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  • One of the biggest secrets of physics is that we still don't fundamentally understand what

  • happens when the smallest things interact with big things - that is, when quantum mechanics

  • meets our everyday world.

  • You've probably heard of the "Schrodinger's Cat" experiment where a particle (in this

  • case a cat) is in a superposition of two states (both dead and alive) at once, until it interacts

  • with the outside world - normally a photon of light that we send in to see what's going

  • on (but it could also just be a random particle that has nothing to do with us).

  • Upon interaction with the outside world, the cat is observed as being either dead, or alive,

  • but not both.

  • The problem is, physics can't explain how the cat, or particle, goes from being in a

  • combination of two states at once to being in "just one", or "just the other"; nor do

  • we know how the "decision" is made.

  • This isn't just a problem with cats, either - it plagues every single quantum mechanics

  • experiment, famous or otherwise, from the double slit experiment and quantum teleportation

  • to the Stern-Gerlach experiment and tests of the Bell inequalities.

  • In every case, we can predict how likely it is for a particle to be in one state or another,

  • but have no clue how it actually ends up that way.

  • That's where the many-worlds picture of quantum mechanics comes in - basically, "many-worlds"

  • proposes the idea that the quantum system doesn't actually decide - rather, at every

  • junction where large everyday stuff interacts with a quantum system, the timeline of history

  • splits and both possibilities happen on different, alternate branches.

  • You know, a choose-your-own-adventure where every possible story happens.

  • In this scenario, we'd think that only one possibility happened because we'd be stuck

  • on one of the branches, in a version of ourselves that only sees one possibility happen.

  • In some ways, this sounds pretty fishy - I mean, it's hard to test the reality of a universe

  • that hides its true nature from us by not allowing us to test or observe its true nature.

  • But anyway, in the many-worlds picture of quantum mechanics, "branch-points" are predicted

  • to happen all the time, everywhere.

  • Pretty much any time subatomic particles interact with each other, or with anything else, anywhere

  • in the universe, there are multiple possible outcomes.

  • Which means a LOT of branching of history.

  • There may even be infinitely many branches.

  • So is the Many Worlds hypothesis true?

  • We don't know - it hasn't yet been tested experimentally.

  • There's a bit of mathematics that supports it, and there are also a number of mathematical

  • models that don't require such an extravagantly big & complex picture of the universe.

  • But luckily, physics is science, not speculation, and eventually, someone, maybe even you, will

  • perform an experiment that helps us

  • discover the truth.

One of the biggest secrets of physics is that we still don't fundamentally understand what


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B1 中級

平行宇宙。許多世界 (Parallel Universes: Many Worlds)

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    林宜悉 發佈於 2021 年 01 月 14 日