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Erwin Schrödinger
Erwin Schrödinger is perhaps the most complex figure in twentieth-century discussions of quantum mechanical uncertainty, ontological chance, indeterminism, and the
statistical interpretation of quantum mechanics.
In his early career, Schrödinger was a great exponent of fundamental chance in the universe. He followed his teacher Franz S. Exner, who was himself a colleague of the great Ludwig Boltzmann at the University of Vienna. Boltzmann used intrinsic randomness in molecular collisions (molecular chaos) to derive the increasing entropy of the Second Law of Thermodynamics.
Most physicists, mathematicians, and philosophers believed that the chance described by the calculus of probabilities was actually completely determined. The "bell curve" or "normal distribution" of random outcomes was itself so consistent that they argued for underlying deterministic laws governing individual events. They thought that we simply lack the knowledge necessary to make exact predictions for these individual events. Pierre-Simon Laplace was first to see in his "calculus of probabilities" a universal law that determined the motions of everything from the largest astronomical objects to the smallest particles.
On the other hand, in his inaugural lecture at Zurich in 1922, Schrödinger argued that the evidence did not justify our assumptions that physical laws were deterministic and strictly causal. His inaugural lecture was modeled on that of Franz Serafin Exner in Vienna in 1908.
"Exner's assertion amounts to this: It is quite possible that Nature's laws are of thoroughly statistical character. The demand for an absolute law in the background of the statistical law — a demand which at the present day almost everybody considers imperative — goes
Several years later, Schrödinger presented a paper on "Indeterminism in Physics" to the June, 1931
"Fifty years ago it was simply a matter of taste or philosophic prejudice whether the preference was given to determinism or indeterminism. The former was favored by ancient custom, or possibly by an a priori belief. In favor of the latter it could be urged that this ancient habit demonstrably rested on the actual laws which we observe functioning in our surroundings. As soon, however, as the great majority or possibly all of these laws are seen to be of a statistical nature, they cease to provide a rational argument for the retention of determinism.
Despite these strong arguments against determinism, just after he completed the wave mechanical formulation of quantum mechanics in June 1926 (the year Exner died), Schrödinger began to side with the determinists, including especially Max Planck and Albert Einstein (who ironically had in 1916 discovered that ontological chance is involved in the emission of radiation).
Schrödinger's wave equation is a continuous function that evolves smoothly in time, in sharp contrast to the discrete, discontinuous, and indeterministic "quantum jumps" of the Born-Heisenberg matrix mechanics. His wave equation seemed to Schrödinger to restore the continuous and deterministic nature of classical mechanics and dynamics. And it allows us to
visualize particles as wave packets moving in spacetime, which was very important to Schrödinger. By contrast, Bohr and Heisenberg and their Copenhagen Interpretation of quantum mechanics insisted that visualization of quantum events is not possible.
Max Born, Werner Heisenberg's mentor and the senior partner in the team that created matrix mechanics, shocked Schrödinger with the interpretation of the wave function as a "probability amplitude."
The motions of particles are indeterministic and probabilistic, even if the equation of motion for the probability is deterministic.
It is true, said Born, that the wave function itself evolves deterministically, but its significance is that it predicts only the probability of finding an atomic particle somewhere. When and where particles would appear - to an observer or to an observing system like a photographic plate - was completely and irreducibly random, he said.
Einstein had seen clearly for many years that quantum transitions involve chance, that quantum jumps are random, but he could not believe it. Although the Schrödinger equation of motion is itself continuous and deterministic, it is impossible to restore continuous deterministic behavior to material particles and return physics to strict causality. Schrödinger did not like this idea and never accepted it, despite the great success of quantum mechanics, which uses Schrödinger's wave functions to calculate Heisenberg's matrix elements for atomic transition probabilities.
Discouraged, Schrödinger wrote to his friend Willie Wien in August 1926
"[That discontinuous quantum jumps]...offer the greatest conceptual difficulty for the achievement of a classical theory is gradually becoming even more evident to me."...[yet] today I no longer like to assume with Born that an individual process of this kind is "absolutely random." i.e., completely undetermined. I no longer believe today that this conception (which I championed so enthusiastically four years ago) accomplishes much. From an offprint of Born's work in the
Why did Schrödinger not welcome Born's absolute chance? It was strong evidence that Boltzmann's assumption of chance in atomic collisions was completely justified. Exner thought chance was absolute, but did not live to see how fundamental it was to physics. And the early Epicurean idea that atoms Could it be that senior scientists like Max Planck and Albert Einstein were so delighted with Schrödinger's work that it turned his head? Planck, universally revered as the elder statesman of physics, invited Schrödinger to Berlin to take Planck's chair as the most important lecturer in physics at a German university. And Schrödinger shared Einstein's goal to develop a unified (continuous and deterministic) field theory. Schrödinger won the Nobel prize in 1933. But how different our thinking about absolute chance would be if perhaps the greatest theoretician of quantum mechanics had accepted random quantum jumps in 1926? In his vigorous debates with Neils Bohr and Werner Heisenberg, Schrödinger attacked the probabilistic Copenhagen interpretation of his wave function with a famous thought experiment (based on an Einstein suggestion) called Schrödinger's Cat. In 1952, Schrödinger wrote two influential articles in the British Journal for the Philosophy of Science denying quantum jumping. They influenced generations of quantum collapse deniers, including John Bell, John Wheeler, Wojciech Zurek, and H. Dieter Zeh. Schrödinger was very pleased to read the Einstein-Podolsky-Rosen paper in 1935. He immediately wrote to Einstein in support of an attack on Bohr, Born, and Heisenberg and their "dogmatic" quantum mechanics. "I was very happy that in the paper just published in P.R. you have evidently caught dogmatic q.m. by the coat-tails...My interpretation is that we do not have a q.m. that is consistent with relativity theory, i.e., with a finite transmission speed of all influences. We have only the analogy of the old absolute mechanics . . . The separation process is not at all encompassed by the orthodox scheme.' Einstein had said in 1927 at the Solvay conference that nonlocality (faster-than-light signaling between particles in a space-like separation) seemed to violate relativity in the case of a single-particle wave function with non-zero probabilities of finding the particle at more than one place. What instantaneous "action-at-a-distance" prevents particles from appearing at more than one place, Einstein oddly asked. [The answer, one particle becoming two particles never appears in nature. That would violate the most fundamental conservation laws.]
In his 1935 EPR paper, Einstein cleverly introduced
Schrödinger challenged Einstein's idea that two systems that had previously interacted can be treated as ψ and _{1}ψ. They cannot, until another quantum event separates them. Schrödinger published a famous paper defining his idea of "entanglement" in August of 1935. It began:
_{2}When two systems, of which we know the states by their respective representatives, enter into temporary physical interaction due to known forces between them, and when after a time of mutual influence the systems separate again, then they can no longer be described in the same way as before, viz. by endowing each of them with a representative of its own. I would not call thatIn the following year, Schrödinger looked more carefully at Einstein's assumption that the entangled system could be separated enough to be regarded as two systems with independent wave functions: Years ago I pointed out that when two systems separate far enough to make it possible to experiment on one of them without interfering with the other, they are bound to pass, during the process of separation, through stages which were beyond the range of quantum mechanics as it stood then. For it seems hard to-imagine a complete separation, whilst the systems are still so close to each other, that, from the classical point of view, their interaction could still be described as an unretardedSchrödinger says that the entangled system may become disentangled long before any measurements and that perfect correlations between the measurements would remain. Note that the entangled system could simply decohere as a result of interactions with the environment, as proposed by decoherence theorists. All the perfectly correlated results of Bell-inequality experiments would be preserved. On Determinism and Free Will
Schrödinger's mystical epilogue to What Is Life? (1944), in which he "proves God and immortality at a stroke" but leaves us in the dark about free will.
As a reward for the serious trouble I have taken to expound the purely scientific aspects of our problem Order, Disorder, and Entropy
Chapter 6 of What Is Life?
Normal | Teacher | ScholarNec corpus mentem ad cogitandum, nec mens corpus ad motum, neque ad quietem, nec ad aliquid (si quid est) aliud determinare potent.' SPINOZA, Ethics, Pt III, Prop.2 |