Sean Carroll
speaker
26,727 appearances
49 recordings
4 series
first heard Apr 2024
last heard 6d ago
Sean Carroll’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 29 in all, peaking in Jun 2026 with 6.
Appearances
And I fire the electrons at a barrier with two openings, two vertical slits as openings, and I have a detector screen on the other side, what will I see?
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If I fire the electrons one at a time, according to quantum mechanics, the electrons are described by wave functions, as long as we're not observing them.
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And therefore, if the electron goes through both slits on the other side,
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It will emerge from both slits as a wave, as two different waves that can then combine and either reinforce each other or cancel each other out.
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And therefore, what we see at the detector for every electron it's just a dot, it's just a where you've detected the electron signal.
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But if you accumulate many, many dots by doing this over and over again, you see an interference pattern.
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You see bands where there's lots of electron dots, bands where there's almost none, and that's interpreted as saying that there was a wave going through the two slits.
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This is evidence of the wave-like behavior of quantum matter.
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And then the spin is, or the twist, I should say, if you try to look for which slit the electron went through, the left one or the right one.
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That means you've made a detection, you've made a measurement, and the wave function collapses in the usual way of talking about it.
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And once that happens, the electron only goes through one slit.
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It goes through the one you saw it go through.
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And therefore, coming out the other side, it is a wave once again.
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You're done detecting it.
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Because you didn't stop it, you just sort of notice which slit it went through.
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Uh but there's only going through one slit, so there's nothing to interfere with.
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There's now only one source.
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And what you see is a pattern on the detector screen, which is just a single slit pattern, a single blob if you want, no interference bands, no oscillating yes-no sort of bands of electron dots.
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And so that's one v very famous thought experiment in um quantum mechanics, which was a first thought experiment.
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Now eventually it's been done.
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