6.3 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Bohr–Einstein debates | 1/7 | https://en.wikipedia.org/wiki/Bohr–Einstein_debates | reference | science, encyclopedia | 2026-05-05T16:35:15.514856+00:00 | kb-cron |
The Bohr–Einstein debates were a series of public disputes about quantum mechanics between Albert Einstein and Niels Bohr. Their debates are remembered because of their importance to the philosophy of science, insofar as the disagreements—and the outcome of Bohr's version of quantum mechanics becoming the prevalent view—form the root of the modern understanding of physics. Most of Bohr's version of the events held in the Solvay Conference in 1927 and other places was first written by Bohr decades later in an article titled, "Discussions with Einstein on Epistemological Problems in Atomic Physics". Based on the article, the philosophical issue of the debate was whether Bohr's Copenhagen interpretation of quantum mechanics, which centered on his belief of complementarity, was valid in explaining nature. Despite their differences of opinion and the succeeding discoveries that helped solidify quantum mechanics, Bohr and Einstein maintained a mutual admiration that was to last the rest of their lives. Although Bohr and Einstein disagreed, they were great friends all their lives and enjoyed using each other as a foil.
== Pre-revolutionary debates == Einstein was the first physicist to say that Max Planck's discovery of the energy quanta would require a rewriting of the laws of physics. To support his point, in 1905 Einstein proposed that light sometimes acts as a particle which he called a light quantum (see photon and wave–particle duality). Bohr was one of the most vocal opponents of the photon idea and did not openly embrace it until 1925. The photon appealed to Einstein because he saw it as a physical reality (although a confusing one) behind the numbers presented by Planck mathematically in 1900. Bohr disliked it because it made the choice of mathematical solution arbitrary; Bohr did not like a scientist having to choose between equations. This disagreement was perhaps the first real Bohr-Einstein debate. Einstein had proposed the photon in 1905, and Arthur Compton provided evidence in 1922 with his Compton effect. Bohr, along with Hans Kramers and John C. Slater asserted that conservation of energy only applied to statistical averages in the BKS theory of 1924. However, after the 1925 Bothe–Geiger coincidence experiment, BKS was proved to be wrong and Einstein's position that energy was conserved in individual collisions was shown to be correct.
== The quantum revolution == The quantum revolution of the mid-1920s occurred under the direction of both Einstein and Bohr, and their post-revolutionary debates were about making sense of the change. Erwin Schrödinger redeveloped quantum theory in terms of a wave mechanics formulation, leading to the Schrödinger equation. When Schrödinger sent a preprint of his new equation to Einstein, Einstein wrote back hailing his equation as a decisive advance of “true genius.” In parallel, Werner Heisenberg's 1925 Umdeutung paper reinterpreted old quantum theory in terms of matrix-like operators, removing the Newtonian elements of space and time from any underlying reality. A year later, in 1926, Max Born, collaborating with Heisenberg, proposed that mechanics were to be understood as a probability without any causal explanation. Both Einstein and Schrödinger rejected Born's interpretation, with its renunciation of causality which had been a key feature of science still present in general relativity. In a 1926 letter to Max Born, Einstein wrote:
[...] 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 [God] is not playing at dice. At first, even Heisenberg had heated disputes with Bohr about whether his matrix mechanics were compatible with Schrödinger's wave mechanics. And Bohr was opposed to Heisenberg's uncertainty principle. However, by the fifth Solvay Conference in October 1927, Heisenberg and Born concluded that the revolution was over and nothing further was needed. It was at that last stage that Einstein's skepticism turned to dismay. He believed that much had been accomplished, but the reasons behind the mechanics still needed to be understood. Einstein's refusal to accept the revolution as complete reflected his desire to see developed a model for the underlying causes from which these apparent random statistical methods resulted. He did not reject the idea that positions in space-time could never be completely known but did not want to allow the uncertainty principle to necessitate a seemingly random, non-deterministic mechanism by which the laws of physics operated. Einstein himself was a statistical thinker but denied that no more needed to be discovered or clarified. Einstein worked the rest of his life to discover a new theory that would make sense of quantum mechanics and return causality to science, what many now call the theory of everything. Bohr, meanwhile, was dismayed by none of the elements that troubled Einstein. He made his own peace with the contradictions by proposing a principle of complementarity that assigns properties only as result of measurements.
== Post-revolution: First stage == As mentioned above, Einstein's position underwent significant modifications over the course of the years. In the first stage, Einstein refused to accept quantum indeterminism and sought to demonstrate that the uncertainty principle could be violated, suggesting ingenious thought experiments which should permit the accurate determination of incompatible variables, such as position and velocity, or to explicitly reveal simultaneously the wave and the particle aspects of the same process. (The main source and substance for these thought experiments is solely from Bohr's account twenty years later.) Bohr admits: “As regards the account of the conversations I am of course aware that I am relying only on my own memory, just as I am prepared for the possibility that many features of the development of quantum theory, in which Einstein has played so large a part, may appear to himself in a different light.”