Gali WeinsteinPhD. Foundations (history, philosophy) of physics. · 5y · Was Albert Einstein troubled by Quantum Physics only because it conflicted with his General Theory of relativity?Einstein the realist did not object to quantum mechanics. His primary difficulty was with a probabilistic interpretation of quantum mechanics and the inseparability (entanglement) in quantum mechanics. He, therefore, strived to derive the main results of quantum mechanics from a deterministic unified field theory (a unification of a refined form of general relativity and electrodynamics) in which there would be no inseparability problem. Of course, particles are not entangled in general relativity and it is a deterministic theory. But Einstein objected to entanglement and to a probabilistic interpretation to quantum mechanics because of his realist position and not because it conflicted with his general theory of relativity. It is our modern point of view (since Stephen Hawking’s studies in the 1970s) that quantum mechanics conflicts with classical general relativity and we thus have to find ways to reconcile the two theories. For instance, we try to do so in the form of quantum gravity. However, this is a modern point of view. It was not Einstein’s view! These are the two primary things Einstein objected to (presented in his own colourful words) in quantum mechanics:“God does not play dice”: Max Born’s probabilistic interpretation of quantum mechanics.“Spooky action at a distance”: inseparability and entanglement.First, “God does not play dice”: Max Born’s probabilistic interpretation of quantum mechanics. Ironically, it was Einstein’s own contributions to quantum physics that had prompted Born to propound his probabilistic interpretation, as Born himself attested in his 1926 paper:I hereby start from a comment of Einstein’s regarding the relation between the wave field and light quanta. He says approximately that the waves are only seen as showing the way for the corpuscular light quanta, and he spoke in the same sense of a “ghost field”. This determines the probability that one light quantum, which is the carrier of energy and momentum, chooses a definite path. The field itself, however, does not have energy or momentum. … it is obvious to regard the de Broglie-Schrödinger waves as a “ghost field”, or even better as a guiding field.Einstein’s “ghost field” was defined as “the waves are only seen as showing the way for the corpuscular light quanta”, that is, a quantum particle has a ghost field (a wave) associated with it or, the particle is guided by a field. Born wrote to Einstein a month before the above paper was published:About me, it can be told that physics-wise I am entirely satisfied since my idea to look upon Schrödinger's wave field as a “ghost field” in your sense proves better all the time.What an irony of fate that Einstein gave Born the idea to look upon Schrödinger's wave function as God playing a dice… Schrödinger introduced the wave function into quantum mechanics and tried to interpret it in terms of a wavelike model. Born wanted to find a way for reconciling particles and waves, and he was relating probability to no other thing but to Einstein’s ghost field! Alas, according to Born the wave function had no physical reality and Einstein’s ghost field became a probability amplitude. Einstein, however, objected to Born’s probabilistic interpretation of Schrödinger's wave mechanics. He also opposed to the transformation of his “ghost field” into probability amplitude! Einstein went back to the blackboard and wrote that light quanta are guided by a wave, a “gohst field” and he wrote to Born a letter on December 4, 1926, in which he expressed his strict objection to Born’s interpretation: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 dice.Einstein tells Born that “He is not playing dice”. Subsequently, Einstein also objected to Heisenberg uncertainty principle. The more you know about something's momentum, the less you know about its position; and the more you know about its position, the less you know about its momentum. This is the Heisenberg uncertainty principle, which Einstein could not accept. Gali Weinstein's answer to What does the quote “God doesn’t play dice with the universe” by Albert Einstein mean? Second, “Spooky action at a distance”: inseparability and entanglement. The Heisenberg uncertainty principle prompted Einstein, his assistant Nathan Rosen and Einstein’s Russian Colleague Boris Podolsky to propose the EPR argument. Here I give a pedestrian explanation of the EPR argument: Gali Weinstein's answer to What is the explanation for EPR paradox? Shortly after the publication of the EPR paper, Schrödinger wrote to Einstein to congratulate him and he added: "The separation process is not at all encompassed by the orthodox scheme" of quantum mechanics, to which Einstein replied (quoted in The Shaky Game):Dear Schrödinger, I was very happy with your long letter, which dealt with my little paper. For reasons of language, this one was written by Podolsky after many discussions. But still it has not come out as well as I really wanted; on the contrary, the main point was, so to speak, buried by the erudition… A Talmudic philosopher [probably Niels Bohr] is anti-realist.To get past the Talmudic philosopher Einstein invoked a supplementary principle, the separation principle. Einstein then explained to Schrödinger what he meant by the separation principle. Consider the two particles A and B that interact and then separate.After the interaction, the real state of AB consists precisely of the real state of A and the real state of B, which two states have nothing whatsoever to do with one another. The real state of B thus cannot depend upon the kind of measurement I carry out on A ('Separation Hypothesis' from above). But then for the same state of B there are two (and in general arbitrarily many) equally justified ψB, which contradicts the hypothesis of one-to-one or complete description of the real states.In 1947 Einstein wrote again a letter to Born:I cannot make a case for my attitude in physics which you would consider at all reasonable. I admit, of course, that there is a considerable amount of validity in the statistical approach which you were the first to recognize clearly as necessary given the framework of the existing formalism. I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance. I am, however, not yet firmly convinced that it can really be achieved with a continuous [unified] field theory, although I have discovered a possible way of doing this which so far seems quite reasonable. The calculation difficulties are so great that I will be biting the dust long before I myself can be fully convinced of it. But I am quite convinced that someone will eventually come up with a theory whose objects, connected by laws, are not probabilities but considered facts, as used to be taken for granted until quite recently. I cannot, however, base this conviction on logical reasons, but can only produce my little finger as witness, that is, I offer no authority which would be able to command any kind of respect outside of my own hand.Einstein the realist tells Born that “physics should represent a reality in time and space, free from spooky actions at a distance”.