Is Time Real?

I mentioned some time back the Closer to Truth series, in which Robert Lawrence Kuhn chats with scientists, philosophers, and theologians about the Big Questions. Apparently some excerpts are now appearing on YouTube — here I am talking about whether time is real.

In one sense, it’s a silly question. The “reality” of something is only an interesting issue if its a well-defined concept whose actual existence is in question, like Bigfoot or supersymmetry. For concepts like “time,” which are unambiguously part of a useful vocabulary we have for describing the world, talking about “reality” is just a bit of harmless gassing. They may be emergent or fundamental, but they’re definitely there. (Feel free to substitute “free will” for “time” if you like.) Temperature and pressure didn’t stop being real once we understood them as emergent properties of an underlying atomic description.

The question of whether time is fundamental or emergent is, on the other hand, crucially important. I have no idea what the answer is (and neither does anybody else). Modern theories of fundamental physics and cosmology include both possibilities among the respectable proposals.

Note that I haven’t actually watched the above video, and it’s been more than three years since the interview. Let me know if I said anything egregiously wrong. (I’m sure you will.)

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63 Responses to Is Time Real?

  1. Ken says:

    Let’s say you have some number of paper clips which you can count. We say the number of paper clips is a reality because it is information derived from raw data. By raw data we mean something that conforms to certain parameters within a prescribed margin of error. The paper clips are”real” because they can be determined to conform to our parameters and their magnitude can be collated from raw data, that is counting up the actual paper clips. But if something cannot be reduced to raw data, meaning it cannot be divided up to conform to our parameters of measurement but can only be detected as an “emergent property” i.e. information derived from collated information we could not state with certainty that the entity was real because there is no way of knowing whether it too is collated information. Let’s say we want to measure magnetism by the number of paper clips a magnet can pick up. But can we say with certainty that something called magnetism actually exists, or is it simply some type of information we cannot determine.

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  2. Pingback: Is time fundamental or emergent? Nobody knows. | Gordon's shares

  3. Closer to Truth is the best series after Carl Sagan’s Cosmos in my opinion. Time is a very tricky business. Until recently I used to think that time is emergent based on non-commutative geometry and its origin is in quantum mechanics. For a physics argument see the Connes-Roveli paper: http://arxiv.org/abs/gr-qc/9406019 To my greatest surprise, last year I discovered that along with the tensor product, time is a fundamental ingredient in deriving quantum mechanics: http://arxiv.org/abs/1303.3935 so it must be the other way around. The true nature of time is a problem whose solution still eludes us.

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  4. Meh says:

    I would say that our universe required the existence of time in order to be created, so time must be something that exists beyond the limits of our universe while also existing within those limits.

    Your opinion could be that time did not exist before our universe, but my reply would be that if that were the case, then it must have been generated from something which we would require a time variable to fully describe and understand.

    The most accurate thing that I would say is that time is the only thing that is truly conservative throughout existence.

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  5. Frank Zollo says:

    The Closer to Truth series is exasperating. Some of the episodes are excellent, exploring dark matter, causation, multiple universes, free will, memory. But others waste time on theological concepts that presume the existence of God because otherwise it’s so obviously stupid to ask questions like “Is God Simple?”, “Is God Self-existent?”or “What Does it Feel Like to be God?”. More alarmingly, some episodes give a forum for intelligent designer proponents (e.g., W. Dembski) or ESP believers to spout anti-science nonsense.

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  6. Sagredo says:

    If we use space-time variables, time is real and there exists a world line of a particle. If we use energy-momentum variables, there is no time and a particle has not any history. Classically this means that we use the integrals of motion; they do not depend on time at all. Finally, instead of ordinary time we can use imaginary time. In this case motion disappears. This is a world of Parmenides. This is a world of statistical mechanics.

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  7. Doc C says:

    It’s amazing to me how long we have survived and thrived without being able to describe time in an abstract way. Our brains know how to define time even if our minds don’t.

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  8. Jack Smart says:

    Hidden due to low comment rating. Click here to see.

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  9. Ramesam says:

    Lee Smolin: Time is fundamental (Time Reborn – From crisis in physics to the future of the universe , Houghton Mifflin) 2013

    Nima-Arkani Hamed: Time and space are emergent (SUSY 2013)

    Advaita Vedanta: Time is imaginary (time is thought = mind)

    Take your pick.

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  10. T.E. Oakley says:

    After thinking about Dr. Lee Smolin’s book “Time Reborn,” (2013), I formulated the following argument, which is relevant to the question of whether “time” is emergent or fundamental in physical theory:
    1. Define “time” OPERATIONALLY as “movement” or “change”; without the concept of “movement” or “change,” the concept of “time” is meaningless; thus,
    2. “Time” and “movement” or “change” are EQUIVALENT.
    3. Due to quantum effects, all physical systems are, on a quantum scale, in PERPETUAL MOTION. No physical system can be brought to absolute stasis, that is, absolute 0 kelvin.
    4. Mass and energy are interconvertible: E=mc2, therefore,
    5. All physical systems are reducible to energy.
    6. This leads to E=t ( “E” is energy; “t” is time). “Energy” and “time” are seen to be EQUIVALENT ONTOLOGICALLY AND CONCEPTUALLY; not in any way distinct.
    It thus becomes apparent that, “time” has masqueraded as “energy,” and “energy” has masqueraded as “time.” So we can conclude that “time” is as FUNDAMENTAL as “energy” in any physical system; therefore, “time” cannot be considered an emergent property.
    I have elaborated these ideas in an email to Dr. Smolin entitled “Special Relativity and Time”; also in a email critique of the Trinity College Cambridge Professor Dr. Huw Price’s review of Dr. Smolin’s book “Time Reborn” as it appeared in the journal “Science,” vol. 341, August 30, 2013. I can forward these to you, Dr. Carroll, if you are interested.

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  11. If I can take a bite out of it, it’s real; otherwise, it doesn’t exist.

     

                                                                                              —Ted Nugent

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  12. Suppose I am a real stupid cat (what might be true, depending on your perspective). Now, for me time is something that is not measurable, because I cannot count more then 3 or 4 (I am really stupid, remember that?). Well, days and nights follow each other and I can feel the passage of days and nights, i.e., I feel hungry and I feel sleepy sometimes, normally around the same hour every day. My “feeling” of time passing is certainly related to the arrow created by energy transformation (dissipation or entropy) or, in other words, by the irreversible processes that just happen before my eyes. If I were a stupid and blind cat, that would be much more difficult to tell. As I an animal and lucky cat, I am not conscious of the way irreversible processes occur naturally, and the damages they continuously impose on any natural evolution I face, from my early embryo to my dusty destine in the stars. So the question of time being real or not is not really fundamental, I believe. The arrow imposed by the natural energy evolution (meaning free energy dissipation) is. Big and generous bang!

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  13. AJ says:

    Hidden due to low comment rating. Click here to see.

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  14. Tienzen (Jeh-Tween) Gong says:

    Hidden due to low comment rating. Click here to see.

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  15. H.H. says:

    Ok, so if I’m following everything correctly, what we experience as “time” is actually entropy. Entropy is possible because the Universe started at a high state of energy. As this energy decays to the point that it can no longer do any work, entropy effective stops, since everything is maximally disordered. At this point, change no longer occurs, so time “stops.”

    In other words, our Universe is a shaken snow globe, and time runs out when the last flake settles on the bottom.

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  16. FrankL says:

    I watched those videos and I have a question. One of Sean Carroll’s statements was that the universe is possibly a local drop in entropy in a “multiverse”. A massively unlikely drop, but in a large enough multiverse, it can easily happen. He also said that when the universe reaches equilibrium, maximum entropy, there will be no time. I wonder about that. If we take a much smaller universe, a container of gas at equilibrium, there will be a certain maximum possible entropy, but the gas will practically never achieve it due to fluctuations, each of which drops the entropy below the absolute maximum. This is not a violation of the second law which holds only in the limit of infinite size, it is just a consequence of the finite size of the system. Suppose for simplicity its a monotomic gas of classical particles that interact only by collision. Then we can plot the entropy as a function of time using the usual formula. There will be rare cases of relatively large drops in entropy, but the entropy will generally rise after that back to a reasonable value. My question is this – will the fluctuations have a “signature” which indicates the forward direction in time? I mean, a drop in entropy probably won’t have a particular signature, but won’t the recovery tend to be exponential “decay” towards the maximum, which would allow you to determine the forward direction of time?

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  17. Bob Zannelli says:

    The problem of time in physics shows up in the Wheeler De Witt equation , which is basically the Schrodinger equation for the whole universe, the Schrodinger equation of everything. This equation takes the basic form of HY=0 ,where H is the Hamiltonian operator and Y is the wave function. This equation has no time parameter.

    There are several things we can say about this. Operationally time is what measured on a clock, a clock being defined as some cyclic process. It’s obvious from this that the notion of time is dependent on the division of observer and observed. Therefore if we write an equation that encompasses everything no such division is possible, therefore the global state is timeless.

    Another way to think of this is in terms of Decoherent histories. As demonstrated by Don Page the Decoherence functional is time symmetric. This would seem to mean that we should get of Decoherent histories that evolve in both time directions. However, all observers can only experience what is for them a history evolving toward their future by definition. When the Decoherence functional is applied to the whole universe, we get a CPT symmetric state which when summed over removes time in an analogous that the superposition of left and right circular polarization ( giving us Horizontal and Vertical Polarization) remove any circular action of the EM wave.

    Finally, as demonstrated by Atkatz and Pagels , only closed universes can tunnel into existence ( locally our universe is open due to inflation but closed globally) A closed universe ,unlike an open universe DOES have a defined energy in General Relativity which is zero. Given that energy and time are conjugate variables zero energy means no time evolution. ( Strictly speaking this isn’t true because time isn’t an operator since locally energy is bound from below, but this wouldn’t apply in this case.)

    So based on the above, the “existence” of time is based on all observers being local, no God’s eye view being available.

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  18. Frame Jumper says:

    Ramesam:

    You forgot Julian Barbour, “The End of Time, The Next Revolution in Physics” For him, “Time truly doesn’t exist.”

    Smolin mentions Barbour several times in his new book. And while I am a fan of Lee’s “The Trouble with Physics,” I just couldn’t find anything of any significance in “Time Reborn.” Sorry Lee, but I’m starting to wonder if this (“Time”) is just the next ‘hot topic’ if one wants to sell a book. I REALLY wanted to buy your book, Lee; honestly! Since I have my own thoughts on the subject, speculation about time is of real interest to me.

    Anyone interested in Barbour’s ideas? How about:
    “…memories and records are in fact present phenomena.”, quoting John Bell
    “…the instants in time (the ‘Nows’, my comment) are in some sense finite. (my italics)” I would agree.
    quoting John McTaggert: “If (an event) is past, it has been present and future…thus all three characteristics belong to each event.” So, each ‘Now’ is present, was past, and will be future. Anything you can say about past or future is encapsulated in the present. The universe is timeless and motionless. There is only the ‘Now.’
    “…all the instants we have experienced are other worlds, for they are not the one we are in now.”
    “…time doesn’t exist…Time is change, nothing more, nothing less.”
    “The universe is its own clock.” (The ‘cosmic clock’, or what I refer to as the “universal clock”, is not time as we currently understand it, i.e., solar time. Time exists in the instant, not the other way around. Like the frames in a movie, each frame is timeless and motionless and more advanced civilizations don’t come from a planet far, far away, they have simply mastered ‘frame jumping’ among multiple, multiplexed, multiverses.”

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  19. John says:

    If you can bend it or warp it or dilate it, it is real. Otherwise, would be to say that we are just modifying equations on a component that actually doesn’t exist, because there is something else fundamentally wrong with the equations. How could we ever say that we have the correct descriptions of mechanism in physics when we modify all of physics in a part of it that actually doesn’t exist? I believe to say time doesn’t exist undermines Einsteins work indirectly.

    Einstein discovered the correct mechanism that needed to be modified that more accurately described the laws of physics. It wasn’t a magic trick done with math that did that by modifying something that didn’t actually exist. If time didn’t actually exist then those modifications would be needed to be put somewhere else. You would in effect just be manipulating nothing to get a more correct answer.

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  20. (Understanding Time in the Pursuit of Science). Time as a component in science is visualized as the sequential progression of the matter distributions that comprise the Universe. The nature of the Universe is perceived by analyzing changes in the distributions of its matter. As a technique to manage and understand the fundamental aspects of the process, sequences of observations are divided into subsets. The discovery and creation of uniform, repetitive phenomena from the rotation of the earth to oscillations of quartz crystals provide the metrics for clocks. This allows subsets to be assigned intervals as a function of reference oscillation patterns. Integrated into this process man has formulated the concept of time.
    The experimental accessibility of observational techniques positions scientists in a light-signal-limited volume of the Universe on the macro scale with sensitivity on the micro scale that can only sample consequences of the population effects manifested by the ultimate components. Hence, only a fraction of universal time, based on the components of matter, can be documented.
    Only the present instantaneous configuration exists and it is never the same for two instants. The past configurations are remember as the past and anticipated configurations are designated the future. Time travel in this scenario is impossible since only the present exists. However, conceptually, science is equally dependent upon present, past, and future.
    Time manifests a record for observations according to which physical laws and theories are developed and documented. Our laws and theories are validated when we are able to predict subsequent phenomena, i.e. the future, from current observations. A reference clock is crucial to analyses of sequences; however, its intervals, often represented as time itself, are passive parameters.
    In totality the distribution of matter contained in the Universe appears to be expanding and the Universe appears to be evolving in such a manner that its entropy is increasing. If we assign this evolutionary property to time, then current time has an arrow, i.e. the increase in entropy. The metric of an oscillator supposedly provides uniform intervals that allow the assignment of intervals to selected sequences from the Universe. The time axis allows the positioning of “instants” in a sequence and if a single body of uniform matter is being followed in a three-dimensional reference frame, it may be utilized in an analogous manner to a geometric axis for spatial positioning with the understanding that time proceeds from the present to the future. When the process is extended to a four-dimensional system, visualization is more difficult.
    Time possesses a mystical quality and becomes a metaphysical entity when we equate it with duration. However, in the practice of science, time need not be considered a mystery. Conceptually, it is the past, present, and future history of the configurations of the physical Universe. The mystery that science cannot explain is how the Universe came into existence.

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  21. Sean, In one of your video clips you say that Earth gives off 20 times more photons than it absorbs from the sun. (a) Does this mean that passage of time has some symbiotic relationship with flow of photons? and (b) How has science established the truth of this 20 to 1 ratio? Thanks.

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  22. Meh says:

    whenever I hear the phrase, “we remember the past but we don’t remember the future”, my urge to nitpick grows like the heart of The Grinch. I think this phrase should be exchanged for something slightly different. I would argue that just because we don’t use the same word, does not mean that it isn’t the same thing; but my explanation just proves your point even further. We remember the past and can predict the future; these are the same actions, though we use different words to imply past and future to reduce the amount of words needed to explain our thoughts and prevent confusion. We predict the future(if smart enough and/or evolved enough) based on the information(laws) that we know in the present. We know this information and these laws in the present because of experiences in the past and present (a bird flies when pushed out of the nest because it quickly realizes that the panicked flapping of its wings produces lift).

    So predicting and remembering are really the same action performed in opposite directions from the present. Consider the present moment the origin, the future = positive direction and past = negative direction. Prediction can be just as accurate as remembering, sometimes more so. They are symmetrical. The flaw in this is that we can only predict the future based on past experiences.

    To sum up my addendum, I would still argue that time is more accurately described as radiating away from the present, the present being a point of origin. That origin is admittedly still moving in the positive direction as a sub-interval of a grander iterative function if we don’t interfere, though it does not have to be if we find a way to work around it. If I roll off a cliff, I would naturally fall to my death; unless I decided to roll off a cliff in an airplane. Electrical power is lost when passed through a wire, unless the wire is superconductive.

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  23. rocken1844 says:

    It is disgraceful how new age pantheists seek to further their own agendas misapplying the nomenclature of physics. In “Wishes Fulfilled” Wayne Dyer claims that Albert Einstein taught (p.146) “that time is an invention of man and essentially an illusion.” No footnote or reference of course. Dyer then ties this idea in with NDE and dream states. The next sentence “Anita’s NDE unconscious state reinforces Einstein’s idea of no time.” On p. 71, after citing Max Planck (again no reference or context) he writes “You simply know you have an imagination and this imagination is the Source of all being.” Rubbish.

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  24. It seems the question as to whether time is “real” depends more on the definition of “real” than on the nature of time itself. There is no question our lives would be different without the invention of clocks to coordinate our daily lives, design our spacecraft, measure our universe, and derive our theoretical physics. Many of man’s accomplishments, especially recent ones–e.g., the GPS, rely on the constant rate of time (at least one lab is working on a clock with an accuracy of one sec. in 300 million years). Time to me is a “real” fundamental feature of nature that has played a central role in man’s achievements since his emergence from the stone age.

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  25. FrankL says:

    It seems to me that Einstein did not have much to say about the aspect of time that is being discussed here. He discovered a more accurate relationship between the measured time and space coordinates of events in spacetime, and the implied relationships between physical quantites, (mass, energy, momentum, electric field, etc.). But we do not directly experience these time coordinates written on a piece of paper. In order to imagine experiencing them, (lets say as an inertial observer in special relativity), we have to imagine ourselves as an unaccelerated particle, a straight-line world line in space time, and our consciousness is a point on that line, moving “forward” along that line at the speed of light. A moving plane perpendicular to the line at that point is what we perceive as “now” in space, with the point itself as “here and now”. Now we can reconstruct what our consciousness would experience, given these data points. But Einstein had no comment, that I know of, about this rather ad hoc reconstruction process, or the fact that you must introduce a “conscious time”, along with this reconstruction recipe, in order to get a sense of what your consciousness would perceive given a set of measured spacetime coordinates, momenta, etc.
    .
    We have to distinguish between time as a parameter in a scientific equation, and our experience of time, which, in some “normal waking state” moves forward rather steadily and in which we experience an ability to remember an uncontrollable past to varying degrees, and to predict and control the future to varying degrees. Unless you are an Orwellian politician (“those who control the past control the present and those who control the present control the future”.)

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  26. John says:

    If time isn’t real, then we shouldn’t be manipulating it to describe things in physics. Physics describes things that are real, not imaginary things so that it just turns out that you got the correct answer. Even if Einstein did say time was only an illusion, the person listening to him or Einstein himself could have possibly just had a brain fart that day. If time isn’t real, and it has to altered in some way, then how do we then know that something like conservation of momentum is even true? If time isn’t real, it would have to be something else that is changing over time, instead of time itself. If you wanted to be smart and accept the laws of physics we have now as being correct, then it would be wise to say that time is real!

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  27. Jack Smart says:

    Time is a meaningless irrelevance without events. Simple – as I posted before.

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  28. Gary Godfrey says:

    Here is a different restatement of the “times arrow” quandary with a suggested answer that we just don’t have the correct fingers to translate macroscopic objects backward in time.

    _____Spatial translations by parameters (x,y,z) obey the axioms of a group. Use your fingers to manipulate an object on your desk to verify that: 1) The product of any two translations is another translation 2) Every translation has an inverse (ie. do it in the negative direction) 3)There is an identity (ie. do nothing) 4) Translations A,B,C are associative A*(B*C)=(A*B)*C.

    _____We d0n’t do a time translation by t with our fingers. Rather, we cross our arms and wait ….. something else causes the time translation.

    _____By special relativity we expect the translations by (x,y,z,t) to all be the same type of mathematical object, since viewing them from a boosted frame mixes them together. We therefore expect time translation to be a group operation. So, we are puzzled when we can not verify axiom #2…Using our fingers we can’t seem to do a time translation by -t. Thus the quandary of “time’s arrow”.

    _____Perhaps this is not because the inverse time translation does not exist, but only because we are not using the correct fingers to do it. For example, 1)In the microworld an electron can be translated in the -t direction by hitting it with a high energy virtual photon (a different type of finger). 2) In the macro world we just haven’t identified a good “finger” to cause the assembly of all the air molecules in a room to translate backward in time and return to the balloon from which they exploded.

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  29. FrankL says:

    @Gary Godfrey – And we can verify that the group of spatial rotations is a group (with our fingers) and we can do a rotation in spacetime with our legs – by walking. Or with a plane, a train, or an automobile … or a rocket ship, anything that changes our inertial frame. But entropy is not a function of rotation angle, only translation along the time axis. If we found such “fingers” for many-particle systems, we would be able to violate the second law of thermodynamics. Or, from another perspective, the second law prohibits us from finding such fingers in its regime of validity (large number of particles).

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  30. The Thinker says:

    What I’m fascinated about is whether the block universe really exists. If our inertial reference frame can mean our “now” is someone else’s future or past who’s time slice is at a different state due to them having a different relative inertial reference frame, then the past, present and future all exist.

    But one potential problem I see for this come from the EPR paradox/experiments
    that Einstein threw into the bunch. If two entangled particles can change “instantly” at large distances, what if one of the particles is traveling near the speed of light relative to the other particle when it’s measured? If the moving particle’s reference frame is skewed due to its movement relative to the other entangled particle, how can they change “instantly”? This would seem to violate the idea of a relative reference frame in favor of a universal or preferred reference frame.

    This has been bugging me for weeks. Does anyone know how this works?

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  31. zephirawt says:

    In AWT neither time neither space are fundamental, as they cannot be defined/measured/observed without underlying space/time.

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  32. Tom Clark says:

    Thinker: “If the moving particle’s reference frame is skewed due to its movement relative to the other entangled particle, how can they change ‘instantly’? This would seem to violate the idea of a relative reference frame in favor of a universal or preferred reference frame.”

    Great point, and it’s an empirical question, is it not, as to whether observed entanglements have involved relative movement between particles? If not, perhaps that would lend support to the block universe view in which there is no special now, in which time is a dimension, not something that flows (e.g., see Brian Greene’s chapter The Frozen River in his book The Fabric of the Cosmos). If so, maybe there’s still a way to incorporate such instantaneous (simultaneous?) effects between particles in relative motion into the block universe view.

    Would love to hear Sean’s take on this.

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  33. Jack Smart says:

    I get the 11 dislikes – but, you do need to consider this:-
    When Sean talks about “Arrow of Time” he is referring to time in the mass noun context – i.e. Time as a (non-specific) composite of events. (If he was referring to Time as the abstract framework he would need to be more specific – and anyway can an abstract framework have a direction?). What other evidence of ‘time’ is there besides events?

    Whereas when, say, Einstein refers to time, he is referring to specific events, and the abstract framework that we use to connect them.

    So, we have a divergence – two people talking about seemingly the same word, but in fact meaning two different (albeit related) things.

    But I presume you all knew this anyway…(though I’ve never seen the distinction made by any scientist).

    Bring on the dislikes…but word meaning matters

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  34. David Redfrost says:

    Time is an artificial framework imagined by monkeys to contain physical processes. Time is abstract and does not really exist except for in the puny brains of the aforesaid monkeys.

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  35. FrankL says:

    @The Thinker – “two entangled particles can change instantly at large distances” is not what’s happening. Also “entangled particles” is an oxymoron, just like “the position of a particle in a momentum eigenstate” is an oxymoron. In a momentum eigenstate, it has no position until you measure it, and then it is not in a momentum eigenstate. For the “entangled particles”, you have a system which does not describe two separate particles, and once you make a measurement that distinguishes the two, you don’t have the system any more.

    What you have is two detectors and if you take many measurements you can describe the statistical correlation of the measurements made by the detectors under different conditions, and you wind up with statistics which are impossible – if you assume that the two detectors are not somehow talking to each other. You can show that any such communication must be instantaneous. But if Alice is at one detector and Bob is at the other, they cannot use that instantaneous communication to send messages to each other, because the information comes from comparing Alice and Bob’s measurements, and they must communicate sub-luminally in order to make that comparison.

    A crucial thing is that nothing strange ever actually happens, its only when you say “if Alice had done such and such, and if Bob had done such and such, then such and such would have happened, and that’s impossible, given what actually happened. The idea that you can talk about “ifs” in quantum mechanics is, well, iffy. You measure the position of a particle, is it proper to ask “what if I had measured momentum instead, would the particle still have had the position I just measured but I would not have known it?” As my quantum professor would say, that’s an improper question.

    The idea that using the word “if” is a proper thing to do is called “counterfactual definiteness” (CFD). Maybe using the word “if” becomes improper as you dive into the quantum world and CFD is not valid. But then what happens to free will? Free will is like “If I do this then A will happen and if I do that, B will happen and I want B so I do that”. Without the if, we just do what we do, and free will is, well, an improper concept. This is were I lose clarity. It’s more comfortable to assume spooky action at a distance, but I sometimes wonder.

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  36. Randolph Brown says:

    Time only makes sense to the observer of change. The illusion of time helps the observer understand what he observers in the now. Movement that results in change is fundamental. Time isn’t.

    A conversation with my son.

    As we sat on the deck, enjoying the fire we had started in the fire pit, I asked Harrison, my son, what words he would use to describe everything that was happening in the universe at this particular moment. He looked confused.

    He needed help in understanding the question. I said look at the fire, what is happening there?

    We started talking about oxidization and chemical reactions inherent in the fire. How would you describe the fire? We realized there is a lot of information generated by a fire and how to describe it accurately.

    I asked him, as we watched the fire burn, what do you think is happening now to the stars in a galaxy on the other side of the universe? He said “they are moving”.

    Now think about all the galaxies right now, what words would you use to describe everything that was happening in the universe at this particular moment. He said “overwhelming”.

    It was then I began to tap his knee. Every few seconds I would tap his knee. I said it looks like I am touching your knee repeatedly. He said yeh, you keep touching my knee over and over again. I said look at the fire, I’ll touch your knee again. Was that the same as when I touched your knee earlier? Harrison said no, the fire was different. So each time I touch your knee its different? Yes, each time you touch my knee its unique.

    I asked Harrison, “What does it mean that something is unique”? He said “it’s one of a kind.” I asked him “if it’s one of a kind, does that make it valuable”? We considered such…

    Harrison is 11 and a half.

    Every moment is unique, it can never be repeated. Its value is incomprehensible.

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  37. Ron Seadler says:

    @rocken1844
    “It is disgraceful how new age pantheists seek to further their own agendas misapplying the nomenclature of physics.”

    It’s not always easy to tell if they mistakenly believe they have found the ultimate truth, or whether they knowingly believe they have found their cash cow.

    In the 70′s I dallied with various concepts (aka belief systems) of consciousness and reality. At some point I found one that benefited me extremely well, and with it the world made profound sense. I was damned pleased to relate my discovery to the wisest person I knew. She merely smiled and said “That’s another wonderful way to view the world.” For a few minutes I felt her comment was a bit dismissive. Then I got it. I’ll never forget that moment. It truly saved my ass.

    There’s the physical reality we exist together in, and there’s our individual conscious point of view. I smartly cling to the rational exploration of facts and evidence. It’s the self-correcting reality we all share. My conscious viewpoint happily morphs and shifts with scientific discoveries, but so it is. There’s probably more personal viewpoints of the universe than there are people to have them.

    It’s also nice to understand precisely why you became an atheist.
    (Disclaimer: Born Catholic with 12 yrs Catholic education)

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  38. John Duffield says:

    I think it’s fair to say that time is real in much the same way as heat is real. But like heat, it isn’t something fundamental. If you open up a clock you don’t see time flowing through it like it’s some kind of cosmic gas meter. You see cogs moving. What clocks actually do is accumulate some kind of regular cyclic motion and show you a cumulative display called “the time”. More and more people are appreciating this, IMHO. What’s actually “out there” is space and motion rather than a static “block universe” comprised of spacetime.

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  39. Ron Seadler says:

    @John Duffield

    Heat would have no identity outside of time. You couldn’t open a clock without the time necessary to do it in. Feels fairly fundamental to me. I’d bet my future on it. Well, maybe later.

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  40. Brett says:

    There are 2 meanings to time in physics(this is my understanding anyway):

    1.) time is change which results in things being different from each other.

    2.) In cosmology, we see the bigger picture. Consider the universe before the big bang as a precise sphere with no differences at all; every single point is exactly the same, called equilibrium. The first change in history occurs and a new property of nature is born, the ability of something to be different. The ability to change. A single mechanism is responsible for this change; the expansion of space. The expansion of space is still occurring. This expansion mechanism means that things get more spread out over time from all the way down to the smallest length possible, all the way up to the entire universe. This is the arrow of time. It is responsible for the 1st property of time in physics. The 1st property listed above can be considered an “echo” of the 2nd property. There are other properties that can be considered ‘echos’…’echoes’? The arrow of time based on entropy is one of them.

    This is why I believe that time is real and it is the most fundamental property in the universe. And now I must get back to my evil lair and plot schemes against Julian Barbour…spreading salt in his yard perhaps, mwoohahahaha.

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  41. John says:

    @ The Thinker

    The problem is that quantum mechanics (QM) violates Einstein’s principle that information cannot travel faster than light, and then they just allowed Einstein’s work and QM to say they are correct because they apply to different fields and they are not compatible with each other. Although, now they think that even galaxies can travel faster than the speed of light (FTL) away from each other, and that is in Einstein’s territory of the macro scale. Then they say this is okay, because space itself is actually traveling FTL as though it is an actual thing. Can you imagine? I don’t think it is really fair to “time” to accept “space” as an actual thing when it comes to this issue…

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  42. Howard Hunter says:

    Fundamental or Emergent – Ekaterina Moreva and friends claim time is emergent. Interesting ideas.

    http://arxiv.org/abs/1310.4691

    summarized here:
    https://medium.com/the-physics-arxiv-blog/d5d3dc850933

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  43. FrankL says:

    Just to clarify the two types of time a bit more. Please note that I have not incorporated quantum mechanics into this, so maybe it’s dead wrong. Hopefully an oversimplified beginning.
    .
    1) There is “physical time” or “time1″ which is just a parameter, another coordinate in the space-time continuum. It has no direction, only an orientation as reflected in the fact that the microscopic laws of physics favor no particular direction in time. Confining things to classical relativity, time1 is not “superdynamic” in the sense that particles, for example, are seen as world-lines in the spacetime. There is no “motion” of these 1-D world lines but rather they represent the dynamic motion of 0-D particles. There is no absolute before, now, or after.

    2) There is “type 2 time” or “time2″ which ideally corresponds to physical time, but with an added “forward” property. It’s a vector rather than a ray.

    Consider 2 particles that approach each other, collide and rebound at the origin, and then move away from each other. Their moment of inertia about the origin is I=m1 r1^2 + m2 r2^2. This moment of inertia function can be seen as a measure of their “dispersion”, so lets call it that. If you look at the dispersion sometime after the collision, it is an increasing function of time2. With regard to time1, the whole thing is two V-shaped world lines in spacetime, and time1 is a whole set of possible axes that could be used to coordinatise that spacetime. There is no “increasing” concept in the sense of any motion of the world lines. The direction along a ray of time can be positive or negative, it doesn’t matter.

    In time2 terms, after the collision, the dispersion is an increasing function of time. Now look at entropy. In time2 terms, the entropy is an increasing function of time for the same reason. The collision between the two particles is a little bang, the origin of the universe is a big bang. For entropy, in time1 terms, there is no “increasing” concept. Just as there may be a parameter (dispersion) with reduced information about the two particles, so entropy is a parameter with reduced information about a huge number of particles. Note that for a single isolated particle, no increasing function of time can be defined that cannot be reversed by a suitable redefinition of the direction of the space axes. Not true for the 2-particle dispersion. Or entropy.

    When you look at things by time1, there are no “superdynamics”. Anything explained in terms of a forward direction in time, is using time2, not time1. With regard to time1, there is no before, now, or after, there is no cause and effect, there is no motion, there is no second law, there is no theory of evolution, there is no spooky action at a distance.

    So what is the deal with time2? Lets look at a human observer from the time1 viewpoint. He or she is a huge mass of twisting and turning world lines of all sorts of particles, obeying microscopic laws, converging at some spacetime distance from the big bang, diverging on the same side, but at a further distance. If we could read and interpret every one of those lines, we would see every experience of that person, every dream, etc. And we would see the equivalent of their ideas about “consciousness” and “before” and “now” and “after” and “forward flowing time” (time2). What is that all about?

    Well, I don’t know what it’s all about except to say that its an emergent thing resulting from the microphysics of the world lines. In other words, time2 is time1 with an emergent “time-forward prejudice” that may well never undo itself for organisms further away from the big bang.

    So with this view, the interpretation of the Bell inequalities as suggesting spooky action at a distance is a result of our time-forward prejudice.

    Now I will read Howard Hunter’s links and perhaps deny that I was ever serious about the above.

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  44. Frame Jumper says:

    Brett:

    You state: “Consider the universe before the big bang as a precise sphere with no differences at all…” Actually, the true believers (those who want a job after graduation and hope to get their papers published by the establishment) tell us that there was no “universe” before the big bang. There was absolutely nothing, no space, no time. Nada. Zip! Or at least that’s the story IF, of course, you’re a “big bang” and miraculous “inflation” promoter. (This outta draw “dislikes.”)

    Right on, Randolph, “Time isn’t.” Like the illusion of time in a movie, it’s just change in the Now – motionless, timeless frames, i.e., your “taps.” This explains pretty much everything including why photons do not experience time (because they only exist in the Now), why clocks “run” at different “rates” (Einstein), why “time” in which matter exists becomes “shorter” as you approach the “speed” of light, and even why particles disappear from one location only to instantaneously reappear in another without traveling the space between (in a movie, in one frame it’s on the right, in the next frame it’s on the left; simple, actually). Perhaps this also explains why a single photon appears to behave the same as many if you stop (one of those misleading “time” concepts built into the language) and think about it.

    If it were possible to travel at light speed (it is not, according to physicists), you, being matter, would enter the realm of the “eternal now” where time truly does not exist – not up for discussion. All of your matter and your motion through time (?) will have been converted to energy. So, are we all just “light beings” (Kalen J. Craig’s, “bundles of sine waves”) in a holographic universe emerging out of some (Bohm/Mandelbrot) implicate order? Aren’t we, after all, just atoms appearing and reappearing?

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  45. John says:

    Stephen Hawking would say that there is no before the Big Bang, as if there is no time before the Big Bang. If there was a transition between there being no time and time, then time would have to be an actual thing that emerged from the Big Bang.

    One growing idea about the early Big Bang is that everything consisted of mostly energy. Then if there was no mass then there wouldn’t be a singularity that the Big Bang would have to escape from. If there was no mass then everything in existence would travel the speed of light. If everything in existence traveled the speed of light, every particles frame in the universe would be contracted. If moments close to the Big Bang had the same laws of physics that we have now (that I find very likely), then spacetime wouldn’t have been really experienced by anything in the universe until the first time energy was converted to mass, so I believe that time is an emergent property that stems from the Special Theory of Relativity itself.

    So then I would have to side with Prof. Hawking and say that there actually wasn’t a “before the Big Bang”, and time would have had to have emerged sometime afterwards.

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  46. Brett says:

    “If there was a transition between there being no time and time, then time would have to be an actual thing that emerged from the Big Bang.”

    But the fact that there was a space without time that turned into a space with time would itself be a function of time. A change occurred. The universe without time and the universe with time would be parts of a larger event in which time was required in order to have occurred. Doesn’t energy require a time variable? I would agree that as far as we are concerned in our universe, there wasn’t a “before the big bang”, but that it doesn’t mean that nothing was happening. It just means that it is beyond our understanding of nature and physics to describe or comprehend a space in that state. In which case, we should just consider there to have been nothing before the big bang. I think it’s sort of a paradox, there was something, but for all intents and purposes, we could accurately say there was nothing. Every possible equation we could use to describe the universe before the big bang would be completely ineffective and utterly pointless. Every answer would be infinity and there would be no boundaries, the only state in which the universe was truly unified. If you can tell me why that changed, please send me an email with the answer and await a very “special” cake baked only for you. You could say that it was a state in which the universe was “pure energy”, but what does that mean? Isn’t that the exact same thing as I described above; nothing but null field values at every infinite measurement?

    How did the discreteness and variability come about? That is when time started. What disrupted the perfect system?

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  47. The Thinker says:

    @ John

    Not sure that answers my question.

    @ FrankL

    Is it just a measurement problem, or is this a real phenomena that travels faster instantaneously? Scientists pretty much agree it is instantaneously. If that is the case, what inertial reference frame does the instantaneous change take place?

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  48. FrankL says:

    @The Thinker – there is no instantaneous change. It’s not a case of “look, I changed something here, something changed over there.” In other words, you cannot send information using the Bell inequalities.
    .
    A very simplified (but still kind of hairy) thought experiment might help. Suppose a machine put two balls onto two chutes, one leading to Alice, one to Bob. The balls can carry instructions. The balls fall into a box with two doors, and some mechanism in the box will then read the instructions, and paint the ball black or white, depending on the instructions and which door is opened, and then deliver the ball to whoever opened the door. The only time Alice or Bob can see the color of the ball is by opening a door. They notice that no matter which door they open, its a 50-50 chance they see a white or a black ball.
    .
    If they both open the left door, both balls are the same color. If they both open the right door, the balls are again, always the same color. If Alice opens the left door and Bob opens the right door, the colors do not match. Ok, it’s easy to model whats going on. The balls coming down the chutes have either BW instructions or WB instructions. BW means if the right door is opened, paint the ball black, if the left door is opened, paint the ball white. WB means the opposite. If BW and WB balls are sent with equal probability, you reproduce all the results for the above three scenarios.
    .
    There is one case we did not consider – Alice opens the right door, Bob opens the left door. The above model says they won’t match, but what actually happens is that they match. This destroys the above model. If the above experiment were quantum mechanics, then quantum mechanics would correctly predict all four of the above results. How do we explain the above results?
    .
    The only way to explain the above results is that somehow each box must know what door was opened on the other box before painting its ball. Even if Alice and Bob are separated any distance, by a million light years, and open their boxes at the same time, the above results always happen. The communication must be instantaneous.
    .
    Notice that Bob cannot send information by this means. Alice opens a box, sees a white or black ball with 50-50 probability, what is she to make of it? Nothing. Over and over, thats all she sees. Only when Alice and Bob share their results, by light-speed (or less) signals, can they compare results. And even then, one run gives nothing, they both say “ok, nothing strange happened, results are as predicted.” Only when they share the results of a number of runs, involving all four possible outcomes, do they say “yes, the predictions are correct, but that’s spooky” and “there must be some information being transmitted instantaneously”
    .
    Actually, there is another way to explain the results – deny counter factual definiteness. In other words, the above results are explained by the fact that Alice and Bob have no choice in the matter, no free will, the universe is a Laplacian pre-ordained clockwork, they were bound to open the doors that they did.

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  49. Is time real and fundamental if the speed of light in vacuum is not invariant?

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  50. John Duffield says:

    @martenvandijk: It’s real, but not fundamental. The speed of light in vacuum varies with gravitational potential. Check out the coordinate speed of light. However the locally-measured speed of light doesn’t vary because you calibrate your rods and clocks using the local motion of light. Then you use them to measure the local speed of light. So you always measure 299,792,458m/s

    @Ron Seadler: Heat is heat. When something is hot, you experience it. It’s real, it’s empirical. But we know it isn’t fundamental, and instead is an emergent property of motion. A hot gas is made up of fast-moving molecules/atoms.

    OK, hold your hands up a foot apart, and you can see the gap, the space between them. Space is real, and empirical, and fundamental. Then waggle your hands, and you can see them moving. Motion is real and empirical and fundamental too. But you can’t see time flowing. You can see literally see things moving through space, but not through time. And when you open up a clock you see cogs moving, not time flowing. What clocks do is “clock up” some kind of regular motion and show you a cumulative display that you call the time. So you don’t need time to have motion, you need motion to have time. It’s that simple: stuff moves, sh*t happens, that’s it.

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  51. Brett says:

    You could just as easily say that motion is the result of time since there is no comprehensive understanding of what time is. I could say that a lack of symmetry in nature is a product of time. If motion is the result of a lack in symmetry, then motion is a result of time.

    What is causing the change which motion is an emergent property of? My answer would be time.

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  52. FrankL says:

    @John Duffield – I think time is as fundamental as space. If two firecrackers go off in front of me, I don’t need the concept of motion to tell me they went off at different times, or the same time, any more than you need the concept of motion when you hold your hands out and see the space between them (or not, if your hands touch). We need a clock to measure time, just like we need a ruler to measure space. We don’t need a clock to sense simultaneity or lack thereof, any more than we need a ruler to sense whether your hands are apart or touching.

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  53. John says:

    @ Brett

    I don’t know how I would send you an email or retrieve one from this blog. The short answer is that electromagnetic energy can just “#$%*” itself or I mean intensify itself.

    Brian Greene talks a lot about a growing problem in physics in his latest book where they are unable to determine the total energy of a particle traveling back and forth inside of a box. It is keeping him from finding solutions to a problem in String Theory regarding the cosmological constant. When trying to solve this problem, they get answers that result in infinity. Then they throw this theory out because they are not allowed to get these kind of answers.

    I think there may be some kind of truth too it, and the conservation laws where basically philosophized into science based on Newtons Laws. Then I don’t know of any actual experiments that took place that reflected energy in a box, basically because the ability to do this had not been invented yet. I find it discomforting that we hold so strongly to classical principals in QM where nothing works classically at all.

    I think there would have to be some kind of free energy mechanism at work near the moment of the Big Bang. If there wasn’t then we would all be made out of some kind of “God Dust” that had these properties of always existing and never having to be created. Then believing in our selves and the world around us could become unscientific, lol!

    Then energy could be anything you could stick in the “E” side of E=mc^2. In a small closed universe there could be more interaction between particles. If the universe grew in size then there would be less interaction. If there was a free energy mechanism from interaction of particles then this process would stop just from the universe growing. At a time like now when a particle traveling the speed of light cannot even go around the universe, there would be no indication of this process still occurring at this time.

    Then particles traveling the speed of light do not experience time because when something would travel the speed of light SR would say that the proper time would be zero…

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  54. Gary Godfrey says:

    @FrankL – Yes, if there is an operator whose expectation value is entropy, then that operator commutes with rotation of the system and does not commute with time translation of the system (ie: as you say the entropy of a system changes as you move the system through time). However, this does not mean that an appropriate finger can’t move a macroscopic system backward in time. The 2nd Law of Thermo just implies that the entropy of the finger would have to increase more than the entropy of the system moving backward in time decreases.
    As you also point out there are several more continuous (Lie) group operations that can be done to an object. I think the full list (excluding gauge transformations) is:
    3 space-space rotations (about the x,y,z axis)
    3 space-space parallelepiped strains (eg: done by a gravitational wave)
    4 squash strains in x,y,z,t (eg: done by a gravitating mass which stretches in t and squashes in r)
    3 space-time parallelepiped strains (also known as boosts in the x,y,z directions)
    3 space-time rotations (I don’t know what does these…it’s just a guess, they are there to fill out SL(5))
    4 covariant translations in x,y,z,t
    4 contravariant translations in x,y,z,t
    These 24 operations and their products might form the mathematical group SL(5) (if translations don’t commute). My intent in expanding your list to 24 operations was to point out that time translation is a group transformation, just like the other 23. Time translation is as real as any of the other 23 operations that can be done to an object. Time translation is not special, an illusion, or mystical. We only think time is different because we empirically don’t have any control of its passage or its direction. Perhaps this is because something like the mass of the universe causes times passage, and our puny mass just can’t influence the time translation very much.
    In order for an object to change, some combination of these 24 operations must be done. All 24 parameters are necessary to specify how the object has changed; t by itself is not sufficient. We document the continuous change of an object by writing down the values of these 24 parameters as they build up from 0 (the identity of the group). It may be convenient to specify where we are along this path in 24 parameters by a length along the curve (call it the evolution parameter T). If only translations were being done for this piece of the path, the evolution parameter dT along this infinitesimal piece of the path would be dT^2=dx(covariant u) dx(contravariant u).
    So, in answer to the original question ‘What is time?”, there is a time (a number t) that specifies the group transformation that corresponds to what we do by only waiting. However, in addition, there is an evolution parameter (a number T) that keeps track of where along the path in 24 parameters the object is. If only dt is done and not any of the other 23 transformation, then dT=dt.

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  55. FrankL says:

    @Gary Godfrey – I see what you are saying. Its sort of a Maxwell’s demon kind of thing, except rather than simply decreasing entropy, it does it in an extremely specific way, so as to reverse the micro-processes by which the system arrived at its high-entropy state.

    Classically, the demon would have to reverse the velocities of every particle, but quantum mechanically I’m not sure. If you had a box with two particles, one at a high energy eigenstate, one at a very low eigenstate, after time, with collisions, the wave function would reflect a more likely energy distribution. I’m not sure how to restore the original wave function, or if its even possible in principle.

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  56. E-motion is caused by electricity.

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  57. Adel Sadeq says:

    My theory which seems to reproduce the laws of physics it indicates that time does not exist. We perceive it as such because of the change in the state of the system, very much along Barbour’s scheme. As a matter of fact my theory has a very similar trait of being conformal similar to Shape Dynamics which is a theory derived from Barbour’s scheme, However, my theory looks more fundamental and the time result is just one small part of it.

    http://www.qsa.netne.net

    http://www.fqxi.org/community/forum/topic/1877

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  58. John says:

    Maxwell’s demon must be responsible for every time my mother makes me clean up my room! LOL, Jk!

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  59. Miao says:

    Hi Sean, I am a huge fan of your blog. I am wondering if you have read this article. I would love to hear your thoughts on it; so if you are both willing and able to spare time to write a blog post about it, I would be over the moon!

    Thank you for writing such a fantastic blog — keep up the good work!

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  60. Tom Clark says:

    Looks like Sean is an eternalist, someone who takes the block universe view of time, as opposed to a presentist, who supposes that time flows:

    “Carroll is more skeptical [about the flow of time being fundamental to physics]. Rather than attempting to change the block universe to explain our experience of time flowing, he says we should concentrate on explaining human experience in light of what our very successful physics tells us about the block universe. That task, he says, is quite achievable. ‘That doesn’t mean that we’ve done it yet, but I see no obstacle to doing it.’” – from “The now delusion” by Michael Slezak in New Scientist.

    The nature of time, e.g., whether it’s fundamental or emergent, is a matter of what the most successful physical theory tells us, then we go about accommodating the commonsense view of time to the facts. The New Scientist article (not free online that I could find) presents several examples of the reverse: trying to come up with a physics that accommodates commonsense and experience.

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  61. I have introduced in physics the difference between endogenous aand exogenous processes. By doing so I have introduced the notion that comparing gravity with pseudogravity (created in an elevator or a rocket) is comparing apples with oranges. Gravity as we experience it continuously is caused by an endogenous process, whereas using an external source of energy to create pseudogravity is an exogenous process. In other words, I don’t think the equivalence principle is right. Likewise, as I understand it the Lorentz transformation is not valid in an endogenous process like gravitation.Gravity is fundamental as a continuous process. Studying the way light behaves under the influence of gravity, I think that it stands to reason that time is fundamental as well. So, if Sean Carroll is an eternalist, I have no reasons tothink he is wrong.

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  62. Brody Facoum says:

    “You can see literally see things moving through space, but not through time.”

    No, you literally see things moving through spacetime. The thing is that looking around you, you will mostly see mesoscale things moving much much further along the timelike axis than along the spacelike ones. Where distance along the spacelike axes are measured in c*seconds and c is set to 1, this becomes readily apparent. In spherical coordinates centred on you at some point in spacetime, a ball in one hand will move essentially not at all along the spacelike axes whereas a ball thrown from the other hand might move tens of nano-(c*second) radially and follow a curve of a few nano-(c*second) up and then down in altitude, and not at all azimuthally. However the thrown ball will have travelled perhaps several seconds along the timelike axis; the held ball and you will also have travelled almost exactly the same several seconds along the timelike axis, along with everything else that you see nearby.

    For nearby objects moving slowly relative to one another, the timelike coordinate varies so little that people generally avoid thinking about it. However, those objects are certainly travelling along the timelike axis at a rate much much faster than the rate at which they travel along any of the spacelike axes.

    Indeed, in the example above, the held ball travels essentially no distance at all along the spacelike axes. However, when working out the spacetime intervals in a block of spacetime surrounding this example, the timelike term totally dominates the thrown ball, the held ball and you at t’ compared to all three at t.

    When you’re looking at your mechanical clock, the arms or the gears inside are also moving in spacetime, dominated by movement along the timelike axis.

    Additionally, the reason that everything appears to be moving uniformly in one direction along the timelike axis is possibly a constraint similar to the constraint from Earth’s gravity against movement in altitude when dealing with the sort of energy you can impart to a ball by throwing it. If you increased Earth’s gravity severalfold, you could only ever manage to send a thrown ball downwards along the altitude axis.

    It is wholly possible that the “clocks” (in the most general sense) ticking away in the example above tick essentially at the same rate of one second per second. Your wristwatch and your mechanical clock will agree very precisely over the several seconds of the patch of spacetime local to the ball-throwing. However note that gravitational potential influences the clocks’ ticking, too, and not just the thrown ball’s altitude.

    cf. the comment by Gary Godfrey above.

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  63. Glenn says:

    Is time real? Perhaps, this may answer your question? I’ll keep it as brief as possible.

    Time is the quale of duration? Duration is the ‘length existence’ (the period between ‘beginning’ and ‘end’) of an event. An event is an action we observe. When we observe we are perceiving, and when we perceive we are assimilating qualia. Time is simply the perception of duration of an event.

    Time, per se, holds no existential reality of its own.

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