On Her Majesty's Secret Service (playing the rule of Mother Nature)

In praise of the noncommutative description of the current phenomenological world

The proper spectral M(atrix) theory to model the dynamics of spacetime and matter has not been completed yet. But an outer voice tells me that it could be the good Jacob's ladder from the electroweak scale to some gauge grand unification. The spectral action principle says a lot and brings us closer to the secret of the "great mother". I, at all events, am convinced that She does roll dice.

The hyper-augmented;-) blogger

In due respect to what we owe to the father of the most famous quote about quantum mechanics

Die Quantenmechanik ist sehr achtung-gebietend. Aber eine innere Stimme sagt mir, daß das doch nicht der wahre Jakob ist. Die Theorie liefert viel, aber dem Geheimnis des Alten bringt sie uns kaum näher. Jedenfalls bin ich überzeugt, daß der nicht würfelt.

Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the 'old one'. I, at any rate, am convinced that He is not playing at dice.

 Albert Einstein, in a Letter to Max Born (4 December 1926)

Waiting for the proper ear to listen how Nature does perform the quantum trick that we definitely see

Since our early childhood we know in our bones that in order to interact with an object we have either to go to it or to throw something at it. Yet, contrary to all our daily experience, Nature is nonlocal: there are spatially separated systems that exhibit nonlocal correlations. In recent years this led to new experiments, deeper understanding of the tension between quantum physics and relativity and to proposals for disruptive technologies...

Many physicists feel uneasy with nonlocality [Some conclude that it must be realism that is faulty. But I don’t see in which sense this could save locality? Moreover, realism is often confused with determinism, an uninteresting terminology issue, see ... Non-realism: deep thought or a soft option?]. A part of the uneasiness comes from a confusion between nonlocal correlations and nonlocal signalling. The latter means the possibility to signal at arbitrarily fast speeds, a clear contradiction to relativity. However, the nonlocal correlations of quantum physics are nonsignalling. This should remove some of the uneasiness. Furthermore, note that in a nonsignalling world, correlations can be nonlocal only if the measurement results were not pre-determined. Indeed, if the results were predetermined (and accessible with future theories and technologies), then one could exploit nonlocal correlations to signal. This fact has recently been used to produce bit strings with proven randomness [4]. This is fascinating because it places quantum nonlocality no longer at the center of a debate full of susceptibilities and prejudice, but as a resource for future quantum technologies. We’ll come back to this, but beforehand let us present a few recent experimental tests of quantum nonlocality.

The pioneering experiment by Clauser[5] suffered from a few loopholes, but these have since been separately closed[6, 7, (*)]. Still, correlations cry out for explanations, as emphasized by Bell[8]. Everyone confronted with nonlocal correlations feels that the two systems somehow influence each other (e.g. Einstein’s famous spooky action at a distance). This is also the way textbooks describe the process: a first measurement triggers a collapse of the entire state vector, hence modifying the state at the distant side. In recent years these intuitions have been taken seriously, leading to new experimental tests. If there is an influence from Alice to Bob, this influence has to propagate faster than light, as existing experiments have already demonstrated violation of Bell’s inequality between space-like separated regions [9]. But a faster than light speed can only be defined with respect to a hypothetical universal privileged reference frame, as the one in which the cosmic background radiation is isotropic. The basic idea is that if correlations are due to some ”hidden influence” that propagates at finite speed, then, if the two measurements are sufficiently well synchronized in the hypothetical privileged frame, the influence doesn’t arrive on time and one shouldn’t observe nonlocal correlations. Remains the problem that one doesn’t know a priori the privileged frame in which one should synchronize the measurements. This difficulty was recently circumvented by taking advantage of the Earth’s 24 hours rotation, setting thus stringent lower bounds on the speed of these hypothetical influences[10]. Hence, nonlocal correlations happen without one system influencing the other. In another set of experiments the two observers, Alice and Bob, were set in motion in opposite directions in such a way that each in its own inertial reference frame felt he performed his measurement first and could thus not be influenced by his partner[11, 12]. Hence, quantum correlations happen without any time-ordering...

To conclude let us come to the conceptual implications. In modern quantum physics entanglement is fundamental; furthermore, space is irrelevant - at least in quantum information science space plays no central role and time is a mere discrete clock parameter. In relativity space-time is fundamental and there is no place for nonlocal correlations. To put the tension in other words: no story in space-time can tell us how nonlocal correlations happen, hence nonlocal quantum correlations seem to emerge, somehow, from outside space-time.

Quantum nonlocality: How does Nature perform the trick?

N. Gisin (Submitted on 8 Dec 2009)

(*) a personal update :  Closing the Door on Einstein and Bohr’s Quantum Debate by Alain Aspect.