher in the past--which for most low-entropy systems is not the case! In fact if we trace the history of a typical low-entropy system backwards, we usually find that the low entropy is a consequence of its interaction with some even lower-entropy system in the past, and this chain of decreasing entropy does go all the way back to the Big Bang.

Thanks JesseM, very interesting and Roger Penrose are brilliant, as always.

There seems to be 'several' http://en.wikipedia.org/wiki/Arrow_of_time#Arrows":

• The thermodynamic arrow of time
• The cosmological arrow of time
• The radiative arrow of time
• The causal arrow of time
• The particle physics (weak) arrow of time
• The quantum arrow of time
• The psychological/perceptual arrow of time

Which are all, more or less, linked to the http://en.wikipedia.org/wiki/Second_Law_of_Thermodynamics" .

One 'peculiar' fact is that if the particle physics (weak) arrow of time would have pointed to the opposite time direction, our universe would be made of anti-matter rather than matter!

I think that the one thing that causes most 'confusion' is why we can remember yesterday, but not tomorrow. My guess is that it’s due to a combination of all arrows of time and maybe mostly causal, thermodynamic and psychological/perceptual arrow of time.

To create memories of the past we need to 'consume' low entropy, thus increasing the total entropy of the universe. Therefore we can’t remember a (universal) higher entropy state than the current state, when we started the memory process ("now").

To make an allegory:

If time is Route 66 highway, and 3D space is our car (with very big tank), and gas is entropy, and low-entropy is full tank, and high-entropy is empty tank.

Now, if Big Bang is our car with full tank in Chicago, and we are heading towards Los Angeles (Heat death ), it’s no 'miracle' that we have to use half tank to get to Amarillo, and we can’t obviously visit Los Angeles before Amarillo.

Yet, we all agree that neither Chicago nor Amarillo generally comes before Los Angeles in time, or vice versa. They are just different places on the map, and all depends on where you started.​

Sean Carroll (Caltech) and David Albert discuss this interesting matter on Bloggingheads.tv:

Time’s Arrow – Why is the past so different, in so many ways, from the future? (12:28)




P.S. TheAlkemist you were right! The quantum arrow of time does depend on wavefunction collapse/decoherence!

 

[DevilsAvocado]

... I don't like the big bang explanation for this. Even if there was a good reason for the entropy of the universe to be very low at the BB, why should that affect us?

I would say it makes all the difference you can think of. Slightly higher entropy at BB, and we would not exist discussing this matter...

 

[shortlk]

Pineal Gland contains nanocrystals, and melatonin which creates your day and night pattern of time. The sun warms the Earth and the axis tilt provides us with different seasons for the different distances we are from the sun during our orbit, which we perceive as one year and 365 days. You have to see now that there is much more to time than what we actually perceive. Time is the product of the entire system as a whole, working in light to communicate to our eyes and produce a colour spectrum through the electromagnetics (electrons) of the particles themselves.
Yes we create our own skewed concepts of perception.

 

[nismaratwork]

Pineal Gland contains nanocrystals, and melatonin which creates your day and night pattern of time. The sun warms the Earth and the axis tilt provides us with different seasons for the different distances we are from the sun during our orbit, which we perceive as one year and 365 days. You have to see now that there is much more to time than what we actually perceive. Time is the product of the entire system as a whole, working in light to communicate to our eyes and produce a colour spectrum through the electromagnetics (electrons) of the particles themselves.
Yes we create our own skewed concepts of perception.

You're just describing some examples of the same fundamental 2nd Law, and there is no need to do so. This is not a skewed perception, and we don't rely on our physiology alone to interpret reality. I have no idea what you're getting at, and it seems a little cranky to me. Obviously we conform to an increase in entropy throughout our biology, but your examples seem a little odd.

 

[TheAlkemist]

P.S. TheAlkemist you were right! The quantum arrow of time does depend on wavefunction collapse/decoherence!

Yesss! *pumps fists*

Just kidding.

 

[SprocketPower]

Time can flow only in 1 directon because you can't have an effect causing a cause and you can't go backwards in time because the very fact that you were back in time would be a change in th e past which would not be there in the 1st place but would if you did which would be impossible. We don't need all these nonsensical and grotesque examples of murdering one's parents or grandparents which no one would do anyways. Also, some one going back in time would not go into another branch any more than going forward in time.

 

[Demystifier]

There was an interesting paper recently by Lorenzo Maccone that tried to explain this. He said that any process that decreases entropy is necessarily decoupled from any observer, in such a way that the observer has no record of the higher-entropy-in-the-past state. I think it relied on quantum effects so I'm not sure it works completely on the classical scale. I prefer the idea that time asymmetry comes from some fundamental rule like that though.

Yes, it is shown recently that it works also on the classical level:
http://xxx.lanl.gov/abs/1011.4173
(Read the introduction!)

 

[DevilsAvocado]

Yes, it is shown recently that it works also on the classical level:
http://xxx.lanl.gov/abs/1011.4173
(Read the introduction!)

This is VERY interesting!

http://xxx.lanl.gov/abs/1011.4173"

The Universal Arrow of Time
...
Due to the interaction, the two subsystems will have the same direction of time for t > t1. But which direction? The probabilistic answer is: The direction which is more probable, given that we know what we already know ... It is this asymmetry in knowledge that makes two directions of time different.

I hope I understand this correct; it’s the psychological/perceptual arrow of time that 'resolves' the thermodynamic arrow of time, right? We know what we know...

Though, David Albert has an 'objection' to this, in a discussion with Sean Carroll:

Time’s Arrow – Why is the past so different, in so many ways, from the future? (12:28)



Albert’s argument is that you can leave your room in a high entropy state (complete mess) and form a memory of this state at t1. You know what you know. At a later moment in time you return to the room, and now someone else has put it in perfect order = low entropy state. Your past memory of high entropy has reversed to low entropy at t > t1 ...


P.S.
A pure personal speculation (maybe totally crazy). As far as I understand, the particle physics (weak) arrow of time points to the opposite time direction, for anti-matter, right? We know that our ordinary matter is the rest "left over" after BB, when all anti-matter was annihilated by matter. Now, if anti-matter = reversed arrow of time, we could say that the reason we have the forward arrow of time is because we are made of matter, and not anti-matter... Right...??

 

[Demystifier]

I hope I understand this correct; it's the psychological/perceptual arrow of time that 'resolves' the thermodynamic arrow of time, right? We know what we know...

Well, not really. Namely, to HAVE a psychological arrow of time (i.e., the phenomenon that we remember the past and not the future), we need a thermodynamic time arrow in the first place. The paper does NOT attempt to explain why there is a time arrow; this remains a mystery. The paper has a much more modest goal - to explain why the time arrow is UNIVERSAL.

As far as I understand, the particle physics (weak) arrow of time points to the opposite time direction, for anti-matter, right?

No! Entropy increases in the same direction for particles and antiparticles.

 

[Careful]

Well, not really. Namely, to HAVE a psychological arrow of time (i.e., the phenomenon that we remember the past and not the future), we need a thermodynamic time arrow in the first place. The paper does NOT attempt to explain why there is a time arrow; this remains a mystery. The paper has a much more modest goal - to explain why the time arrow is UNIVERSAL.

I have always had trouble with this concept of thermodynamic arrow of time and it is by no means clear for me that the second law of thermodynamics should universally hold. All proofs so far in the context of the holographic principle contain loopholes and assumptions which may very well not be true. The concept of a psychological arrow of time is much more fundamental in my opinion and does not require an increase of global entropy whatever that may mean. So I disagree with you that there is a necessary logical connection between them.

PS: as you are probably very much aware, this issue cannot be debated within conventional quantum theory at least not if you take the Von Neumann definition seriously. I know people have been looking for notions of dynamical entropy, but then you are not adressing the increase of total entropy of the entire universe (that one is ZERO and remains so forever). But such constructions typically split the universe into ''(isolated) system'' and ''rest of universe'', perform a partial trace over the ''rest of universe'' and use usual Shannon-Von Neumann on the remaining density matrix. But in those cases, the entropy does *not* need to be increasing in time.

Now, it's your turn.

 

[DevilsAvocado]

Well, not really. Namely, to HAVE a psychological arrow of time (i.e., the phenomenon that we remember the past and not the future), we need a thermodynamic time arrow in the first place. The paper does NOT attempt to explain why there is a time arrow; this remains a mystery. The paper has a much more modest goal - to explain why the time arrow is UNIVERSAL.

Ahh! Got it, thanks!

... but isn’t the No. 1 reason the time arrow is what it is (asymmetrical, forward, universal) due to the very special initial condition of low entropy at BB, bringing us back to square one ...??

No! Entropy increases in the same direction for particles and antiparticles.

Ouch! I knew I was on exceptionally thin ice here... (I just have to say that to save my face! )

The source for my misunderstanding was too fast and sloppy reading of an (maybe a little 'vague') text on Wikipedia:

http://en.wikipedia.org/wiki/Arrow_of_time#The_particle_physics_.28weak.29_arrow_of_time"

This arrow is not linked to any other arrow by any proposed mechanism, and if it would have pointed to the opposite time direction, the only difference would have been that our universe would be made of anti-matter rather than from matter. More accurately, the definitions of matter and anti-matter would just be reversed.

Shame on me.

 

[Careful]

No! Entropy increases in the same direction for particles and antiparticles.

? Are you saying here that you have TWO notions of entropy ? Let's make this discussion into a serious one and start by defining entropy and then we will talk. All this babbling about what entropy is supposed to do gets me nervous

 

[DevilsAvocado]

All this babbling about what entropy is supposed to do gets me nervous

Hehe! Relax, take it easy... have some https://www.physicsforums.com/showpost.php?p=2771643&postcount=6". Don’t be chicken!

 

[Careful]

Hehe! Relax, take it easy... have some https://www.physicsforums.com/showpost.php?p=2771643&postcount=6". Don’t be chicken!

Sure, but it is a very hard subject; those papers which even try to study it seriously never really define entropy: they just posit the existence of some entropy current which has to satisfy some ''reasonable'' conditions. If you want to truly learn something about this issue, you may study the work of Wald, Marolf and the excellent review paper by Rafael Bousso on the holographic principle. The issue of entropy is so well understood that someone like Ilya Prigogine gave his entire life to it So I am very suspicious about those people who talk about this as if they have understood it.

 

[nismaratwork]

Sure, but it is a very hard subject; those papers which even try to study it seriously never really define entropy: they just posit the existence of some entropy current which has to satisfy some ''reasonable'' conditions. If you want to truly learn something about this issue, you may study the work of Wald, Marolf and the excellent review paper by Rafael Bousso on the holographic principle. The issue of entropy is so well understood that someone like Ilya Prigogine gave his entire life to it So I am very suspicious about those people who talk about this as if they have understood it.

So, this is your roundabout way of saying you believe in The Holographic Principle? I haven't seen people claim some unreasonably complete knowledge of entropy, just working with various theories that have been very successful to this point.

 

[Careful]

So, this is your roundabout way of saying you believe in The Holographic Principle? I haven't seen people claim some unreasonably complete knowledge of entropy, just working with various theories that have been very successful to this point.

Well, I am pretty sure the holographic principle holds but the real question is ''what information are be talking about?''. If you would care to read this review paper by Bousso, you would understand there is reasonable support for it (especially for the Bousso formulation). The original formulations by 't Hooft and Susskind are known to fail. Moreover, all this is just classical work... we are still far away from adressing it in the quantum language.

So it is not a matter of belief really, it is more a matter of getting it precisely right. But the core of the idea is undoubtely correct. Whether it is a fundamental property of nature (like some string theorists believe) or a derived one (like I think) is a different discussion.

 

[nismaratwork]

Well, I am pretty sure the holographic principle holds but the real question is ''what information are be talking about?''. If you would care to read this review paper by Bousso, you would understand there is reasonable support for it (especially for the Bousso formulation). The original formulations by 't Hooft and Susskind are known to fail. Moreover, all this is just classical work... we are still far away from adressing it in the quantum language.

So it is not a matter of belief really, it is more a matter of getting it precisely right. But the core of the idea is undoubtely correct. Whether it is a fundamental property of nature (like some string theorists believe) or a derived one (like I think) is a different discussion.

What do you mean by, "...am pretty sure the holographic principle holds..." when that simply isn't true. It COULD be true, but it's barely a conjecture right now, and certainly not an accepted theory with broad support. I'd call it an area of inquiry, and nothing more at this point. I appreciate what I've seen on paper, but if it really is physical reality, well... the work so far is minute. Personally I love the idea, but that doesn't mean it's true.

 

[Careful]

What do you mean by, "...am pretty sure the holographic principle holds..." when that simply isn't true. It COULD be true, but it's barely a conjecture right now, and certainly not an accepted theory with broad support. I'd call it an area of inquiry, and nothing more at this point. I appreciate what I've seen on paper, but if it really is physical reality, well... the work so far is minute. Personally I love the idea, but that doesn't mean it's true.

It is a conjecture with LOADS of support. You sound like a mathematician to me who needs a watertight proof that something is true. Well, go and proof then that the world has 3 spatial dimensions - if you want to, we could argue about that for hours. Did you actually read the more than 50 page thick Bousso paper? So I don't care a damn whether it is generally accepted or not because most people simply don't understand it good enough. And you just proved that by calling it 'barely' a conjecture; the paper of Wald and Marolf actually treats it in rather much detail.

If you want the reference, here it is:
http://arxiv.org/abs/hep-th/9908070
and here is a Bousso review paper
http://arxiv.org/PS_cache/hep-th/pdf/0203/0203101v2.pdf

So, if you still say you think it is 'barely' a conjecture, argue then on basis of those actual results.

By the way, the holographic principle *has* to enter the discussion here if you want to know something about the total entropy of the universe. There is nothing roundabout about this, it's a crucial ingredient to actually understand what is going on. Actually, if you have a better way to even just define a generalized second law of thermodynamics, go ahead. I invite you to share your deep insights with us.

I just saw the video with Carrol and he seems to ''think'' that things like breaking an egg and remembering yesterday but not tomorrow have the same origin :-) Holy Christ, and he wrote a book about it!

 

[Demystifier]

? Are you saying here that you have TWO notions of entropy ?

No. I'm saying that it is misleading (at least in this context) to think of antiparticles as particles moving backwards in time. It is better to think of them as particles with the opposite charge.

 

[Careful]

No. I'm saying that it is misleading (at least in this context) to think of antiparticles as particles moving backwards in time. It is better to think of them as particles with the opposite charge.

Ok then, that's what I thought but I had to know for sure (it wasn't clear from your phrasing though). But what I would like to know is why you state with the utmost conviction that a psychological arrow of time *needs* a thermodynamic one. That would be an interesting ground for further discussion.

 

[nismaratwork]

It is a conjecture with LOADS of support. You sound like a mathematician to me who needs a watertight proof that something is true. Well, go and proof then that the world has 3 spatial dimensions - if you want to, we could argue about that for hours. Did you actually read the more than 50 page thick Bousso paper? So I don't care a damn whether it is generally accepted or not because most people simply don't understand it good enough. And you just proved that by calling it 'barely' a conjecture; the paper of Wald and Marolf actually treats it in rather much detail.

If you want the reference, here it is:
http://arxiv.org/abs/hep-th/9908070
and here is a Bousso review paper
http://arxiv.org/PS_cache/hep-th/pdf/0203/0203101v2.pdf

So, if you still say you think it is 'barely' a conjecture, argue then on basis of those actual results.

By the way, the holographic principle *has* to enter the discussion here if you want to know something about the total entropy of the universe. There is nothing roundabout about this, it's a crucial ingredient to actually understand what is going on. Actually, if you have a better way to even just define a generalized second law of thermodynamics, go ahead. I invite you to share your deep insights with us.

I just saw the video with Carrol and he seems to ''think'' that things like breaking an egg and remembering yesterday but not tomorrow have the same origin :-) Holy Christ, and he wrote a book about it!

I may sound like a mathematician, but I'm far from one... I just recognize the difference between a relatively new and radical conjecture, a theory, and a theory like GR or QM that is productive. Nothing in what I've read, including your links, claim a level of confidence beyond conjecture... so what's the problem? The Luminiferous Aether was a "conjecture with loads of support," of the kind you mean... i.e. the support of authority... didn't make it reflect a physical reality however.

I think you need to take all of this a bit less personally.

 

[Demystifier]

The concept of a psychological arrow of time is much more fundamental in my opinion and does not require an increase of global entropy whatever that may mean. So I disagree with you that there is a necessary logical connection between them.

To avoid difficult problems associated with consciousness and subjective human feel of the flow of time, let me put it this way: The thermodynamic arrow of time can explain why COMPUTERS remember the past and not the future. Would you agree with THAT?

For my opinion on the SUBJECTIVE CONSCIOUS flow of time, see:
http://www.fqxi.org/data/essay-contest-files/Nikolic_FQXi_time.pdf

 

[Careful]

I may sound like a mathematician, but I'm far from one... I just recognize the difference between a relatively new and radical conjecture, a theory, and a theory like GR or QM that is productive. Nothing in what I've read, including your links, claim a level of confidence beyond conjecture... so what's the problem? The Luminiferous Aether was a "conjecture with loads of support," of the kind you mean... i.e. the support of authority... didn't make it reflect a physical reality however.

I think you need to take all of this a bit less personally.

I don't take it personally but I think your reasoning is of the ''sociological'' kind and not of the scientific one. If you dismiss everything which does not belong to well tested standard science as a conjecture, then you may do that for everything. In my opinion, those theories are not on a higher plane than -say the holographic principle is- because we know they fail at high energies and in the low infrared (which is not so for the holographic principle). So, I challenge you, what in those papers makes you come to the conclusion that there is not sufficient support for those ideas?

 

[Careful]

To avoid difficult problems associated with consciousness and subjective human feel of the flow of time, let me put it this way: The thermodynamic arrow of time can explain why COMPUTERS remember the past and not the future. Would you agree with THAT?

No :-) I may give you a more elaborate answer if you tell me how you would construct such arrow of time from microscopic variables. And euh, why do you think computers wouldn't have a low form of consciousness?

 

[Demystifier]

All proofs so far in the context of the holographic principle contain loopholes and assumptions which may very well not be true.

Are you saying that there are attempts to explain the arrow of time from the holographic principle?
If so, can you give me a link?

 

[Careful]

Are you saying that there are attempts to explain the arrow of time from the holographic principle?
If so, can you give me a link?

Well sure, the whole point of the Bousso construction is to derive the second law for the combined gravity/matter system ASSUMING that it holds for ordinary matter (that is one loophole). See the paper of Wald, Marolf and Flanagan I referred to, but first I advise you to read to original Bousso paper (published around 2000 I believe).

 

[Demystifier]

I may give you a more elaborate answer if you tell me how you would construct such arrow of time from microscopic variables.

What exactly do you mean by "such"?

And euh, why do you think computers wouldn't have a low form of consciousness?

I never said that I do. But computers are better example than humans because we understand them much better than humans, and we do not NEED consciousness to understand how they work.

 

[Demystifier]

Well sure, the whole point of the Bousso construction is to derive the second law for the combined gravity/matter system ASSUMING that it holds for ordinary matter (that is one loophole).

It seems trivial to me, so that I am no longer interested in such a "derivation".

 

[Careful]

What exactly do you mean by "such"?

Well, give me one, and we can discuss scientifically.

I never said that I do. But computers are better example than humans because we understand them much better than humans, and we do not NEED consciousness to understand how they work.

Really? I could argue that it is precisely our consciouness which makes computers do whatever they do, but I believe computers are more self-supporting than that. Again, you think too classical here. A Schrodinger ''cat-like'' computer doesn't do sh*t.

 

[Careful]

It seems trivial to me, so that I am no longer interested in such a "derivation".

Really ? Then you really don't understand the nontrivial ideas which go into it. I mean someone like Wald is not going to write a paper about a trivial subject, is he?

For example, what does gravity do with entropy of matter ?

 

[Demystifier]

Really ? Then you really don't understand the nontrivial ideas which go into it. I mean someone like Wald is not going to write a paper about a trivial subject, is he?

I haven't seen the paper, my conclusion is based solely on your description.

 

[Demystifier]

Well, give me one, and we can discuss scientifically.

OK, macroscopic entropy defined through coarse graining of microscopic degrees of freedom. Do I need to explain?

 

[Careful]

OK, macroscopic entropy defined through coarse graining of microscopic degrees of freedom. Do I need to explain?

Well, if you could All these ideas run into deep sh*t with general covariance, but I guess this word is not so important in your dictionary Ok, suppose I am willing to accept that (which I am really not, since if you learn Bousso's paper you will see that gravitational entropy is attached to three dimensional null surfaces and not to some naive notion of space), then you can only apply this trick to the whole universe. All systems in nature are open, that is why WE exist, so what for God's sake would a global thermodynamic arrow of time tell you about the ''local'' functioning of the memory of a computer? The information in the computer might go up and it might go down, if I clean my hard disk the we would agree that by any reasonable definition of information, the latter would go down right? If I download the newest version of Windows Vista (if that still exists :-)) , then you know ''information'' would go up, right?

So, I repeat myself, the psychological arrow of time is much more fundamental - even for computers. For now, this discussion has been entirely classical, if we would repeat it quantum mechanically it would become even more evident that no entropical arrow of time can exists since entropy is and remains always zero whether you make measurements or not. So, unless gravity somehow destroys global unitarity, there is even no way to make sense of a global arrow of time in this context. But again, that would still not explain why computers observe only the past and not the future.

 

[Demystifier]

If I download the newest version of Windows Vista (if that still exists :-)) , then you know ''information'' would go up, right?

If you find Windows Vista on your computer, then you can be sure that it was downloaded in the PAST, but you cannot infer from that that it will be downloaded in the FUTURE. More generally, the CURRENT state in the computer memory tells you more about the past than about the future.

 

[Careful]

If you find Windows Vista on your computer, then you can be sure that it was downloaded in the PAST, but you cannot infer from that that it will be downloaded in the FUTURE. More generally, the CURRENT state in the computer memory tells you more about the past than about the future.

Sure, nobody objects that. The only thing I say is that a thermodynamic arrow of time is not explaining it. This is even so for humans, the local information in your brain may go down actually from time to time - a bottle of Vodka may assist you here Or in the worst case, you have a cerebrial bleeding and yeh many things are wiped out. So information *currents* cannot explain why time 'flows forwards' LOCALLY.

So yeh, I think someone like Carrol has a deep misunderstanding on this point.

 

[Demystifier]

The only thing I say is that a thermodynamic arrow of time is not explaining it.

I think it does, but I cannot explain it simply, and I don't have time to explain it in detail.

In relation to this, you might find this
http://lanl.arxiv.org/abs/gr-qc/0403001v2
interesting.

 

[Careful]

I haven't seen the paper, my conclusion is based solely on your description.

Then you don't understand why this is nontrivial, so my conclusion remains the same.

 

[Demystifier]

... general covariance, but I guess this word is not so important in your dictionary

General covariance is very important in my dictionary:
http://xxx.lanl.gov/abs/hep-th/0601027
http://xxx.lanl.gov/abs/hep-th/0202204
http://xxx.lanl.gov/abs/gr-qc/0111029

For a relation with the arrow of time. see also
http://xxx.lanl.gov/abs/gr-qc/0403121