"Forget time" by Carlo Rovelli

Vesselin Petkov:

Thanks for your comments. Time and space are what I call relationship structures. They are geometric entities which tie kinematic entities to dynamical ones. As such I tend to suspect that science is unable to tell us in much on whether these actually exist. For that matter the term exist or existence is a bit of strange, and ontological categories appear to have a measure of "relativity" to them.

Fotini has an interesting paper which appears to be getting less attention on how time exists and space does not. I have yet to comment on this paper, mainly because I need to come up with something substantial, but it is curious that one would choose to say time exists but space does not --- an apparent complementary view to Rovelli's. To be honest I wonder if the apparent Carlo-Fotini dualism here suggests something.

The evolving block world might be captured within my Escher disk perspective on AdS. Each tessellation of the AdS is a particular tiling of the spacetime. How each "cell" joins other cells is a way in which a quantum path might split. So a particle which leaves the BTZ black hole horizon the AdS contains, or leaves the boundary at v ~ c will follow an arc or path, but there are at each vertex a set of crossing paths. These are other amplitudes, which in a decoherence or measurement etc may push the particle onto. So in that setting the "block" is the set of all possible paths, but the "evolute" is the particular path a particle may take as it approaches the boundary with v ---> 0.

Lawrence B. Crowell

[My apologies to Carlo for breaking into his thread]

On Dec. 16, 2008 @ 02:58 GMT, Vesselin Petkov wrote:

"Yes, of course, the evidence that time flows is indeed overwhelming, but that evidence is not physical."

If the evidence were physical, there would be some bona fide (Dirac) observable in GR, which would reveal the source and the origin of the "dynamic dark energy", and the ether will come back.

Therefore, we should not expect to catch any *physical* evidence for the flow of time.

You also wrote (ibid.): "... the macro scale evidence supporting the block universe view is overwhelming."

Please see a startling confession by Thomas Thiemann in astro-ph/0607380 v1:

"The puzzle here is that these observed quantities are mathematically described by functions on the phase space which do not Poisson commute with the constraints! Hence they are not gauge invariant and therefore should not be observable in obvious contradiction to reality."

More in my post to Gavin Crooks from Dec. 13, 2008 @ 20:55 GMT.

Dimi Chakalov

Lawrence B. Crowell wrote,

"Fotini (Markopoulo) has an interesting paper which appears to be getting less attention on how time exists and space does not. I have yet to comment on this paper, mainly because I need to come up with something substantial, but it is curious that one would choose to say time exists but space does not --- an apparent complementary view to Rovelli's. To be honest I wonder if the apparent Carlo-Fotini dualism here suggests something."

I am curious about that myself, because way back in this thread I commented on that apparent duality coming from the Perimeter Institute, based on Carlo's previous papers on partial and complete observables. I wrote:

"...there may exist theories of complete observables and theories of partial observables that are dual to each other. That is, where a mathematically complete prediction corresponds to the partial observable event probability 1.0. I think that, consistent with Smolin's theme of 'the present moment in quantum cosmology,' it is the principle of least action that preserves the present moment ..."

I never got a reply, and maybe it isn't worth one. However, I remain curious.

Tom

I will try to read Markopoulo's paper again this week. It takes a bit to pick through the list of them here. As I have said there are two different views of time in GR and QM. GR considers the interval as the relevant defintion of time, while QM requires the use of the coordinate time to define wave equations. Of course it might be argued this is an artifact of our representation of quantum states in spacetime more than anything fundamental to QM. On my little #370 space I argue how on a GR frame that proper interval must be measured by some oscillating system which executes some small non-geodesic motion, possibly requiring the use of a coordinate time.

The dualism between our two concepts of time, GR v. QM, might manifest itself under some categorical or functorial map as a matter of either time or space disappears.

Lawrence B. Crowell

Just want to add my 2 cents to the debate between the Block Universe (BU) and the Evolving Universe (EU) viewpoints.

It should be quite obvious that the BU viewpoint is indefensible once quantum phenomena are taken into account. More specifically, the objectivity of indeterministic and probabilistic transitions in quantum mechanics is completely at odds with a BU viewpoint (as pointed out by George Ellis).

On the other hand a EU viewpoint is not at odds with special relativity (SR), because all that's required is that the space-time events, after they've become determinate (through quantum measurement), obey the kinematics of SR, at least in the macro scale. Thus, contrary to popular misconception (e.g. claims by Vesselin Petkov above), SR does not demand the existence of 4-dimensional objects, it only demands that the space-time events which constitute macroscopic objects (like rods and clocks) should obey the kinematics of SR, SR has nothing to say about whether these space-time events are part of a 4-D object, or an evolving 3-D object, or something else entirely.

It is perhaps understandable why Einstein and other classical theorists who denied the reality of quantum phenomena should accept the BU viewpoint, but it's rather inconceivable to me why any theoretical physicist today can still subscribe to the BU viewpoint...

1. My comments on George Ellis' post above will be posted on his thread later today (Montreal time).

2. On Chi Ming Hung's label placing. I believe we all have been enjoying the generally constructive discussions on this forum. Unfortunately, your latest post cannot be regarded as constructive. I would suggest that before criticizing (in your post it is worse - placing labels) a view try to do the obvious - make sure that you understand it first.

2.1. You stated: "Thus, contrary to popular misconception (e.g. claims by Vesselin Petkov above), SR does not demand the existence of 4-dimensional objects". I provided arguments; that you ignored them does not transform them into claims. I am afraid it is your position that reflects popular misconception. Here is the argument (not a claim) why I think so - sometimes people are making claims like yours because they do not bother to analyze in depth the relativistic effects (not even the special relativistic effects); try to do it now by answering the questions about length contraction I asked (and also check my post on George Ellis' thread). The length contraction and relativity of simultaneity arguments are given in more detail in Sec. 2 of my essay; even deeper analyses of them and also of time dilation and the twin paradox are given in Ch. 5 of my book "Relativity and the Nature of Spacetime" (Springer, 2005). It is shown there that these relativistic effects, and more importantly the experiments that confirmed them, would be impossible if the physical objects involved in those experiments were three-dimensional; in my previous post I attached a diagram demonstrating that the length contraction of a rod would be also impossible if the rod were a growing worldtube (and also briefly addressed a possible objection). Analyzing the relativistic effects by explicitly asking what the *dimensionality* of the physical objects involved in them is you will be in a better position to comment on whether or not special relativity demands "the existence of 4-dimensional objects".

2.2. You also stated: "It should be quite obvious that the BU viewpoint is indefensible once quantum phenomena are taken into account. More specifically, the objectivity of indeterministic and probabilistic transitions in quantum mechanics is completely at odds with a BU viewpoint (as pointed out by George Ellis)." Frankly, it is beyond my comprehension how you could write this.

First, you ignored not only the arguments demonstrating that relativity would be impossible if the physical objects were three-dimensional; you also ignored what I specifically wrote (to help those who post not to repeat the common misconception that quantum mechanics is incompatible with the spacetime picture of the world): "the probabilistic behaviour of quantum objects does not necessarily contradict the forever given spacetime picture of the world." I did not elaborate in order not to make the post too long. What I meant is briefly explained in Sec. 5 of my essay; the reference to the developed idea is also given there.

Second, how do you know "that the BU viewpoint is indefensible once quantum phenomena are taken into account"? Like anyone else you have no idea what is really going on in the quantum world. You wrote "the objectivity of indeterministic and probabilistic transitions in quantum mechanics" with which I completely agree, but believe that the block universe view is the correct view that is compatible with both relativity and quantum mechanics. Have you asked yourself "indeterministic and probabilistic transitions" of *what* we are talking about? Ultimately, we mean processes involving *quantum objects*. But we do not know what the quantum object is (just do not tell me we can't ask such a question). Only when we have the answer to that question we will know whether that answer will contradict or support the block universe view. For now, you have an example in my essay that demonstrates both (i) that the probabilistic behaviour of quantum objects does not necessarily contradict the forever given spacetime picture of the world, and (ii) that one can envisage a paradox-free quantum mechanics; these are possible when an implicit assumption - that the quantum object exists continuously in time - is identified and abandoned.

In these difficult times in fundamental physics, instead of being quick at placing labels, it will be much more helpful to try to understand one another to the best of our abilities. This is one of the necessary conditions for achieving the next breakthrough in physics.

Vesselin Petkov

Vesselin,

I wasn't "label-placing", merely stating what I think is a misconception, and I wasn't trying to offend anybody, sorry if you took it that way...

And no I didn't ignore your arguments, but I thought I already answered them in my comments... Perhaps I need to elaborate more on what I meant.

Your arguments about length contraction and relativity of simultaneity are classical special relativistic arguments, and based on just that, your conclusion about a block universe (BU) viewpoint is not subject to controversy, but they don't take into account quantum phenomena.

Specifically, rods and clocks are nothing but correlated collections of space-time events. You're correct that nobody knows exactly what goes on in the quantum world which gives rise to these correlated collections of space-time events we call rods and clocks. But it's safe to assume that whatever is going on, we should end up with correlated collections of space-time events which look and behave like rods and clocks in special relativity (SR), because otherwise we can't have faith in either SR or quantum mechanics (QM).

But can we infer from this that rods and clocks are 4-D objects? No I don't think we can, or at least it doesn't serve any useful purpose to do so. The reason I said SR has nothing to say about this matter is because the end results would be the same: there are no 4-D or 3-D objects, only correlated collections of space-time events.

It's true that my arguments are of the hand-waving sort, but until we have a better theory of the transition from quantum to classical phenomena, that's the best we can do for now.

On the other hand, your arguments about length contraction and relativity of simultaneity are also of the hand-waving type because they didn't take into account the quantum nature of rods and clocks.

As for the objectivity of indeterministic and probabilistic transitions in quantum mechanics, the evidence should be abundant: radioactive decay, single-photon double-slit experiment, Stern-Gerlach experiment etc. etc. Yes there have been attempts to explain these as outcomes of deterministic theories (like Bohm's) but only at the cost of introducing yet more hidden unobservable stuff (like pilot waves), so in this case I invoke Occam's razor and just take the evidence at face value...

P.S. While I haven't read your essay in detail, I've read the section "Worldlines and Quanta", and believe it or not, some of your ideas resonate with those of mine, though I don't think they prove the compatibility of BU with QM... But I guess I should comment more about this (and your other arguments like that of the EPR-type experiemnts) later on your essay's forum, not here... In fact I think we should continue this discussion (if you like) in your essay's forum, because it's getting off-topic here...

Chi (or Chi Ming please correct me),

I also think this discussion should continue on my essay's webpage. Here I will briefly comment just on:

"Your arguments about length contraction and relativity of simultaneity are classical special relativistic arguments, and based on just that, your conclusion about a block universe (BU) viewpoint is not subject to controversy, but they don't take into account quantum phenomena."

This is precisely what I mean. Quantum mechanics tells us nothing about the relativistic effects; these are macro scale effects confirmed by experiment. And as Minkowski anticipated these effects and experiments are manifestations of the four-dimensionality of the macro world.

Now, the interesting question is whether the quantum world is a block universe. I think it is, but in order to have a definite answer we need the answer of another question - what is the quantum object?

Vesselin Petkov

Dear Carlo Rovelli,

On a way to creation of the quantum theory of gravitation except for time other obstacles can meet. For example, a zero energy density of the gravitational field, as it is presented in an essay The Theory of Time, Space and Gravitation. Gravitational quanta with zero energy will be very strange. Before creation of the quantum theory of gravitation or before creation of the theory of everything the fuller research of properties of the gravitation is necessary.

Yours faithfully

Robert Sadykov

Dear Dr. Rovelli

You say: In short, I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time.

I would say: Relations between variables run into atemporal space. We describe them in time as a mind model.

yours amritAttachment #1: 1_Phenomenology_of_Time_and_Quantum_Gravity.pdf

Vesselin Petkov wrote on Dec. 17, 2008 @ 06:14 GMT

"Now, the interesting question is whether the quantum world is a block universe. I think it is, but in order to have a definite answer we need the answer of another question - what is the quantum object?"

Regarding this "interesting question", please notice my posting from Dec. 15, 2008 @ 20:05 GMT, about fish and bicycles.

As to "what is the quantum object?", please check out the fist posting at George Ellis' thread, from Dec. 2, 2008 @ 07:02 GMT, and my latest posting there, from Dec. 18, 2008 @ 10:59 GMT. It's all about an _arrow of spacetime_ . We should not separate time from space -- recall Hermann Minkowski.

Dimi Chakalov

Hello Carlo,

Hope all is well!

In this BBC video, Lee Smolin states, "Einstein taught us that space is not a background that things move in. Spoace is a network of relationships that are ever dynamical, ever evolving, part of the world. The geometry of space evolves and changes--WIGGLES--just like anything else==just like electromegnetism, just like particles."

http://www.youtube.com/watch?v=3bLwqnIfLRA&feature=related

So it is that dimensions move.

All that my theory--Moving Dimensions Theory--does is note that the fourth dimension is expanding relative to the three spatial dimensions, as attested to the photon which is ageless in relativity and nonlocal in quantum mechanics.

From MDT's simple postulate and equation dx4/dt=ic, all of relativity is derived.

Give me a universe wherein we have four dimensions x1, x2, x3, x4 and the fourth dimension is expanding relative to the three spatial dimensions, or dx4/dt=ic, and all of relativity arises.

This is a simple, buautiful postulate and principle--indeed, Einstein's principle of relativity descends form MDT's postulate. And MDT is more succinct than relativity, for from MDT's single postulate and equation comes both of relativity's postulate.

Also from MDT's simple postulate and equation comes a natural *physical* model for time and all its arrows and assymetries, as well as entropy, quantum nonlocality and entanglement, all the dualities--space/time, mass/energy, wave/particle--and both Heisenbergs' and Huygens' principles.

dx4/dt=ic (underlying relativity) suggests that the fourth dimension is expandingh at c.

xp-px = ih (underlying quantum mechanics) suggests that the wavelength of this expansion is Planck's length.

So it is that MDT sets both Planck's constant and the veloicty of light, while also maintaining the ocnstancy of the velocity of light by giving rise to all of relativity.

Lee Smolin also states in the video, "We've forgotten how audacious science is and how it rages sometime -- how the ideas that turn out to be true are so often outrageous... we've forgotten the lessons of the people like Einstein, who come from the outside but have exactly the right insight and right idea." --http://www.youtube.com/watch?v=3bLwqnIfLRA&feature=related BBC Hard Talk

"Openness, the inclusion of different points of view, like in anything else, is essential to progress." --Lee Smolin http://www.youtube.com/watch?v=3bLwqnIfLRA&feature=related BBC Hard Talk

In light of all this, I was hoping for some more dialogue; as there is nothing to lose by discussing foundational questions in a collegial, professional manner, and everything to lose by silence and solitude.

Too, too many established professors and researchers refuse to partake in dialogue, and this grates against the spirit of greats such as Wheeler, Einstein, and Galileo.

"I have never met a man so ignorant that I couldn't learn something from him." --Galileo Galilei

"Curiosity is more important than knowledge." --Einstein

Lee Smolin also says that a theory should "come in a coherent whole--it should start with a beautiful principle, like the principle of indeterminacy of quantum mechanics or the principle of relativity, and there then should be a beautiful equation that flows out form that principle to a myriad of consequnces." --Lee Smolin

MDT's beautiful principle: The fourth dimension is expanding relative to the three spatial dimensions at c with a wavelength of the Planck Length.

MDT's beautiful equation: dx4/dt=ic

MDT's myriad of consequences: all of relativity, time and all its arrows and assymetries, entropy, quantum nonlocality and entanglement, wave-particle/space-time/mass-energy duality, the gravitational slowing of light and time, and the single velocity for all entities through spacetime--c.

Well, Carlos, your silence on MDT after having promised to read the paper has lead me to believe that you see nothing wrong with MDT, as unlike LQG and Sring Theory, it passes Dr. Smolin's criterion for a good theory. And too, MDT predicts all of relativity along with quantum nonlocality and entanglement, as well as entropy, by proposing a novel, deeper feature of our *physical* reality.

Best Wishes!

Soon these comments will be frozen for all time, while the fourth dimension yet marches on at the rate of c!

I look forward to sending you a copy of my book, HERO'S JOURNEY PHYSICS & MOVING DIMENSIONS THEORY: FROM HERACLITIS, TO PLATO, TO ARISTOTLE, TO COPERNICUS, TO BRUNO, TO KEPLER, TO GALILEO, TO NEWTON, TO PLANCK/EINSTEIN/BOHR/BORN--AND YET IT MOVES! Unifying relativity, quantum mechanics, entropy, and time's arrows and assymetries with a new universal invariant: dx4/dt=ic."

Eppur si muove!

Dr. E (The Real McCoy)

"Books on physics are full of complicated mathematical formulae. But thought and ideas, not formulae, are the beginning of every physical theory." --Einstein/Infeld, The Evolution of Physics

MDT's *physical* idea: the fourth dimension is expanding relative to the three spatial dimensions at c, or dx4/dt=ic.

Do I smell a potential confrontation brewing here? I haven't seen anything like this since Apollo Creed tried to get Rocky Balboa back in the ring for a rematch. Can you imagine the excitement that a debate would bring:

Ladies and Gentlemen - Now for the main event. In this corner, we have our challenger:

He's the master of moving dimensions - Elliot "The Real McCoy" McGuckennnnn!

And in this corner: With the best overall combination of restricted and public votes so far - The Thermodynamical Wonder - Carlo "Leave your wristwatch at home" Rovelllllli!

Okay guys, normally, I would recommend a twelve round debate(three minutes each) but since none of us are sure of what the nature of time is yet - just come out typing when you hear the sound of the bell and keep going until we have a winner.

Good luck!

Vasseline, George and Rovelli,

What is deterministic in this Universe is the Universe itself with whatever it unfolds before us. Science of Physics is not deterministic , as it attempts to evolve some concepts to understand what is observed to be happening in this universe of ours. We only try to understand how the things are happening and not the why's. The observed facts are supreme and any theoretical model that we may evolve based on limited facts and not the entirety of observed facts. That is we need consistency when we explain one phenomenon, with explanations provided for other observed phenomena too.

As i understand it, the block universe and the Expanding Block Universe are one and the same. It is just a difference that in the former time is a parameter while in the latter it is intrinsically built into the explanation. Thus, i don't see any scope for personal confrontations, as our individual opinions have little significance unless born out by experimental facts that have been confirmed reasonably well by independent research workers. That much is enough as we seek better and better relative truths in Physics about the various physical phenomena as such. May i just say that it may not be wise to conclude that we have understood the working of the human brain fully through Physics 'alone'. The human mind and the human 'soul' do not entirely lie in the domain of current Physics. The Nobel winner, Prof. Eccles of Oxford while studying the neuron activity of the Supplementary Motor Area (SMA) of the brain observed activity when none was expected from within the body involved. He asserted that there appears to be a non-physical sheath that surrounds the SMA that is capable of recording such outside interactions that the neurons in SMA are experiencing. He further believes that this non-physical covering survives with such a record of 'outside interactions' beyond the death of that body!

Let us therefore keep our discussions open in a reasonable way to permit later innovations, instead of making categorical statements about the finality of any approach or explanation. i am sorry if anyone takes me as personally critical of another person, as i myself can not be absolutely sure about things that i am supposed to know well.

Der Dr Rovelli

Science can not exist without time, we just have to give time right position in scientific models of the universe.

My recent idea is that time is a "coordinate of motion".

Theory of Relativity describes motion of elementary particles and massive bodies. With clocks one measures duration and numerical order of this motion. Time is what is measured with clocks: the duration and the numerical order of motion of elementary particles and massive bodies in space. In the Theory of Relativity time as a "fourth coordinate" describes motion of massive objects and elementary particles in space. In that sense fourth time coordinate is the "coordinate of motion". Time is not a part of space. Space-time is not a physical reality into which material change run. Space-time is a math model only used for description of motion of objects in space where time is a coordinate of motion. Space itself is atemporal.Attachment #1: In_The_Theory_of_Relativity_Time_is_a_Coordinate_of_Motion__Sorli_2009.pdf

Awaiting response if any on my post of Dec., 22, 2008

- Opinion of C. Rovelli (December 12) that one can easily get rid of Space at a fundamental level... this opinion is just incredible!

It proves that Rovelli's algebraic idea of Space is based... on Time idea (Words/Language), no matter the kind of scale he is choosing, boiling water in a valley or on top of a mountain.

- Of course Aristotle has nothing to do with Rovelli, Aristotle for whom Space IS Matter, Water, Ether or other elements. Time is for Aristotle deforming Matter.

- But Descartes cannot be quoted here by Rovelli either. Descartes wants to get rid of TIME in his ballistic ('Essay on Static') experiences. Even if Descartes did not understood some of Aristotle's lessons, he is aware of the relationship between matter and space that Scientists mostly are stating: distances in the Universe are often deduced on Spheric Earth or Moon dimensions; and if World is not 'fundamental'?

- And Newton cannot be asked for help by Rovelli too, even if Newton principles are somewhere ambiguous like Descartes principles. Here must the metaphysical Ether be evoked because Space is collapsing on this point (Is Ether full or empty Space?).

Debate between Huygens and Netwon about Ether is Christian metaphysical Debate.

- Rovelli has more to do with G. Berkeley for whom language is more real than reality itself, or with Einstein General Relativity (and E=mc2 in which matter and space are conjured away). Problem of Rovelli is that he wants to forget Einstein on whom he is based. He is catched in the reference as a fly on a web.

'Dualism' of Rovelli or String theoricians is this one: when he is speaking about metaphysics: this is ballistic science; but when he is speaking about ballistic science: this is metaphysics.

When you tell me that my point of view is 'refreshing', Narendra Nath, do you mean like the refreshing comment of the child in the Andersen Tale: 'But the King is naked!'

Le Rouge, i just mean that it is both meaningful and innovative, with little bias from what is 'known'. i am not familiar with Anderson Tale, may be i have forgotten. Therefore, your quote from there is out of context for me. Never mind, the essay discussion soon closes and i wish you and all other authors the best of life ahead.