The Nature of Time by Julian Barbour

Thanks for the paper!

I also greatly enjoyed your book: THE END OF TIME.

Loved your quote: "As Ernst Mach said (1883) [3]: It is utterly beyond our power to measure the changes of things by time ... time is an abstraction at which we arrive by means of the changes of things; made because we are not restricted to any one de¯nite measure, all being interconnected. Einstein, an admirer, quoted this passage in his obituary of Mach, calling it a gem. Oddly, Einstein never directly attempted a Machian theory of time, but in fact such a theory of `time without time' sits hidden within the mathematics of his general theory of relativity [4], the foundation of modern classical physics."

Mach uses that word "change" twice, and yet it does not seem that change was ever woven into Einstein's and Minkowski's spacetime, until now.

Finally we have been liberated from frozen time and the block universe, with a simple postulate and equation--the fourth dimension is expanding relative to the three spatial dimensions at the rate of c, or dx4/dt=ic.

This naturally implies x4 = ict, and thus all of relativity may naturally be derived from this postualte and equation of Moving Dimensions Theory.

Give me a 4D universe where

x1=x

x2=y

x3=z

and

x4=ict

And all of relativity will naturally arise--all because of a fundamental invariant--dx4/dt=ic--the fourth dimension is expanding relative to the three spatial dimensions.

Now a great thing about this hitherto unsung universal invariant--the expansion of the fourth dimension--is that as an invariant, it can also easily account for the slowing of light and time by gravity, as well as the gravitational redshift, as is done in the attached paper.

For the first time in the history of relativity, change has been woven into the fundamental fabric of spacetime with dx4/dt=ic.

Loved the Shakespeare quote too (from one of his sonnets), which tells us that change does indeed need to be woven into the fundamental fabric of spacetime, which is exactly what Moving Dimensions Theory does:

When forty winters shall besiege thy brow,

And dig deep trenches in thy beauty's ¯eld,

Thy youth's proud livery, so gazed on now,

Will be a tattered weed of small worth held.

Wheeler oft quoted Shakespeare. Modern physicists could benefit infinitely from a more classical liberal arts education--there's something about that heroic spirit, which underlies the advancement of art and science, that our academies are failing to teach these days.

I think you will enjoy my paper: Time as an Emergent Phenomenon: Traveling Back to the Heroic Age of Physics by Elliot McGucken :

http://fqxi.org/community/forum/topic/238

"In his 1912 Manuscript on Relativity, Einstein never stated that time is the fourth dimension, but rather he wrote x4 = ict. The fourth dimension is not time, but ict. Despite this, prominent physicists have oft equated time and the fourth dimension, leading to un-resolvable paradoxes and confusion regarding time's physical nature, as physicists mistakenly projected properties of the three spatial dimensions onto a time dimension, resulting in curious concepts including frozen time and block universes in which the past and future are omni-present, thusly denying free will, while implying the possibility of time travel into the past, which visitors from the future have yet to verify. Beginning with the postulate that time is an emergent phenomenon resulting from a fourth dimension expanding relative to the three spatial dimensions at the rate of c, diverse phenomena from relativity, quantum mechanics, and statistical mechanics are accounted for. Time dilation, the equivalence of mass and energy, nonlocality, wave-particle duality, and entropy are shown to arise from a common, deeper physical reality expressed with dx4/dt=ic. This postulate and equation, from which Einstein's relativity is derived, presents a fundamental model accounting for the emergence of time, the constant velocity of light, the fact that the maximum velocity is c, and the fact that c is independent of the velocity of the source, as photons are but matter surfing a fourth expanding dimension. In general relativity, Einstein showed that the dimensions themselves could bend, curve, and move. The present theory extends this principle, postulating that the fourth dimension is moving independently of the three spatial dimensions, distributing locality and fathering time. This physical model underlies and accounts for time in quantum mechanics, relativity, and statistical mechanics, as well as entropy, the universe's expansion, and time's arrows."

Thanks for the paper & all the best,

Dr. E (The Real McCoy)Attachment #1: 12_MOVING_DIMENSIONS_THEORY_EXAMINES_THE_GRAVITATIONAL_REDSHIFT_SLOWING_OF_CLOCKS.pdf

Julian Barbour is again trying to suggest that (quote) "time should be banished" (end of quote), but the simple proof against his hypothesis is the fact that his brain is working.

Namely, no living brain can operate in a "block universe", because it will have to function as a Turing machine installed in some IGUS, and the perpetual "encoding of information", by any conceivable "code", will lead to decreasing of the entropy of the "hard drive", until the poor Turing machine develops severe structural damages and breaks down with a stroke.

Please check out the essay 'Quantum Mechanics 101'.

Dear Dimi,

A Turing machine can be viewed as a succession of states, and the relation (transition, in a temporal view) between states is governed by the physical laws. Any Turing Machine can be embedded in a block universe, exactly as any algorithm can be stored on a storage device. You are right that the entropy is the enemy of such a machine, but nobody claims that our brains will live forever (although Tipler seems to overcome this problem).

Cristi Stoica

"Flowing with a Frozen River",

http://fqxi.org/community/forum/topic/322

Dear Dr. Barbour,

Contrary to the common impression, that the Newtonian Mechanics provides too little room for a more profound analysis of time, your essay proves the contrary. Thank you for this beautiful exposure.

Cristi Stoica

"Flowing with a Frozen River",

http://fqxi.org/community/forum/topic/322

Dear Julian,

As with your recent talk at the Perimeter Institute on the same subject, I enjoyed your essay. I also very much agree with you that duration/interval does not exist and is merely an out-flow of motion. I have a question though. Do you still believe that instants and instantaneous magnitudes exist? If you perhaps do, and I get the impression from reading your essay that this is the case, I think that your view about time has some issues. Firstly, as they would constitute the building blocks of time, if one assumes the existence of instants (and instantaneous magnitudes), one also necessarily assumes the existence of time. Secondly, to deny the existence of interval, and yet hold onto instants, is not consistent, as, by definition, an interval is simply a duration bounded by two instants; as long as the instants are still there, the interval will be too. Indeed, if such instants existed, it can be shown that they would render change, motion, and as such, the idea of a clock, impossible.

Best wishes

Peter

Peter, not that I'm trying to answer for Julian, but I believe that the existence of instants does not necessarily have to entail the existence of intervening durations/intervals. In fact I argued in my essay that one can have a perfectly consistent theory of Time and Becoming where only instants (or moments of Becoming) are real, while the supposedly continuous happenings (e.g. the evolution of the wave function) in between instants are just mathematical artifacts. Let me give an example of how one might define intervals/durations in a theory with only instants:

Consider a certain number of cycles of a certain stable regularly recurring process, say 9192631770 cycles of the process corresponding to the radiation from the transition between the two hyperfine levels of the ground state of the Caesium 133 atom. We DEFINE this to be our unit of Time (it's the actual definition of a second). All other "intervels/durations" of Time are then measured with respect to this process. e.g. if two instants of certain events coincide with the 10th and 11th cycles of the photon process above, then we say the duration/interval between the two instants is 1/9192631770 second. That doesn't mean that anything real has to happen or exist in this duration/interval, because we can define change as simply the discrete transition from the state at one instant to the state at the next instant, WITHOUT ANYTHING HAPPENING IN BETWEEN. There's nothing wrong with such a theory of change, and in fact it seems to me that quantum mechanics demands such a theory of change.

Dear Chi Ming:

You say, "That doesn't mean that anything real has to happen or exist in this duration/interval, because we can define change as simply the discrete transition from the state at one instant to the state at the next instant, WITHOUT ANYTHING HAPPENING IN BETWEEN." But you can then do away with any concept, such as velocity, or length, or energy, because you don't know anything about it, if you are not observing it. There isn't anything wrong with this, but is it especially useful? You make an assumption, regardless of whether you choose to believe that something is in between, or not.

Commenting more generally:

It seems to me that there is no physics in the choice between time emerging from relations between events and relations between events reflecting an underlying time. If time must be eliminated to explain observations, then there will be physics; but this was not demonstrated in the essay, even if you assume (see the end of the essay) a finite universe and no black holes.

In the end (again, see the end of the essay), the argument comes down to Occam's razor. There is no problem with arguments based on Occam's Razor, I have used it myself; and, in the end, it is often necessary. But is anything really simplified by eliminating time? I don't think so; because you are not only left with events, but also an ordering of them. And what does time do? It orders events. Even if you eliminate time, you must keep the ordering. The replacement of the concept of time, with some other conceptual ordering does not get you anything; even if you want to call it purely abstract, it is just time, by another name.

Or, with different semantics: Either you have time plus events producing an emergent order, or events plus an order producing an emergent time - there is a difference, but not a simplification; so Occam's Razor cannot choose.

Finally, note that there is another essay, arguing for time but no space, at:

http://fqxi.org/data/essay-contest-files/Markopoulou_SpaceDNE.pdf

I think that you can define away space, just as easily as you can define away time; but, again, I see no physics in it (yet).

Take care,

Ken.

http://fqxi.org/data/essay-contest-files/Sasaki._TDoT.pdf

I forgot to add, to my initial comments, that this essay did a really great job of presenting some very interesting material.

Ken.

Dear Chi Ming Hung,

Thanks. I would recommend having a look at my essay for an explanation of what is I think is wrong with that idea.

Best wishes

Peter

Ken,

I disagree that there's no physics if we "define away time". First of all, I'm not advocating the elimination of Time like some in the quantum gravity camp (and Julian) are advocating. The idea I'm trying to put across is that we should eliminate the Time **CONTINUUM** as something unphysical, because there's no need for it except as a mathematical convenience.

And this is not just a matter of convention either, because by treating Time as though it's a physical continuum, physicists are led to the inevitable paradoxes between continuous unitary evolution between measurements, and discontinuous non-unitary transitions during measurements. And to make matters worse, most physicists seem to think that the UNOBSERVABLE continuous evolution of the wave function is the true physics while the OBSERVABLE quantum jumps are the aberrations that needed to be explained away (e.g. using decoherence). This seems most illogical to me.

I think we can all learn a lesson from how things are done in the early days of Quantum Mechanics, when Heisenberg and company were trying to work out Matrix Mechanics in order to explain the correlations between observables (and only observables) like the frequencies of light from atomic spectra and their relative intensities, with a minimum of mathematical assumptions. It's true that even Heisenberg and company assumed the time continuum and wrote exp(-iwt) for a process of frequency w (omega), but my point is that we should keep the physically unobservable mathematical assumptions in our theories to a minimum and recognize that's what they are: just mathematical assumptions. In fact I think Quantum Mechanics would have developed very differently (and much more logically) had Heisenberg and company gone all the way with their philosophy and eliminated even the unobservable exp(-iwt) from their equations...

And you're right that if we eliminated the Time continuum, then all we're left with are just instants and their orders. But that's all we need! My contention is that modern physics (esp. Quantum Mechanics and General Relativity) can be recast into physics about only instants and their orders, and when this is done, we can gain deeper insights into physics that have been hidden from us by the unphysical Time continuum.

And I think that's not very far from Julian's ideas...

Dear Chi Ming:

Thank you for your comments.

You state, "And this is not just a matter of convention either, because by treating Time as though it's a physical continuum, physicists are led to the inevitable paradoxes between continuous unitary evolution between measurements, and discontinuous non-unitary transitions during measurements." You also state that you find certain attempts, to reconcile the continuous with the discontinuous, to be "most illogical".

I don't think that discretizing time is necessarily objectionable; but I think that there should be a real reason, based on observation. I do object to the idea that there is any utility in abandoning the concept of time entirely. In addition, I agree that there are certainly discontinuities in QM; and, if time must be discretized, to prevent a paradox, then doing so is mandatory. But is there really a paradox, as you say - a logical contradiction - in continuous time evolution, with discontinuities at certain interactions; or is it just something that seems odd? If there is a logical contradiction, can you please explain it to me?

Consider also that, while there are situations that observably demonstrate discontinuity (EPR and other entanglement situations; many worlds not withstanding), most situations do not. Note also that "collapse of the wave function" is peculiar to certain interpretations of QM, but not all. If you are going to discretize time, to make everything look like wave-function collapse, then you are, in effect, choosing certain interpretations, over others; and to do this, you should have an observation that supports those interpretations, over the others. Can you please tell me if you have such an observation?

Take care,

Ken.

Ken,

you seemed to have misunderstood me when I said:

"And to make matters worse, most physicists seem to think that the UNOBSERVABLE continuous evolution of the wave function is the true physics while the OBSERVABLE quantum jumps are the aberrations that needed to be explained away (e.g. using decoherence). This seems most illogical to me."

What's illogical a priori is not that we may have a theory with "continuous time evolution, with discontinuities at certain interactions", but rather that physicists are treating the **UNOBSERVABLE** part of the wave function evolution as true physics, while treating the **OBSERVABLE** quantum jumps as aberrations. To me, it should be the other way round, treating observable phenomena as true physics, while relegating the unobservable part of physics as mere mathematical convenience.

As for the reality of quantum jumps or wave function collapses, I suppose many physicists are still unwilling to accept it because it contradicts what they believe to be the true physics behind quantum mechanics, namely the continuous and unitary evolution of the wave function. I guess what I prefer to call reality is not something that lives in a Platonic world of mathematical ideals, but rather what I see with my own eyes (and with the help of instruments): I see always a world of definite states, never fuzzy quantum superpositions. You asked me for evidence of my "interpretation" over others, that's what I submit.

But let me ask you for evidence to the contrary: Please show me any physical evidence of a wave function that evolves continuously in time. I don't think you can, because BY DEFINITION, it's unobservable! The best you can do is to point out experiments (e.g. interference and entanglement experiments) that INDIRECTLY implies the existence of a wave function that evolves continuously in time, but that's all. You never see a ghostly ether-like wave leisurely traversing space and time, all you ever see are dots and discrete events in your screens and instruments.

I'm not arguing against the utility of using a mathematical wave function that evolves continuously in time, what I'm arguing against is to take this mathematical convenience too seriously and think that it is physical reality.

The development of 20th century physics has taught us that what's not directly observable should not be treated as real. Such is the case for the ether, the absolute time of Newton, and a list of other ideas. My contention is simply that the Time continuum and the denizens that evolve in it should join the list and be recognized as what they are: mathematical conveniences, not physical realities.

(P.S. I should apologize to Julian for hogging the forum for his essay. I think we should continue this discussion in our essays' forums...)

Dear Julian,

I appreciate your attempt to provide "an equation of time," thereby demoting time from its otherwise fundamental status. I've a question concerning this proposal that I'm hoping you will answer.

In order to use your definition, I need to unambiguously identify entities in different configurations, e.g., THAT planet in configuration 2 is Mars and it is the SAME planet I called Mars in configuration 1. I need this identification process articulated so I can measure the delta d's, for example. How do you define this identification process without bringing time in the back door? Isn't this identification process precisely the basis of "trans-temporal identification?"

Thanks,

Mark

Dr. Julian

I am impressed with your handling of the "Big Picture".

The way I understand your proposal is, to answer Mark Stuckey above, yes time comes in the back door as the sidereal choice necessary to make eq. (3) a relational, quantitative measure. Then time is led right back out the front door when its utility is exhausted in finding the principle of least action it defines in the motion observed.

I found your analogy of the synchronous relation of arcs swept out by the tips of hands of different clocks very enlightening.

It seems both you and Carlo Rovelli propose time should emerge From and As the kinematics of observable (local) variables via the principle of general relativity.

i.e. "extremal curves" are not absolute but locally finite.

Your ideas on time can apply with equal efficiency to mass and space, for once you have set mechanics "fully adrift" in the relativistic sea, all three dimensions emerge in a similar way. Your "extremal curve" is a physical constant, an observable that is defined by its dynamical equivalent observed in the constancy of the speed of light. The kinematics expressed by the principle of least action arise from the dynamics that define the three fundamental dimensions as different aspects of the same thing.

Although my essay won't win or place in this competition and few will even realize what I've said, I am very grateful for your work here as both you and Carlo have offered methodology to my madness. The model I've presented is so far adrift in general relativistic scope, no one would dare jump aboard without the compass you have designed.

Dr. Barbour,

Terrific essay. My questions are:

If the universe can tell perfect time and could be considered the perfect clock, how would that assumption be affected if it is determined that there is no absoulte age of the universe? If I am living on a far away galaxy accelerating at a much faster velocity than ours - then (assuming I take enough vitamins to live through the whole process) how old do I think the universe is from my perspective? Or, how old is the universe to me if I am near a black hole or better yet - If a very long time ago I watched the big bang from a safe distance (where my gravity and velocity would be very different compared to being "inside" the universe) how old would I think the universe is right now? Who would be correct?

Take care,

CJ

"Duration" is not physical. It can't be found in the heavens. It has meaning only in the presence of an observer.

Hi,

I thought your paper was fun. The ending was good.

I will say right off that I think the issue of whether time exists or not is irrelevant, even though time has some mysterious elements to it. I do think it is something which is operational with respect to the universe, and not something which the universe operates according to. I found your section one relative timess,in particular on page 7 with the ratio of times for two solar systems interesting. My paper #370 illustrates how time is a scaling principle. I illustrate a program for a renormalization group system for energy (or its conjugate time) on different scales. Your classical mechanical example at its kernel is I argue for.

cheers,

Lawrence B. Crowell

Dr. Barbour:

Your paper was interesting for me to read, as it arrives at the same conclusions as mine, although clearly in a much more rigorous way.

After all that we have learned from science in the last few centuries, one might think that we would have learned to separate physical reality from what our senses perceive. Clearly, though, there are few that are ready to take that step.

James Tyson

Dear colleagues,

I'm afraid there is no sense in posting our comments and questions here, because Julian Barbour lives in a different world, and just doesn't care.

Dimi Chakalov