Essay Abstract

When a mountaineer is ascending one of the great peaks of the Himalayas she knows that an entirely new vista awaits her at the top, whose ramifications will be known only after she gets there. Her immediate goal though, is to tackle the obstacles on the way up, and reach the peak. In a similar vein, one of the immediate goals of contemporary theoretical physics is to build a quantum, unified description of general relativity and the standard model of particle physics. Once that peak has been reached, a new (yet unknown) vista will open up. In this essay I propose a novel approach towards this goal. One must address and resolve a fundamental unsolved problem in the presently known formulation of quantum theory : the unsatisfactory presence of an external classical time in the formulation. Solving this problem takes us to the very edge of theoretical physics as we know it today!

Author Bio

Associate Professor, Tata Institute of Fundamental Research, Mumbai, India. Research Interests : Quantum Gravity, Foundations of Quantum Mechanics, Cosmology. Three time winner of the Gravity Research Foundation Essay Competition [3rd Prize (1998); 4th Prize (jointly with Cenalo Vaz, 2004); 2nd Prize (2008)]

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GR physical systems are spatially separable into independent components. Three or more particle systems require cluster separability (macroscopic locality). System into subsystems, overall mathematical description reduces to descriptions of the subsystems (scattering problems with two or more fragments). QM allows entangled states (superpositions of product states) that require a fundamental irresolvable connection within empirical physical systems (two-slit diffraction, EPR paradox). Macroscopic locality is violated: Measuring the state of one slit in a double slit experiment obtains single slit diffraction patterns (quantum eraser experiments).

GR models continuous spacetime beyond conformal symmetry (scale independence) to symmetry under all smooth coordinate transformations - general covariance (stress-energy tensor re local energy and momentum) - resisting quantization. GR predicts evolution of an initial system state with arbitrary certainty. QM observables display discrete states. Heisenberg Uncertainty limits knowledge about conjugate variables in a system state, disallowing exact prediction of its evolution.

The Standard Model is a curve fit and massless. SM requires explicit insertion of 6 quarks', 3 leptons', W, Z, and Higgs bosons' masses); 3 neutrino masses and 4 parameters for the Maki-Nakagawa-Sakata matrix, electromagnetic and strong coupling constants, four parameters for the Cabibbo-Kobayashi-Maskawa matrix... The Higgs is absent. SUSY partners are absent; no solar axions (CERN Solar Axion Telescope). Protons do not decay (Super-Kamiokande). The Standard Model predicts what it already knows. U(1)xSU(2)xSU(3) or S((U2)xU(3))?

You conclude, "Perhaps its fair to say that in the end Einstein will turn out to be the winner after all. Unification will be achieved by a generalization of general covariance to the noncommutative case." That is 1931 teleparallel gravitation (Einstein, Cartan, Weitzenböck) with chiral anisotropic vacuum. Conservation of angular momentum through Noether's theorems fails. How would you test your contentions?

"Autoritätsdusel ist der größte Feind der Wahrheit," Albert Einstein, 1901.

Dear Uncle Al,

Thank you for your comments. For more details on the relation between noncommutative geometry and the standard model you may want to have a look at the paper of Chamseddine and Connes that I cite in my essay.

Regarding the merger of general relativity and quantum theory, the philosophy I am espousing is that there is an underlying theory, different from both, of which the two are approximate limits. Thus, the underlying theory neither has a spacetime continuum, nor does it obey the linear superposition principle of quantum mechanics.

I think the most direct way to experimentally test these ideas in the foreseeable future is to test if wave function collapse during a quantum measurement is being caused by a nonlinearity in the Schrodinger equation. The test will be very similar to what is described in the paper by C. Papaliolios, [Phys. Rev. Lett.18, 622 (1967)]. I and my colleagues are working on a theoretical proposal in this regard.

Thanks also for the information on teleparallel gravitation. That is a classical theory, isn't it, unlike what I am suggesting?

Tejinder

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Mr. Singh,

Thank you for an interesting essay.

One thing which I'll wager you *won't* view from the summit (unless it's a false summit) is a device which purports to be a working time machine. You'll find the reason for this assertion in my essay 'On the Impossibility of Time Travel,' which appears elsewhere among these collected essays.

If I correctly understand your thinking about the desirability of eliminating external classical time from quantum mechanics, I believe that you'll find my perspective on time to be consistent with that aim.

Dear Mr. Smith,

Thank you for your comments. You may well be right in your essay when you argue about the impossibility of a time-machine. In my essay I was taking the stance that (in my opinion) a question such as this one can be answered only after we have the requisite theory in hand [in this case quantum gravity).

With regard to the question of time, I think it is a purely clasical concept. I am very smpathetic to the idea of a `block Universe' in quantum gravity. This is consistent with what we see in a noncommutative spacetime - if time and space do not commute, they both become non-loal entities and we can no longer label spatial sections by a flowing unidirectional time. This of course is analogous to the position-momentum noncommutation in ordinary quantum mechanics.

Thus a`time' which does not commute with `space' is clearly a very different concept from ordinary time. And yet, time must emerge from noncommutative geometry, in the clasical limit. Here, perhaps Connes observation of the existence of a `God-given time' in noncommutative geometry, on the basis of the so-called Tomita-Takesaki theorem, might help. Maybe, it might have soething to do with the Lorentzian signature of spacetime, but that remains to be seen.

Tejinder

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Dear Tajendra,

it is a pleasure to note some conceptual similarities between yours and my essay on this forum. You have used the term ' mesomic ' for the region of Physics where neither the classical nor the quantum physics is likely to be valid strictly. You have correctly indicated such a theory to act as a significant link in order to make Physics become comprehensive. As an experimetalist, my own essay indicates the missing link as one where the Planck's constant 'h' can neither be considered as negilgible nor its full significance is relevant in certain physical processes that have yet to be encountered experimentally on account of practical limitations. i am sure in the days ahead both theoretical people like you and the younger generation of experimental physicist will explore such possibilities specifically. i personal will welcome your comments on my essay too, if you can spare the time to go through it too!

Dear Narendra,

I am very pleased to note that we agree that the physics of the mesoscopic domain is likely to be different from that of the microscopic and the macroscopic domain.

I have read your essay with interest. I am curious to know how you are led to the above conclusion regarding the mesoscopic arena. It seems to me you have a strong intuitive grasp of the related physics! For me, it came from issues having to do with quantum theory. Also, would you have uggestions about how to develop a mathematical theory of the mesoscopic domain, which will have the correct limits?

I agree it is very important at this stage to get experimentalists working on quantum mechanics to get interested in this problem. I would venture to state that what we can hope to learn from such table top experiments in the next decade or two will be no less revealing than the large scale accelerator experiments, and the enormous amount of cosmological data that is coming in.

Thanks,

Tejinder

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Dear Tejinder,

First I want to congratulate you a very good essay. I have a few comments and questions.

You say: "there must exist an equivalent formulation of quantum mechanics, which does not refer to an external classical time"

And indeed there is one and moreover, the right way to understand it is in the non-commutative framework. Please see my essay: "Heuristic rule..." and Emile Grgin's essay: "A Historical Approach...". I am talking about the algebra of quantions. (You can see an overview of it at: arXiv:0901.0332, but ignore the second section, it is superseded by my essay as my understanding deepened after its publication).

One feature of this algebra is that it also has a "God-given time" and I was trying to read Connes archive paper (arXiv:math/1100193) but I could not find it. Is the reference correct?

This algebra generates a peculiar (non-commutative) state space that is no longer the usual Hilbert space and has a larger degree of freedom and no dimensionality as far as I can tell for now.

Another question I have is regarding the use of nonlinearity to explain the wavefunction collapse. Why we cannot understand the collapse simply as gaining knowledge in a Bayesian approach? I would expect that any nonlinear model of the collapse to be at odds with relativity.

Dear Florin,

Thank you for your very kind remarks. I have already been going through the very interesting papers by you and Emile and hope to respond soon. It will be wonderful if we agree, coming from different paths, that a time-independent formulation of quantum mechanics must exist, and that it will be in a noncommutative framework.

There is a typo in my reference to the paper of Connes. It should read

math.qa/0011193, NOT math.qa/1100193. My sincere apologies. The relevant discussion is on page 8. You may also want to see the related paper

gr-qc/9406019 by Connes and Rovelli (perhaps you already know of it).

Regarding nonlinearity : could you please explain at some stage what you would mean by `collapse as knowledge gained in a Bayesian approach'? In my picture, the nonlinearity is forced upon us, during the measurement process. I would say that it is unavoiadable; rather than it is being invoked by hand to invoke collapse.

Also, I feel more comfortable if I think of a quantum measurement as a process in which an individual quantum sytem interacts with an individual macroscopic apparatus, and we ought to provide a dynamical explanation of this process. I will be glad to know your views on this.

As for the question of incompatibility between relativity and nonlinear quantum mechanics, I feel it is a debated and controversial issue, not yet fully resolved. We could discuss it in this forum perhaps, at some time. In any case, it probably would not directly affect the ideas I suggest because the nonlinearity is arising in the experimentally untested mesoscopic domain. Radical though it might seem, its fair to say that Lorentz invariance and causality has not been tested either, for mesoscopic systems. Perhaps there is some relation with EPR ...I do not know.

Thanks,

Tejinder

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Dear Tejinder,

Thank you for the updated archive reference, I look forward to reading it. For the second link, I was already aware of it and I even cite it in my essay. I concur, it will be wonderful if we arrive at the same destination coming from different perspective, and this validates further that we are on the right track.

Nonlinearity is indeed unavoidable, but I do not quite see it necessary to explaining the wavefunction collapse. If the collapse is due to nonlinearity (and conceivably this involves irreversibility), how can the quantum erasure (un-collapsing the wave function) be explained then? The Bayesian approach is much more natural. Suppose someone gives me a pair of gloves and I only look at one and see it is red. At that moment I know that its pair is red as well and there is no mystery in this knowledge gain process. You can object that this is not quantum mechanics, but the only difference between classical and quantum mechanics is that the pure state space is continuous and in QM even pure states are not immune to collapse.

The measurement problem is however not solved because one can show that there is no consistent mathematical description of a mixed classical-quantum system. So Zurek's decoherence and Bayesian's explanation of the collapse goes a long way towards solving the measurement problem, but not all the way. One has to show that either everything is quantum mechanical, or everything is classical mechanical. The proof is highly non-trivial even with Kochen Specker, or Bell, because of 't Hooft's program of emergent QM from a deterministic theory.

Florin

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i have posted some comments in response to yours on my essay site. May be you see and then respond as you may desire

Dear Florin,

Thank you for your remarks. I would distinguish between a quantum erasure experiment and a conventional quantum measurement. In a quantum erasure experiment, the information about entanglement is not lost. This is what allows the erasure. On the other hand, conventional quantum measurement destroys entanglement, and this is indeed an irreversible process.

I would like to treat a quantum-classical system as one large quantum syatem. I believe this is the modern outlook most physicists would agree with. The establishment viewpoint on quantum measurement then is that it is to be explained by decoherence, in conjunction with the many worlds interpretation. The many worlds part is crucial, because decoherence, while it destroys interference amongst alternatives, it continues to preserve superposition, since it is working within the framework of the linear theory. Only the Everett-type branching into many worlds can result in us seeing only one out of the various superpositions.

I am fully in support of the decoherence process - it is physically a very clear and inevitable process, which is also experimentally observed. However, when it comes to the many worlds branching, I have two serious concerns, which are not philosophical. How is one to test experimentally whether the many worlds picture is correct? Secondly, does many worlds explain the Born probability rule. That is not sorted out till date, to my understanding. I believe this rule needs to be explained.

If one does not accept many worlds, then its unavoidable that quantum mechanics will have to be modified to explain measurement. I do not claim that nonlinearity is the only possible modification. It could be something else, such as the Ghirardi-Rimini-Weber theory of spontaneously induced collapse.

I think experimentalists will have to examine the measurement process much more minutely, as and when technology permits. As of today, it is as if the duration over which a measurement lasts is taken to be zero. When technology permits, we must examine measurement as a process of finite duration, and study what happens to the wave function of the quantum system.

Thanks,

Tejinder

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Dear Tejinder,

I am not a believer either in many worlds interpretation, although it is surprisingly widespread in conjunction with Wheeler-de Witt. I am much more inclined to accept Rovelli's relational interpretation of the wavefunction as observer-dependent. In classical mechanics one has a crisp difference between uncertainty and pure states. There the information gaining via the Bayesian interpretation is intuitive and non controversial because the pure states are safe from collapse. In QM the boundary is blurred and moreover for a given state one may even have nonunique decompositions of quantum mixtures. Quantum mechanics is first and foremost a different kind of statistical theory. Because of the Bayesian interpretation of the collapse as simply gaining knowledge there is no need for the many worlds interpretation (and therefore the wavefunction does not have an intrinsic ontological value).

I think that the right mathematical foundation of QM is not in state space, but in the algebra of observables. Here there is nothing un-intuitive and because of the GNS construction this formulation is well defined. (Also the Hilbert space is rather uninteresting because it is only determined by its dimensionality; the true action happens in the operator algebra.)

The measurement problem has two parts. First is the actual experimental setup and the freedom to choose what to measure (currently not captured by QM). Second, there is the actual interaction with the apparatus and the emergence of the superselection rules. Superselection rules are necessary to avoid inconsistencies on a classical-quantum system description, and they are definitely not derivable from a pure QM foundation.

I am currently not following Penrose's ideas of combining QM with gravity, but he may be on the right track. When I will have some free time I will try to understand his ideas. My intuition/speculation about superselection rules stems from the problem of force separation from the unification energy going down on the energy scale. If at high enough energies all interactions are unified, why is that at lower energies they no longer interact? This is also a kind of superselection rule prohibiting force mixing. If we can understand this mechanism then we are one step closer to understanding the measurement problem in general. So here is a wild idea. Maybe our whole universe is a giant relativistic (quantionic) wavefunction and the classical parts of our universe (including classical space-time) are just the manifestations of quantionic superselection rules.

Florin

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Dear Professor Singh,

I enjoyed your essay. I particularly liked the concept of a mesomic region between quantum mechanics and classical physics. I believe I have a graph of this region that you may find interesting. It is located in the essay "Gravity from the Ground Up". I start with the concept of digital waves. This is where particles move digitally and therefore experience discontinuous space and time even though the space time fabric is continuous. So, time is not quite classical, but I do not think it is the timelessness you expressed for quantum mechanics. I am interested in any opinions you may have.

I also liked your ending quote by Einstein, and think it will be proven correct.

Thank you,

Don Limuti

Thanks for your comments Don.

Its gratifying that you too think that there may be interesting *new* physics near the Planck *mass* scale. Perhaps you already knpow that besides Penrose, Feynman also suggested the possibility of gravity induced modification of quantum mechanics. I cite a remark from Feynman in this regard at the beginning of my article arXiv:0711.3773 [gr-qc]

In my view, it is crucial to experimentally test the mesoscopic domain for departures from both quantum mechanics and classical mechanics. These experiments will perhaps be as important as the Michelson Morley experiment. A null result will be a great victory for standard quantum mechanics. I have talked a bit with experimentalists from the group in Vienna - they would be interested if a clean doable experiment can be proposed.

One prediction I have is the following : there is a dynamical equation of motion for a perticle of mass m. If this mass is near about Planck mass, but much larger than atomic mass, and much smaller than a macroscopic mass, the dynamic equation differs both from the Schrodinger equation and from Newton's laws. In this equation, Planck's constant is replaced by a Planck parameter, which depends on the mass of the particle. Can one do an experiment with a mesoscopic particle to measure this Planck parameter - for m near Planck mass, a significant departure is expected.

I am posting some comments regarding your essay on your site.

Thanks,

Tejinder

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Dear Tejinder,

From my viewpoint the problem is how do things stay together to make for a stable "hop". It is like a rigidity test in mechanics. Electrons are excellent hoppers because they have no parts. Protons may have parts, but when it hops it is rigid. Buckyballs C60 are big and distributed but the forces holding it together keep it rigid enough so that it hops and has QM properties. Nothing has been found to date that is bigger (more massive) than the buckyball that has QM properties.

At the Planck mass there are things like "fleas" that are far from quantum mechanical. So, the experiment would be to find a QM flea! It will be a ferocious flea.

Beyond the Planck mass I believe space time does not allow anything to hop.

I like it that you have given a name to these missing massive particles "mesoscopic Particles" and you abbreviate it m-mass. I think it is going to stick.

Best of luck,

Don L.

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Dear Dr. Tejinder Singh

You wrote:

Consider, as a thought experiment, a Universe which has only quantum mechanical particles, such that their total mass-energy is much less than Planck mass. There is no longer a classical spacetime and no point structure, but in principle there is an equivalent reformulation of the quantum theory.

Consider a thought experiment that space-time is merely a math model and cosmic space itself is timeless. Physical time is run of clocks in timeless space. I see this thought experiment a possibility to resolve "action on distance" by gravity.

Gravity works between quanta of timeless space. Gravity is result of curvature of timeless quantum space. More mass is in a given volume of quantum space more space is curved. Curvature of quantum space depends on its density. More mass is in given volume of quantum space, less space is dense and more is curved. Density of quantum space Ds in a centre of massive object is Ds = 1/m, where m is a mass of stellar object.

Fg = G/Ds1 x Ds2 x r on square.

yours amritAttachment #1: 5_TIMELLESS_QUANTUM_SPACE.doc

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Dear Tejinder,

1. You may want to contact these researchers in Vienna. This info came from the Physics World Archive.

"The interference pattern formed when a beam of electrons passes through a double slit is clear

evidence that electrons can behave as both waves and particles. This wave-particle duality lies at

the heart of quantum mechanics, but physicists remain intrigued by the boundary between the quantum

and classical worlds. Neutrons, atoms and small molecules have all shown quantum-interference

effects. Now Markus Arndt and co-workers at the University of Vienna have observed the wave-like

behaviour of carbon-60 molecules. The "bucky-ball" molecules are at least an order of magnitude more

massive than any other object where wave properties have been observed (Nature 1999 401 680)."

2. I did some "Googling" on "His Dark Materials" and found I had made a mistake. The university

involved is Oxford and not Cambridge. I could not discover weather Pullman actually met Penrose, but

they were linked in this article: http://www.telegraph.co.uk/technology/3340760/The-quest-for-dark-

matter.html

"Pullman's imaginary dark matter, Dust, is a name for what happens when matter begins to understand

itself. That's why it plays such an important role in the trilogy in which church scholars fret

that it could even bring down God. Pullman made a leap in inventiveness by making Dust "a way of

picturing human consciousness, the most mysterious thing in the universe".

Some of the inspiration for this idea lay nearby, in the university, in the controversial

suggestion of mathematician Sir Roger Penrose that consciousness is somehow linked with the yet-to-

be developed theory of quantum gravity, which will unite the quantum theory of the very small with

general relativity, the current theory of the very big (and gravity). "It is an extraordinary

idea," said Pullman."

3. I have been assuming that the transition from quantum to classical is gradual and that a buckyball is

not quite as good quantum mechanically as an electron. The transition to classical is complete at

the Planck mass. The m-mass region should contain a mixture of QM and classical stuff. These are just

my notions. What do you think?

4. If you think I can be of any help please let me know.

Thanks,

Don L.

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i am fascinated with gravity as it seems to be the main mystry that lead the many we still have in Physics. Its connection with quantum mechanics is still doubtful. To me gravity may have different strengths and nature too, e.g both attractive and repulsive, depending on the sitaution faced in nature. After all , stong nuclear changes both its strength and nature as it encounters distances less than the nucleon size! At the level of cosmos it is difficult to plan test experiments and so also in a lab. on earth. Its long term manifestations are making us sense this inetraction , the first to emerge on the horizon, followed by strong, electromagnetic and nuclear weak. ay be gravity has different components too!

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Dear Tajinder,

i await your response to some off beat suggestions i made for your mesascopic region studies on my essay site as also some others on your essay site. Perhaps

you have pressure on time that i do not have in my retired life.