Physicist Proposes Solution to Arrow-of-Time Paradox

Aug 27, 2009 By Lisa Zyga feature
Physicist Proposes Solution to Arrow-of-Time Paradox
A new theory suggests that we don’t observe phenomena where entropy decreases because all evidence from these processes is erased when correlations are removed from the system. Image credit: cguu.com.

(PhysOrg.com) -- Entropy can decrease, according to a new proposal - but the process would destroy any evidence of its existence, and erase any memory an observer might have of it. It sounds like the plot to a weird sci-fi movie, but the idea has recently been suggested by theoretical physicist Lorenzo Maccone, currently a visiting scientist at MIT, in an attempt to solve a longstanding paradox in physics.

The laws of physics, which describe everything from electricity to moving objects to energy conservation, are time-invariant. That is, the laws still hold if time is reversed. However, this time reversal symmetry is in direct contrast with everyday phenomena, where it’s obvious that time moves forward and not backward. For example, when milk is spilt, it can’t flow back up into the glass, and when pots are broken, their pieces can’t shatter back together. This irreversibility is formalized through the second law of thermodynamics, which says that entropy always increases or stays the same, but never decreases.

This contrast has created a reversibility paradox, also called Loschmidt’s paradox, which scientists have been trying to understand since Johann Loschmidt began considering the problem in 1876. Scientists have proposed many solutions to the conundrum, from trying to embed irreversibility in physical laws to postulating low-entropy initial states.

Maccone’s idea, published in a recent issue of , is a completely new approach to the paradox, based on the assumption that is valid at all scales. He theoretically shows that entropy can both increase and decrease, but that it must always increase for phenomena that leave a trail of information behind. Entropy can decrease for certain phenomena (when correlated with an observer), but these phenomena won’t leave any information of their having happened. For these situations, it’s like the phenomena never happened at all, since they leave no evidence. As Maccone explains, the second law of thermodynamics is then reduced to a mere tautology: physics cannot study processes where entropy has decreased, due to a complete absence of information. The solution allows for time-reversible phenomena to exist (in agreement with the laws of physics), but not be observable (in agreement with the second law of thermodynamics).

In his study, Maccone presents two thought experiments to illustrate this idea, followed by an analytical derivation. He describes two situations where entropy decreases and all records of it are permanently erased. In both scenarios, the entropy in the systems first increases and then decreases, but the decrease is accompanied by an erasure of any memory of its occurrence. The key to entropy decrease in the first place is a correlation between the observer and the phenomenon in question. As Maccone explains, when an interaction occurs between an observer and an observed phenomenon that decreases the entropy of the correlated observer-observed system, the interaction must also reduce their quantum mutual information. When this information is destroyed, the observer’s memory is destroyed along with it.

In the first situation where entropy decreases, Maccone describes a situation where Bob sends Alice some energy in the form of light, initially in a zero-entropy state. Using detectors, Alice receives the light and observes her detectors warming up, revealing that heat has been lost and entropy is increasing in her isolated lab.

However, Bob can theoretically manipulate the situation by withdrawing the energy he has sent Alice, and then erasing all evidence of the energy’s existence - including erasing her memory and the notepads where she wrote the detectors’ temperatures. First, to recover the energy, Bob must return the energy to a zero-entropy state. He does this by erasing all correlations between the energy and Alice, and any other macroscopic systems in the lab. By erasing all initial correlations, Bob can enable the system to lose entropy. Although the act of decorrelating requires energy, Maccone explains that it doesn’t necessarily cause entropy to increase.

“Any physical transformation requires energy (no energy implies no time evolution, i.e. a static system),” he told PhysOrg.com. “This, however, doesn't automatically imply that entropy is increased. Entropy increases when (part of) the energy employed becomes unusable as waste heat.

“Some energy is employed in the decorrelation transformation. Not only is such energy still available afterwards, but the decorrelation might also decrease the entropy in two systems, and that can ‘free’ some more energy that was previously unavailable (as it was locked up as heat).”

The second situation where entropy decreases involves a quantum measurement instead of a classical one. Here, Bob sends Alice a particle in a specific spin state. Alice performs a quantum measurement that consists of coupling the particle with a macroscopic reservoir, which increases the entropy of the system. But once again, Bob can theoretically manipulate the situation, this time by inverting the transformation of Alice’s measurement. This action decorrelates all records of Alice’s measurement results from the spin state. Although Alice remembers performing the experiment, she has no memory or evidence of what the measurement result was, and the spin is back to its initial zero-entropy state.

Although theoretically possible, these situations in which entropy decreases would be very difficult to demonstrate experimentally, due to the difficulty in manipulating macroscopic correlations. That is why, for all practical purposes, these phenomena are unobservable by physics. Still, as Maccone explains, the theory is a straightforward application of quantum mechanics when applied to macroscopic systems, and could potentially be verified.

“I think that if quantum coherence can be indubitably proven on a macroscopic observer (not necessarily a human being), then my approach would be verified,” he said. “An experiment of the sort of the second thought experiment, for example. The state of the art of experiments is quite far from anything of that sort. The biggest system where quantum coherence has been experimentally shown is, I think, some biological molecule composed of a few hundred atoms by A. Zeilinger's group in Vienna.”

The explanation may also provide insight into understanding entropy in the universe. The approach supports the idea that the universe may be in a state of zero entropy, even though it appears to us observers to have higher . As Maccone explains, the universe is in a zero-entropy pure state because it cannot be entangled with any other system.

“My theory requires that the global state of the observer plus the environment be in a quantum pure state,” he said. “This means that it works only if we consider a sufficiently large system that it cannot be correlated with any other system. However, correlations (entanglement, in quantum systems) are very sticky; namely, systems get correlated very quickly also if they are very weakly interacting. This is why, when one considers macroscopic systems, the only safe choice is to consider the whole universe, which cannot be correlated with any other system, since, by definition, it comprises all physical systems.”

More information: Lorenzo Maccone. “Quantum Solution to the Arrow-of-Time Dilemma.” Physical Review Letters 103, 080401 (2009).

Copyright 2009 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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User comments : 105

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earls
1.2 / 5 (5) Aug 27, 2009
Wow, this is scary on more than one level.
rgw
1 / 5 (6) Aug 27, 2009
Wow, this is level on more than one scary.
Scryer
3.4 / 5 (5) Aug 27, 2009
pretty interesting...
Velanarris
Aug 27, 2009
This comment has been removed by a moderator.
nuge
1.3 / 5 (4) Aug 27, 2009
If I get a sieve, and use it to separate noodles and water, have I not decreased entropy?
Japones
2.3 / 5 (3) Aug 27, 2009
If I get a sieve, and use it to separate noodles and water, have I not decreased entropy?


No.
AnnieDeakin
1.3 / 5 (4) Aug 27, 2009
cool

interesting

furniture editor
Alexa
Aug 27, 2009
This comment has been removed by a moderator.
Sauvignon
3.3 / 5 (8) Aug 27, 2009
Gobbledygook. Mysticism. There is no measurable effect on the universe. It's supernatural. A thing that leaves no PHYSICal trace is not in the realm of PHYSICS.
podizzle
3 / 5 (2) Aug 27, 2009
so the theory is entropy can decrease without time reversing? or does time reverse?
Mr_Man
4.4 / 5 (7) Aug 27, 2009
If I get a sieve, and use it to separate noodles and water, have I not decreased entropy?




No.


This is why the physics world and the culinary world never come together.

jsovine
2.8 / 5 (5) Aug 27, 2009
Sounds like a bunch of BS
iknow
3.6 / 5 (9) Aug 27, 2009
I call tosh on this.... I can certainly understand what the author means, but really? To withdraw "energy" and erase memories and notepads? This would require time to reverse taking along with it the whole history of the universe...hmmm....or it could be a local phenomena ...but thats even more rubbish.

Good read tho, but the idea of saying "sure. it can be done, tho you will not remember it and no trace will be left" is like when I used to lie to mum ..."yeah i cleaned the room...it just got dirty again"
Slotin
2 / 5 (13) Aug 27, 2009
Article is basically right if its adhering to thermodynamical definition of time arrow. But how to reconcile it with definition of space-time in relativity? Aether Wave Theory (AWT) proposes a solution.
Velanarris
3.5 / 5 (6) Aug 27, 2009
I call tosh on this.... I can certainly understand what the author means, but really? To withdraw "energy" and erase memories and notepads? This would require time to reverse taking along with it the whole history of the universe...hmmm....or it could be a local phenomena ...but thats even more rubbish.



Good read tho, but the idea of saying "sure. it can be done, tho you will not remember it and no trace will be left" is like when I used to lie to mum ..."yeah i cleaned the room...it just got dirty again"

You're decoupling time and entropy, which you cannot do as the only measurement of time passing is entropy.
Mr_Man
4.8 / 5 (4) Aug 27, 2009
so the theory is entropy can decrease without time reversing? or does time reverse?




No, because there are still plenty of external sources where entropy is still increasing.



If you are referring to entropy decreasing in a vacuum, then it could probably have the appearance that time is in fact reversing.



But what is causing the decrease of entropy? There needs to be some energy/force causing this. This is what I don't understand about the theory.. It describes "Bob" manipulating the test - so he would be putting energy into making the entropy of the particles decrease, as well as erasing/negating (either him physically erasing or the information being indirectly erased) of "Alice's" data.



Also, if you take a gas and the entropy of the particles decrease, that doesn't necessarily mean time went backwards - the particles still had to get to a point where they could reverse in entropy. If the particles never experienced an increase in entropy, then a decrease of entropy would be impossible. To make a decrease in entropy possible, there would have to be the time it took for the particles to increase in entropy as well as the time it took for the particles to decrease. It really shouldn't even matter if the particles all took the exact same paths during the decrease in entropy as they took during the increase - on a quantum level it wouldn't matter anyway because on a sub atomic level particles behave randomly.



Given an infinite amount of time, the particles of a gas in a box may eventually all coagulate to a corner of the box - if they are moving randomly then it is inevitable (given infinite time) that the particles can all end up in a small area of the box which would give the illusion of a decrease in entropy (or maybe it would actually be considered a decrease in entropy).



So even IF the particles decreased in entropy and they all took the exact same paths back, on a quantum level they would behave a bit differently than they did during the increase of entropy, therefore you couldn't say time was reversing because different events were occurring.



I think the author is arguing that with negative entropy occurring there would be no PROOF that positive entropy ever occurred (no observation, no measurements, no data), so we would never know if it did. I think he is just creating an argument for the possibility of its existence.

EDIT: My post was all on the assumption that entropy does not equal time, which was probably evident by everything I said. I might be incorrect in my assumption, after all, my name isn't Mr Man Ph.D
Slotin
3 / 5 (6) Aug 27, 2009
We are facing two time arrows at the same moment, because we cannot ignore fact, one half of Universe evaporates into radiation, while the second one agglomerates by gravity. So what we are observing are two processes separated by CMB/human scale. Objects, which are large then 1.73 cm tends to agglomerate in their gravity field into larger ones. This is essentially negentropic process, related to inverse time arrow!

Whereas object smaller then CMB photons are evaporating into radiation. This is indeed common entropic process. The human/CMB space-time/energy density scale appears to be quite universal boundary between past and future because of omnipresent activity of CMB photons and it forms the middle of dimensional scale of observable Universe.

http://en.wikiped...imension
http://www.physor...776.html
Alexa
2.8 / 5 (9) Aug 27, 2009
If we consider the dual thermodynamical time arrow for our space-time, we can propose more general, cosmological time arrow, which is independent to entropy of Universe (which remains the same all the time), but it's defined by the combination of the above processes. At the moment, when we would observe separation of large objects while the smaller one would condense, we could say, not just thermodynamical, but cosmological time arrow gets reversed, too.
http://en.wikiped..._of_time
Simonsez
4.5 / 5 (2) Aug 27, 2009
Reversing entropy is as simple and plausible as reversing time. Fundamental physics!
Mercury_01
3 / 5 (1) Aug 27, 2009
Haven't we always known that reality is a consensus among parts of a system, and that the observer and the observed must correlate quantum information for there to be an observation? I'm no physicist, but I would have thought we already know this. There are a lot of particles inside a human that would all have to agree that time is in reverse at a given moment. Probability dictates that this correlation wouldn't happen, any more than it would be probable for all the people of the earth to suddenly agree that it would be a socially acceptable to eat babies.
Question
1 / 5 (4) Aug 27, 2009
When a cloud of hydrogen gas condenses and forms a star, isn't that decreasing entropy? When a kid uses magnifying glass to start a fire from sunlight, isn't that decreasing entropy? When iron is made from iron ore, isn't that decreasing entropy? Is time reversed when things like this happen?
Velanarris
3 / 5 (4) Aug 27, 2009
When a cloud of hydrogen gas condenses and forms a star, isn't that decreasing entropy? When a kid uses magnifying glass to start a fire from sunlight, isn't that decreasing entropy? When iron is made from iron ore, isn't that decreasing entropy? Is time reversed when things like this happen?

No it isn't. The AWT'er is confusing people by calling aggregation negentropy, which it isn't.


Alexa
2.1 / 5 (11) Aug 27, 2009
When gas expands into vacuum, entropy increases. When it collapses into nebula or even star, entropy decreases, i.e. negentropy increases. It's as simple, as it is.

Furthermore here are many other evidences of inverse time arrow, like antiparticles and supersymmetry.
Alexa
2.5 / 5 (11) Aug 27, 2009
..Is time reversed when things like this happen?..
In AWT Universe is entropy symmetric. It simply behaves like dense gas, which forms and dissolves density fluctuations repeatedly. The larger these fluctuations are, the slower is that process but it doesn't change qualitatively. Whenever some matter dissolves, some other is formed somewhere else, therefore we have many time arrows here. From global perspective Universe is behaving like quantum gas, where no apparent time arrow exists in the same way, like at Planck scale.
Velanarris
3.8 / 5 (11) Aug 27, 2009
When gas expands into vacuum, entropy increases. When it collapses into nebula or even star, entropy decreases, i.e. negentropy increases. It's as simple, as it is.



Furthermore here are many other evidences of inverse time arrow, like antiparticles and supersymmetry.

You have absolutely no idea what you're talking about, and this finally seals it.

Alexa
Aug 27, 2009
This comment has been removed by a moderator.
Foolish1
4.7 / 5 (6) Aug 27, 2009
I must be a complete moron because this sounds as absurdly unhelpful as a buddist truisim to me.

My problem with the article is the use of outlandish examples used for popular attention that do not effect physical reality.

They cause morons like myself to assume mystical things about what is being said that are not true or even being stated.

Like schrodingers cat any coherence issues are out the door and settled long before any cat is killed or not. These kinds of "thought experiments" do not help people to understand fine points about entanglement/coherence or see the quantum world as transactional or nondeterminstic state charts -- they only confuse the hell out of them!!

If you have a non-imaginary point to add other than admitting there is no way for you to prove your idea or use it to further any research then please make it.
Mercury_01
5 / 5 (2) Aug 27, 2009
You jerks are like old friends to me. I love how you flame each other.
VOR
5 / 5 (3) Aug 27, 2009
What I find such BS is the way its sometimes exampled by events on macro scale like a glass breaking then self-reassembling. Maybe it has particle relevance, and math/theoretical relevance, (i wouldnt know). But the macro examples, and the use of wording that people's memories would get erased is of course all nonsense. Its a misapplication of what may be a useful theory. I wish people would stop this practice. Leave the theory in its pure form without trying to use totally ill-fitting analogies or applications. Another example of this is time travel where you meet yourself--utterly rediculous. Macro matter can NEVER be in two places at once regardless of quantum level behavior. Time NEVER flows backwards and events NEVER 'unhappen' (but a new event could occur that appears to undue previous event of course).
Mr_Man
1 / 5 (5) Aug 27, 2009
I apologize - this kind of gets off topic a bit later in the post.

Another interesting thought regarding a decrease in entropy would be the theoretical "Big Crunch". The Big Crunch would be the perfect definition of decreased entropy. Physicists never mention a "reversal of time" when speaking of the Big Crunch, but that isn't my point here.



My point is - lets say the Big Crunch does happen, all matter falls back into itself and the result is the singularity of all matter, just as it was before the Big Bang. Does that mean our Universe as we knew it ceases to exist? Well, not entirely. The matter/energy is all still there, its just in a different state. But evidence that the Universe ever existed as we see it now? That might be hard to prove. Any physical information may no longer exist, but that doesn't mean the Universe (our Universe) never happened - it doesn't reverse time.



One question remains - is there empty space left over where the matter once was? Does the Dark Matter remain? After all, it seems to not be effected (or repels) gravity (please correct me if I am wrong here).



So maybe the evidence of our Universe after the Big Crunch is the fact that there is empty space where the matter once filled, or Dark Matter remains and is evidence that their was once something filling the space.



But we are to understand that before the Big Bang there was no "empty space", there was only the possibility of space.



This is why I don't believe in the Big Crunch. If its a repeating cycle, it had to have started somewhere.



Also, if there was no "space" before the big bang - all matter, everything was compressed into the infinitely small and dense singularity, how could there be an expansion? If the space / dark matter we have in the universe actually came from the singularity, then it leads me to think that the "expansion" of the universe is an illusion - yes, galaxies and stars are moving outward from each other, but what is actually causing this is an increase in Dark Matter - or it is being converted from an energy or material that always existed.



Therefore - the Universe has always been the same size, its just that the Singularity was the size of the Universe. ...That may not have been the best way to explain my point, I'm just not sure of a better way to explain it now. Maybe this is better: Everything was compacted into the Singularity, all matter and energy. It would almost seem like the Dark Matter was created somehow and pushed the matter away from each other..



If the Singularity exploded, wouldn't there have to be more pressure inside the singularity than outside of it? How can there be less pressure outside of it if there IS no outside?



Please - Anyone that knows what they are talking about (I mean really educated in the field) please correct me where I am wrong, I am here to learn!







Mr_Man
2.3 / 5 (3) Aug 27, 2009
What I find such BS is the way its sometimes exampled by events on macro scale like a glass breaking then self-reassembling. Maybe it has particle relevance, and math/theoretical relevance, (i wouldnt know). But the macro examples, and the use of wording that people's memories would get erased is of course all nonsense. Its a misapplication of what may be a useful theory. I wish people would stop this practice. Leave the theory in its pure form without trying to use totally ill-fitting analogies or applications. Another example of this is time travel where you meet yourself--utterly rediculous. Macro matter can NEVER be in two places at once regardless of quantum level behavior. Time NEVER flows backwards and events NEVER 'unhappen' (but a new event could occur that appears to undue previous event of course).


You are right on.

I love watching shows on Discovery about physics, its all pretty much simplified, which of course is necessary to keep people interested, after all - at its core it is still supposed to be entertainment. But one show I watched explained how a photon can be in two different places at once, and they were somehow applying that to the idea that there may be another identical planet Earth in the Universe along with another you, another me, etc..

I was all like "Woah- wait a minute, now you guys are just spreading lies. At least have the audacity to give us a few minutes to find and load our bongs before discussing abstract thoughts that have almost no factual basis."
nkalanaga
4.3 / 5 (3) Aug 27, 2009
If the universe is infinite, then yes, somewhere there is another Earth with another you, and me, on it. There are a finite number of particles in the Earth, and a finite number of ways to arrange those particles. If the universe is large enough, there will be more planets with identical particles than ways to combine them, and the combinations will have to start repeating.

On the other hand, any such duplicate is probably far beyond the edge of the visible portion of the universe, and it's very unlikely that we'll ever find evidence of its existence.
defunctdiety
5 / 5 (1) Aug 27, 2009
"Woah- wait a minute, now you guys are just spreading lies. At least have the audacity to give us a few minutes to find and load our bongs before discussing abstract thoughts that have almost no factual basis."

First of all, why don't you already know where your bong is? And second, audacity isn't really... ...ahh f*** it, where's my lighter?
NeilFarbstein
2.8 / 5 (6) Aug 27, 2009
sounds bizarre if bob is erasing all of Alice's observations and notes it sounds very anthropomorphic and not like a natural phenomenon.
It not credible.
MorituriMax
4 / 5 (2) Aug 27, 2009
If this is true, and he thinks of decreasing entropy and how to do it, wouldn't it have been erased from his memory, and in the next few minutes won't this article disappear and take our memories of reading it with it?
MorituriMax
5 / 5 (1) Aug 27, 2009
"He does this by erasing all correlations between the energy and Alice, and any other macroscopic systems in the lab. By erasing all initial correlations, Bob can enable the system to lose entropy. Although the act of decorrelating requires energy, Maccone explains that it doesn%u2019t necessarily cause entropy to increase."

Wouldn't all those actions he is taking to erase all the conditions to return the entropy back to zero, in turn generate their own entropy? Or are we just saying it's magic and he can do whatever he needs to do to hand-wave everything away?

Plus it seems to me that bob is still following that invariant arrow in the same direction as he executes each step to return to the beginning of the entropy-state he began with.
MorituriMax
not rated yet Aug 27, 2009
"The explanation may also provide insight into understanding entropy in the universe. The approach supports the idea that the universe may be in a state of zero entropy, even though it appears to us observers to have higher entropy. As Maccone explains, the universe is in a zero-entropy pure state because it cannot be entangled with any other system."

I can almost visualize that, by thinking of the universe in the zero-entropy pure state, say at the precise moment of the big bang when everything is coexistant in a singularity, we have a big bang, entropy increases over time, the universe expands, then collapses again at some point in the ">future."

Once it collapses into a singularity are we not then back where all entropy has effectively been "reset?"
MorituriMax
1 / 5 (1) Aug 27, 2009
Sauvignon,
Gobbledygook. Mysticism. There is no measurable effect on the universe. It's supernatural. A thing that leaves no PHYSICal trace is not in the realm of PHYSICS.


Ah HAH! But if we can MEASURE that there is no trace, it is no longer mysticism! Heh.
MorituriMax
5 / 5 (2) Aug 27, 2009
When a cloud of hydrogen gas condenses and forms a star, isn't that decreasing entropy? When a kid uses magnifying glass to start a fire from sunlight, isn't that decreasing entropy? When iron is made from iron ore, isn't that decreasing entropy? Is time reversed when things like this happen?


I think in each of those cases you have to also consider the conditions that allowed that event to occur. Those other conditions are also increasing entropy. Example: for the kid to have sunlight to start the fire, the sun has to be converting hydrogen in a fusion process, the kid is alive and breathing which is creating waste heat, the magnifying glass was made in a factory which caused more waste heat, etc. etc.
MorituriMax
5 / 5 (1) Aug 27, 2009
Mr.Man "One question remains - is there empty space left over where the matter once was? Does the Dark Matter remain? After all, it seems to not be effected (or repels) gravity (please correct me if I am wrong here)."

I'll take a stab at this part, everybody crush me if I am totally off.

If space-time is created by the presence of matter and all matter (and I mean ALL of it) falls back into a Big Crunch, I would think that space and time go with it.

In other words, since the Expansion of the Universe creates space as the universe expands, when the universe contracts, it follows that this would also affect space itself by removing that space when there is no longer ANY matter to create it.
Slotin
Aug 27, 2009
This comment has been removed by a moderator.
damnfuct
4.7 / 5 (3) Aug 27, 2009
If is the case that our consciousness flows "forward" through time along an axis of increasing entropy, would free will and consciousness be an illusion? Would the concept of the future being unknown or unset merely be a product of us not being able to experience any information from the "future"?
Slotin
2.6 / 5 (5) Aug 27, 2009
Free will is undeniable consequence of Heissenberg uncertainty principle. Every simple particle has a "free will" from this perspective - so why not large system of neurons inside of human head?
earls
5 / 5 (1) Aug 27, 2009
damnfuct, that's sort of what I had in mind with my original post.

Suppose our current "forward" is actually the Universe's "backwards." The future, previously written and then rewound is now being played forward again (from our perspective) but may actually be the Universe returning to its original state.

Absolutely scifi, but intriguing concepts nonetheless.
YawningDog
3.5 / 5 (4) Aug 28, 2009
The first Great Law of the Universe is: Stuff happens.

Corollary: Stuff does not unhappen.

Build the rest of the laws from this point.
abadaba
3.3 / 5 (3) Aug 28, 2009
hate theories like this. Rather than think maybe there are flaws in the fundamental generalizations of physics, just make up some crazy explanation that is theoretically possible but could never be proven. "oh it happens, but if you see it your memory is erased"...seriously, couldn't we explain everything we don't understand with theories like this?

@andragogue, thank you that gave me a good laugh
thingumbobesquire
1 / 5 (1) Aug 28, 2009
This thesis parallels the monkeys typing a Shakespeare play in infinite time. It proves that given even an infinite amount of time a physicist of the reductionist sort will never discover that he has a brain. I.e., the human mind is proof of a non entropic process (when its applied, that is.)
GPhillip
5 / 5 (5) Aug 28, 2009
It's really quite simple. All our physics allow time to flow in either direction, but it will always appear to us as though time is only flowing in the "forward" direction. This is because if time is flowing "backward", all evidence and memory of things that happened in the "future" are errased as time flows "backwards". So at any particular instant we can only remember the past, since any evidence of the "future" has been completely errased.

Another more accurate but somewhat more complex way to look at it is that all time from the instant of the big bang to the end of the universe exists in a 4th dimension. Being three dimensional creatures, we can't experiance the entirety of that whole 4th dimension, but rather just an infinately thin slice of it, our instant of reality. So in reality, time isn't "flowing" at all. It is us, three dimensional creatures, moving through the four dimensional space that gives the impression of time "flowing". We may move in any direction through this 4 dimensional space, but regardless of which way we move, we will always experiance time moving "forward", from one infinately short instant to the next. The reason is that if we move "backwards" in time, all evidence and memory of the future is erased and we still only remember the past and think we are still moving forward. In reality we may very well move around randomly, forward, sideways and backward through this fourth dimension of time, but it will always appear to us that we are moving "forward", proceeding from one instant to the next, since that's all we will ever remember or have evidence of.

This is all consitent with good physics and math, but unfortunately, it can not be tested or falsified and it can not be used to make any predictions. So in the end, it does answer the question of the arrow of time, but the answer is useless to us poor three dimensional beings.

Well, perhaps not totally useless, since any knowlege is of intrinsic value. And there is the possibility that the process of "errasure" isn't perfect. Due to quantum uncertianty, it is barely possible that some tiny trace of the future could tunnel into the past. So if you have a strong "hunch" of what the next lottery ticket numbers will be, go fo it! Hust don't bet your house on it. After all it is by definition, uncertain.
jbikkyou
3 / 5 (2) Aug 28, 2009
@Alexa/Slotin - aggregation and condensation don't imply negentropy.

The simplest (and probably best way) to think of Entropy is as a statistical measure of the amount of information in a system. Negentropy is an increase of information and "regular" entropy is a decrease in information.

In your "gravity makes everything clump" example you are actually losing information - the original location of all the items that clumped together.

I'm not certain you need all the hocus-pocus above to explain the uni-directional arrow of time. Take the breaking glass as an example. There are say 10^24 atoms in the glass so there are (10^24)! ways to rearrange them - a number so big there are probably not enough atoms in the universe to represent the number! If every arrangement is as likely as any other then rearranging themselves into the "whole glass" is say 1 : (10^24)! ... or put it another way to all intents and purposes impossible.

Then you have to add in the fact that "information" was put into the glass in the form of energy to arrange the atoms in a specific state - and this energy state is quite unstable in the big picture. So the probability of reaching this state is even more unlikely than our first prod at working out the likelihood - so even more unlikely than totally unlikely.

Plus all the likely states are the lowest energy - least information - ones - so for the glass at least its most likely state is a set of shattered pieces.

So entropy boils down to every physicists favourite law - the law of least action - or minimal energy - and the laws of probability - if something can have n states then there is only 1 : n chance of being in a given state.


GPhillip
not rated yet Aug 28, 2009
A couple corrections. The last two sentances should read:

So if you have a strong "hunch" of what the next lottery ticket numbers will be, go for it! Just don't bet your house on it. After all it is by definition, uncertain.

Also, you can't go "sideways" through time unless time is two dimensional, which it could be, but that's unproven.

Have a nice day.
Alexa
3.3 / 5 (7) Aug 28, 2009
..In your "gravity makes everything clump" example you are actually losing information - the original location of all the items that clumped together..
Such location could be restored simple by reversal of sign of gravity in each moment, because gravity itself is deterministic force. After all, such situation just occurs, because our Universe expands in omnidirectional way like object falling into black hole.
Alexa
3 / 5 (6) Aug 28, 2009
..If every arrangement is as likely as any other then rearranging themselves into the "whole glass" is say 1 : (10^24)!
It's not so bad, because exact location and state of atom isn't known due the Heissenberg uncertainty principle. AWT considers human brain evolution as a random process as well at the general level.

Small or large quantum objects like black hole are quite simple objects with respect of time arrow reversal - they're behaving like undulating blobby amoebas in both directions. We shouldn't confuse time arrow flow with motion - at the moment, whe we aren't able to distinguish, whether time directions was reversed, time arrow is actually zero despite the number of particles involved.
Alexa
3 / 5 (6) Aug 28, 2009
Try to imagine large volume of gas, where molecules are moving randomly. With respect to thermodynamics, time arrow is highly irreversible here.

But is it really so? If we would reverse time like in movie running backwards, the motion of gas would appear exactly the same! Here's no testable experiment, how to prove, the time goes in reversal direction in such system, because atoms are changing their states randomly, so we cannot distinguish them each other.

This means, large volume of gas is effectivelly atemporal system and speed of time is zero here. Please note, that with respect to surface water spreading even underwater is effectivelly atemporal system, so that surface waves cannot propagate in it. Here's no space-time for surface waves.
Alexa
3.4 / 5 (5) Aug 28, 2009
Or try to imagine solar system, where every motion is reversed. Could we detect, something is wrong with such solar system and its time arrow? Just at the case of rare events of individual collisions or at the scope of very long period we could detect, behavior of solar system is not normal due the absorption of very weak gravitational waves instead of radiation - but at macroscopic level such system remains reversible and effectively atemporal again.
Velanarris
3.4 / 5 (5) Aug 28, 2009
It's very simple. Like acceleration, there is no negative.

There's no such thing as negative entropy because any change in the system results in change in and of itself. To have negative entropy implies that you can "undo" time, and as the abstract states above, you would have to remove energy and information from existence, violating the conservation principles.

Simply put, time's arrow does not flow backwards.

Mr_Frontier
not rated yet Aug 28, 2009
If the entropy of our universe is calculable, then is the system open or closed?
GPhillip
3.7 / 5 (3) Aug 28, 2009
In a closed system there can be a reduction of entropy. Your refigerator removes heat reducing the entropy inside the refigerator. But of course in a quantum sense that refigerator is corrolated with it's environment, dumping the heat into the air around it at the expense of the electricity coming in through the wall plug, so entropy overall increases, as the second law says it must. But inside the closed system of the refigerator, entropy decreases. Of course their is no negative enrtopy, as that would imply something with more than perfect order, which just can't be. But time reversing doesn't require negative enrtopy, it only requires that entropy decrease, which as I pointed out, can happen inside a closed system.

When you are talking about a larger system, like the universe as a whole, then entropy must increase, since there is no where for the outside energy to come from to reorder it, and nowhere for the waste heat to go from this process.

But that is looking at it from a three dimensional view. Looking at it from a four (or more) dimensional view, time doesn't flow at all, neither forwards or backwards. Time just exists as a dimension and we move through it. We can move backwards, but we would never remember the future, since moving backwards through time is the same as reordering everything to a previous point in time, including all our memories and records. So unless you can find some bit of future information that has tunneled into the past, there is nothing for physics to study and no record of anything ever moving into the past. Things that aren't observable and testable aren't science. But don't let me get me off into string theory.

Time here is the more fundamental component, since you can reduce the entropy of a closed system, like inside a refigerator, but not effect it's time. Time is always a Universal dimension, not subject to local distortion, excluding the apparent local distortion of relativity. Entropy is easily changed localy in a closed system.

So essentially, you can't reverse the arrow of time locally, because anything local is corrolated with the time of the universe as a whole. And if you reverse the arrow of time for the whole universe, nothing happens, because it still looks the same to us.

In four dimensional reality (three space one time)you may actually be walking backwards with a reversed time arrow, but in our infinately thin experience of the instant of time that we are passing through, we don't remember the future steps, only the past ones, since the future has been errased, or reordered into the current instant or state, as we moved into the past. It's very simeple, but untestable, and therefore belongs more to the realm of religion than science.
Velanarris
2.3 / 5 (3) Aug 28, 2009
You're assuming that time exists and isn't a byproduct of observational reference.

In a closed system there can be a reduction of entropy. Your refigerator removes heat reducing the entropy inside the refigerator.

Removal of heat does not result in a more ordered system. You are not reducing entropy in your example, just energy content. So you're only talking about entropy in relation to thermodynamics, which is a flawed view.

Entropy on the whole has to deal with information. Removal of energy does not remove information. Entropy can never decrease from an informational standpoint, which is why there can never be negative entropy.
Dodder
not rated yet Aug 28, 2009

How about this? (And this is just a stab at a thought experiment.)

I'm standing in one place and I'm going to walk a certain distance forward.
You the observer are standing some distance away viewing the midsection of my path at a perpendicular angle.

I proceed to travel half of my path.
Entropy is increasing to the system as a whole and to you as an observer.
When I reach half way you close your eyes.
I proceed to walk the last half of the path and then return to the exact halfway mark. (even through any given path and any length of time.)
Throughout this entropy is still increasing to the rest of the system's observers but not to you the reference observer.

Given that you are no longer able to observe, entropy is in a zero or reference state to you.
Once I return to the exact location at the moment you closed your eyes you re-open them.
Once you have opened your eyes you observe that nothing has happened, as I haven't changed.

Now only one of two events can occur.
1. All of the increased entropy that occured that you were not able to observe now has to be erased to you the observer. That is the decrease in entropy.
2. Or you become aware of the events that occured since you closed your eyes and you see the associated increased entropy.

Any observers besides yourself will see the increase. That is why no observation, memory or record of the event can exist.
If you had observed the whole thing you would have observed it as increasing entropy just like the rest of the system.
And in fact, if you were provided the observations from one of the other system's observers you would see the increase of entropy.

If the universe is a closed system with no external observer then entropy within that system is free to increase and decrease as the closed system is in a zero state of entropy.

This applies to the Shreodinger's Cat problem as the box is a closed system.
Not only is the cat neither alive nor dead, but it can actually be oscillating between the two states continually increasing and decreasing in entropy.
Though I think it would be easier to imagine as moving back and forth between states as opposed to being in one unknown static state as time progresses until it is observed.

To me using "increasing", "decreasing" and "entropy" rather than say "right", "left", "static(or reference)" is confusing as those words have other significant connotations to me.
Velanarris
3.2 / 5 (5) Aug 28, 2009
I proceed to travel half of my path.

Entropy is increasing to the system as a whole and to you as an observer.

When I reach half way you close your eyes.

I proceed to walk the last half of the path and then return to the exact halfway mark. (even through any given path and any length of time.)

Throughout this entropy is still increasing to the rest of the system's observers but not to you the reference observer.



Stop right there. You broke your thought experiment.

"Time" passes to the observer. Even though the observer does not have ALL of the information, he still has information, meaning entropy has increased due to the perceived passage of time.

Even idle time in a physical process is an increase in informational entropy due to the passage of "time".

You're correct that the connotations screw up the message. Think of it this way. You're driving and accelerating to 100mph. You then "de-celerate" to 50 mph.

Problem is acceleration quite literally is the change in velocity over time. So by slowing down to 50, you're still "accelerating" because you've changed your velocity over time.
Slotin
3.3 / 5 (8) Aug 28, 2009
..It's very simeple, but untestable..
Yep, that's the point. Physicists are believing in many things, which are untestable by their definitions. For example most (if not all) people is believing, light path is straight and space-time is curved inside of gravitational lense, so it's a relativity phenomena. But it's just a belief, because we never put a clock into such lense to make sure, space-time is really curved here. From outside perspective we can say only, light path is curved and space-time is flat.

These subtleties are making substantial part of contempory physics formally correct, but conceptually incomplete, if not wrong. From the same reason we shouldn't extrapolate existence of time arrow to the cases, where it cannot be observed actually.
E_L_Earnhardt
1 / 5 (5) Aug 28, 2009
"INTELLIGENCE" is the missing primal factor! If "LAWS" govern "ACTION" and "REACTION" they must be "ENFORCED"! NOTHING proceeds without a PLAN!
Velanarris
2.5 / 5 (4) Aug 28, 2009
Yep, that's the point. Physicists are believing in many things, which are untestable by their definitions. For example most (if not all) people is believing, light path is straight and space-time is curved inside of gravitational lense, so it's a relativity phenomena. But it's just a belief, because we never put a clock into such lense to make sure, space-time is really curved here. From outside perspective we can say only, light path is curved and space-time is flat.


I don't think you understand what "testable" encompasses.
dziemann
not rated yet Aug 28, 2009
It doesn't really matter because very soon all of our memories of this research will have disappeared.
Alizee
Aug 28, 2009
This comment has been removed by a moderator.
fortinbras
5 / 5 (1) Aug 28, 2009
I disagree with the idea that there is no memory of the more highly entropic state. Though a system with smooth distribution of entropic correlations would experience the erasure of any markers of the previous more highly entropic states, --a system with an uneven distribution of entropy may experience an uneven unravelling of correlations, leaving observable markers in the form of preserved correlations (and their spooky effects). Information about what happened before may be preserved like fossils beneath the terrain of entropic distribution.
Alizee
Aug 28, 2009
This comment has been removed by a moderator.
Alizee
Aug 28, 2009
This comment has been removed by a moderator.
fortinbras
5 / 5 (1) Aug 28, 2009
Some Sci Fi fun with this topic: Presuming that, like ice forming on a freezer, and crystal formation in the earth, there is some kind of entropy threshold for memory... is it possible to have two paired particles maintain their pairing through a de-entropic event (such as the reversal of time)? Such that both particles may find themselves paired across different timelines?
kvj4
5 / 5 (1) Aug 28, 2009
All well and good, but who is to say which way is the arrow facing for us. It can easily be said that a decrease of entropy could leave a memory for those who spend their existence where the arrow of time faces the other way. Whole objects could be completely missing from observation due to a natural decrease in entropy. Then in fact differing levels of entropy whether tive or neg- could have the same effect because how could you ever draw a 0 point. An observer with a higher entropy then ours may think we have a Neg entropy score on their own scale.
Slotin
3 / 5 (6) Aug 28, 2009
..is it possible to have two paired particles maintain their pairing through a de-entropic event...
As far I know, matter-antimatter particle pairs are behaving in such way at certain level reality: at the situation when electron condenses into larger particles, positron should release and evaporate - so we can find it only in highly dispersed antimatter.
http://aetherwave...ter.html
..who is to say which way is the arrow facing for us..
At very general level Universe is behaving like quantum gas, which evaporates and condenses reversibly. At cosmological scale here's no apparent time arrow at such level in the same way, like here's no apparent time arrow at Planck scale. And we are moving along counter-moving pair of time arrows inbetween.
http://superstrun...rane.gif
Nevinyrral
not rated yet Aug 29, 2009
I think Orson Scott Card did this one during his Ender's Saga. There was an "outside" area in which the only thing that existed was entropy and it was basically the "heat sink" for entropy in which no one could detect until a computer entity found a way to access it. However, in order to go there the travelers must be held in memory or else they would be destroyed and all memory of them would be erased. However in the paradox of equality if someone thought of something different they would be changed as the exisitance in the "entropy sink" must correlate to the memories currently at hand. Therefore, one could essential create themselves over again in a younger version if that is the way they thought about themselves.





Trippy.

However, I thought you could change the entropy of a SYSTEM but not the entropy of the UNIVERSE. The entropy of a system could decrease if you put WORK into it. Basically what this guy is saying is that the system can tank energy and do work with it which is kinda cool. But it is kind of a weird way of saying the same thing.
Weir
1 / 5 (2) Aug 29, 2009
First a point on General Relativity. In its derivation the spacetime continuum is assumed to be distinct from gravitational mass embedded in it, thus introducing curvatures in the continuum. Einstein also insisted that singularities had to be cut out because the theory was based on a smoothed out universe similar to a gas on a cosmic scale. This problem along with the contradiction of a beginnng to space and time in space and time is not addressed in Big Bang cosmology. Late in life Einstein doubted that physics could be based on the continuous field concept in which case quote: my castle in the sky, including the theory of gravitation, amounts to nothing but so does the rest of modern physics. The only alternative is a discontinuous universe. See the article Gravity, Quantum Relativity & Cosmic Order at www.cosmic-mindreach.com.

Second point. A seed falls to the earth, germinates and grows into a plant. Every chemical process within the plant obeys the second law of thermodynamics and yet the plant as a whole matures, goes to seed, and dies to fertilize its bed for more plants to grow. It enriches its environment. It stores order. In this terrestrial sense living process are negentropic and there is no reversal of time involved. The energy however is provided by the sun in galaxies of suns, so it is not a closed system, a requirement for the second law.

Plants however feed animals that have evolved into humans who scour the fossil and natural records for historical evidence that can provide a credible basis for an integrated framework of understanding that is all embracing. We seek a framework of understanding that transcends and subsumes the whole of history. We seek universal insight into the cosmic order that underlies the whole of creation. That insight if it is real must implicitly transcend creation. It must be a realization that is not subject to the second law of thermodynamics. The realization itself must be timeless. The patterns of change that are specified by the cosmic order are not themselves subject to change. An infinite number of clouds can form and dissipate in the atmosphere but the process by which it happens is not itself subject to change.
ben6993
1 / 5 (1) Aug 29, 2009
Time passes for us in the direction of time's arrow. And time's arrow points in the direction of increasing entropy. But is that a cause (increasing entropy) and an effect (increasing time) or is it just a correlation?

If I plunge into a cool swimming pool for a while, time does not reverse for me (though I lose heat) but continue forward for the pool (as it gains my heat)? Though if the pool is too cold I might wish I could reverse time and take the sauna instead. Is taking a sauna a fast-aging process? But undone when you cool down afterwards?

And are the scientists who are routinely making lots of observations aging quicker via gaining information? And will I age quicker if I read their analyses of observations. And will I age slower if I refuse to take any information in? Like being in a sensory deprivation chamber?

This is in the opposite direction to the relativity aspects of time where I could travel through time more slowly if I sped off at a fantastically high speed.

And, isn't heat caused by motion? If I did speed off, and slow down time relativistically, would not my heat increase and consequently speed up my passage through time too?

It looks like a non-causal correlation?
KBK
1 / 5 (4) Aug 29, 2009
Oddly enough, it has been postulated many times that dreams come to a given person in a single 'flash' (appearing the mind in a single instant) as they are postulated by more than one group or source to be recollections of a reflection of the multi-dimensional self but occur in a dimension where time and energetic flow is considerably different from here, specifically- non-entropy rules, ie 'intelligent organization' is the predominant factor, not the '3-d physical'.

Thus, when we remember a dream it comes in a 'flash' (we receive it in a backward single flash and organize it in a linear fashion but seemingly jumbled anyway) and then the important bit:

We cannot retain it.

We loose it..the same scenario outlined in this article on the given paper.

it is also postulated in some sources that we, as 'physical objects' are a creation of n intelligence that flows out of this other space. Ie, all we see is 'intelligent design from another dimension of comparable organization but not the same interactive or flow characteristics. THIS... all the mystics say and agree on, to almost a single man or group, across all recorded works on the subject.

The more powerful the creational aspects of the given 'dream', with respect to the creation of a '3-d reality' within that given OTHER space, the more we retain of the 'dream' as the creation aspect is more relative and relevant to this 'dimension'.

Food for thought.
ben6993
5 / 5 (1) Aug 29, 2009
Does this mean that in the future, when we are using quantum computers, the button to retrieve emails that you wish you had never sent will be so effective that even we will forget that we ever sent them?
Velanarris
5 / 5 (1) Aug 29, 2009
It does. It leads into crystallization or condensation, i.e. formation of system with decreased entropy content by process known as spontaneous symmetry breaking. By theory presented in article we should never remember such event - which is apparent nonsense.

Which is exactly why there is no decrease in entropy because there is an increase in information. Making your statement here:
Just the existence of "spontaneous symmetry breaking" is the evidence, entropic time arrow is in fact reversible.

completely contradictory.

Information creation is entropy. Time cannot flow backwards. Decreases in systemic entropy do not erase information, time's arrow must flow forward.
Alexa
Aug 29, 2009
This comment has been removed by a moderator.
NicoleTedesco
not rated yet Aug 30, 2009
This makes perfect sense from a "Digital Physics" perspective: http://www.digita...phy.org/

Fredkin proposed that quantum systems are reversible while in the "quantum state". The cut from quantum to classical, in fact the definition of "classical", is DEFINED BY a loss of information and an accompanying generation of heat. In his proposal energy, and in turn entropy, is DEFINED by ANY information loss event. Since information loss is by definition irreversible, and since information loss DEFINES the "classical" world, our arrow of time is (primarily) one way.

Since the machinery of human cognition, and human memory itself, is (primarily) a classical phenomenon, we perceive the arrow of time to be irreversible. If memory were a quantum phenomenon we would be able to recall events where the arrow of time ran in both directions. Even if subjective experience (qualia) is a quantum phenomenon our recollection of quantum events is unfortunately limited by classical mechanisms.
ben6993
not rated yet Aug 30, 2009
Postscript:

"And are the scientists who are routinely making lots of observations ageing quicker via gaining information? And will I age quicker if I read their analyses of observations. And will I age slower if I refuse to take any information in? Like being in a sensory deprivation chamber?"
...............................

Sorry, I was mixed up, when writing the above, in the correlation of information with entropy. Information loss is associated with entropy gain and the arrow of time. (Although information overload can make you feel you are aging too quickly, which is probably what tripped me up.)
ggg
4.5 / 5 (2) Aug 30, 2009
@dziemann, one would think this notion would be discounted but physics has shown a resilience the other way - such as string theory.

This is just more nonsense from the world of physics.

I also abandon hope with the world of physics at the notion of time travelling in two directions.
If it moves at 1 and -1 it may as well elapse at any fraction or multiple it likes unfettered even by the likes of gravity.

Makes good science fiction though.
Encourages people to get into science too.
So maybe the nonsense is necessary?
ben6993
4 / 5 (1) Aug 30, 2009
Assume that the BB universe started with zero entropy and maximum information. Loss of information is equated with increase of entropy and also with quantum wave collapse. Wave collapse is caused by interaction of a state with its environment which is not thermodynamically reversible.

If the BB universe was initially free of collapsed states then it must have interacted with something outside the BB universe to trigger that first collapse of the first quantum state to fall. (Unless there is another way to collapse a quantum state within a group of quantum states without an outside interaction?) So this is evidence of the BB being set within an outer environment, and interacting with it?


As entropy increases in the BB universe with time, does that mean that the set of superimposed states available to collapse around us is diminishing with time? Will the universe end with there being no superimposed states left to collapse?

As time is not an issue for superimposed states, are they a large pool of available states to collapse at any time, anywhere, or is there a continuity law which somehow means the availability of superimposed states is limited at a particular time and place? I.e does a superimposed state come date-stamped with its own time even though it may not not partipate in movement through time? Ie is it the passage of time which is a classical phenomenum or it is time itself?

To preserve information indefinitely it seems necessary to pass the baton on in a relay race from big bang to big bang etc. To do that we need to be observed outside the BB universe. This seems to be possible as it already may have happened at time zero.
Brimstone_Halo
4 / 5 (1) Aug 30, 2009
I guess there is always the convienient way of throwing in the possability of"Memory Loss" into the equation for the "observer" but honestly is a theory i refuse to buy into. Just like time travel...if we could truly move ahead or backwards then the point of existance would have been solved as everything has already occurred in our life and this is just residue of a past memory. If memory loss is part of the said equation than it is a theory that could NEVER be proven...I call that the "Mr Aloysius Snuffleupagus Principle" because i am a self proclaimed genius and just CAN'T see it
Velanarris
Aug 31, 2009
This comment has been removed by a moderator.
Fakeer
not rated yet Aug 31, 2009
That Bob is one devious researcher or even a pervert rummaging through Alice's lab!
Nekronomiv
5 / 5 (1) Aug 31, 2009
I don't deny the feasibility of the hypothesis but in each of these examples the author leaves out one major observer.

Entropy does not decrease for Bob since he is the one performing the experiments. Perhaps in aggregate relative to something else it may decrease but this seems to me like another example of decrease in one locality but a fundamental increase in the system as a whole.

However, the Dao tells us that with every absolute positive there is also an absolute negative and while we can only observe/comprehend a relative positive change in our interaction of time-space; to preclude an absolute negative change from existing would be a myopic view of which there is no substantial evidence.

If we consider a cyclical nature to time, it appears to always flow forward for an invested observer but to an abstracted observer, the concepts of forward and backward lose their meaning by lacking a point of reference.
Karlsbad
not rated yet Aug 31, 2009
Oh. I supposed it happened all the time. But as I lived in the entropics I wouldn't remember this sort of Devil's Triangle.

I'm up the creek without a paddle, and I still manage to splash the water backwards, but the leakage sent all my right socks into the entropic sink.

So Bob is your naughty uncle?
We must remember to keep him clear of the recycle bin.
ben6993
not rated yet Aug 31, 2009
Bob cannot complete the removal of the observation because he will forget the plot part way through the reversal procedure?

Is there any other evidence in physics of the reversal of a quantum wave collapse?

In a many-world interpretation, Bob could try to get from World A to a prior World Z, but I doubt if World Z would be available to him as it has been left behind by history. Assuming parallel worlds (or superimposed states) are in another dimension(s), each point in our spacetime would have its own set of nearest neighbour states in these other dimension(s). In other words, superimposed states may not travel through time yet they are each linked with their own specific time. Once the observation is made, classical time has moved on and the old superimposed states should not be accessible?

Re-creating and manipulating superimposed states sounds impossible, though for quantum computers to work it is just the sort of thing that is needed.
Karlsbad
5 / 5 (2) Aug 31, 2009
It's true. All right socks contain a wee bit of dark matter, which not only makes them scarce, but decreases their local entropy in the dryer, so as to erase any hope of entangled pairs.
JukriS
Sep 01, 2009
This comment has been removed by a moderator.
Myria83
2.5 / 5 (2) Sep 01, 2009
There was a young man who said "God
Must find it exceedingly odd
To think that the tree
Should continue to be
When there's no one about in the quad."
"Dear Sir: Your astonishment's odd;
I am always about in the quad.
And that's why the tree
Will continue to be
Since observed by, Yours faithfully, God."

(Berkeley's thought experiment summarized in a limerick by Ronald Knox)
ben6993
1 / 5 (1) Sep 01, 2009

FREE WILL v BOB

The extract below concerning free will is taken from:
http://medgadget....all.html
(April 2008)


"In contrast, Haynes and colleagues now show that brain activity predicts even up to 7 seconds ahead of time how a person is going to decide. But they also warn that the study does not finally rule out free will: "Our study shows that decisions are unconsciously prepared much longer ahead than previously thought. But we do not know yet where the final decision is made. We need to investigate whether a decision prepared by these brain areas can still be reversed.""



But now we know who is making the'final decisions' and why we do not have, apparently, a free will!!! Bob is manipulating events unbeknown to us during those seven seconds...

(NB I am writing this as a joke, I think, .... or is it Bob again?)
Myria83
1 / 5 (1) Sep 01, 2009
Mutatis mutandis, is Bob a sort of Maxwell's demon?
Sour
1.7 / 5 (3) Sep 03, 2009
Perhaps the reason there's a paradox is because the "basic understanding" of things such as entropy are wrong and have just been around so long that they're taken for granted.

New rule: If your theory results in a paradox your theory is wrong. If your theory being wrong disproves a long held theory (or even a law) then it must be wrong also.
GPhillip
not rated yet Sep 03, 2009
For those who have had more information theory than thermodynamics, if I record my favorite band, ZZ Top, on a blank CD, I have decreased the entropy of the CD, locally, at the expense of the electricity used and the waste heat generated. I have not locally reversed time. The entropy decrease is a result of time reversal (returning to a more ordered state, not a cause. If time reverses, entropy must decrease, but just because entropy decreases doesn't mean time must reverse.

This is the reason we could never remember the future. Even if we experienced it, everything has returned to the more ordered state of the past, before that memory was formed.

As far as the thought experiment of corrolating two particles and moving one into the past, and would they still be corrolated? I can see teo answers. One is they would still be corrolated since QM doesn't care about their location in the dimension of time (it's not in the equations). The other answer is they would not be corrolated, since one particle has moved into the past, before the corrolation occured, so once one particle moves to a point ion time to before they were corrolated, they are no longer corrolated. Perhaps someomne else has an opinion on this thought experiment?
Velanarris
2 / 5 (4) Sep 04, 2009
The entropy decrease is a result of time reversal (returning to a more ordered state, not a cause. If time reverses, entropy must decrease, but just because entropy decreases doesn't mean time must reverse.

This is correct. This is the only observationally functional explaination. In addition to working perfectly with observation, it creates a methodology by which to explain time.
GPhillip
2 / 5 (1) Sep 04, 2009
With respect to Myria83's little limerick, QM answers the question, if a tree falls in the woods and no one is there to hear it, does it make a sound? QM says no. If no one observes the event, then it is not an event, it is just a probability of the event happening.

If the tree falls (a probability of an event occuring) but no one is there to observe it, the quantum waveform of the probability cannot colapse, so the sound it would make is just a probability of a sound, not an observed sound itself.

Now ask yourself, if a rabbit observes the tree fall, does it make a sound? The answer is no. The observation must be by human, or at least an intelligent sentient creature capable of analyzing the cause and effect relationship of the tree falling and the sound it makes. Sorry rabbit, QM is for humans, not for rabbits.

So how about a baby, incapable of analyzing the situation and communicating the results? Nope, sorry, in QM babies don't count anymore than rabbits. How about a two year old human, just barely able to communicate, "Tree fall, big noise!". Yep, the toddler just coplapsed the quantum probability wave and the event occured. This is all in agreement with experimental evidence and the math of quantum mechanics.

Welcome to the world of quantum wierdness. Cool, eh? Embrace it. It's really the greatest of fun!
ben6993
5 / 5 (1) Sep 04, 2009
If it were true (is it?) that "an intelligent sentient being" is required to collapse a wave function, then that would be a good alternative test (alternative to the Turing test) of a sentient being. How to distinguish between a computer and a sentient being? Only a sentient being can collapse a wave function? But is that correct?
macrumpton
not rated yet Sep 04, 2009
This seems to imply that parts of the past can be undone. Wow, with the right combination of events Al Gore can have been elected president in 02. This is worthy of more research.
macrumpton
5 / 5 (1) Sep 04, 2009
If it were true (is it?) that "an intelligent sentient being" is required to collapse a wave function, then that would be a good alternative test (alternative to the Turing test) of a sentient being. How to distinguish between a computer and a sentient being? Only a sentient being can collapse a wave function? But is that correct?

How would you determine the result of a test of this without a sentient being to evaluate it?
ben6993
not rated yet Sep 04, 2009
How would you determine the result of a test of this without a sentient being to evaluate it?
- - - - - - - -

A good question.

Put a computer in the box with Schroedinger's cat. The cat is alive when the box is sealed. The computer is equipped with sensors to determine the time of death of the cat. After a while open the box. Repeat this experiment until the box is opened and the cat has died.

Do we trust the computer reading if it (say) indicates that the cat died two hours ago? We can do an autopsy to confirm time of death at two hours ago. Will we then assume that the computer collapsed the quantum waves two hours ago? Or will we think that the waves did not collapse until we opened the box? Can the cat die in the box without us observing it?

The time may come when computers are more intelligent than us, with more senses, faster etc. Like HAL, in "2001". It may be difficult to convince them they are not sentient. It may also be difficult to convince the super-intelligent computers that we humans are sentient, while we maintain that they are not.

In the many-worlds interpretation, I believe, we would not need a quantum wave collapse. We would assume under that interpretation that the particular world we find ourselves in has a dead cat which died two hours ago. We would have to rely on the continuity of spacetime and the continuity (or is that contiguity?) of the neighbouring quantum superpositions to keep the cat dead and not oscillate between alive and dead in the various worlds/superpositions. It would be unsettling if the many-worlds interpretation were true and the cat oscillated between life and death before our very eyes. I suppose such oscillations could happen from one Planck time interval to the next, as death is also difficult to define. But after a run of deadness for one second's worth of Planck intervals it would be virtually impossible to have a nearest neighbour world to move to in which the cat was alive. (After one second we could be up to 10 to the power 43 worlds away from the time when the cat was last alive.)
Slotin
3.4 / 5 (5) Sep 05, 2009
It's very simple. Like acceleration, there is no negative. There's no such thing as negative entropy because any change in the system results in change in and of itself. To have negative entropy implies that you can "undo" time, and as the abstract states above, you would have to remove energy and information from existence, violating the conservation principles. Simply put, time's arrow does not flow backwards.
Acceleration can indeed be negative and it's called deceleration, after then. Entropy can be negative and it's called a negentropy after then. Here are many spontaneous negentropic processes in Nature, for example inside of gravitating systems. You should learn some physics first and the guys, who valued you by five points as well.
ben6993
5 / 5 (1) Sep 05, 2009
P.S.

"How would you determine the result of a test of this without a sentient being to evaluate it?"
- - - - - - - -

And how does the quantum wave itself detect that it is being observed by a sentient being, rather than by a non-sentient, and therefore know that it must/may collapse? Either (1) a wave collapse has nothing to do with physical properties of spacetime or (2) a wave collapse does not really need a sentient observer? Or ...?
Velanarris
1.8 / 5 (5) Sep 05, 2009
Acceleration can indeed be negative and it's called deceleration, after then.


Entropy can be negative and it's called a negentropy after then. Here are many spontaneous negentropic processes in Nature, for example inside of gravitating systems. You should learn some physics first and the guys, who valued you by five points as well.




In physics, deceleration is still a change in rate of speed. Meaning it is acceleration with a negative value. This does not equal "negative acceleration". You sir, are the one who will need to spend more time with the physics books.

Slotin
3.4 / 5 (5) Sep 05, 2009
...acceleration with a negative value.. does not equal "negative acceleration".
LOL.. Just show us hyperlink to documented example of "negative acceleration" with positive value and/or positive acceleration with negative value to prove your stance.
Zeta
5 / 5 (1) Sep 05, 2009
Correct me if I'm wrong (I may be oversimplifying things) but acceleration is simply the rate of change in velocity, isn't it? Unless you're changing reference frame in the middle of a calculation, then negative acceleration occurs any time the instantaneous rate of change in velocity is negative (ie, the velocity is decreasing). You can call that "positive in another direction" but you've arbitrarily changed your reference frame, which makes Newton and Einstein cry.

The only way I can see negative acceleration not existing is if someone is talking about "reverse acceleration" where objects fly towards forces acting against them, as would appear to occur if time were (magically) reversed. That isn't "negative" though, and it's a poor word to slap onto a reversed process. The sign is still the same, the activity differs, which isn't "negative" at all!
Velanarris
1.6 / 5 (7) Sep 06, 2009
...acceleration with a negative value.. does not equal "negative acceleration".
LOL.. Just show us hyperlink to documented example of "negative acceleration" with positive value and/or positive acceleration with negative value to prove your stance.


The formula for acceleration is a=F/m. Since you can't have negative mass, or negative force your A must be positive. Welcome to the world of physics. Enjoy your stay, but check your AWT at the door.
Alexa
3.4 / 5 (5) Sep 06, 2009
The formula for acceleration is a=F/m
This is formula for "inertial acelleration" only and force can indeed become negative depending on choice of reference frame. Definition formula for acceleration is a = dv/dt. Now I'm expecting your comments. Anyway, it's apparent, you're a crackpot by now without further arguments.
Velanarris
2 / 5 (4) Sep 07, 2009
The formula for acceleration is a=F/m
This is formula for "inertial acelleration" only and force can indeed become negative depending on choice of reference frame. Definition formula for acceleration is a = dv/dt. Now I'm expecting your comments. Anyway, it's apparent, you're a crackpot by now without further arguments.

Ha. Well your army of downrank clones will surely make that appear so.

Enjoy your ignorance.

Just out of curiosity, aren't deltas an absolute value in your Newtonian physics?

Oh yes, they are.
AlIIII
not rated yet Sep 08, 2009
What big crunch? The universe is speeding up. You know dark matter and all.
MorganW
4 / 5 (1) Sep 08, 2009
This is silly. Remember Sensitive dependence on initial conditions from Chaos Theory? You're telling me that you can reverse the arrow of time on a broken glass as easily as a hurricane? And WITHOUT increasing entropy? Not in THIS dimension! Maybe if you're using FM Technology (I can't tell you what F stands for but M is for Magic).
You might convince me that you can go backward in time, but you can't undo what's been done. I know this because my wife tells me so all the time... ;)
Alexa
2.7 / 5 (7) Sep 09, 2009
..you can reverse the arrow of time on a broken glass as easily as a hurricane? And WITHOUT increasing entropy? Not in THIS dimension!
You can heat cracked glass on transformation temperature and you would see, how tiny cracks are healing spontaneously. Voila! A negentropic process mysteriously occurs here. Under prolonged heating glass would even start to crystallize.
Velanarris
2.3 / 5 (3) Sep 10, 2009
..you can reverse the arrow of time on a broken glass as easily as a hurricane? And WITHOUT increasing entropy? Not in THIS dimension!
You can heat cracked glass on transformation temperature and you would see, how tiny cracks are healing spontaneously. Voila! A negentropic process mysteriously occurs here. Under prolonged heating glass would even start to crystallize.

And this has zero to do with entropy.

You're lying in bed. You get up, shower, and go to work. When you get home and lay back down in bed, the day still happened. Regardless of what transformation mechanism you want to use the change never unhappens. It can't unhappen. Return to original state is not "negentropy". Removal of information doesn't happen. There's no such thing as negentropy on any scale from any frame of reference. Information cannot be destroyed.
Slotin
1 / 5 (1) Sep 10, 2009
There's no such thing as negentropy on any scale from any frame of reference. Information cannot be destroyed.
Negentropy is abstract stuff, in the same way, like entropy. I didn't invented this stuff.

http://en.wikiped...gentropy

Entropy is connected with destroal of initial information about system - so when you claim, information cannot be destroyed, you're just opposing 2nd law of thermodynamics and your previous sentence about negentropy, in fact.

All these controversies are illustrating, you're anonymous troll, which cannot be taken seriously - sorry.
Velanarris
1 / 5 (1) Sep 10, 2009
What are you talking about? There's no destruction of information in the second law. Secondly and perhaps this is translation error on your part, but abstract typically is exactly that, a journey of fantasy. Your link states exactly what negentropy is. It's syntropy. The removal expenditure of energy in a system as transmitted to a larger system. This is also known as localized negative entropy and is not congruent with the scope of our discussion.

You take pot shots at my credentials when all you can provide is "One can imagine" instead of "One can observe". I'm no anonymous troll, I simply don't accept that "AWT" is even marginally accurate to describe anything other than what you fill your slack time with at work.



Slotin
Sep 12, 2009
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Velanarris
Sep 13, 2009
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Alexa
Sep 13, 2009
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Alizee
Sep 13, 2009
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Alexa
Sep 14, 2009
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