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Archive 1 |
This looks like something that the editor read somewhere, but didnt quite understand, and somehow avoided actually describing the basis for this analogy between the workings of the brain and the workings of universe being somehow related in physics. In describing a theory (perhaps valid, but why unattributed?) as to how our perception of time may be related to time via the analogy of work, the meaning of "work" here is far too general. In the end the idea seems to rests upon a notion that the expense of brain energy is somehow equivalent or related to an "expense" of temporal inertia, which in and of itself doesnt seem to hold water, regardless of the problems with the second part. - S V 23:06, 27 Sep 2004 (UTC)
"It is not impossible for the molecules in the large container to separate out, just so very unlikely as to never actually happen – even if given the lifetime of the Universe to do so. The liquids start out in a highly-ordered state and their entropy, or their disorder, increases with time."
If it's not impossible, it's possible. This section is self-contradictory, pick one side or the other.
I am removing the following statement
" Like gravity most physical laws can be described by relatively simple mathematical equations (momentum can be described as F=ma for example), and most mathematical operations are reversible (if you multiply a value by a number you can take the result and divide it by the same number to obtain the original value). So it is no suprise that most physical processes are also reversible and that most laws are symmetrical. The fact that there are exceptions the symmetry is one of the greater mysteries that science is currently exploring. "
as it seems to be a mostly meaningless, somewhat misleading collection of words (I started out by correcting misspeled word "mathematical", but then realized that the whole thing is beyond repair). Indeed: "most physical laws can be described by relatively simple mathematical equations" - is this even a statement? Simple relative to what? Is an example of simple? How about equations of motion in Lagrange form, are they simple? Is Hamiltonian approach simple? Are forces, or fields simple, are classical dynamical systems simple? The adjective most, this indeterminate quantifier, that we'll soon see again and again, effectively nullifies the argument. For, you see, until 1956 or so, not most, but all known laws of physics appeared to be T-invariant. The violations are pretty damn rare. Much more so, than "relatively complicated" physical laws...
Next, saying "momentum can be described as F=ma" is an awkward way to express an idea at best, for momentum (as well as coordinates, for example) is indeed contained in the equation, but indirectly, and what the equation is normally describing is, depending on what's given, is either force or acceleration. Of course.
Then there is a claim that most (again!) mathematical operations are reversible. Now what does this mean? Most by what measure? Finally, an extraordinary assertion is made that since "most" functions are bijections (right?), "it is no suprise that most (Ah!) physical processes are also reversible". Now, the claim that it is no surprise indicates, to me, an unsubstantiated POV, at best, a completely misleading analogy at worst.
Moreover, it's pure idealism. Fact of the matter is, that the laws of classical mechanics (and also Electromagentism, Special and General Relativity, and Quantum Electrodynamics) -- in any form, simple or not, for form is irrelevant here, we are talking substance -- appear, as a result of an observation, a posteriori, to possess certain symmetry, which is expressed mathematically not by reference to arbitrary invertible transformation, but very precisely: as a symmetry of all of the laws above w.r.t time reversal. This invariance, and again, a posteriori, appears not to be a universal law of nature, which is most spectacularly seen in CP-violation (that, due to CPT invariance, implies T-violation). It's fine to apply mathematics to look for an underlying reason for T-symmetry being so pervasive, being violated so ever slightly and (as far as I know) only in the weak interactions. But "reversibility" of "most mathematical operations" has nothing to do with the issue. It's fruitless pseudomathematical mysticism (formally, a POV). A claim that the time symmetry of (most of) the physical laws could be known a priori is simply factually false. Isn't it?
But, if you disagree, by all means, just put the piece back to the article. I just wanted to explain that I have no intention to vandalize it. To the contrary, I think it has already suffered enough... Feodor 22:38, 24 January 2006 (UTC)
I've come across some entries for a few books which may be applicable to this subject, but as I haven't seen the books I can't say for definite. They are:
Mike Peel 19:05, 13 April 2006 (UTC)
Sorry if the question is silly, but while it is true that I never saw a broken plate come together spontaneously, I have also never seen a stone going up spontaneously. Does it mean that the law of gravity is also irreversible, just as the law of entropy ? Can we use the fall of objects to infer the arrow of time ? Or is there something more to it ? Would it be useful to clarify this in the article ? Pcarbonn 11:25, 20 May 2004 (UTC)
Thanks ! I think I've got it. The fall, i.e. the conversion of potential energy to kinetic energy, is indeed reversible. What is not reversible is the stop of the fall, i.e. the conversion of mechanic energy to heat. This is what the second law of thermodynamics says, and that's why I have never seen a stone go up...
I guess I still don't get it. Gravity is always attractive in the forward direction of time, and always repulsive is the reverse direction. I guess electric charge can be either attractive or repulsive in both directions, but what about the other forces? Why isn't the irreversibility of attractive force as important to the arrow of time as entropy? -- Jackdavinci 18:23, 5 August 2006 (UTC)
The past is memory, the future is anticipation, now alone is real Saint Augustine.
Awareness is a present moment function which compares what seems to be experienced externally to what is being experienced internally. The difference attributed to an experience identified as memory is called the past. The psychological future, like a projection in a mirror, makes what is behind such as expeirences, anticipations, desires, dreams, hopes, and goals, seem ahead of the observer. The ability compare novel experienced events and imagined events to countable repeating events and chart them is called time. The consistant increase in memorable novel experiences creates the psychological illusion of an arrow of time since no current experience seems totally indentical, to any prior one and no retracing or reversing of even a single moment of the universe in total is ever noticed. Since the universe seems to be expanding it seems impossible for any current experience to be anything like a prior one since all prior experiences have an apparently smaller universe in total. Jiohdi 15:27, 3 September 2006 (UTC)
Missing references is probably the major weakness of the whole article. I have made a start by citing a reference news article for my recent addition to the section on the psychological/perceptual arrow of time. I hope this will prompt other users to do likewise. DFH 19:55, 26 September 2006 (UTC)
It is said in the article that such motions are reversible. There are 2 or more problems here. One is that chaos may be present, so that over a sufficiently long time, the orbits will have a divergence from each other that is so sensitive to initial conditions it is impossible to predict which set it the right one. (see Lyapunov Exponent). Another is that there are many small bodies present, from asteroids down to meteorites and even dust, that make it impossible to work backwards, and even make forward predictions diverge initially by meters a year, and eventually in a Lyapunov manner (exponentiallyI. See Standish E. M., and Fienga A.: 2002, Accuracy limit of modern ephemerides imposed by uncertainties in asteroid masses. Astron. and Astrophys, 384, 322 Carrionluggage 04:29, 29 September 2006 (UTC)
Where does the excessive energy of biological evolution comes from ? doesn't the oredered state of things now ,as opposed to less orederly in the past contradicts the second law of thermodynamics? where does the system draw it's "order" from ? what is it that becomes less ordered as biological system evolve? Diza 09:26, 8 December 2005 (UTC)
Actually biological system can introduce even more disorder. E.g. cow by eating grass destroys more order (enclosed in the grass) then creates new order (in a form of own tissues and giving birth to new cows). It is not true of the grass so. If there no grass whole solar energy will be absorbed by the soil and dissipated into the heat. The grass uses part of it build itself and create the order.
Diza 18:25, 16 December 2005 (UTC) Narutally all the excessive energy for the functions of life comes from the sun's rays,This cpudl be the answer. So all of the order that has been built in the whole history the biological evolution could be explained the the sum of all dicipated heat from the planet ? this still bugs me. becasue there are other plantes. maybe one could say the biological system CONCENTRATE their order in one location ,so that they have a higher order density.
We (any inertial reference frame) always have non-zero complex speed vector in Minkowski space with constant norm c ( speed of light in vacuum). The unit vector of that vector is our (that inertial reference frame's) Arrow of time.
In other words, even if we don't notice that while apparently at rest, we are always moving along our world lines toward the future with maximal (and minimal..., in fact only possible one) speed c.
I am aware that this, of course, is a circular definition, but it perhaps sheds some more light (or casts some more shadow, whatever) on the notion. As much as there is no absolute time, there also isn't neither any absolute Arrow of time nor absolute rest.
I add a unreferenced verification template stamp to the section about the radiative arrow of time since it seems to me to be very vague about what experiments it refering too in the sentance "This arrow has been reversed in carefully worked experiments".
I felt like one of the experiment is was implying was time-reversal of electrodynamic wave involving nonlinear optics (aka what wikipedia calls "optical phase conjugation"). Now would be a good time to read on optical phase conjugation at http://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase_conjugation . Especially note that 100% reflective mirror have never been made, so this mean that the phase conjugate beam is a fraction of the source beam. Hence, there is a energy loss during optical phase conjugation, which I believe but am not 100% sure can be interpreted as an increase in entropy. Thus I did not want to suggest optical phase conjugation since it may not violate the second law of thermodynamics.
However, if not optical phase conjugation then what experiment does the article mean? —Preceding unsigned comment added by 68.214.39.193 ( talk) 20:24, 8 May 2009 (UTC)
== Removing Unclear Paragraph ==Consequently unless a native Chinese person can support the contention that these meanings somehow cause the Chinese to view time differently I think they are just artifacts of the differing usage of words like 'behind', 'after' 'front' in different languages. —Preceding unsigned comment added by 114.77.67.48 (talk) 09:05, 6 August 2009 (UTC) I'm removing this paragraph (emphasis added)
I think that there may be an interesting point in there, but it's not presented clearly. Anyone know how to clean it up? 20:09, 24 March 2006 (UTC)
It is now written in the article:
This seems to me total nonsense, in more ways than one. First, there is a powerful tradition in the literature which says that memory erasure equals entropy increase. (Landauer and Bennett come to mind, see the final chapter of my http://philsci-archive.pitt.edu/archive/00002201/ ) This is the exact opposite of what the current article says, since it equates memory creation with entropy increase. This is strange. (It is also proof of the rampant confusions surrounding the notion of entropy!)
Second, the notions of "memory" and "correlation" used here must be made much more specific before the claim can even be understood. In a deterministic Hamiltonian world, any time slice of the Universe implies its state at all other times; no correlations can form which do not already exist at the outset. If an indeterministic (but still unitary!) quantum mechanics somehow changes this, tell us how. As it stands, the claim that "the Second Law of Thermodynamics is equivalent to the growth with time of such correlations" seems to me at least unclear and probably false.
Third, even if the physics and the information theory is sorted out, it is still not clear that the psychological arrow is linked to the thermodynamic arrow. We don't form memories of the future when we temporarily lower the entropy of our brain (for instance, by sticking our head in a fridge). If there is a link, it needs to be argued for in much more detail.
Fourth, the article claims that the psychological arrow "is thought to be reducible" to the thermodynamic arrow. Thought by whom? This is again too vague. Victor Gijsbers ( talk) 16:51, 18 June 2009 (UTC)
"This arrow has been reversed in carefully worked experiments which have created convergent waves": I recall reading something about this years ago, probably in Scientific American or Physics News Update. IIRC, these waves were emitted from a source and reconverged onto it. Paradoctor ( talk) 02:53, 28 January 2010 (UTC)
This section have been in the article at least since 2006, but it contains no reference to published sources or citations. -- Dc987 ( talk) 06:02, 5 November 2009 (UTC)
{{cite book|author=P. C. W. Davies|title=The physics of time asymmetry|url=http://books.google.com/books?id=9saLoa7by8oC&pg=PA154|accessdate=1 June 2010|year=1974|publisher=University of California Press|isbn=9780520028258|pages=154–184|chapter=6 Time Asymmetry in Quantum Mechanics}}
"There is a close analogy between the destruction of microreversibiliy in the classical system by coupling to the outside world stochastically through the walls of the container (see section 3.5), and the same destruction in a quantum system due to external coupling with the 'measureing apparatus'." p.168
"...the quantum system under observation is capable of changing in two distinct ways: (1) reversibly during the normal evolution of the system as described by the Schrödinger equation, (2) irreversibly during the measurement process, which cannot be described by the Schrödinger equation." p.170
"[Thermodynamic metastability] is an indispensable prerequisite for amplification of the quantum signal which triggers the [macroscopic measurement] apparatus. As a result of this amplification, the apparatus proceeds fairly rapidly to a stable equilibrium condition, which is correlated with the initial state of [the microscopic observable], and is macroscopically distinct from its neighbour states which are correlated with different states of [the microscopic observable]. Such amplification obviously involves a coarse-grained entropy increase (though not fine-grained). Thus, although the nature of quantum measurement irreversibility depends on coherence times of macroscopic systems, the origin of the irreversibility lies squarely in the domain of thermodynamics (as in the Everett interpretation), which in turn is related (as described in chapters 3 and 4) to the formation of branch systems, and ultimately to the origin of the universe, and the nature of gravity." p.174
Would any of these work?— Machine Elf 1735 ( talk) 12:54, 1 June 2010 (UTC)
... well... that feels like speculation, rather than hard science. True, very likable speculation, but... -- Dc987 ( talk) 08:11, 3 June 2010 (UTC)"although the nature of quantum measurement irreversibility depends on coherence times of macroscopic systems, the origin of the irreversibility lies squarely in the domain of thermodynamics (as in the Everett interpretation), which in turn is related (as described in chapters 3 and 4) to the formation of branch systems, and ultimately to the origin of the universe, and the nature of gravity."
I found the article referenced for the Andean tribe seeing time "backwards" quite interesting, but its only mention of the Chinese perspective is that they specifically are NOT an exception to the usual rule. I think we DEFINATELY need a citation for the Chinese claim, for as the above article itself mentions, words can be very tricky and misleading when trying to pin down what people really think from them, including a few odd examples of english seeming backwards in much the same way as these Chinese examples do... Elgaroo ( talk) 16:32, 5 August 2008 (UTC)
I agree. The Chinese words may not be sufficient to attribute different cultural ideas of time. For example:
The Chinese word for 'day after tomorrow' 后天 hou tian does literally mean 'behind day' but it could be interpreted to mean that the 'day after tomorrow' is chronologically behind today just as the number 4 is behind the number 3 on a number line.
The Chinese word for 'day before yesterday' 前天 qian tian does literally mean 'front day' but it could be interpreted to mean that the 'day before yesterday' is chronologically in front of today just as the number 3 is in front of the number 4 on a number line.
Consequently unless a native Chinese person can support the contention that these meanings somehow cause the Chinese to view time differently I think they are just artifacts of the differing usage of words like 'behind', 'after' 'front' in different languages. —Preceding unsigned comment added by 114.77.67.48 ( talk) 09:05, 6 August 2009 (UTC)
The article states that it often appears that there is "an obvious direction (or flow) of time." The words "(or flow)" should be removed. The arrow of time refers to an asymmetry of the universe with respect to time, and perhaps to some other flows with respect to time, but not to any flow of time itself.
Flow in relation to what?
Psychologically, and experientially, there is a present moment, and this moment changes, but this is not an objective phenomenon. Objectively, a moment in time is considered past, present, or future only in relation to other moments, and there is nothing dynamic about those relationships. Thus no flow. Certainly our experience of a dynamic universe is often modeled as though our awareness moves through time, but this is an apparent flow of awareness through time, not a flow of time itself. Poetically, time is the stream bed through which the stream of our awareness flows.
This movement of awareness (i.e. the seemingly dynamic character of our experience) cannot be a function of objective facts about the universe except as a kind of illusion because the objective facts about all particular points in space-time are fixed, indeed the objective facts are what define space-time. Lest I be misunderstood, I do not hold that our experience is an illusion, only that if it isn't an illusion then no objective description of reality can be complete.
Even if we take it that our awareness only apparently moves forward in time, in the direction of the arrow, then the flow of time with respect to our awareness would be in the opposite direction—not with the arrow of time but against it. So the reference to the flow of time in the article is less than helpful.
It is like thinking of the arrows on a one-way street as being the direction that the street moves. Mazzula ( talk) 15:48, 15 March 2011 (UTC)
Regarding the statement: :If this arrow of time is related to the other arrows of time, then the future is by definition the direction towards which the universe becomes bigger. Thus, the universe expands - rather than shrinks - by definition. on the section on Cosmological Arrow of Time.
I think the term "related to" is pretty vague and I cannot see how the relationship would require the universe to be expanding (positive scale factor)?
Indeed, the fact that negative energy has not been observed is suggests that the universe seems to be populated entirely with objects that travel in one direction in time, regardless of the reversibility of their interactions. That is in my opinion a more fundamental property.
-- Jallberg ( talk) 17:30, 16 July 2011 (UTC)
This uncited statement completely and utterly threw me off. What I find confusing here, is that the example reverses time in a single case of the cause and effect, without reversing the entirety of cause and effect. I've always considered reversing cause and effect to be quite simple - in a "backwards" perception of time, cause follows effect, leading to a decrease in entropy. Floors don't throw cups, but time-reversed gravity pushes things up. So instead of cause = hand opening | effect = falling cup, you have rising cup "causing" the hand to open. Therefore the property that causes scattered pieces to form a cup are the very same forces that hold the cup together as a solid until the moment it hits the ground. The causal relationship already 'cannot be perceived' forwards, and it makes no more or less theoretical sense backwards. For an example, centrifugal force does not become centripetal force purely because you looked at in the order of cause following effect. gmip Talk 13:49, 1 November 2011 (UTC)
Though the main article focuses on scientific aspects of the arrow of time, it seems odd that there is not even a passing reference to any teleological aspect. For theists this must surely be an important philosophical/ theological consideration. Moreover, even science itself used to be known as natural philosophy. Many other articles in Wikipedia treat difficult theological and philosophical ideas with a fair degree of competence. For example, the articles on predestination and determinism – which, by the way, are not the same thing – so I would suggest that there is a gap in this page that needs filling. For the time being, I am content merely to draw this to your attention. DFH 16:27, 23 September 2006 (UTC)
I've tentatively removed the citation BinaryPhoton added to what appears to be his own paper, which was recently published in what is (as far as I can tell) a very low-impact journal. (I'm in no position to judge the scientific merits of the paper itself, though I can say that the style of it doesn't resemble any peer-reviewed journal article I've ever read.) The sentence to which this editor has added the citation long predates his paper; surely if the claim needs a citation at all then it had better be to the paper in which it was first advanced, or to a secondary source which summarizes the past research. — Psychonaut ( talk) 12:22, 27 June 2012 (UTC)
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"Quantum uncertainty then gives rise to entanglement, the putative source of the arrow of time.
The idea that entanglement might explain the arrow of time first occurred to Seth Lloyd about 30 years ago, when he was a 23-year-old philosophy graduate student at Cambridge University with a Harvard physics degree. Lloyd realized that quantum uncertainty, and the way it spreads as particles become increasingly entangled, could replace human uncertainty in the old classical proofs as the true source of the arrow of time." Here [1] is more in the article. Kartasto ( talk) 18:07, 12 August 2014 (UTC)
How come, if Lochschmidt's paradox is resolved by the Fluctuation theorem, the problem of the arrow of time is not? i.e. how do these two actually differ?
Does inflation explain why entropy is not maximized in our universe?
Most possible worlds have higher entropy. Although each decoherence event is reversible, most possible events increase entropy. Isn't that the basis of the seond law? Fairandbalanced 04:16, 10 Oct 2003 (UTC)
There are websites that indicate that entropy and disorder are the same (ie. as described on this wiki page); and there are websites that indicate that they are not the same; and there are websites that say disorder in the entropy sense is not the same as disorder in the widely used sense. Please clarify.
I support your main point but not your example -- linking temperature and "hotness" is misleading. Temperature is akin to the amount of motion in a confined space i.e. add energy, get more particles moving faster = higher temperature. That we perceive that as "hotness" on our skin or so forth is secondary, which is why you were able to find examples of equivalent temperature with different perceived "hottness" levels -- we assume. For entropy, think complexity vs. simplicity. It takes energy to build up ordered or complex forms and maintain them -- on the macro level -- thus, over time's forward arrow, you get less complexity... whether the heat death of the universe, the destruction of complex atoms into simpler forms, or eventually just the end of matter itself. Chesspride
66.19.84.2 (
talk)
07:33, 28 February 2015 (UTC)
Would a manifold explain — Preceding unsigned comment added by 184.17.111.128 ( talk) 01:09, 19 September 2013 (UTC)
I think this is irrelevant
Roadrunner 05:53, 31 May 2004 (UTC)
hey — Preceding unsigned comment added by 124.83.11.178 ( talk) 02:30, 14 July 2015 (UTC)
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Glaringly missing from this page. Some calculations are not reversible. Suppose that a computer accepts two inputs and adds them together. The result is 42. The inputs are erased from memory. There is no way to tell whether the numbers were 21 and 21 or any other particular combination. The past state of the machine cannot be computed from the present one.
It may be in fact this arrow to which the others are hinged.
Even in a totally deterministic universe, there can be a forward time arrow.
Suppose that a cup falls on the floor and breaks in a deterministic universe, resulting in a spill, fragments and various artifacts of the dissipation of energy such as vibrations and heat.
That result is like the number 42 in the earlier example. More than one pattern of fall of more than one cup could produce exactly the same results. If time is reversed, there is no way to get to the past state because, for instance, if any future state depends on addition calculations over the previous state, we run into the problem that sums cannot be decomposed into the original terms. The information is simply not there. The broken cup pieces can be reassembled into more than one cup because of ambiguities. As soon as we find two cup fragments which have an identical shape, but are distinguishable (by some surface imperfection, marking or embedded inpurity), it means that we do not know which of two possible cups were broken. Perhaps the place where those pieces landed could tell us, but that itself could be subject to ambiguities.
The basic idea is that the universe is based on processes and processes irretrievably replace previous states with new states which do not contain enough information to unambiguously recover the previous states.
192.139.122.42 ( talk) 01:39, 20 November 2012 (UTC)
— Preceding unsigned comment added by 2A02:2149:8454:7C00:B5E4:9F1C:7F91:538D ( talk) 05:30:11, 25 December 2017
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
This looks like something that the editor read somewhere, but didnt quite understand, and somehow avoided actually describing the basis for this analogy between the workings of the brain and the workings of universe being somehow related in physics. In describing a theory (perhaps valid, but why unattributed?) as to how our perception of time may be related to time via the analogy of work, the meaning of "work" here is far too general. In the end the idea seems to rests upon a notion that the expense of brain energy is somehow equivalent or related to an "expense" of temporal inertia, which in and of itself doesnt seem to hold water, regardless of the problems with the second part. - S V 23:06, 27 Sep 2004 (UTC)
"It is not impossible for the molecules in the large container to separate out, just so very unlikely as to never actually happen – even if given the lifetime of the Universe to do so. The liquids start out in a highly-ordered state and their entropy, or their disorder, increases with time."
If it's not impossible, it's possible. This section is self-contradictory, pick one side or the other.
I am removing the following statement
" Like gravity most physical laws can be described by relatively simple mathematical equations (momentum can be described as F=ma for example), and most mathematical operations are reversible (if you multiply a value by a number you can take the result and divide it by the same number to obtain the original value). So it is no suprise that most physical processes are also reversible and that most laws are symmetrical. The fact that there are exceptions the symmetry is one of the greater mysteries that science is currently exploring. "
as it seems to be a mostly meaningless, somewhat misleading collection of words (I started out by correcting misspeled word "mathematical", but then realized that the whole thing is beyond repair). Indeed: "most physical laws can be described by relatively simple mathematical equations" - is this even a statement? Simple relative to what? Is an example of simple? How about equations of motion in Lagrange form, are they simple? Is Hamiltonian approach simple? Are forces, or fields simple, are classical dynamical systems simple? The adjective most, this indeterminate quantifier, that we'll soon see again and again, effectively nullifies the argument. For, you see, until 1956 or so, not most, but all known laws of physics appeared to be T-invariant. The violations are pretty damn rare. Much more so, than "relatively complicated" physical laws...
Next, saying "momentum can be described as F=ma" is an awkward way to express an idea at best, for momentum (as well as coordinates, for example) is indeed contained in the equation, but indirectly, and what the equation is normally describing is, depending on what's given, is either force or acceleration. Of course.
Then there is a claim that most (again!) mathematical operations are reversible. Now what does this mean? Most by what measure? Finally, an extraordinary assertion is made that since "most" functions are bijections (right?), "it is no suprise that most (Ah!) physical processes are also reversible". Now, the claim that it is no surprise indicates, to me, an unsubstantiated POV, at best, a completely misleading analogy at worst.
Moreover, it's pure idealism. Fact of the matter is, that the laws of classical mechanics (and also Electromagentism, Special and General Relativity, and Quantum Electrodynamics) -- in any form, simple or not, for form is irrelevant here, we are talking substance -- appear, as a result of an observation, a posteriori, to possess certain symmetry, which is expressed mathematically not by reference to arbitrary invertible transformation, but very precisely: as a symmetry of all of the laws above w.r.t time reversal. This invariance, and again, a posteriori, appears not to be a universal law of nature, which is most spectacularly seen in CP-violation (that, due to CPT invariance, implies T-violation). It's fine to apply mathematics to look for an underlying reason for T-symmetry being so pervasive, being violated so ever slightly and (as far as I know) only in the weak interactions. But "reversibility" of "most mathematical operations" has nothing to do with the issue. It's fruitless pseudomathematical mysticism (formally, a POV). A claim that the time symmetry of (most of) the physical laws could be known a priori is simply factually false. Isn't it?
But, if you disagree, by all means, just put the piece back to the article. I just wanted to explain that I have no intention to vandalize it. To the contrary, I think it has already suffered enough... Feodor 22:38, 24 January 2006 (UTC)
I've come across some entries for a few books which may be applicable to this subject, but as I haven't seen the books I can't say for definite. They are:
Mike Peel 19:05, 13 April 2006 (UTC)
Sorry if the question is silly, but while it is true that I never saw a broken plate come together spontaneously, I have also never seen a stone going up spontaneously. Does it mean that the law of gravity is also irreversible, just as the law of entropy ? Can we use the fall of objects to infer the arrow of time ? Or is there something more to it ? Would it be useful to clarify this in the article ? Pcarbonn 11:25, 20 May 2004 (UTC)
Thanks ! I think I've got it. The fall, i.e. the conversion of potential energy to kinetic energy, is indeed reversible. What is not reversible is the stop of the fall, i.e. the conversion of mechanic energy to heat. This is what the second law of thermodynamics says, and that's why I have never seen a stone go up...
I guess I still don't get it. Gravity is always attractive in the forward direction of time, and always repulsive is the reverse direction. I guess electric charge can be either attractive or repulsive in both directions, but what about the other forces? Why isn't the irreversibility of attractive force as important to the arrow of time as entropy? -- Jackdavinci 18:23, 5 August 2006 (UTC)
The past is memory, the future is anticipation, now alone is real Saint Augustine.
Awareness is a present moment function which compares what seems to be experienced externally to what is being experienced internally. The difference attributed to an experience identified as memory is called the past. The psychological future, like a projection in a mirror, makes what is behind such as expeirences, anticipations, desires, dreams, hopes, and goals, seem ahead of the observer. The ability compare novel experienced events and imagined events to countable repeating events and chart them is called time. The consistant increase in memorable novel experiences creates the psychological illusion of an arrow of time since no current experience seems totally indentical, to any prior one and no retracing or reversing of even a single moment of the universe in total is ever noticed. Since the universe seems to be expanding it seems impossible for any current experience to be anything like a prior one since all prior experiences have an apparently smaller universe in total. Jiohdi 15:27, 3 September 2006 (UTC)
Missing references is probably the major weakness of the whole article. I have made a start by citing a reference news article for my recent addition to the section on the psychological/perceptual arrow of time. I hope this will prompt other users to do likewise. DFH 19:55, 26 September 2006 (UTC)
It is said in the article that such motions are reversible. There are 2 or more problems here. One is that chaos may be present, so that over a sufficiently long time, the orbits will have a divergence from each other that is so sensitive to initial conditions it is impossible to predict which set it the right one. (see Lyapunov Exponent). Another is that there are many small bodies present, from asteroids down to meteorites and even dust, that make it impossible to work backwards, and even make forward predictions diverge initially by meters a year, and eventually in a Lyapunov manner (exponentiallyI. See Standish E. M., and Fienga A.: 2002, Accuracy limit of modern ephemerides imposed by uncertainties in asteroid masses. Astron. and Astrophys, 384, 322 Carrionluggage 04:29, 29 September 2006 (UTC)
Where does the excessive energy of biological evolution comes from ? doesn't the oredered state of things now ,as opposed to less orederly in the past contradicts the second law of thermodynamics? where does the system draw it's "order" from ? what is it that becomes less ordered as biological system evolve? Diza 09:26, 8 December 2005 (UTC)
Actually biological system can introduce even more disorder. E.g. cow by eating grass destroys more order (enclosed in the grass) then creates new order (in a form of own tissues and giving birth to new cows). It is not true of the grass so. If there no grass whole solar energy will be absorbed by the soil and dissipated into the heat. The grass uses part of it build itself and create the order.
Diza 18:25, 16 December 2005 (UTC) Narutally all the excessive energy for the functions of life comes from the sun's rays,This cpudl be the answer. So all of the order that has been built in the whole history the biological evolution could be explained the the sum of all dicipated heat from the planet ? this still bugs me. becasue there are other plantes. maybe one could say the biological system CONCENTRATE their order in one location ,so that they have a higher order density.
We (any inertial reference frame) always have non-zero complex speed vector in Minkowski space with constant norm c ( speed of light in vacuum). The unit vector of that vector is our (that inertial reference frame's) Arrow of time.
In other words, even if we don't notice that while apparently at rest, we are always moving along our world lines toward the future with maximal (and minimal..., in fact only possible one) speed c.
I am aware that this, of course, is a circular definition, but it perhaps sheds some more light (or casts some more shadow, whatever) on the notion. As much as there is no absolute time, there also isn't neither any absolute Arrow of time nor absolute rest.
I add a unreferenced verification template stamp to the section about the radiative arrow of time since it seems to me to be very vague about what experiments it refering too in the sentance "This arrow has been reversed in carefully worked experiments".
I felt like one of the experiment is was implying was time-reversal of electrodynamic wave involving nonlinear optics (aka what wikipedia calls "optical phase conjugation"). Now would be a good time to read on optical phase conjugation at http://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase_conjugation . Especially note that 100% reflective mirror have never been made, so this mean that the phase conjugate beam is a fraction of the source beam. Hence, there is a energy loss during optical phase conjugation, which I believe but am not 100% sure can be interpreted as an increase in entropy. Thus I did not want to suggest optical phase conjugation since it may not violate the second law of thermodynamics.
However, if not optical phase conjugation then what experiment does the article mean? —Preceding unsigned comment added by 68.214.39.193 ( talk) 20:24, 8 May 2009 (UTC)
== Removing Unclear Paragraph ==Consequently unless a native Chinese person can support the contention that these meanings somehow cause the Chinese to view time differently I think they are just artifacts of the differing usage of words like 'behind', 'after' 'front' in different languages. —Preceding unsigned comment added by 114.77.67.48 (talk) 09:05, 6 August 2009 (UTC) I'm removing this paragraph (emphasis added)
I think that there may be an interesting point in there, but it's not presented clearly. Anyone know how to clean it up? 20:09, 24 March 2006 (UTC)
It is now written in the article:
This seems to me total nonsense, in more ways than one. First, there is a powerful tradition in the literature which says that memory erasure equals entropy increase. (Landauer and Bennett come to mind, see the final chapter of my http://philsci-archive.pitt.edu/archive/00002201/ ) This is the exact opposite of what the current article says, since it equates memory creation with entropy increase. This is strange. (It is also proof of the rampant confusions surrounding the notion of entropy!)
Second, the notions of "memory" and "correlation" used here must be made much more specific before the claim can even be understood. In a deterministic Hamiltonian world, any time slice of the Universe implies its state at all other times; no correlations can form which do not already exist at the outset. If an indeterministic (but still unitary!) quantum mechanics somehow changes this, tell us how. As it stands, the claim that "the Second Law of Thermodynamics is equivalent to the growth with time of such correlations" seems to me at least unclear and probably false.
Third, even if the physics and the information theory is sorted out, it is still not clear that the psychological arrow is linked to the thermodynamic arrow. We don't form memories of the future when we temporarily lower the entropy of our brain (for instance, by sticking our head in a fridge). If there is a link, it needs to be argued for in much more detail.
Fourth, the article claims that the psychological arrow "is thought to be reducible" to the thermodynamic arrow. Thought by whom? This is again too vague. Victor Gijsbers ( talk) 16:51, 18 June 2009 (UTC)
"This arrow has been reversed in carefully worked experiments which have created convergent waves": I recall reading something about this years ago, probably in Scientific American or Physics News Update. IIRC, these waves were emitted from a source and reconverged onto it. Paradoctor ( talk) 02:53, 28 January 2010 (UTC)
This section have been in the article at least since 2006, but it contains no reference to published sources or citations. -- Dc987 ( talk) 06:02, 5 November 2009 (UTC)
{{cite book|author=P. C. W. Davies|title=The physics of time asymmetry|url=http://books.google.com/books?id=9saLoa7by8oC&pg=PA154|accessdate=1 June 2010|year=1974|publisher=University of California Press|isbn=9780520028258|pages=154–184|chapter=6 Time Asymmetry in Quantum Mechanics}}
"There is a close analogy between the destruction of microreversibiliy in the classical system by coupling to the outside world stochastically through the walls of the container (see section 3.5), and the same destruction in a quantum system due to external coupling with the 'measureing apparatus'." p.168
"...the quantum system under observation is capable of changing in two distinct ways: (1) reversibly during the normal evolution of the system as described by the Schrödinger equation, (2) irreversibly during the measurement process, which cannot be described by the Schrödinger equation." p.170
"[Thermodynamic metastability] is an indispensable prerequisite for amplification of the quantum signal which triggers the [macroscopic measurement] apparatus. As a result of this amplification, the apparatus proceeds fairly rapidly to a stable equilibrium condition, which is correlated with the initial state of [the microscopic observable], and is macroscopically distinct from its neighbour states which are correlated with different states of [the microscopic observable]. Such amplification obviously involves a coarse-grained entropy increase (though not fine-grained). Thus, although the nature of quantum measurement irreversibility depends on coherence times of macroscopic systems, the origin of the irreversibility lies squarely in the domain of thermodynamics (as in the Everett interpretation), which in turn is related (as described in chapters 3 and 4) to the formation of branch systems, and ultimately to the origin of the universe, and the nature of gravity." p.174
Would any of these work?— Machine Elf 1735 ( talk) 12:54, 1 June 2010 (UTC)
... well... that feels like speculation, rather than hard science. True, very likable speculation, but... -- Dc987 ( talk) 08:11, 3 June 2010 (UTC)"although the nature of quantum measurement irreversibility depends on coherence times of macroscopic systems, the origin of the irreversibility lies squarely in the domain of thermodynamics (as in the Everett interpretation), which in turn is related (as described in chapters 3 and 4) to the formation of branch systems, and ultimately to the origin of the universe, and the nature of gravity."
I found the article referenced for the Andean tribe seeing time "backwards" quite interesting, but its only mention of the Chinese perspective is that they specifically are NOT an exception to the usual rule. I think we DEFINATELY need a citation for the Chinese claim, for as the above article itself mentions, words can be very tricky and misleading when trying to pin down what people really think from them, including a few odd examples of english seeming backwards in much the same way as these Chinese examples do... Elgaroo ( talk) 16:32, 5 August 2008 (UTC)
I agree. The Chinese words may not be sufficient to attribute different cultural ideas of time. For example:
The Chinese word for 'day after tomorrow' 后天 hou tian does literally mean 'behind day' but it could be interpreted to mean that the 'day after tomorrow' is chronologically behind today just as the number 4 is behind the number 3 on a number line.
The Chinese word for 'day before yesterday' 前天 qian tian does literally mean 'front day' but it could be interpreted to mean that the 'day before yesterday' is chronologically in front of today just as the number 3 is in front of the number 4 on a number line.
Consequently unless a native Chinese person can support the contention that these meanings somehow cause the Chinese to view time differently I think they are just artifacts of the differing usage of words like 'behind', 'after' 'front' in different languages. —Preceding unsigned comment added by 114.77.67.48 ( talk) 09:05, 6 August 2009 (UTC)
The article states that it often appears that there is "an obvious direction (or flow) of time." The words "(or flow)" should be removed. The arrow of time refers to an asymmetry of the universe with respect to time, and perhaps to some other flows with respect to time, but not to any flow of time itself.
Flow in relation to what?
Psychologically, and experientially, there is a present moment, and this moment changes, but this is not an objective phenomenon. Objectively, a moment in time is considered past, present, or future only in relation to other moments, and there is nothing dynamic about those relationships. Thus no flow. Certainly our experience of a dynamic universe is often modeled as though our awareness moves through time, but this is an apparent flow of awareness through time, not a flow of time itself. Poetically, time is the stream bed through which the stream of our awareness flows.
This movement of awareness (i.e. the seemingly dynamic character of our experience) cannot be a function of objective facts about the universe except as a kind of illusion because the objective facts about all particular points in space-time are fixed, indeed the objective facts are what define space-time. Lest I be misunderstood, I do not hold that our experience is an illusion, only that if it isn't an illusion then no objective description of reality can be complete.
Even if we take it that our awareness only apparently moves forward in time, in the direction of the arrow, then the flow of time with respect to our awareness would be in the opposite direction—not with the arrow of time but against it. So the reference to the flow of time in the article is less than helpful.
It is like thinking of the arrows on a one-way street as being the direction that the street moves. Mazzula ( talk) 15:48, 15 March 2011 (UTC)
Regarding the statement: :If this arrow of time is related to the other arrows of time, then the future is by definition the direction towards which the universe becomes bigger. Thus, the universe expands - rather than shrinks - by definition. on the section on Cosmological Arrow of Time.
I think the term "related to" is pretty vague and I cannot see how the relationship would require the universe to be expanding (positive scale factor)?
Indeed, the fact that negative energy has not been observed is suggests that the universe seems to be populated entirely with objects that travel in one direction in time, regardless of the reversibility of their interactions. That is in my opinion a more fundamental property.
-- Jallberg ( talk) 17:30, 16 July 2011 (UTC)
This uncited statement completely and utterly threw me off. What I find confusing here, is that the example reverses time in a single case of the cause and effect, without reversing the entirety of cause and effect. I've always considered reversing cause and effect to be quite simple - in a "backwards" perception of time, cause follows effect, leading to a decrease in entropy. Floors don't throw cups, but time-reversed gravity pushes things up. So instead of cause = hand opening | effect = falling cup, you have rising cup "causing" the hand to open. Therefore the property that causes scattered pieces to form a cup are the very same forces that hold the cup together as a solid until the moment it hits the ground. The causal relationship already 'cannot be perceived' forwards, and it makes no more or less theoretical sense backwards. For an example, centrifugal force does not become centripetal force purely because you looked at in the order of cause following effect. gmip Talk 13:49, 1 November 2011 (UTC)
Though the main article focuses on scientific aspects of the arrow of time, it seems odd that there is not even a passing reference to any teleological aspect. For theists this must surely be an important philosophical/ theological consideration. Moreover, even science itself used to be known as natural philosophy. Many other articles in Wikipedia treat difficult theological and philosophical ideas with a fair degree of competence. For example, the articles on predestination and determinism – which, by the way, are not the same thing – so I would suggest that there is a gap in this page that needs filling. For the time being, I am content merely to draw this to your attention. DFH 16:27, 23 September 2006 (UTC)
I've tentatively removed the citation BinaryPhoton added to what appears to be his own paper, which was recently published in what is (as far as I can tell) a very low-impact journal. (I'm in no position to judge the scientific merits of the paper itself, though I can say that the style of it doesn't resemble any peer-reviewed journal article I've ever read.) The sentence to which this editor has added the citation long predates his paper; surely if the claim needs a citation at all then it had better be to the paper in which it was first advanced, or to a secondary source which summarizes the past research. — Psychonaut ( talk) 12:22, 27 June 2012 (UTC)
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"Quantum uncertainty then gives rise to entanglement, the putative source of the arrow of time.
The idea that entanglement might explain the arrow of time first occurred to Seth Lloyd about 30 years ago, when he was a 23-year-old philosophy graduate student at Cambridge University with a Harvard physics degree. Lloyd realized that quantum uncertainty, and the way it spreads as particles become increasingly entangled, could replace human uncertainty in the old classical proofs as the true source of the arrow of time." Here [1] is more in the article. Kartasto ( talk) 18:07, 12 August 2014 (UTC)
How come, if Lochschmidt's paradox is resolved by the Fluctuation theorem, the problem of the arrow of time is not? i.e. how do these two actually differ?
Does inflation explain why entropy is not maximized in our universe?
Most possible worlds have higher entropy. Although each decoherence event is reversible, most possible events increase entropy. Isn't that the basis of the seond law? Fairandbalanced 04:16, 10 Oct 2003 (UTC)
There are websites that indicate that entropy and disorder are the same (ie. as described on this wiki page); and there are websites that indicate that they are not the same; and there are websites that say disorder in the entropy sense is not the same as disorder in the widely used sense. Please clarify.
I support your main point but not your example -- linking temperature and "hotness" is misleading. Temperature is akin to the amount of motion in a confined space i.e. add energy, get more particles moving faster = higher temperature. That we perceive that as "hotness" on our skin or so forth is secondary, which is why you were able to find examples of equivalent temperature with different perceived "hottness" levels -- we assume. For entropy, think complexity vs. simplicity. It takes energy to build up ordered or complex forms and maintain them -- on the macro level -- thus, over time's forward arrow, you get less complexity... whether the heat death of the universe, the destruction of complex atoms into simpler forms, or eventually just the end of matter itself. Chesspride
66.19.84.2 (
talk)
07:33, 28 February 2015 (UTC)
Would a manifold explain — Preceding unsigned comment added by 184.17.111.128 ( talk) 01:09, 19 September 2013 (UTC)
I think this is irrelevant
Roadrunner 05:53, 31 May 2004 (UTC)
hey — Preceding unsigned comment added by 124.83.11.178 ( talk) 02:30, 14 July 2015 (UTC)
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Glaringly missing from this page. Some calculations are not reversible. Suppose that a computer accepts two inputs and adds them together. The result is 42. The inputs are erased from memory. There is no way to tell whether the numbers were 21 and 21 or any other particular combination. The past state of the machine cannot be computed from the present one.
It may be in fact this arrow to which the others are hinged.
Even in a totally deterministic universe, there can be a forward time arrow.
Suppose that a cup falls on the floor and breaks in a deterministic universe, resulting in a spill, fragments and various artifacts of the dissipation of energy such as vibrations and heat.
That result is like the number 42 in the earlier example. More than one pattern of fall of more than one cup could produce exactly the same results. If time is reversed, there is no way to get to the past state because, for instance, if any future state depends on addition calculations over the previous state, we run into the problem that sums cannot be decomposed into the original terms. The information is simply not there. The broken cup pieces can be reassembled into more than one cup because of ambiguities. As soon as we find two cup fragments which have an identical shape, but are distinguishable (by some surface imperfection, marking or embedded inpurity), it means that we do not know which of two possible cups were broken. Perhaps the place where those pieces landed could tell us, but that itself could be subject to ambiguities.
The basic idea is that the universe is based on processes and processes irretrievably replace previous states with new states which do not contain enough information to unambiguously recover the previous states.
192.139.122.42 ( talk) 01:39, 20 November 2012 (UTC)
— Preceding unsigned comment added by 2A02:2149:8454:7C00:B5E4:9F1C:7F91:538D ( talk) 05:30:11, 25 December 2017