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Quantum Mechanics

The sixth Solvay Conference, 1930: Einstein presents Bohr with the photon-box thought-experiment.

 


 

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The following information is from the documentary "Atomic Physics And Reality."

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Whenever Einstein and Niels Bohr met, there was always one question they always discussed passionately: Can the properties of an atomic particle be measured without disturbing it?

Einstein believed it was possible. At the sixth Solvay Congress of 1930 he wanted to show Bohr how.

By means of this apparatus, he claimed it would be possible to register the precise moment at which a particle of light was emitted from the opening at the side of the box and, at the same time, measure its weight.

The physicist Leon Rosenfeld was present at the discussion. He recalls it was quite a shock for Bohr to be faced with this problem.

He didn’t see the solution at once.

During the whole evening he was extremely unhappy, going from one to the other, trying to persuade them that it couldn’t be true.

I shall never forget the vision of the two antagonists leaving the club: Einstein, a tall, majestic figure, and Bohr trotting near him, pleading that, if Einstein’s device would work, it would mean the end of physics.

But the next morning Bohr returned triumphantly. Einstein had forgotten to take his own theory of relativity into account. Clocks are affected by gravity.

But Einstein wasn’t satisfied. He couldn’t accept Bohr’s claim that it was impossible to measure the properties of an atomic particle without disturbing it. This would mean that we would never be able to obtain a complete picture of physical reality.

 

Dr. John Wheeler: “Einstein admired Bohr, and Bohr admired Einstein, and you’ll recall that Einstein felt that reality exists, in effect, ‘out there,’ something independent of us, and the position of Bohr was rather this, that reality is only a word, and we have to learn the right way to use that word.”

 

 

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