Monday, January 05, 2009

Guestpost: Dan Falk on the Nature of Time

[I met Dan Falk early last year at the SciBar Camp in Toronto, and later again at PI's multiverse conference. As most science writers I've met, he brings a cheerful interest in whatever the so-called edge of research currently discusses that is impossible to maintain if you happen to dance on that edge. He has written two books, neither of which I read, but I have occasionally come across his articles in the Globe and Mail which are always a pleasure.]

What better time than the start of a new year to reflect on the nature of time. (Thanks, Sabine, for letting me post here on this subject!)

Today’s atomic clocks can measure time to within a fraction of a billionth of a second per day – so well, in fact, that they reveal the irregularities in the earth’s rotation. As a result, we have to insert a “leap second” into the day every few years, as we did recently on the evening of Dec. 31 – a subject I discussed in an essay in the Toronto Star.

The technology that allows for this ultra-fine dissecting of time is indeed impressive. Yet our science – and perhaps our philosophy – may have some catching up to do. Indeed, one can legitimately ask: What is it, exactly, that these clocks are measuring?

I’ve given a lot of thought to this question of the last few years, as it lies at the heart of my latest book, In Search of Time: Journeys along a Curious Dimension (McClelland & Stewart, 2008).

Physics – perhaps surprisingly – has less to say on the subject than we might expect. Einstein’s relativity tells us all about the rates at which clocks tick: We know that a clock whizzing by at high speed will be seen to tick more slowly than one that appears to be stationary; that a clock in a strong gravitational field will tick more slowly than one on the surface of the earth.

Yet Einstein’s equations do not distinguish past from present or present from future. Just as with Newtonian physics, they say nothing of time’s “flow,” its relentless passage. Indeed, physics considers all moments to be alike, with space and time laid out in a vast, static “block.”

But this is not how we experience time: We seem to inhabit a single moment, a fleeting “now.” The explanation for this, it seems, may lie not in physics but in psychology or philosophy; indeed, many thinkers suspect that time’s alleged flow – this “moving now” – may be little more than an illusion, a trick of the mind.

Einstein once spoke of this dilemma. His friend, the philosopher Rudolf Carnap, recalls Einstein admitting that “the experience of the Now worried him seriously.” The experience of the Now, Einstein told him, “means something special for man, something essentially different from the past and future, but that this important difference does not and cannot occur within physics.”

And so the question remains, where does this difference occur? Why do we feel that time passes? Perhaps it will take an intellect even greater than Einstein’s to illuminate the mystery of time’s apparent flow.

Related posts:


  1. Hi Dan,

    It sounds to be an interesting book about a topic of discussion that is being taken seriously by physicists more and more as of late. One thing that's certain it's something that has always been interesting to me, with the first serious discussion I read on the topic being Paul Davies’ “About Time”, written back in 1995.

    As of late its Lee Smolin who is currently leading the charge with opinions and conclusions that I find more then just a little baffling to say the least. This has also come up within things Bee has written in this blog on the subject as I’m sure you are aware. I’ll certainly put in on my list of must reads as I hope that it may cover some of these more recent thoughts in regards to the subject.



  2. Hi Dan,

    "First then, in my judgment, we must make a distinction and ask, What is that which always is and has no becoming; and what is that which is always becoming and never is? That which is apprehended by intelligence and reason is always in the same state; but that which is conceived by opinion with the help of sensation and without reason, is always in a process of becoming and perishing and never really is. Now everything that becomes or is created must of necessity be created by some cause, for without a cause nothing can be created.Genesis Timaeus 27c-34a

    Where do these scientists get their ideas and scripting from?:)

    I thought I might leave you with a quote from Einstein. That you point to a philosophical relation, is new to me. Empirically, it makes sense when moved to spacetime.

    Since there exist in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. Albert Einstein

    Now, with some poetical inflection and a relation to any "Gedanken-thought experiment" it's basis held to a scripting of a kind(?), logically can end in "no time?"

    Time is of your own making;
    its clock ticks in your head.
    The moment you stop thought
    time too stops dead. Angelus Silesius

    Einstein was "very playful" in his hot stove analogy-"Conclusion:The state of mind of the observer plays a crucial role in the perception of time."

    "What if"... time did not exist? How would we measure our most happiest moments versus those that are held in dread?

    A "long time" and "short time," would find a difficult association, yet, relevant in the nature of the human being in becoming. Everyday a new day, and a better comprehension.

    So in the world of the Dirac's matrix we might say that there is a "negative value embedded?" That, "lightcones" don't exist?


  3. Seems like if everything in the universe is always moving then time cannot be an illusion of our minds and/or biology. Biology is movement too, time is inseparable from these moving things.

  4. Feynman's sprinkler is the robust arrow of time (angular momentum). That covers spin and mirrors. Theorists will provide the smoke.

    (Motion picture film can with one port normal to and at its broad face center, second port tangent to its edge. Fill with water, then pump more through. It is a diode allowing water flow in only one direction. It thereby defines the direction of time.)

  5. Sorry for going off topic Dan.

    Uncle Al:Theorists will provide the smoke

    You know very well then that if one can simplify as Feynman did by developing toy models from Dirac's algebraic works, that summing over histories can be done by theorists too. Its all in how you "now" want to look at things.:)


  6. So, there is no known physical consequence of not having a NOW? If so, then how can physics address the question?

  7. I thought when something moves, it only 'exists' in (approximately) single location. So when something moves in time - to future, to new 'now' - isn't it effectively removed from the past? If so, I would say that the past is significantly different from 'now'.

    If not so, should we get some sort of interference with the near past and now? Don't close by moments of time overlap due to uncertainty principle? Does it work for time?

  8. Dear Arun: Good question. In a nutshell that was the point I was trying to make in my post on the Block Universe (btw, the guy, Petkov, who wrote that paper I was commenting on there indeed invited me for a seminar). Best,


  9. Hi Timo,

    I don’t know what Bee’s answer would be yet for me this is where Feynman’s “Sum over Histories” is a poor choice of words, for it should be “Sum over all possible nows” with what’s left after cancelling being the actual now. The uncertainty is the part where the cancelling can’t determine the actual or what is impossible to know as to discern. In this respect the futures are only virtual until realized. There is a great difference between a possible future and an actualized one for that is reality or the now.



  10. Hi Timo, Phil,

    Things don't "move" in time because they are not localized in time. They just 'are'. That's why we have 'worldlines' to describe physical objects. If they were just points you could 'move' them in time, but it would mean they would only be there in a moment, and not before that and not after that - which is in conflict with energy conservation.



  11. Hi Bee,

    I don’t think what I said conflicts with what you said, unless what’s to be conserved exists beyond the now. Could you not say that instead of things moving through time that time is moving through things where the point of intersection being the now?



  12. Just thought I'd better explain what I saw in mind when I posted comment to Uncle above.

    Summing Over Histories

    So how does all this come together into a physical theory? It turns out that the proper procedure is to construct every possible diagram allowed by the theory (for a given state of input and output particles and how they're moving) and add up the corresponding complex numbers. The result is essentially the "wave function" for that specific input-output state combination, and by squaring that number you can determine the probability that the given input will result in the given output. Doing that is how theorists at particle accelerators earn their keep. See more here.

    Exploring the unknown? How so?

    It should not go unnoticed that Susskind himself wanted to explore the region "inside the blackhole" so he needed to see the elephant( it could be a very symbolic figure in terms of the poem on the six men and the elephant :)) in/out of the blackhole at the same time.


  13. How does time locally flow during a tunneling event compared to its surroundings?

  14. Bee,

    I'm not easily convinced that conservation of energy can say that past must remain unchanged. How do we know what really is the scope of conservation of energy?

    I'm toying with the idea that past is actually destroyed in the process of coming up with a new 'now'. I would be glad if this (claim about time) can be somehow shown to be invalid. But right now I don't see that there would be a problem with conservation of energy: all the energy is conserved when it flows to new 'now'.

  15. Dear Uncle,

    While trying to keep to the Theme here.

    What is the "smallest measure of time" and where is it?

    I am going to take you on a, "journey to the mountains" if that is okay?:)


  16. Indeed, it is not possible to define "time" in strictly logical terms. Math does not model flowing time itself, despite our use of axes with "t" in them - the constructions are nevertheless just "configurations" in a block-like mathematical space that we use to model "real time". Does that mean that "real time" isn't "real" after all? Well, I am suspicious of any reference to "X is an illusion ..." and note that ironically, our minds would have to be even more mysteriously special to have an experienced quality not even part of the universe as is.

    But time isn't the only or the worst problem, "material existence" is as well. As some have argued astonishingly but correctly, there is no strictly logical way to define “substantive existence” - such as to distinguish what we might call incarnate possible worlds (like we feel ours to be) versus Platonically real possible worlds that are not “incarnated”. Logic per se simply doesn’t have the tools to explain what “existing” is in what we want to call the material sense versus say, that there “exist” two roots of y = sqrt(4). IOW, the argument of Modal Realism ( as I often spring on folks here and about.

    Max Tegmark says he accepts this with his “world made of math” and also the it from bit folks more or less, but they don’t really seem to appreciate the consequences. Ironically I don’t agree with MR anyway because I don’t think everything can be defined in strictly logical terms, but if you do think they can - you have no choice but to be a modal realist, trust me. I believe OTOH that there is more to the universe than being a logical construct or, equivalently IMHO, fully characterizable by logical constructs, so for me non-math based"existence", true flowing time, and consciousness are real and all three are beyond strict logical definition.

  17. PS: I figure someone posting as "Plato" would be interested in Modal Realism and such issues ... what do you think?

    As for extra support that fits right in with Platonism considerations:
    It is indeed preposterous to think that “the” universe requires no explanation. One has to either be a modal realist which is a grand stupefaction but has its problems, or evade the logical asymmetry of one or some possible worlds existing and not others. There just being “this here” enjoying a special incarnate status among possible traits is absurd, whatever anyone may think (I have said, it is like the number 23 being made up in brass numerals, alone among the numbers, despite all of them being abstractions to start with. The same problem BTW applies to any subset of numbers or analogous field of descriptions, mindscape, etc.)

    Isn't it a hilarious irony, that materialists go around as so logical and yet their basic point is fundamentally irrational? Indeed, it can't even be coherently stated, except via "experiential" references (!), believe it or not.

    Heh, I have been accused by finger-wagging reductionists of being "a Platonist" even though I go beyond it ...

  18. In the block universe, it is still true that if you look in one direction entropy is lower, on average, and in the other, it's higher. So if our perception of the flow of time is illusory, it seems reasonable to conclude that it still depends on this asymmetry to keep things ordered. Otherwise, why do we experience and remember events in sequence? It's well known that life, pretty much by definition, generates local order non-randomly, and avoids violating the second law of thermodynamics by producing heat and other jumbled waste. Perhaps the perception of the flow of time is a kind of waste product?

    I don't know. I'm suspicious of mind-based hypotheses. Aside from what strike me as hand-waving appeals to entropy to give us a sense of direction, it's not clear to me why brains can't occasionally malfunction in such a way as to scramble our perceived path through the block universe. It's not as if we can't hallucinate with relative ease, so what else could go wrong? In other words, can we assume déjà vues are necessarily more illusory than "normal" temporal perception, and instead are not due to random out-of-sequence scans of the block universe? I'm not seriously arguing that, of course, I just have to wonder if the second law is enough to save us from that. If not, what does?

  19. Hi Uncle Al,

    “How does time locally flow during a tunneling event compared to its surroundings?”

    Awkwardly :-)



  20. Neil,

    I know these are ole articles.

    Are we staying on topic here by speaking of a "faster then light measure?" It seems to put the microscopic blackhole issue into perspective. Quickly dissipative, what happens in the translation? It depends on how you look at things?

    Chiao's group at Berkeley, Dr. Aephraim M. Steinberg at the University of Toronto and others are investigating the strange properties of tunneling, which was one of the subjects explored last month by scientists attending the Nobel Symposium on quantum physics in Sweden.

    "We find," Chiao said, "that a barrier placed in the path of a tunneling particle does not slow it down. In fact, we detect particles on the other side of the barrier that have made the trip in less time than it would take the particle to traverse an equal distance without a barrier -- in other words, the tunneling speed apparently greatly exceeds the speed of light. Moreover, if you increase the thickness of the barrier the tunneling speed increases, as high as you please.
    Signal Travels Farther and Faster Than Light

    and here for consideration....

    "String theory and other possibilities can distort the relative numbers of 'down' and 'up' neutrinos," said Jonathan Feng, associate professor in the Department of Physics and Astronomy at UC Irvine. "For example, extra dimensions may cause neutrinos to create microscopic black holes, which instantly evaporate and create spectacular showers of particles in the Earth's atmosphere and in the Antarctic ice cap. This increases the number of 'down' neutrinos detected. At the same time, the creation of black holes causes 'up' neutrinos to be caught in the Earth's crust, reducing the number of 'up' neutrinos. The relative 'up' and 'down' rates provide evidence for distortions in neutrino properties that are predicted by new theories." Scientists May Soon Have Evidence for
    Exotic Predictions of String Theory

    Wishful thinking of extra dimensions? One has to consider then how such collisions could take one to think about Gran Sasso or IceCube, or Sno.

    One definitely needs to be lead by science.


  21. Low math & all,

    Let us assume that (1) (state of) later time is constrained by earlier time. I also assume that (2) this constraint applies to everything, including our selves, both physical and mental state.

    The above statements would make it impossible to show anything about flow of time. As a thought experiment, imagine someone pressing play, stop, pause and seek buttons for the time that we experience. Due to the constraints (1) and (2) this would be completely undetectable to us!

    Our experienced 'point of time' could even be set in random fashion, yet due to the constraints - everything would appear linear to us.

    I think we are trapped to our experience of time, with little hope to break out.

    I think déjà vu is purely a psychological and neurophysiological thing which does not violate the constraints.

    Finally, I don't think humans are special in any way concerning time. 'Memory' feature can be found virtually everywhere.

  22. Neil,

    I thought you might be interested in past information that has been contributed. Lets see how much Obama relies on the "inaugural speech of Lincoln."

    “Some people have difficulty with accepting Plato’s mathematical world as being in any sense ‘real’, and would gain no comfort from a view that physical reality itself is constructed from abstract notions. My own position on this matter is that we should take Plato’s world as providing a kind of ‘reality’ as mathematical notions (and as I’ve tried to argue for forcefully for in the case S1.3) but I might baulk at actually attempting to physically identify physical reality within the abstract reality of Plato’s world. I think that Fig. 34.1 best expresses my position on this question, where each of three worlds, Platonic-mathematical, physical and mental-has it’s own kind of reality, and where each is (deeply and mysteriously) found in one that precedes it ( the worlds take cyclicly). I like to think that, in a sense the Platonic world may be the most primitive of the three, since mathematics is a kind of necessity, virtually conjuring its very existence through logic alone. Be that as it may, there is a further mystery, or paradox, of the cyclic aspect of these worlds , where each seems to be able to encompass the succeeding one in its entirety, while itself seeming to depend only upon a small part of its predecessor.”
    (Page 1028-The Road to Reality- Roger Penrose- Borzoi Book, Alfred A. Knoff- 2004)

    Okay, so I am ole fashion, with a bend towards the light. No body is perfect.:)

    ..underwriting the form languages of ever more domains of mathematics is a set of deep patterns which not only offer access to a kind of ideality that Plato claimed to see the universe as created with in the Timaeus; more than this, the realm of Platonic forms is itself subsumed in this new set of design elements-- and their most general instances are not the regular solids, but crystallographic reflection groups. You know, those things the non-professionals call . . . kaleidoscopes! * (In the next exciting episode, we'll see how Derrida claims mathematics is the key to freeing us from 'logocentrism'-- then ask him why, then, he jettisoned the deepest structures of mathematical patterning just to make his name...)

    * H. S. M. Coxeter, Regular Polytopes (New York: Dover, 1973) is the great classic text by a great creative force in this beautiful area of geometry (A polytope is an n-dimensional analog of a polygon or polyhedron. Chapter V of this book is entitled 'The Kaleidoscope'....)"

    It is always important to see the context of what the mathematics is doing in abstraction. It is trying to get a purer construct and idea structure which "approximates the birth" of what constitutes the reality.


  23. Hi Timo:

    I'm not easily convinced that conservation of energy can say that past must remain unchanged. How do we know what really is the scope of conservation of energy?

    I didn't say that. I said if you'd have things that are points in time (as opposed to worldlines), and that you thus could 'move' in time (as you said) they would be in conflict with energy conservation. Not their motion, but their mere existance (unless they don't carry any energy in which case I'd say they don't exist).

    If you have a deterministic evolution you can't change the past without changing the future.

    If you have an evolution with a non-deterministic ingredient (like e.g. quantum mechanics) you have wiggle room with the past. As long as the outcome is the same, you can in principle change it. None of these possible evolutions however should be in conflict with energy conservation.

    I'm toying with the idea that past is actually destroyed in the process of coming up with a new 'now'. I would be glad if this (claim about time) can be somehow shown to be invalid.

    It is a meaningless statement unless you explain what it means to 'destroy' a moment of time.

    I don't think humans are special in any way concerning time. 'Memory' feature can be found virtually everywhere.

    Indeed, and this was the point I was making in the above mentioned post Every Now and Then. Best,


  24. Thanks Plato, and I find myself essentially agreeing with Penrose on those fundamentals (as well as his take on the inadequacy of decoherence attempts to explain collapse of the WF, and I have coined the derisive terms "decollusion" for that IMHO failed effort.)

    As for the nature of time, the issue of reversibility bothers me. Consider the implications of the old saw about interfering in a time-reversed world:
    Consider a world where events are “moving backwards” and something intervenes in the flow of those events. The results are not symmetrical with what we expect for our universe. Consider yourself an “outsider” that is not part of the reversing time flow. A bullet that (to the backwards universe) was fired “out of” a gun is now approaching that gun (in your reckoning) to go back into it. You push the bullet, or the gun, out of the way. Now what? It is imaginable in a world of normal time flow, what really happens if I fire a gun and then push the bullet out of the way later as commonly understood in time sequence. But if we allow the intervention to be conceived as happening in a world where time is running backwards the result is absurd: the bullet now misses the gun and does, what? It’s re-reversed behavior would be absurd, it would have to spring out of e.g. a tree that was behind the shooter, etc.

    With this distinction between whether past or future is affected by an intervention in the chain of events, how can time-reversal be merely relative? An intervention changes “the continued past” of the time reversed world and “the continued future” of a normally progressing world. Sure, even the intervention itself wouldn’t be modeled the same way in both worlds, but that isn’t the point. The point is, the intervention can be done in the TRW and the effects work backward to ruin the rational structure of the supposed past of that world. How can a TRW be vulnerable, even in principle, to such a "past"-changing action if not really different in principle from a normal world?

    This question is indeed relevant to the idea of “thermodynamic reversibility” and challenges the notion of TRWs. IOW, they are said to have a tiny change of maintaining the reverse flow, and if anything “went wrong” it all falls apart. However, we consider our universe “robust” and interventions would only affect the “true future.” That makes common sense, but violates the supposed inherent physical equivalency of time-reversed processes.

    So then what accounts for the thermodynamic process going the way it does? You can say “chance” etc, but why does the chance favor the “correct” flow of time and make our world robust under alterations, but leave the world in reversal at constant risk for drastic screwup if any little thing doesn’t fit together right? If there’s no real absolute time, how can the worlds even be different from each other? That is a deep philosophical issue and I hope the pros around here will remark on it, tx.

  25. Noether's theorem couples mass-energy conservation to homogeneity of time. Tunneling violates a classically forbidden energy barrier (frustrated total internal reflectance). Is time locally naughty in kind?

    Mass-energy has non-conservation events as vacuum ZPF (Casimir effect, Lamb shift). If mass-energy fluctuates then time symmetry is broken or Noether's theorem is broken.

    Bond glass fiber with less than lambda/e thickness fluorophore (emitter-spacer-SiCl3 on glass). Is fluorescence emission identical for identical narrow band optical pumping from the inside out (tunneling) and from the outside as the excitation window is scanned? Snug absolute zero to kill thermal line broadening.

  26. Uncle Al,

    Information is conserved coming from the blackhole. Albeit, badly scrambled. It is readable from a Holographic standpoint. We know there is a history there. Again "ole references" to bring people up to date.

    Strominger: That was the problem we had to solve. In order to count microstates, you need a microscopic theory. Boltzmann had one–the theory of molecules. We needed a microscopic theory for black holes that had to have three characteristics: One, it had to include quantum mechanics. Two, it obviously had to include gravity, because black holes are the quintessential gravitational objects. And three, it had to be a theory in which we would be able to do the hard computations of strong interactions. I say strong interactions because the forces inside a black hole are large, and whenever you have a system in which forces are large it becomes hard to do a calculation.

    The old version of string theory, pre-1995, had these first two features. It includes quantum mechanics and gravity, but the kinds of things we could calculate were pretty limited. All of a sudden in 1995, we learned how to calculate things when the interactions are strong. Suddenly we understood a lot about the theory. And so figuring out how to compute the entropy of black holes became a really obvious challenge. I, for one, felt it was incumbent upon the theory to give us a solution to the problem of computing the entropy, or it wasn't the right theory. Of course we were all gratified that it did.
    Black Holes and Beyond:Harvard's Andrew Strominger on String Theory


  27. Neil,

    The view you you are describing is indeed a difficult one to understand. For a layman like myself most troubling too, to explain a "psychological state" in terms of that memory. Lets try and stay to the science then.

    Reverse chronology — narrating a story, or parts of one, backwards in time — is a venerable technique in literature, going back at least as far as Virgil’s Aeneid. Much more interesting is a story with incompatible arrows of time: some characters live “backwards” while others experience life normally.

    Sean Carroll referenced a new movie recently of someone who starts out old and then becomes young?:) Interesting scenario as it sounds familiar?:)

    I can show you a picture of the Sun in Gamma and presuppose that other sources in the universe can now be held to that context. This can only be done by our measure. This does not tell us about the sources of information we now have or our understanding the locations reveal about what can be transformed and lost in translation? Holographic information, is unscrambled, from that state of uncertainty.

    So, I have denoted a location/s.

    I show where we can question the nature of the blackhole "in another view," now, we know what by what measures we have.

    These views are current. Does not invalidate your troubling question. Take a moment and see my current post, "Lost in Translation."

    Yet, it helps one to realize that looking back, "our/universe memory" is not totally revealed.

    Such birthing requires "clear and concise definition" and by the mathematics, we are not there yet.


  28. Phil mentioned earlier a relationship between Lee Smolin and (?). It was philosophically based on the question of time. I was having difficulty remembering that relation. Thus the quote below points to work done in that regard by example of Phil's post.

    Julian Barbour

    In my "The End of Time" I argue that the wave function of the universe is static and that the appearance of the flow of time emerges because the wave function of the universe is concentrated on configurations of the universe that we recognize as records. Edward Anderson and I are currently trying to develop this idea and create a theory of records. If successful, this work promises to explain the origin of the arrow of time at a fundamental level.


  29. Physics has to say a lot about time - just because time existence cannot be derived mathematically.

  30. Time is closely related to motion as well as forces. If time stops motion stops and forces dissappear. Time may be just presence of motion and forces. You may visit for more info on this line of thinking.


COMMENTS ON THIS BLOG ARE PERMANENTLY CLOSED. You can join the discussion on Patreon.

Note: Only a member of this blog may post a comment.