Does the experiment where a single photon goes through 2 slits really show the universe is constantly dividing into alternate realities?

Question

Probably not well worded (bad at Physics!)

In: Physics

Answer 1

The double-slit experiment is a good demonstration of some key parts of Quantum Mechanics. In it, we see some ‘non-classical behaviour’ like ‘wave-particle duality’ and how that raises things like ‘the measurement problem’, and so on.

We see plenty of other evidence for Quantum Mechanics in other experiments too, but the double-slit-experiment (especially when done with 1 photon at a time) is one very clear/pure example, and so is a convining example that Quantum Mechanics must have something right.

Once you accept that Quantum Mechanics is (at least approximately) correct, it does raise questions as to what the results of the theory *means*. The ‘measurement problem’ technically doesn’t need to be solved for us to be able to use the theory; we can still ‘shut-up-and-calculate’ and get useful and correct predictive answers (to help with other expimernts or technology) without knowing why or how it is correct, but the meaning or metaphysics remains mysterious.

So, there are philosohpical ideas that try to answer the ‘measurement problem’ and thus attempt to explain a bit of the ‘why’ behind Quantum Mechanics.

* You may have heard of the idea of Quantum Mechanics resolving to chance in a ‘wavefunction collapse’, like you have a 50% chance of measuring a photon over here, and a 50% of measuring it over there, and that randomness is just part of reality. That’s one possible interpretation (the ‘Copenhagen interperetation).
* You’re talking about the ‘Many Worlds interpretation’, where instead of imagining some true randomness to a single world, we instead imagine every possbility happens. And one way to allow for that is to imagine that new worlds are generated to accomodate each possibility, i.e. the universe is split/cloned.
* There are also other interpretations. I think one is called the ‘handshake’ and another is ‘superdeterminism’.

These different interpretations are difficult (and perhaps in some cases, impossible) to even imagine testing, let along actually deigning an experiment around (I think I’ve heard arguments that perhaps ‘superdeterminism’ could realistically be tested, but tbh I don’t think I understood the argument so I can’t say whether that was valid or not).

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So, in summary, it is not the case that the double-slit experiment confidently shows that the universe splits with each measurement.

However, the double slit experiment does make a compelling case for Quantum Mechanics, and that raises the “measurement problem”, and the “many worlds interpretation” is one proposed answer to the measurement problem.

We could perhaps phrase it as something like:

>The Double-Slit experiment shows that we need an interpretation of Quantum Mechanics, but it doesn’t help point to which one to pick. You could pick the Many Worlds Interpretation instead of some other interpretation, but we don’t have any evidence that helps us know which interpretation to pick.