Nice question :-) However, didn't you implicitly use the notion of 'time' as a transformation parameter already with the definition of a state (i.e. at a certain 'time' there has been a measurement in order to identify the 'state')? Then you are already stuck with the notion or concept to have a transformation acting on that state in order to change it to another state (implicitlky assuming that at another 'time' you'll find different observables in order to identify the state change...) :-)

"For a change in state space to be able to occur in the fist place, isn't the pre-existence of something like time a prerequisite ?"

Suppose for a minute that there is no space time at the fundamental level. So change is fundamental and from it space and time can be defined.

Lets take the example of a toy world. Suppose that this world is a mechanical clock. You can define changes in this clock as relations among parts without any reference to time. Then you can define time as the position of the arrows of the clock.

Louis, true,

But the question is - what is the *something* that permits the occurrence of this change to take place at all ?

Referring to the toy world you describe: it may very well be envisioned as a set world in which no change is ever possible - it could be just a frozen, set, hardened, 'erstarrt' world - the world just sits there, period (at least seen from within that world).

Now for the world to be capable of undergoing change, there must be something, a pre-existent built-in or underlying feature or an attribute of this 'erstarrt' world, that enables the change to occur in the first place.

Isn't that attribute time itself ? In this 'emergent' time definition, there seems to be a strong chicken-and-egg issue. You could perfectly envision a frozen world that would not have this capability and would just stay there.

It's exactly what happens to the 2-D world on a Schwarzschild horizon, by the way: Time cannot be emergent from from such a 2D world

Chris,

"what is the *something* that permits the occurrence of this change to take place at all ?"

Science is about the permanent relations among changing aspects of the universe. Science does not explain why change happens. That changes happens is a primary fact of the universe which we do not explain. All that we can talk about are the relations that do not change.

The real change in the universe is what is created NOW. The whole universe is what has been created in the past. So your question is "What is Creation?" Bergson called that "Duration".

Louis,

I'm not trying to explain *why* change happens, but *what* enables change to happen (my word 'permits')

There are a number of external scenarios in the universe, local and nonlocal, that can totally block change from happening. Whenever change can happen, it must be enabled by an underlying feature.

Why it happens is a separate issue.

Time does appear to be an inherent part of the universe but unfortunately within science, especially physics, time seems to be a time-keeper rather than an engine of change. This means that time as understood in physics appears to play no role other than acting as a way to keep track of change. Does this mean that there is no time as understood in a human way, meaning as the driver of change, and that things just happen? Thinking in this way means that science can never ask really fundamental questions involving time. At the moment the drivers of change appear to be forces/fields which attract or repell so-called elementary particles, this also means that no true change ever takes place since science assumes that all "new" aspects of reality are merely re-arrangements of these particles rather than than anything truly unexpected or indeterminate. And yet human beings possess a sense of newness when it happens, at least if they pay attention. Does then true change occur? Bergson believed that this happens constantly so that nothing ever truly repeats. I find this approach far more interesting than a kind of static universe.

Frank,

We say that physics describes reality. But it is not really the good picture. Physics express invariant aspects of reality using the relational mathematics language. It describes the laws of nature. But the laws of nature are like the laws in human societies. They do not describe what makes human societies evolve and changes. But human societies have transformed themselves by adopting laws which regulates it so to enable a us to exercise our freedom. The world has evolved in similar way, the law of physics did not exist in the origin of the universe, everything including the laws have evolved. Like in human societies, this laws have emerged out of the underlying interactions and all the layers of evolution of life have also evolved through layers of enabling laws. So change is the underlying reality that we do not have access. Knowledge can only express these laws of nature which have enable the maximum harmony in the overall interaction call the cosmos. This is continuing in our societies.

There is no such a thing as a driver of change. Physics describes the boundary within which freedom can be express , these boundaries are the laws of nature and of our societies. What drive the changes is the creativity in nature and in ourselve. What is creativity: it is true time.

Louis

"the law of physics did not exist in the origin of the universe, everything including the laws have evolved. "

I am sorry but this is nonsense! As this would then mean, for example, an iron atom now is not the same as an iron atom billions of years ago!!

Also, what you are saying would then refutes any sort of cosmological science, because we couldn't judge what was happening in the past, because the laws of nature themselves would have been different.

This is what Cambridge University Professor Martin Rees said when asked 'What do we mean by law of nature':

"One of Einstein’s most hackneyed sayings is, ‘The most incomprehensible thing about the universe is that it is comprehensible.’ What Einstein meant is that the laws of nature seem to apply not just here on earth, but everywhere in the universe. We could imagine a universe where there were no laws at all, completely anarchic, every atom being different. And were that the case, we’d make no progress at all in making sense of the external world."

Laws are regularities that work everywhere the same. If there were no laws, we could understand nothing. But we understand a great deal. Regularities, Rees says, makes science possible.

“The progress of science has been understanding that there are patterns in nature and discerning successive unifications of these patterns,” he says. “And this, of course, makes it possible to make predictions, which means that we don’t need to remember so much—we needn’t record the fall of every apple because we know how it happens.”

The laws of physics did exist at the onset of the Big Bang. However, the physics is different. At the moment we don't have a satisfactory theory of quantum gravity that can describe this episode of the BB. If the laws of physics did not exist in the origin of the universe, the universe now would be completely anarchic. You, me and the rest of us would not be here!

Issam,

That mathematics is outside of the universe, desimbodied is a very old and wrong idea. There is a natural mathematics embodied in our world, it emerged out of the stabilisation of the relations in nature. Either you conceive the universe's origin scenario as: a dualistic universe with one part eternel , mathematics containing all the laws of nature and desimbodied and you get the second part , our embodied universe which is like a puppet of the other one. I am not a platonist, I reject this dualistic view in favor of a monistic naturalistic view of the evolution of everything including the laws. It is why the attempt to unify physics with separate hilbert space framework are doomed. Mathematics has to be part of the natural evolution and embodied and naturalized.

Have a look at:

http://blogs.discovermagazine.com/cosmicvariance/2012/10/18/feynman-on-initial-conditions-evolving-laws-and-what-we-consider-physics/#.URhSJR00XTo

Feynman on Initial Conditions, Evolving Laws, and What We Consider Physics

I also think that this model can explain why the laws of physics are fine tuned for the evolution of life without the spooky multiverse.

It can also explain the super-low initial enthropy.

Louis

There is nothing in the article that says what you claim" the law of physics did not exist in the origin of the universe"

Further, what I think is meant by laws of physics evolving is perhaps that there are different scale regimes for which different laws of physics apply. Quantum gravity, quantum mechanis to classical Newtonian physicsal laws. Hwever, the laws of physics, once they are within their own domain, do not change.The laws of physics themselves do not change but we use different laws for different scales.

One of the most vigorous on-going fields of research in physics is classical-quantum correspondence. This field of research is concerned with the discovery of how the laws of quantum physics give rise to classical physics in the limit of the large scales of the classical level.

That's metaphysics. If laws change, we change too and don't see the laws the same way. All we can say is that the logics coded into our brain allow us to perceive "regularity" which are usefull for our survival. That is physics. At worst, cosmology may be viewed as metaphysics.

You are quite right Claude. I am also not happy with the use of the word "evolve". It seems what was metaphysics 50 years ago may still be so now. However who knows if a time will come in the future and Feynman proves us all wrong!

It may be important to separate at least two things in this interesting question. One is the notion of time that emerges from our perception. The other is the notion of change (and its relation to time) that exists independent of our existence/perception of it.

The former is bound to give rise to some regularities by virtue of coincidences that our sensors/transducers detect at multiple time scales (e.g. photoreceptors in the retina sending impulses to the visual system on the order of 60-100 ms vs. some hair cells in the cochlea detecting vibrations in the air at sub-millisecond scales). Provided that all things are working correctly and the person's genetic code is more or less working OK, we'll get everyone consistently detecting change and regularities. This will emerge from the entrainment of our rhythms and the rhythms of the external physical world. Our perception of time will emerge there and also will be distorted when the physics change: as in an earthquake for instance. We have created ways to tally the changes and we have agreed on various scales to do so. To see that this particular notion intrinsically depends on our central and peripheral nervous systems one would just have to deal with patients who never quite get it or who lose it (e.g. children or adults with autism spectrum disorders, adults with advanced Parkinson's disease, Alzheimer's, etc. whose circadian rhythms work differently).

The other notion, the one that exists independent of our existence is the one that seems more interesting (intriguing). It may be that change (which may give rise to time) at different scales emerges from the disparity of forces in the universe and the differential effects that different types of forces may have on matter. The overall combination of the forces and the matter may give rise to different detectable coincidences and to transient regularities that nonetheless fluctuate in non-trivial ways. Those non-trivial fluctuations out of transient stability generate changes. When such changes are systematic they can be tallied.

It may just take a system with capabilities to detect change and to care about it enough to wonder about regularities and their systematic appearance. That system would necessarily have to have a memory or a metric to measure that the event now has been experienced as it matches some other previous event. It would not have to be the human race... But how a disembodied notion of time would exist and who/what would be there to care for it is the question that I find interesting.

I suggest to have a look at the contribution "Time in Quantum Theory" of Zeh (Link see below). Also, the "emergent" character of time seems to be related to Mach's point of view., that there is no absolute time, but only the relations of the entities of the physical world.

http://www.rzuser.uni-heidelberg.de/~as3/TimeInQT.pdf

Actually Herbert, I've just finished reading Zeh's 'Physik Ohne Realität: Tiefsinn oder Wahnsinn' by Zeh, it's flawlessly excellent.

His 'Physical Basis of the Direction of Time' was good too, but somewhat dated now.

I had an email exchange with Zeh some time ago, we kind of disagreed on the role of mathematics in the universe. He saw it as a mere calculation tool, whereas I tend see it as a layer sitting on top of physics in the hierarchy of what creates reality ... a view which I believe has overwhelming evidence in its favor.

This can be misinterpreted of course, and it seems to me that those who are vehement in rejecting that view read things into it that are just not there. There is no feeling or opinion in classifying, say, physical chemistry below physics (bearing in mind of course the advent of multiple top down pyramids at every level, AND the phenomenon of non-linear 'emergence' at every level too)

Now the questions are, of course, in no particular order:

- What sits, if anything, above maths

- are we ready or prepared for the consequences of maths ? (for instance, as Zeh convincingly shows, a version of the multiverse idea is an unavoidable consequence of Schrödinger's equation)

- etc., etc.

I'd like to hear the 'physical' explanation of those who view math as a mere invented way to count bushels of corn, by the way, of why Bell's theorem actually works in apparent utter defiance of any conceivable material explanation, of why the term e=mc² is not just a meaningless artefact , and countless other such phenomena, which seem to be smoking guns for the fact that in nature, a valid mathematical equation shall just not be falsified.

Incidentally, if I may add a comment about the 'smoking gun'

Material explanations were sought for Bell (for a very good but now somewhat dated review, see e.g. Huw Price's "Time's Arrow") . All these explanations suffer from 3 drawbacks:

1- They entail extraordinary complex and narrow baggage, all of it seeming furiously ad hoc. Some of the scenarios that work entail backward causation coupled with total loss of free will, or even more exotic scenarios.

2- They are not proven, and indeed most are mutually incompatible.

3- None of these scenarios work to explain the *other* smoking guns, the e=mc² 's of the world, the astonishing cases that arise from current leading-edge, Fields-medal level abstract math

So you could legitimately say that what the mathematics layer does is only paper over our ignorance - it seems to sit atop physics in the Auguste Comte hierarchy because of our ignorance - we just do not know which arcane theory explains Bell, for instance, and any other weird real-world case where math seems to dictate to physics.

Unfortunately, this skirts very close to looking for hidden variables - which, math again, is fairly well ruled out by Gleeson's theorem .....

Quote:

Time can be viewed as an emergent property ...But isn't this circular reasoning ?

I agree it's circular, a common logic problem in the wording of the "problem statement." Correcting the wording of the "problem statement" would lead to meaningful answers, pertinent to your thesis, I think.

Quote:

The only way out of this conundrum is that all elementary state space changes must happen out of time, i.e. instantaneously (with a delta time = 0.)

Or reword the problem statement ... but to answer in the spirit of the qualifications you provide in the excerpted paragraph, physicists have mapped the dimensional universe to a second one that has one less dimension. Many papers exist on this mapping and it's implications. Most came out of the idea of 3D entropy of a black hole being mapped to the 2D surface of the "event horizon."

Inside this event horizon, the laws of physics are different, dramatically so, and should be part of this discussion. Some interpretations of the math have the time-like being swapped with the space-like. The details are outside of the scope of my post. However, the idea of "laws of physics/equations" in one section of "space-time" do not match that of an adjacent space-time, needs the posters on this page to take into account.

To extrapolate to the creation point, call it the Big Bang, the 'laws of nature/equations' that exist today, those known today by mankind, must be extrapolated "as is" to time = 0, is in my opinion, an assumption. Recent papers published last year have done this extrapolation, and I look forward to having spare time to read them.

That said, I'll like to define "physics" as not limited to the use of mathematics to express "laws of nature." It's far more than 'equations.' It's a thought process, word problems, thought experiments, some of which is backed up with math, and some that is communicated to others in a precise form using a common language called math, so that it can be further discussed, and either be "proven" or "disproven" with a rigorous symbolic logic method. So, posts that limit themselves to the 'equations' are missing a huge segment of what physics is about.

A qualification on this question I pose is "Which came first, time or space?" To be fair, my answer is time. And space dimensions emerged from/during/over time. Which dramatically poses a "problem statement" in stark contrast to the original question. Perhaps a better worded problem statement?

- I have made a Comment on: "Should we distinguish Course and Time Arrow of Time? '

By EtienneKlein

It says that on Physics:

- Agree to distinguish the time course of the arrow of time, the latter being connected to causality and irreversibility of phenomena.

-However, allow me to disagree with your assertions about Prigogine.

- Having taught for many years Thermodynamics, according to Prigogine, (and having known it), he was given also lead to some reflection on TIME.

- First, the Second Law of Thermodynamics, as it was formulated axiomatically by Ilya Prigogine, can clearly and definitively distinguish Reversible and Irreversible processes, which was not the case before him!

- The extensive variable entropy S, varying over time dt, operates by:

- dS/ dt = de S/ dt + di S/ dt

-

- de S/ dt is the flow that the entropy exchange system, in both directions, with the outside.

- P(S) = di S/ dt is the internal production of entropy

- Indicating that entropy is a quantity dissipative

- The second principle then reduces to:

- P (S) = 0 for a reversible processes

- P (S)> 0 for irreversible processes

- Note that for the conservative variables, mass (M) and energy (E), the same formalism remains valid, with:

- di M = 0 et dM = de M

-

- di E = 0 et dE = de E

- What reformulated more generally the first principle including the mass !

So: The entropy production is defined by: P (S) = S di / dt

This means that production takes place over time

There is no question of "entropic time" in this axiomatic

This does not exclude that the physical time went on, the arrow of time is revealed during an irreversible process (P (S)> 0)

The best example simple (while remaining in the linear domain) is the coexistence of micro-reversibility at the molecular scale * (Brownian motion) and macroscopic irreversibility in a transfer (Diffusion).

In this case, the causal comprises a concentration gradient (or chemical potential)

The irreversibility of the transfer (flux flowing from the chemical potential of the highest to the lowest chemical potential) ARROW SHOWS TIME.

It remains that, over time, the Brownian motion continues to exist.

There is one area, however, where the ambiguity may be attributed to Prigogine and his collaborators is that of cosmology.

In this case, the thermodynamics is added to General Relativity and Quantum Physics. (Cf. Example: Thermodynamics of cosmological matter creation, I.Prigogine, J. Geheniau, E. Gunzig, P; Nardone, PNAS. USA, 85, 7428, 1988)

It is here that during the creation of our universe, we can note, I think he said, there simultaneous creation of entropy and time, time would be of entropic nature, it would be the intrinsic arrow .

* Also note that the micro-reversibility introduced by Lars Onsager in 1935 to establish its phenomenological equations requires a temporal correlation, which in modern terms is:

For position fluctuations xi and xj, the correlation function is

Rij = where < > indicates the time average

Here t is the current time and the correlation time τ

Microscopic reversibility is expressed by:

Rij = Rji

-

That is to say, we are going from t to τ in both directions!

Dan VASILESCU

Professor Emeritus at the University of Nice-Sophia Antipolis

There is psychological time where time has different lengths depending on whether or not we are enjoying ourselves . There is artificial time where we mark things out such as on a clock . This time is related to the movement of the earth . Weirdest of all the quantum world works on numerical time and its' value is 9 . Lastly, in our real world , there is a variety of real times which Shakespeare pointed out . If my compatriots are going to ding me for these statements I might as well throw out that this universe is essentially run on the number 3.

Perhaps followers of this question would be interested in contributing to the Research Topic I am hosting at Frontiers-- here is the link

http://www.frontiersin.org/Perception_Science/researchtopics/The_long_and_short_of_mental_t/2182#

After reading your reference James, it occurred to me that we have two locations for time . One is in our three dimensional world which you are exploring and one in the quantum world . Time in our three dimensional world has broken out into all types of time, whereas in the quantum world it is entirely different . I suspect that the quantum world doesn't literally have travel through space but we think it does because our measurements fit our conception of travel through space. I suspect that particles in the quantum world travel using time . This process is similar in principle to electrons having to gain sufficient energy to jump from orbit to orbit and don't literally move through space as we understand the process in order to get from A to B. If we observe a travelling particle in the quantum world , we convert it from quantum ( travel ) time to our three dimensional time . We live in a three dimensional world which utilizes space / time and the quantum world is based on energy and time or is an energy / time world . Energy is either gathered before something happens or released where we see it as radiation of some type.

Chris,

''The only way out of this conundrum ...''

Another way out of the conundrum is to avoid defining time as a parametrization of change but to consider it as change itself. When there is change there is time. If something exist and change then there is time. Change has to be assumed to exist always because assuming any interuption would necessarily implied the end of change forever. So change is primary or intrinsic to what exist NOW or what exists NOW changes and cannot cease to do so.

Chris,

''Time can be viewed as an emergent property''

Time is change. Change is not a property of a physical system but change of the physical system and its properties.

I agree with Louis.

If we assume time is change, then if nothing is going on, by inference time has stopped . If time has stopped, then time exists in the real world and has a parameterization . Of course, it all comes down to how you define time . If some things in the real world continue no matter what, then time never stops and therefore never exists in our real world accept as a series of abstract concepts .My contention is that time in the quantum world is parameterized and in our real world completely abstract even with clocks . I say this because you don't have travel through time in the quantum world except in the abstract ( it's an illusion ) . In other words the quantum world is the reverse of the real world .

Bob,

There are some extreme platonist physicist that would consider that the world does not change ; these physicist use a variable for time in this timeless world. Change in that world are change along time line; it is what happen we one move along those line but this is an observer effect of moving along a time line. For them there is no objective change. This point of view is very hard to smallow. Some of them like Julian Barbour even denies that there is a time line because he can demonstrated it can do without it in the physical description. In fact I find logical that Barbour can demonstrated that parameter time, spatial time is illusory because any physical description by definition is a pack of sings on a sheet of paper and they do not change. I accept Barbour conclusion that there is no change in this description because it is obvious that the sign on the papers do not change and so cannot include change. So the greatest physical innovation of all time was the use of the parametrization of time for entering body movement dynamics in a platonic world of mathematics, was also its biggest illusion. That dynamic description captures what is invariant in this dynamic and thus what can be predicted from it and leaves all other aspects of reality out, i.e. all other aspect the truly change, which means everything that exists. When the changes are slow with respect to the experimental context, then this mistake does not matter.

I think the possibility of finding a complete explanation of the nature of time is beyond the limits of human cognition. I do not need to make any experiments to realize that first I thought it is impossible for us to explain the nature of time and later I started to write this and that's something I cannot change. Our perception of time is "wired" at a very low level in our thinking machine. It appears to me that it is impossible for us to imagine a universe where nothing changes and this is because the concepts of change and time (even if it's only psychological change and time) cannot be conceived separately. Temporal order is implicit even in our explanations:

:explanations our in even implicit is order Temporal .separately conceived be cannot (time and change psychological only it's if even) time and change of concepts the because is this and changes nothing where universe a imagine to us for impossible is it that me to appears It .machine thinking our in level low very a at "wired" is time of perception Our .change cannot I something s'that and this write to started I later and time of nature the explain to us for impossible is it thought I first that realize to experiments any make to need not do I .cognition human of limits the beyond is time of nature the of explanation complete a finding of possibility the think I

Edit:

I have a computational analogy to explain what I just wrote. Consider this program:

#include

#include

main(){

long i=0;

while(1){

sleep(1);

printf("Time= %ld seconds. State = waiting.\n",i++);

}

}

If we compile it and run it, we will find that there is a clock inside the computer. Now, what kind of experiment can we make, restricting ourselves to use the monitor, the keyboard, and the mouse ( No Internet: the universe comes without a user manual.) to find out what is the mechanism of this clock?

Time in our real world has many different values. In any instant of time ( time is still moving, even slightly ) each of us experience time from a hard wired viewpoint which is usually coordinated with our enjoyment of doing something. I think the concept of time is right up there with Einstein's experimentally proved space . If mass can flex space then space is real and could be constructed for the sake of argument by strings and therefore must physically exist . Julian Barbour's denial that there is a time line because he has demonstrated that he can do without it in physical descriptions reminds me that some mathematical equations can only be resolved by excluding time from the equation . In short, it means that if we're not required to use something all the time, it doesn't mean that something doesn't exist . To put an interesting twist on the concept just because occasionallly you and I aren't exchanging words in Researchgate it doesn't mean that you and I don't exist in between these times ( couldn't resist ). Of course, there is always the possibility that when a tree falls in the forest it means it doesn't make a noise if no one is available to hear it . In short you and I disappear out of reality ( time ) when we aren't communicating which is an interesting thought .

Bob,

I define time as change. In physical equation, nothing by definition change. There is a variable there called 't' that allow to paramaterize the change of other variables. This is the predicted changes of these variables in function of t. But you will notice that there is no special time in these equation called 'NOW'. It is not even specified what is the positive direction of time where all phenomena are occuring. So this variable ''t'' is not like the time we experience in the ''NOW'. These equations are about a fixed world, not really our world that is always in the 'NOW'. But our world is structured. This structure is the part of the past we can experienced in the 'NOW'. Physical equations are about the structural aspect of our world (the past in the now) that do not change. Predictions are thus partially possible when nothing really new is being created in the experimental conditions, and in such well controled conditions, the equations are usefull. At the quantum level, we are not able to apply any such equations for individual phenomena because we are almost touching the changing nature of reality. At that level, the equations are probabilistic only.

Louis,

Under your definition of time as being change itself, time then becomes local, and endlessly manifold: say in the Universe, somewhere a particle changes quantum states (for instance an electron changes orbits) : that event can only affect things inside the 'light cone' arising out of that particular event, and nowhere else.

In the still-static Universe outside that light cone - i.e., the vast majority of the rest of the universe both in space and in 'time' - time still does not exist.

Then say that many such events happen all over the place everywhere in the universe: time has now become infinitely fragmented, endlessly reset, and general 'time' then becomes a statistical phenomenon emergent from a huge slew of disparate and independent events.

Not sure if that can be the whole story - I'm not sure at all how Bell's inequality would then be capable of emergence, nor how delayed choice experiments could emerge from this simple scenario ....

Time is very difficult concept. We invented clocks and arbitrarily divided up time . The clocks tell us when things happened and gives our lives consistency and order . Just because we invented time doesn't mean that it is not an emergent property . Everything has its' own time and therefore it is an emergent property in all of us as well as events in nature . For instance, the sun cycles every 11 years .

Since light moves with velocity c, the information arriving by photons to us or to every location in space-time has arrived there along the light cone of that location. However, the photons have also been red-shifted which gives us another information about how much time has passed since the photons were emitted. Using that measure of time and c, we can work out a distance to the emitter.

I don't see what is gained by calling time an emergent property.

Chris,

Thank you for your response. If sometime I may give the impression that I know what time is, it is a false impression. Just let say that I try to find out and I know that you know a lot that I do not know and it is why I was talking to you.

There seem to be a lot of phenomena in quantum physics that seem to do not care about the light cone. As you know, quantum mechanics is not a local theory and so the world is not. I read in the book of Lee Smolin: time reborn that in the new formulation of GR in shape dynamic , there is a notion synchronicity for the whole universe. I cannot explain that to you, probably you can explain it better to me, but again light cone seems obsolete. Stating with Galileo looking at a pendulum at the ceiling of a church and timing is period with its pulse and stating that there is a law, come a strange notion of imputing to the observed system the time of an external device: the clock. Galileo conceives one of the first mechanical clock. It is not a coincidence because it is central to methodology of modern science to include in the property of a system what is obviously external to it: the time of a clock.

Louis,

Thanks for an interesting answer - I found Lee's book rather questionable, as many others did (see Peter Woit's review, and so on)

This being said yes, the light cone indeed is not the whole story , as we've known since Bell's inequality - addressing all these questions is book length ....

Chris,

I would very much like to ear some of your thoughts on Lee'book on my

thread:

https://www.researchgate.net/post/Time_Reborn_What_do_you_think_about_the_ideas_presented_by_Lee_Smolin

Chris,

I agree that time as an emergent property is a step in the right direction.

The next step is that there is no universal emergent tick. Simply there is no time at all.

Things change interact in one common reality. Some of them are selected as clocks to compare with other states. All I see is a vast number of changing coexisting states of coexisting objects.

I see some relevance of the concept of traffic. It emerges from the properties of vehicles that move. There is no point you can put your finger and say this is traffic. You finger will always point to a vehicle. Traffic is an abstract concept, like time it "flows" and you can calculate flow rate (number of cars in my street per number of cars in the reference  street both between dawn and dusk) .

Newton's concept of absolute time has not been abolished as it is claimed, but it has been multiplied and shifted to each inertial frame. We need one more step to abolish it altogether and free ourselves from this entanglement.

But change as such, and memory of past states is a bit of a mystery so there is plenty of interesting problems yet to be solved by science.

Ilya Prigogine

https://www.youtube.com/watch?v=2NCdpMlYJxQ

Louis

This is a great link. And Ilya makes a great statement there

My role as a scientist is not to invent the universe but to describe it.

Despite his statement about the existence of time I believe that concept is derived from perceived change not an existing entity.

It is a handle convenient to describe change.

The core issue is that objects with transient existence can either coexist whereby one can affect another in both directions or they vannot, Then only the older object can affect the younger through changes it made to the environment. 

But to the best knowledge none of them exists without pior cause.At least as far as macroscopic objects are concerned. 

interesting question

my question is who or what will measure the change

change needs to be detectable in order for it to count

and as soon as we place a fame of reference or a set of them to express the origin of the (detectable) change we will also need to deal with other issues such as distance metrics, magnitudes, directions, etc

interestingly, as far as I know there are no known time receptors in the brain or the nervous systems

in that domain time emerges as a property of the neuronal firing patterns (as in the cochlea for example)

we know of neuron's preferred directions and maps in sensory space but not of preferred "time" maps, and we can derive those from spatial maps in some cases

I don't think that the interesting and very cultured lecture by Ilya Prigogine contributed anything useful to a physicists conception of time. A physicist must be able to express  time evolution of a physical process in the formal language of mathematics without references to Bach's music.

 Elizabeth,

In my opinion, change is easy to detect by humans as well as by inanimate systems. A human perceives change through long and short memory and images from the past with the help of sensors.

You compare the way your home looks today with the memory of the moment you moved in or by viewing your pictures taken then. Watching a movie shows short memory in action when the perception of the current frame is confronted with memories of a few past frames. There is no complexity in understanding the change perception. When you try to model it it is a different issue.

Sensors on some missiles detect Line of Sight (LOS) direction to the target. The change of that position can be compared to the previous position memorised in the previous frame which is controlled by a tick of an oscillator. It is easy to find if the current LOS is changing or not by comparison of the current and the memorised previous state. 

The difference can be used by the system to correct its velocity vector to keep the LOS relatively constant and therefore to catch the target in the future location.

All this can be accomplished either by modelling the control system based on detailed physical model of the system using Newon's dynamics.

But it can also be done without knowledge of the actual system dynamics detailed mathematical model by using a few rules of thumb and a fuzzy logic plus some experimental tuning of the fuzzy parameters. 

Quite frankly no concept of time is necessary to accomplish the proportional guidance law as it is called. Dumb fuzzy guidance often outperforms sophisticated mathematical model based control systems - in particular when the system is not linear.

To the best of my knowledge bats use the proportional guidance law to catch insects based on the reflected ultrasound waves they produce and listen to. And they know nothing about time. They perceive change and control the flight to nullify the change.

 Matts,

I agree with your last post. It is quite counterproductive when some scientists (in particular the celebrities) become preachers of their own philosophy that appears to them as consistent with their scientific knowledge.

I acknowledge the value of analysing metaphysical concepts in the context of science but this should be kept separate. 

Look at the famous "God does not play dice". What value this statement has to the progress of knowledge other than that even the most celebrated scientists follow their own prejudices?

I think that the concept of time as its currently understood, is a prejudice and and it is as strong as a religion and therefore it will defended till one's death.

To my best knowledge no one has successfully defined time as an existing entity without circularity or creating an arbitrary rule. 

On the other hand Mach's notion of time as an emergent property is rational but this does not appeal to people's beliefs.

Thanks Andrew,

But I do not think it is that trivial at all. Your explanation assumes a couple of things a priori. One is that memories are stored and retrieved easily. The other one is that you set a ticking clock somewhere to keep counting. The latter defies the very concept of self emergence and the former is such a non trivial problem for neuroscience that there is an entire subfield trying to figure it out. What you store as a memory is a big question mark, and how you retrieve it is even more complex. Then, even after you solve the memory storage-retrieval problem, what constitutes change requires a metric to measure it and that is non-trivial as well. So, the explanation that you provide is one that has already assumed many things. I was looking for something to build from first principles. But thanks again. Oh BTW, Newtonian mechanics won't do it, and it requires time-dependent quantities and objects, so we are back to a pre-definition of time to define the very thing one is trying to find as an emergent thing. No good.

Elizabeth

I may have not understood the context of your question. I am not  trivialising the redearch of time perception in the brain. This is not simple and I am not an expert to comment. But as a person  applying science I was commenting on change detection on an abstract level with practical examples.

In computer application context, change is detected by comparing the content of memory element A versus it's copy B  in the previous iteration.

It is simple but you can make it arbitrarily complex by analysing every part of the cpmputer system evolution leading to this simple detection. The reasoning process naturally is based on elementary concepts acquired through learning and is not a simple thing to explain.

The very concept of change is temporal in nature, arising from the fact that the same object may exist in mutually exclusive states. If you acknowledge this as a fact then it is clear that elementary object cannot be aware of anything but one state. You need multiple objects acting as memory to detect change which is the confirmation of two instances of mutually exclusive states. 

The question to supporters of time as an independent existing entity is: What does it do to objects and how. And how to define it so it is not a function of objects such as clocks.

What is an emergent quantity?

Someone here proposed that individual cars are not traffic, but together they form the emergent quantity traffic.

Individual molecules in a gas have velocity but not temperature, but the collective motion of the molecules and the statistical distribution of their velocities define temperature. So temperature is an emergent quantity.

Time is a book-keeping device for all physical processes which are not in absolute rest at absolute zero temperature, and a linear coordinate like a spatial coordinate on a map. I don't see why call it emergent? The interval a-b between two times a and b takes its meaning from the definition of time as a coordinate.

H Chris Ransford said that "whenever the state space of the universe undergoes any change - then Time itself happens". I disagree, the time coordinate is always present outside regions of the Universe where nothing happens, like in absolute rest at absolute zero temperature, It is not an emergent quantity.

Someone referred to a talk by Ilya Prigogine about time. I listen to it and concluded that it was philosophy, not physics.

Andrew, I like your answer much better this time, and the question that you pose at the end gives me something to think about. Thanks!!!

Elizabeth ,

Time is not pre-existing to changes.  It is induced from changes and so has no reality of its own prior to changes.  

''there are no known time receptors in the brain or the nervous systems''

The nervous systems are coordination centers of bodies in motion and these have plenty of sub-systems with inherent time constant or natural frequencies.  The nervous systems is in intimate feedback with thousand of cyclical process in the organism.  In a way it is filled with clocks. Thousand of process are self-timing at different temporal-scale and are also coordinate to synchronize for specific coordination events.  Take for example the capacity that human have to interact with music in dancing where all kind of rythms in the music are synchronized with different motor systems.  But all that is known to you and so I do not understand your question.

Elizabeth,

It is interesting to follow interdisciplinary studies where time is the focus. Science domains other than space time physics bring their unique view of temporal relations.

You say:

as far as I know there are no known time receptors in the brain or the nervous systems

It is new to me that someone has formulated such problem. We are used to statements like "time exists" or time is "what clock measures" but both introduce problems.

Sensing time is quite interesting and I would say that if time is a tangible existing entity it could be "sensed". Like gravity, it is everywhere and it and it can be sensed when needed.

What I am interested is how one can go about proving the absence of time sensors in the nervous system?

Proving non-existence is hard because if at all, it is only possible in limited space and duration under strict assumptions.

You say:

time emerges as a property of the neuronal firing patterns

For me it is one more confirmation of my simplistic first order position which in this context could be expressed as:

1. You cannot sense time unless you make an arbitrary definition of it based on selected objects behaviour

2. Organised systems have implicit or explicit reference processes that contribute to their temporal behavior.

3. Why such processes are possible no one would probably know, but one can discover laws by which they appear to operate.

For example, living organisms respond to daily and yearly cycles because they depend on light and temperature not a clock. The roots of plants however need gravity sensing mechanism which force the growth in the right direction.

The statement here that time emerges as a property of the neuronal firing patterns has a very limited application. Time can be used to date geological structures. To date is not to emerge.

Louis,

"Time is not pre-existing to changes. It is induced from changes and so has no reality of its own prior to changes."

I could not agree more with you. So much so that as soon as I finished my undergrad studies in math I went on to design and propose a little equation that tackles this issue in motor control. I have gotten plenty of empirical support for this proposition in the realm of intentional (goal-directed) self-produced motions in an intact nervous system.

Yet along the way I came across spontaneous motions (motions embedded  in movements that are co-occurring largely beneath our awareness). There and in cases where the nervous systems break down (e.g. autism, schizophrenia) things change in ways that I need to better understand. I have devoted the last few years to trying to understand what goes on in those cases.

"The nervous systems are coordination centers of bodies in motion and these have plenty of sub-systems with inherent time constant or natural frequencies."

Yes, absolutely so, but how the system integrates this information (e.g. microsecond time scales within a certain frequency range in the auditory system and millisecond time scales with other freq ranges in the visual system) in a coherent way that systematically gives rise to a consistent solution invariant to changes in dynamics, context and other things, is an open question.

And how in the feedback process the various systems that control motion (the very motions whose coordinations will give the outside observer some sense of time) do so while compensating for internal transduction and transmission delays of the electrochemical signals is also another open question.

Unfortunately the whole formulation of these important problems  in the field that I initially targeted is Newtonian and as such time dependent. So, any trajectory that people manage to obtain as the solution of some very complex set of equations yield a pre-defined temporal profile already. In this sense what you see as research in Neuroscience is the opposite of the above statement. There (rather unfortunately for me) time precedes change and defines it.

The whole thing is backwards to that field and they are banging their heads against the wall with no progress that in my eyes is worth a thought.

I went solo a long time ago, so I work on other things from a totally different perspective, a perspective that is very much in line with your statement above but that now takes into consideration the stochastic nature of these processes.

Thanks for your comments which I find very illuminating.

Andrew,

"For example, living organisms respond to daily and yearly cycles because they depend on light and temperature not a clock."

Yes, and we also have temperature and motion receptors across the nervous system that detect changes in external and internally self-produced motions. We also have receptors for circadian rhythms. (Some people do research in that area or disruption in circadian rhythms in blind people to the extent that there are now drugs to treat sleep disorders linked to that, but I am not entirely familiar with that literature).

I do know that the motion and temperature channels help us with corporeal awareness to build frames of references to track changes in our self-produced motions and also in the motions that we manage to perceive externally. These signals also feedback to centers in the brain via precise afferent channels and help with the formation of body maps in the sensory and in the motor cortices and also in sub-cortical very primitive structures for motor control.

I never thought when I learned about these things that we would need explicit time information directly encoded because it can be deduced from changes detectable as signal in various sensory domains. Now, an interesting outcome from my research in the last few years has been that in systems with neurodevelopmental disorders where the child cannot socially connect to others, the information on motion as internally sensed by their peripheral nervous systems is corrupted by noise and randomness; while the temperature information as registered by instrumentation sensors from the skin has an incredibly reduced range as compared to typical ranges. 

If I were to think of motion as the thing to help us keep track of events and form a memory of systematic events leading to some outcome, these children could not do so based on their internal feedback (because it is random and highly noisy). As such it carries very little signal conducive of an expected value. Then if we were to think of temperature as the thing that gave me support in the range of values that make the change in that signal detectable (i.e. wrt the signal I just experienced), that support would be so narrow that the memory never quite gets to form. In other words the person would only live "in the here and now".

So, cycles based on consistent information and temperature seem to be good contributors and potentially good candidates for us to rely on to deduce temporal dynamics of processes that nervous systems experience.

I'm just beginning to scratch the surface on their contributions to our existence as social beings. So far those who do not have these signals rightly processed in their nervous systems coincide with folks with a diagnosis of autism and schizophrenia (both considered social disorders), but it is just correlation, not causation of social disorders. My lab has been the first to point this out in a quantitative way, and it is still very recent, so we have no clue as to why it is that their motion and temperature dysregulation is so prevalent.

One thing we know now is that corporeal self-awareness is nearly non-existent in these fellows and as such anchoring motion (external or internal) to a frame of reference is not possible for them, neither is time estimation from their motions in any consistent way.

"The roots of plants however need gravity sensing mechanism which force the growth in the right direction."

Beautiful way to put it. We also have receptors in the vestibular systems that help us cope with gravity and motion

Once again, thanks for your comments!

Elizabeth

Your area of research is fascinating and in fact may be a key contributor to clear understanding of physical nature of time. After  all even the most abstract ideas have their origin in the nervous system. Even the most static reasoning like boolean algebra has an underlying implicit temporal aspect.The mutual exclusion of truth and falsehood means that a logical variable is allowed to change and change is temporal as opposed to difference that isn't. 

It may as well be that time is only the concetual tool to organise our thoughts about the reality not a physical entity at all.

Some say that time is relative and/or an illusion but it is no more than life is.

Andrew, very deep indeed. Lots of things to think about.

Thanks!

Elizabeth,

I recently went on your research site at Rutgers and I learned of your interest in the connection of deficiencies in motor control and autism.  It was the first time I heard about it immediatly made sense to me.  It Is well known that autism is associated with a deficiency in a person empathic ability.  The word ''empathy'' comes from the German's aesthetic philosophical tradition (http://plato.stanford.edu/entries/empathy/, Robert Vischer, Theodor Lipps ),   It was first used as related to our ability of ''feeling into'' an artwork and it was associated with our motor capacity to embodied/re-enact the movement in the artwork. It was about the same period hypothesized by people likeLipps and  Dilthey ( http://c-cs.us/configuring/Dilthey.html) that our empathic capacity towards other people was based in our built-in simulation of other motor system, as a sensory-motor re-enactment of the other.  More recently in neuro-science this has been partially re-discovered in the research on mirror neurons. We look at the face of another human and re-enact it and this re-enaction allow us to feel-in the other person emotions by re-enacting them.  The use of botox in the face do paralyse some of the face muscle reducing facial expression and also the empathic capacity of interpreting other facial expression.  So it makes perfect sense to some problem in someone’s motor control will reduce their empathic capacities like in autism.

There is a complex tradition where time do not define motion but is defined by it.  This is the relative tradition: Leibniz, Kant, Mach, Tarde, Bergson, Whitehead, Pierce,Deleuze, Smolin, etc.

An inspiring thought from Goedel:

"As we present time to ourselves, it simply does not agree with fact.

To call time subjective is just a euphemism .

An entity corresponding in all essentials to the intuitive idea of time ... in relativity theory exists only in our imagination"

"A relative lapse of time, however, if any meaning at all can be given to this phrase, would certainly be something entirely different from the lapse of time in the ordinary sense, which means a change in the existing. The concept of existence, however, cannot be relativized without destroying its meaning completely."

Is science serious allowing time travel as a viable reality? - ResearchGate. Available from: https://www.researchgate.net/post/Is_science_serious_allowing_time_travel_as_a_viable_reality#562e6c355e9d9729f98b459e [accessed Oct 27, 2015].

Dear All,

In all the previous posts I don’t see any reference to the thermal time hypothesis by Carlo Rovelli and Alain Connes in their 1994 article "Von Neumann Algebra Automorphisms and Time-Thermodynamics Relation in General Covariant Quantum Theories" (A. Connes, C. Rovelli, Class.Quant.Grav. 11:2899–2918, 1994).

Generally co-variant theories do not have a notion of a distinguished physical time with respect to which everything evolves. However, it is not needed for the full formulation and interpretation of the theory. The dynamical laws are determined by correlations which are sufficient to make predictions. But then a mechanism is needed which explains how the familiar notion of time eventually emerges from the timeless structure to become such an important ingredient of the macroscopic world we live in as well as of our conscious experience.

A possible solution to this problem has been put forward by Carlo Rovelli and Alain Connes, both in the classical and quantum theory, and goes by the name of the thermal time hypothesis. It postulates that physical time flow is not a priority given fundamental property of the theory, but is a macroscopic feature of thermodynamical origin.

In the abstract the authors say "We consider the cluster of problems raised by the relation between the notion of time, gravitational theory, quantum theory and thermodynamics; in particular, we address the problem of relating the "timelessness" of the hypothetical fundamental general covariant quantum field theory with the "evidence" of the flow of time. By using the algebraic formulation of quantum theory, we propose a unifying perspective on these problems, based on the hypothesis that in a generally covariant quantum theory the physical time-flow is not a universal property of the mechanical theory, but rather it is determined by the thermodynamical state of the system ("thermal time hypothesis"). We implement this hypothesis by using a key structural property of von Neumann algebras: the Tomita-Takesaki theorem, which allows to derive a time-flow, namely a one-parameter group of automorphisms of the observable algebra, from a generic thermal physical state. We study this time-flow, its classical limit, and we relate it to various characteristic theoretical facts, as the Unruh temperature and the Hawking radiation. We also point out the existence of a state-independent notion of "time", given by the canonical one-parameter subgroup of outer automorphisms provided by the Cocycle Radon-Nikodym theorem"

I would appreciate your comments on this interesting hypothesis which is not easy to grasp for me as I don’t know anything about von Neumann algebras.

Marc,

'' notion of time eventually emerges from the timeless structure''

This sentence is self-contradicting.  How can anything change or emerge into a structure which is said to be timeless, i.e. unchanging????

Thank you Marc for this reference to Carlo Rovelli. I found that he has many papers and essays and even a book on time, so there is no need to go back to a complicated 1994 paper. Do taka a look at the essay "Forget time" in arXiv:0903.3832.

Matts,

Thank you very much for the reference.

In his 2009 article “Forget time” written for the FQXi contest on the Nature of Time  Carlo Rovelli wrote: "Here I argue for a possible answer to the question 'How should we think about time in the future quantum theory of gravity?'. The answer I defend is that we must forget the notion of time altogether, and build a quantum theory of gravity where this notion does not appear at all. The notion of time familiar to us may then be reconstructed in special physical situations, or within an approximation, as is the case for a number of familiar physical quantities that disappear when moving to a deeper level of description (for instance: the “surface of a liquid” disappears when going to the atomic level, or “temperature” is a notion that makes sense only in certain physical situations and when there are enough degrees of freedom.)".

Matts and Louis,

The following quote from Rovelli's 2009 paper illustrates the reasoning of the author:

"The relativistic coordinate t is a freely chosen label with no direct physical interpretation. This is a well known consequence of the invariance of the Einstein equations under general changes of coordinates. The physical content of a solution of Einstein’s equations is not in its dependence on t, but rather in what remains once the dependence on t (and x) has been factored away.

What is then the physical content of a solution of Einstein’s equations, and how is evolution described in this context? To answer, consider what is actually measured in general relativistic experiments. Here are some typical examples:

Two clocks:

Consider a clock at rest on the surface of the Earth and a clock on a satellite in orbit around the Earth.

Call T1 and T2 the readings of the two clocks. Each measures the proper time along its own worldline, in the Earth gravitational field. The two readings can be taken repeatedly (say at each passage of the satellite over the location of the Earth clock.) Let (T′1,T′2), (T′′1,T′′2), ... ,(Tn1,Tn2), ... be the sequence of readings. This can be compared with the theory. More precisely, given a solution of the Einstein eqs (for gravitational field, Earth and satellite), the theory predicts the value of T2 that will be associated to each value of T1. Or vice versa.

Solar system:

The distances between the Earth and the other planets of the solar system can be measured with great accuracy today (for instance by the proper time on Earth between the emission of a laser pulse and the reception of its echo from the planet.) Call dp the distance from the planet p, measure these distances repeatedly, and

write a table of quantities d′p , d′′p, d′′′p, ...dnp, .... Then we can ask if these fit a sequence predicted by the theory. Again, given a solution of Einstein’s equations, the theory predicts which n-tuplets (dp) are possible.

Binary pulsar:

A binary pulsar is a system of two stars rotating around each other, where one of the two is a pulsar, namely a star that sends a regular pulsating beep. The frequency at which we receive the beeps is modulated by the Doppler effect: it is higher when the pulsar is in the phase of the revolution where it moves towards us. Therefore we receive a pulsating signal with frequency increasing and decreasing periodically. Let n be the number of pulses we receive and N the number of periods. We can plot the two against each other and describe the increase of N as a function of n (or vice versa).

The moral of these examples is that in general relativistic observations there is no preferred independent time variable. What we measure are a number of variables, all on equal footing, and their relative evolution. The first example is particularly enlightening: notice that it can be equally read it as the evolution of the variable T1 as a function of the variable T2, or viceversa. Which of the two is the independent variable here?

The way evolution is treated in general relativity, is therefore more subtle than in pre-relativistic theory. Change is not described as evolution of physical variables as a function of a preferred independent observable time variable. Instead, it is described in terms of a functional relation among equal footing variables (such as the two clock readings (T1,T2) or the various planet distances dp, or the two observed quantities n and N of the binary pulsar system).

In general relativity, there isn’t a preferred and observable quantity that plays the role of independent parameter of the evolution, as there is in non-relativistic mechanics. General relativity describes the relative evolution of observable quantities, not the evolution of quantities as functions of a preferred one. To put it pictorially: with general relativity we have understood that the Newtonian “big clock” ticking away the “true universal time” is not there".

Chris and others,

No comments?

Well, everybody can look up all Rovelli's papers on the SAO/NASA ADS database,.not only those he sent to arXiv. I don\t see why we should quote them here in extenso.

Also, yo need not agree with him.