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Cosmological Data Hint at a Level of Physics Underlying Quantum Mechanics [Guest Post]

The views expressed are those of the author and are not necessarily those of Scientific American.

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Two weeks ago, I blogged about David Bohm’s interpretation of quantum mechanics. Like Einstein and Louis de Broglie before him, Bohm argued that quantum randomness is not intrinsic to nature, but reflects our ignorance of a deeper level of reality. One physicist who has developed the idea further is Antony Valentini of Clemson University. Last week, he and a colleague published a paper suggesting an observational test—a rarity in this subject. I’ve invited him to write a guest blog post. I also recommend his lecture on YouTube and an article he wrote for Physics World magazine. For a slightly different take on de Broglie and Bohm’s theory, see this paper.—George Musser

By Antony Valentini

In the late 19th century, some physicists were concerned about the far future of the universe. Eventually the stars would burn out and everything in the universe would reach the same temperature. The new principles of thermodynamics showed that, in such a universal state of thermal equilibrium, it would be impossible to convert heat into work. It would also be impossible to escape the equilibrium state, and all significant change would come to an end. This rather depressing picture came to be known as the thermodynamic “heat death” of the universe.

Needless to say, the feared thermodynamic heat death has not yet occurred. The stars will continue to burn for a very long time to come. But is it possible that there is a deeper level on which something like a heat death has in fact already happened? For more than 20 years I have been arguing that this is indeed the case. Recent cosmological data from the Planck satellite may provide a hint of support—just a hint, but an intriguing one.

The suspicion that we are victims of a kind of heat death arises from an apparent conspiracy in the laws of physics. On the one hand, quantum physics seems to contain what Einstein called a “spooky action at a distance,” with superluminal influences between remote entangled systems. On the other hand, quantum physics also makes it impossible to send faster-than-light signals. It is as if something is going on behind the scenes which we are not allowed to control. Why is our world fine-tuned in this way? One answer is that a quantum analogue of classical heat death has already occurred in our universe—at the deeper level of so-called hidden variables.

Hidden variables are hypothetical features of the world (what physicists call “degrees of freedom”) that can explain the apparently random outcomes of quantum measurements. The best-known example of a hidden-variables theory is the pilot-wave theory proposed by Louis de Broglie in 1927 and further developed by David Bohm in 1952. There the hidden variables are simply trajectories for whatever particles or fields a system may contain. Normally quantum mechanics says that there are no well-defined trajectories.

A hidden-variables theory will agree with quantum mechanics only if the variables have a special quantum equilibrium distribution, analogous to thermal equilibrium. It is because of quantum equilibrium that superluminal influences cannot be used for superluminal signaling. When hidden variables have the equilibrium distribution, the signals average out to zero. If the hidden variables instead had a nonequilibrium distribution, the underlying superluminal signals would become observable and controllable. Relativity theory would be violated; time would be absolute rather than relative to each observer. The Heisenberg uncertainty principle would also be violated.

By this reasoning, there is no real conspiracy. We cannot use entangled systems to send superluminal signals simply because we happen to be stuck in a state of quantum equilibrium, just as hypothetical beings in a classical heat death would not be able to convert heat into work.

But why exactly are we stuck in quantum equilibrium? Pilot-wave theory itself suggests an answer. Theoretical studies and computer simulations have shown that, if a system begins with a nonequilibrium distribution, then, because of the complex motions, it settles very rapidly into equilibrium. This process is analogous to thermal relaxation—the way, for example, gas molecules rapidly spread out uniformly inside a container (figure at left).

Now, all the matter that we see has a long and violent astrophysical history that ultimately traces back to the big bang. If the universe began in a state of quantum nonequilibrium, relaxation may have taken place very rapidly in the earliest moments of the hot big bang. Today, everywhere we look we should expect to find quantum equilibrium, as indeed we do. The feared heat death of the universe has in fact already occurred! To be sure, it takes a rather different form than could have been anticipated in the 19th century.

Even granting that all this could be true, one might conclude that no evidence for hidden variables will ever be found, since there would be little prospect of finding nonequilibrium today, nearly 14 billion years after the big bang. There may, however, be a way. Using the relic radiation known as the cosmic microwave background (CMB), it is possible to test quantum mechanics in the very early universe, potentially probing a time before the quantum heat death took place.

The CMB provides a snapshot of the universe as it was about 400,000 years after the big bang (figure at top). At that time, the universe was almost but not quite homogeneous. As a result, the CMB contains a pattern of hot and cold spots—small ripples in temperature. According to the leading model of the very early universe, known as inflationary cosmology, these ripples were seeded by fluctuations in a quantum field that existed at much earlier times during a period of accelerating expansion. If this early quantum field was in a state of quantum nonequilibrium, anomalies would appear in the pattern of ripples in the CMB.

What kind of anomalies should we expect? There are many possibilities, but one stands out as particularly simple and natural. A rapid expansion of space in the very early universe can suppress or retard the relaxation process over sufficiently long distances. We would then expect anomalies in the CMB at the longest wavelengths. Specifically, at such wavelengths we would expect to see a quantum noise deficit, because complete relaxation would not have taken place at these wavelengths.

Recently, Samuel Colin of Clemson University and I have developed a detailed computer simulation that illustrates this. The figure at left shows the time evolution when space is not expanding. The right column is the (changing) probability distribution predicted by quantum mechanics; the left shows a nonequilibrium distribution that evolves in time according to pilot-wave theory. (Time runs downwards.) The two distributions quickly become virtually identical: the system relaxes.

The figure at right shows the comparable time evolution when space is expanding. Now, the system does not fully relax. In particular, at the final time the width of the nonequilibrium distribution is smaller than the width of the quantum distribution. This translates into fewer fluctuations in the CMB on large scales.

Intriguingly, the Planck satellite has observed just such a lack of large-scale fluctuations. Our model provides a natural mechanism that can explain it. There could, of course, be other explanations. The deficit might even be just a chance fluctuation. Further analysis is required to settle its true nature.

Has new physics been observed in the CMB? We do not yet know. But one thing is certain: inflationary cosmology provides us with a fascinating new laboratory in which to test the foundations of quantum mechanics.

Antony Valentini is professor of physics at Clemson University. He is co-author, with Guido Bacciagaluppi, of Quantum Theory at the Crossroads

CMB image courtesy of ESA and the Planck Collaboration; diagrams by Antony Valentini

George Musser About the Author: is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. He is the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Percival 8:27 am 11/19/2013

    Let me see if I have this straight; the idea is that for a brief time after the universe began it was in a state of quantum nonequilibrium, the opposite of its present state.

    That is to say that back then what we refer to as hidden variables were *not* hidden, and had fixed values.

    The array of side effects from absolute time to no Heisenberg Principle slightly terrifies me. That would be some strange country to live in; I’d like to read a _Flatland_-ish treatment of it.

    At about 400ky after the big bang, the universe crossed some threshold and equilibrated but apparently the process was subject to a sort of dispersion, first occurring over small distances then finally over very large scales.

    What I want to know is- is the threshold related to the then-extant temperature of the universe, its density, the (presumably stronger-than-now) long range curvature of spacetime, or what?

    Is it dependent on something we might be able to reproduce in the laboratory? If it’s out of our experimentally-accessible grasp, might we observe it in one of Nature’s laboratories, like black holes, neutron stars, or quasars?

    Might such objects host a non-equilibrium condition nearby them? Could a localized non-equilibrium condition explain some strange features of accretion discs and/or polar jets or the spectra of such objects?

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  2. 2. vulcantaylor 8:31 am 11/19/2013

    “If the hidden variables instead had a nonequilibrium distribution, the underlying superluminal signals would become observable and controllable.” Could superluminal signaling after the big bang explain why the universe is flat, homogeneous, and isotropic? Would this make inflation theory unnecessary, solving the problems with inflation described at:

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  3. 3. Francis Higgins 12:40 pm 11/19/2013

    With respect, unless Philosophical deductions can be made for any theory, the discussion becomes speculation, not Philosophy.
    To comment that time ‘runs backward’ has no more legitimacy than that pertaining to the nonsense of ‘Time Travel’.

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  4. 4. Arbeiter 12:58 pm 11/19/2013

    if a system begins with a nonequilibrium distribution, then, because of the complex motions, it settles very rapidly into equilibrium” On the contrary: oscillating chemical reactions (Belousov-Zhabotinsky, Briggs–Rauscher, mercury beating heart); fractals. Bohm’s physics is facile but untenable short of empirical validation. The following is elegant, rigorous, amazing, and wrong. The construct is flawless. Find the loophole that is not there.

    A hermetically isolated hard vacuum envelope contains two closely spaced but not touching, in-register and parallel, electrically conductive plates having micro-spiked inner surfaces. They are connected with a wire, perhaps containing a dissipative load (small motor). One plate has a large vacuum work function material inner surface (e.g., osmium at 5.93 eV). The other plate has a small vacuum work function material inner surface (e.g., n-doped diamond “carbon nitride” at 0.1 eV). Above 0 kelvin, spontaneous cold cathode emission runs the closed isolated system. Emitted electrons continuously fall down the 5.8 volt potential gradient. Evaporation from carbon nitride cools that plate. Accelerated collision onto osmium warms that plate. Round and round. The plates never come into thermal equilibrium when electrically shorted. The motor runs forever. (No Schottky barrier – heavily doped metal-semiconductor interface.)

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  5. 5. Wayne Williamson 6:50 pm 11/19/2013

    I thought that quantum physics does allow faster than light signals…ie entanglement allows “far” objects to interact with each other instantaneously…just wondering…

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  6. 6. Zephir_AWT 9:23 pm 11/19/2013

    Compare the article “Ether returns to oust dark matter[1] ” (New Scientist, August 2012).

    Louis de Broglie was indeed an aetherist too and he stated : “When in 1923-1924 I had my first ideas about Wave Mechanics I was looking for a truly concrete physical image, valid for all particles, of the wave and particle coexistence discovered by Albert Einstein in his “Theory of light quanta”. I had no doubt whatsoever about the physical reality of waves and particles.”

    “This result may be interpreted by noticing that, in the present theory, the particle is defined as a very small region of the wave where the amplitude is very large, and it therefore seems quite natural that the internal motion rythm of the particle should always be the same as that of the wave at the point where the particle is located.”

    “I called this relation, which determines the particle’s motion in the wave, the guidance formula. It may easily be generalized to the case of an external field acting on the particle. Any particle, even isolated, has to be imagined as in continuous “energetic contact” with a hidden medium..”

    “The “energetic contact” with a hidden medium is the state of displacement of the aether. If a hidden sub-quantum medium is assumed, knowledge of its nature would seem desirable. It certainly is of quite complex character. It could not serve as a universal reference medium, as this would be contrary to relativity theory. A moving particle has an associated aether wave.”

    This hypothesis was brought forward[3] some forty years later by Bohm and Vigier[4] , who named this invisible environment the “subquantum medium”. It can shown[5] , that the de Broglie waves can be derived as real collective Markov processes on the top of Dirac’s aether.

    So far we already have entropic theory of gravity and quantum mechanics, based on Boltzmann gas concept. Thanx to Couder we already have water surface analogies of quantum mechanics. It’s just a matter of time, when this model will be exploited geometrodynamically, i.e. not just with steady-state models based on entropic balance. The trend of contemporary physics is therefore quite apparent.

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  7. 7. skeam 3:48 am 11/22/2013

    I would like more explanation of how quantum equilibrium causes there to be a difference between signaling with speeds above or below the speed of light, and changing absolute time into relative time, if there is no such speed limit in the underlying deeper level of reality, rather than e.g making ALL signaling impossible?

    Or is there still this speed limit in the underlying level of reality? But how can time then be absolute on this level, without causing inconsistent results?

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  8. 8. vulcantaylor 11:32 am 12/3/2013

    I was wrong. Superluminal signaling could only occur between entangled particles. Particles would need to be initially in contact to be entangled. Inflation is still needed to smooth out temperature differences after the big bang between parts of the universe that would otherwise have been too far apart to ever influence each other.

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