After the FQXi Essay Contest, I was asked to comment on some of the essays besides my own, but I never did. Mostly because I didn’t take the time to read them all (there were an awful lot), but also because I just don’t know what to say about many of them. In her essay (which I liked), Fotini Markopoulou divides the world in two:
There are two kinds of people in quantum gravity. Those who think that timelessness is the most beautiful and deepest insight in general relativity, if not modern science, and those who simply cannot comprehend what timelessness can mean and see evidence for time in everything in nature. What sets this split of opinions apart form any other disagreement in science is that almost no one ever changes their mind…
That’s just about right (although perhaps there are also other splits with the same quality). Julian Barbour, whose essay finished first in the judging, has famously championed the view that time does not exist, even writing quite a successful book about it. In a recent Bloggingheads discussion with Craig Callender, Barbour talks a bit more about his view.
To which all I can muster is: I don’t get it. There are a set of technical arguments, which for the most part I do get, that can be used to make it seem as if time does not exist. In ordinary classical mechanics, we can perform some formal tricks to remove the time variable from the conventional equations of physics. More dramatically, in general relativity or quantum gravity we can express Einstein’s equation (at least in certain circumstances) in a form where time does not appear. On the other hand, we can usually re-write any of these equations in a form where time does appear (at least, again, in certain circumstances).
But none of these technical arguments are really the point. What I don’t understand — and this is a sincere lack of understanding on my part, not an indirect claim that this perspective is wrong — is what’s supposed to be so great about timelessness. What are we supposed to gain from thinking in this way? What problems is it supposed to solve?
Put it this way: clearly time appears to exist, at first glance. Even the timelessness crowd somehow manages to submit their essay competition entries by the deadline, and finish their Bloggingheads dialogues within an hour. So the claim “time does not exist” certainly doesn’t mean the same kind of thing as “unicorns do not exist.” It must mean (I suppose) that, while we all find time very useful in our everyday lives, there is a deeper level of description in which time doesn’t appear at all; it only emerges in some sort of approximate description of reality. But that approximate description seems extremely valid and useful, including all of the phenomena in the observable universe. Surely it behooves us to take this purportedly-non-fundamental notion seriously, and attempt to understand some of its puzzling features? Moreover, even if “time” doesn’t turn out to be fundamental, why would that tempt you into saying that it doesn’t exist? Protons are made of quarks, but you don’t hear particle physicists going around claiming that protons don’t exist.
The problem is not that I disagree with the timelessness crowd, it’s that I don’t see the point. I am not motivated to make the effort to carefully read what they are writing, because I am very unclear about what is to be gained by doing so. If anyone could spell out straightforwardly what I might be able to understand by thinking of the world in the language of timelessness, I’d be very happy to re-orient my attitude and take these works seriously.
You are neglecting the coolness-factor of claiming that time doesn’t exist. Or that anything else doesn’t exist which obviously seems to exist for the average human being. Like space, vacuum, free will, etc.
I find it puzzling though Fotini writes the fact that almost no one ever changes their mind sets this issue apart from other disagreements. In my impression no one ever changing their mind is the rule rather than the exception. If you need any evidence consider how scarcely somebody tells you did you know X changed their mind on Y.
What is meant is time in the sense of a pointer that points to what really exists: the present moment, while the future and the past do not exist. Time in this sense does not exist, or at least, is difficult to reconcile with modern physics.
Simple examples:
In special relativity, you have the Andromeda Paradox:
http://en.wikipedia.org/wiki/Rietdijk-Putnam_Argument
In quantum physics, you could consider a big closed box inside which everything evolves according to unitary time evolution. But then the past and the future exist in the same sense as the present moment, because they are all relatated to each other via unitary transformations.
Isn’t this similar to saying, I don’t see the point of a statistical mechanical description of heat and entropy, when the thermodynamic one works just fine? Or: I don’t see the point of an atomic description of nature when I can do chemistry at the test-tube level? Physics is about probing deeper, no?
You’ve put your finger on the problem exactly. What is the instrumental value to Barbour’s hypothesis? It’s like intelligent design in this sense — even if true, so what?
Aside from lack of instrumentalism, there are a few key points in his essay that I believe are either false or partly false.
http://brokensymmetry.typepad.com/broken_symmetry/2009/03/comments-on-julian-barbours-essay-the-nature-of-time.html
I haven’t read Barbour’s book, and my understanding of this extends about as far as I hear tell the time variable simply drops out of the Wheeler-DeWitt equation, which some folks think is very profound. Perhaps some of these folks are being semantic provocateurs? So maybe time is emergent, and not fundamental. I’ve seen the mass of the proton referred to by some as “emergent”, and I think all agree that the great majority of it isn’t “real”. That’s not to say it doesn’t “exist”, just that it is largely due to the contribution of virtual particles, and not the “real” quarks that make up the proton. So are they really trying to say time isn’t “real”?
I think the whole thing is an argument about semantics really. Whether the statement “Time does not exist” is elegant or useless is a matter of taste, and there is no accounting for that.
I agree with Sean.
I would say to Those-who-have-transcended-Time:
“OK, I surrender, you got me, time doesn’t exist.
“Now please explain to me why time appears to exist.”
But I have much the same attitude about the much-vaunted many-worlds interpretation of quantum mechanics:
“OK, I get it, the universe doesn’t have to choose which branch of the fork / eigenvalue / eigenvector to pick, it just takes them all.
“Now please explain to me how I ended up in this one.”
What I never understood about the arguments of the “timeless” crowd was why, according to them, time doesn’t exist but space does exist. In relativity, time and space are on an equal footing, apart from a mere difference in signature in the metric. And in QFT, both time and space translations are carried out by unitary transformations—again, they’re on an equal footing.
So you could just as easily eliminate the time variable as any of the three space variables. But nobody seems to be wandering around wide-eyed saying “The y-direction doesn’t exist!”
The other issue is that causality is an extremely powerful principle in physics. Nature appears to exhibit a causal ordering of events, at least inside of light cones. So even if a particular choice of time parametrization is arbitrary, that causal ordering is still there—it’s “diff invariant”—and that causal ordering is precisely what most physicists mean by “time” anyway. Do the timeless people claim to have gotten rid of causal ordering? If not, then what are they even really talking about?
Now, most physicists already fully anticipate that notions of space and time may both begin to break down near the Planck scale. But understanding what’s going on there will require some new theory of Nature beyond relativity or QFT—something like string/M theory or its successor. And that’s not the issue we’re even discussing here—we’re not talking about the breakdown of time (or space) at the Planck scale due to bizarre stringy effects or what-not. What the timeless people claim is that we can already see the breakdown of time—that time cannot be fundamental—already at the level of semi-classical relativity at everyday energies! How do they justify this assertion?
Sean, I agree with something you once posted about crackpots, that if someone who challenges an accepted idea wants to be taken seriously and have his papers get read, then the first thing he needs to do, right at the beginning, is answer the most obvious questions. The timeless people have never attempted to do that.
The closer you get to the speed of light, the slower time flows, right, time dilation! If you reach the speed of lght, c, time would stop flowing, true?
That’s not my exprience. But given that both B and Fotini are at the Perimeter Institute, it could be that the people there are like that. 🙂
“The closer you get to the speed of light, the slower time flows, right, time dilation! If you reach the speed of lght, c, time would stop flowing, true?”
Yeh and one day soon man might learn how to travel back through time and travel back to the real year 2001! Then we can escape from the black hole that the universe fell into, I could the say the Earth but that would not make any sense.
I guess I’m just not smart enough, but….
In GR, if you’re working in a spacetime with a metric that’s got one timelike and three spacelike dimensions, how can you make time go away altogether? Isn’t it implicitly lurking down there somewhere?
Am I just too facile in my understanding of GR?
The closer you get to the speed of light, the slower time flows, right, time dilation! If you reach the speed of lght, c, time would stop flowing, true?
Actually, not really true– and the problem is that it’s a poorly phrased statement. You *can’t* reach the speed of light, not if you’re a massive particle.
In fact, you’re always at rest, at least with respect to yourself.
While I tend to agree with the posting, what would be cool in this situation is if we could invite Julian Barbour to respond, and try to address these issues. To make us see what the point is.
Is that possible, Sean? No-one sufficiently inspired by timelessness has appeared in the comments.
Yet.
(I wanted to end with a good time-related pun, but that was the best I could manage.)
There are two kinds of people in physics. Those who think that quantization is the most beautiful and deepest insight in modern science, and those who simply cannot comprehend what quantization can mean and see evidence for continuous divisibility in everything in nature. What sets this split of opinions apart form any other disagreement in science is that almost no one ever changes their mind…
Hi Sean,
I would agree with what Count Iblis suggested: they are not suggesting that *time* does not exist, so much as that *now* does not exist, in the sense of a borderline between that which is past/certain/fixed versus future/undetermined/malleable. Perhaps it would be better to say that ‘becoming does not exist’.
I think you are supposed to derive comfort from this idea in the sense that all of the good times and people you experienced in the past are just as real as ‘now’ (which is nothing special). Even if this is true, however, the illusion is a persistent one, as someone wise once said.
Also, while I’m here and since you mentioned the last one, let me note that FQXi has launched a new essay contest — see http://www.fqxi.org/community/essay
Anthony
I’m decidedly an amateur in these matters and not a technically sophisticated one. But here’s my question. When you drop the time variable from the basic equations of physics to get these timeless models, are you eliminating potentially redundant information, or just recasting equations into a different but mathematically equivalent form?
To put it another way: what about two instantaneous states of the universe that are identical physically, but exist at different times? It would seem that, if time is “real,” then these two states are truly distinct; but if there is no time (in Barbour’s sense) then they are, quite literally, the same. Maybe this difference would have some further statistical implications?
Again, as a total non-expert, I’m commenting more in the hopes of being told why I’m wrong than in order to answer the question correctly.
I find James and George Musser’s comments to be the most insightful.
My perspective (or rather, the perspective I have arrived at after thinking about how to respond to this for approximately 30 seconds) is that timelessness is seen as an insight into the “fundamental structure of nature.” What does that mean, operationally? It means that our ultimate theory-of-everything should not contain time in its fundamental description, and so we can use this as a guiding principle while searching for it. Perhaps a good analogy is with background independence: one might claim that “a fixed spacetime background does not exist,” with the meaning that we should be looking for background-independent theories as we search through TOE-space.
Obviously time should emerge, so as to reproduce our everyday experience—just as, in James’s example, the continuous world should emerge from the quantum. But this isn’t the point that timelessness advocates (myself included, I suppose) are trying to make, or even care about.
Perhaps saying that Time does not exist will have some testable consequences, as does my saying that Magnetism does not have an independent existence, and is not a force in its own right.
Magnetism is an artifact of continuous electrostatic field lines and the finite speed of light. If the speed of light were infinite, there would be no “magnetic force”, or lateral shift in the direction of the electrostatic field lines of force. That being so, I predict that magnetic monopoles will never be found, because they do not exist. Neither do centripetal monopoles exist.
I’m afraid Sean has put his finger on exactly what was wrong with the FQXi essay contest [apart, that is, from the failure to weed out the obvious cranks]. There was way too much vague talk about timelessness and such stuff, and way too little about actual concrete physical models of anything. I was tempted to submit an essay, was dissuaded by the cranks, and was very glad that I hadn’t bothered when I saw who won.
For sure there is an interesting issue lurking here — but whatever it is, what is needed at this point is a deep physics argument with lots of equations.
It seems to me the whole idea of trying to eliminate the idea of time is sort of like trying to negate one’s entire experience as a human being. What’s the point? We are born, we age, and we die, and we define these stages by the ordering of events in our own experience of time. We all experience these things and it seems to me only someone who experiences these things in a significantly different way from most of us would dare claim that time is not an extremely useful concept. It strikes me as a sort of dilletantism bordering on arrogance to think that time should not be a beautiful concept.
My own feeling is that the commonality of description of time in the quantum and classical world relates to the appearance of change with the passage of time. Things change around us and within us even if we try to avoid it. Similarly I think fluctuations in space time are the equivalent to the passage of time in the classical world, but happening in discrete steps.
I seldom agree with Sean but I wholeheartedly agree with him on his reaction to eliminating the idea of time. Even if you can reduce time as an emergent property of fluctuations in space related to thermodynamics, what’s the point. A rose by any other name would smell as sweet.
I was going to comment on this, but I don’t have time.
Peter, perhaps you’ll find time later?
As someone pointed out elsewhere “Time is there to keep everything from happening at all at once”
I don’t see how you can eliminate time and retain causality in any meaningful way. I am not a professional scientist but I am sort of attached to the notion of causality as a fundamental feature of reality.
e.
@ Qubit and Rob Knop
What about tachyons?