This discussion explores the concept of realism in quantum mechanics, focusing on the EPR paradox and superdeterminism.
Quantum mechanics describes a universe of fundamental indeterminacy, where physical properties emerge from observations. Some physicists and philosophers propose that reality is fundamentally subjective and exists primarily as a consequence of observation, while others prefer to think of the universe as having a concrete existence independent of the observer. This view is known as realism.
The EPR paradox, proposed by Einstein, Podolsky, and Rosen, challenges the observer-centric view of quantum mechanics. It suggests that if reality is fundamentally realist, then the universe must have a deterministic nature, violating the principle of locality.
Superdeterminism, a theory that the universe evolves in a uniquely predictable way based on its initial state, is suggested as a possible solution to the EPR paradox. However, it requires a kind of conspiracy of interactions to ensure that two messy meat computers make the right choices based on marginal interactions arbitrarily far in the past.
The Bell theorem, derived by physicist John Bell, is a mathematical statement that is true in the case that the electron spins are set from the beginning and contained within the electron, but false if standard quantum mechanics is right and spin is undefined until observation. The theorem states that any local-realist theory must obey the Bell inequality.
The EPR paradox and superdeterminism have been tested through various Bell-type tests, which have shown apparently entanglement is real and as spooky as Einstein feared. However, the results of these tests are not convincing evidence against realism itself; the world may still have a non-subjective existence.
In conclusion, the discussion suggests that either locality or realism are wrong, or there are multiple realities, or the universe evolves in unalterable lock-step determinism. The question of free will and the physical, even deterministic, substrate of our choices remains open for philosophical discussion.
Here are the key facts extracted from the text:
1. Quantum mechanics suggests that the universe exists in a state of fundamental indeterminacy.
2. Photons passing through two slits at once, electrons being spin up and down, and cats being both alive and dead are examples of quantum superpositions.
3. These superpositions only collapse into single states when we try to measure them.
4. Physicists and philosophers have debated whether reality is fundamentally subjective or objective.
5. Realism is the view that the universe has a concrete existence independent of the observer.
6. Pilot wave theory, objective collapse models, and the Many Worlds interpretation are examples of realist interpretations of quantum mechanics.
7. Superdeterminism is a hypothetical concept that suggests the universe evolves in a way that is uniquely predictable by the laws of physics and its initial state.
8. Erwin Schrödinger and Albert Einstein were proponents of realism.
9. The EPR paradox was proposed by Einstein, Boris Podolsky, and Nathen Rosen to refute the non-realist implications of pure quantum mechanics.
10. The Bell inequality is a mathematical statement that is true in the case that electron spins are set from the beginning and contained within the electron.
11. The Bell test was first performed by Alain Aspect in 1980 and has been repeated numerous times since then.
12. The results of the Bell test have consistently supported standard quantum mechanics.
13. Superdeterminism is a loophole in the Bell theorem that suggests the universe evolves in a way that preserves correlations between measurement subject and measurer.
14. The cosmic Bell test was performed by Anton Zeilinger's group in 2017 using the light from distant stars.
15. The test pushed back any possible local-realist influence more than half the age of the universe.
16. The strong force symmetry is known as the Special Unitary Group of order 3 (SU(3)).
17. Fundamental lengths, distances, energies, etc. can be used to translate units between different systems.
18. Planck units, or the energies or masses or decay timescales of common particles and elements, can be used as a reference point.
19. The second law of thermodynamics can be used to determine the time direction used by a civilization.
20. Any basic description of the universe beyond the actual laws of physics would reveal the physics conventions used by a civilization.