Rating= ♥♥∑ƒ∞√ ( a bit involved ) !
This last monday, January 16th 2012, Catherine participated to a very interesting discussion at the Institut de France, about Carlo Rovelli’s new interpretation of Quantum Mechanics (QM). Here is her field report of this event.
The discussion was led by the great physicist and Templeton price Bernard d’Espagnat and were present physicists, philosophers and personalities with some interest beyond pure physics. The theme of the day was to discuss in depth he the interpretation of Quantum Mechanics that physicist Carlo Rovelli has recently proposed to the scientific community.
Carlo was present at the discussion, but his theory was presented by a young philosopher. Here is a small summary of what Catherine understood ( sorry Carlo if it is not completely complete, but I will make it as simple as possible) .
The discussion was about the EPR paradox. EPR stands for Einstein, Prodolsky, Rozen, and the paradox was suggested by the EPR team to the scientific community at the beginning of the century in order to shed light on one of the most astonishing properties of QM, namely non locality. Suppose two particles are entangled into a single quantum state at time zero. Say those two particles are constituted of one electron and one positron (a positive electron) which are entangled in a singlet of spin. At later time we split the pair and the electron is sent to the left and the positron is sent to the right. Now two observers are present, Alice ( to the left) and Bob ( to the right). Alice observes and measure the spin of the electron and she finds one result (spin up). Now Bob, who stands to the right, far away form Alice, has no idea about what is the result that Alice has obtained. If Bob makes an independent measure of the spin of the positron he will find that his result is precisely the opposite of the one of Alice. But Bod and Alice didn’t talk, didn’t exchange information. Everything happens as if the quantum system itself had kept a memory of the time when it was entangled : the spin of the positron sort of “remembers” that its electron companion, now very far away, had the opposite spin with it. Since the electron and the positron are now far away form each other, we say that there is a non local correlation of information between the two, or we say, in simpler words that this property denotes the non locality of quantum mechanics. Einstein didn’t believe that this property would ever be observed, since he wanted until the end of his life QM to be deterministic, and in that sense he was proven wrong by numerous experiments, the last in date, and definitive one, being the one of Alain Aspect.
Recently Carlo has proposed a very interesting new interpretation of QM which put in perspective the notion of observer and observed. In very short, Carlo advocates that the notion or proper states per se of QM doesn’t exist without relation to an observer. Namely you cannot say anymore that a particle is in state |α> anymore, but you have to say that the particle is in the state α as observed by observer O; we note this |α>O. This simple shift of concepts enables him to give a very elegant interpretation of the EPR paradox. Suppose Alice make her measurement first. When Bob makes his own measurement, it is believed in the usual theory of QM that Bob knows nothing about Alice’s findings. But Carlo says this is not true, Carlo says that when Bob makes his measurement, since Alice has already made her own, Bob knows “something” about Alice’s results and as such his own measurement will be corrupted with Alice’s one. In a sense the system Alice + Bob itself is entangled in time, and the measurement of Alice will influence the one of Bob.
To understand in greater depth what a revolution it is one has to come back to the notion of what is a measurement. Typically, a measurement, is made by an observer which is a classical object. By classical,we mean a big enough object having roughly 10 ^23 particles, or 10 0000000000000000000000 ( 23 zeros should be there) particles. Any kind of measure apparatus in you house has at least this number of particles. It is believed that classical systems such as this one behave classically. If two such systems are sufficiently far away in space, there is separation, and it is impossible for one observer to know what the other one is doing without contact through a physical force. What Carlo is telling us, is that even big classical systems Alice and Bob are not fully separated, that they remain entangled, even for a very very very tiny bit.
In Carlo Rovelli’s interpretation of QM , total separation doesn’t exist, all the objects of the universe are entangled, although sometimes it is for a very very tiny portion of all the information they carry. Roger Balian told me he came to the same conclusion with his own interpretation of QM.
I find extremely enlightening that two very bright and most respected scientists of our time do find new interpretation of QM which seems to go in the same direction of the perennial Truth of non dual Traditions : we are all One.
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