Hardy's Paradox | Quantum Double Double Slit Experiment

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This video is about Hardy's Paradox, wherein an electron and positron (or photons polarized horizontally and vertically) pass through Mach-Zehnder interferometers that overlap such that the particles have a chance of annihilating. If they do annihilate, then the interference pattern changes and there is a probability for both particles to be detected in the "dark arms" of the detector, that is, where previously there was no probability for detection for either particle. The paradox has implications for local realism, contextuality, lorentz elements of reality, and has been used as an experimental setup for weak measurements.

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

[Ostbuggen]

At some point the cat metaphor actually makes it harder to follow and that point was now

[sammy]

What.
I don't think the addition of cats helped 😭

[RealJoshBinder]

the cat part threw me off... do cats = particles  in this example?

[farazshaikh]

Cat analogy did not help much...it would have been much better with electrons🙁

[craig.]

I tried this and the cat scratched the shit out of me. I was gonna try with two at once next but I don't think I'm going to now.

[allthingsfascinating]

I started watching Henry way back in 2011. I was still in college and this guy had made this physics explainer video using stop motion on paper, and it looked so damn cool. 7 years later and now so many YouTubers are doing this. You have come a long way. Keep making such awesome stuff.

[dak]

Stop using innocent cats in those quantum experiments!

[razeke]

I'm worried about your obsession with cats.

[-TheRF]

1:17 you lost your chance to make the anti-cat be a dog... whole video ruined there lol

[thespanishinquisition]

I believe the coming of the anti-cat will spell doom for mankind

[AlejandroBravo]

Why can't two cats pass through the same slit? I mean, the wavefunction does not have a volume like macroscopic objects.

If one is a particle and the other its antiparticule, then it's true they won't pass through the slit, even though there should still be a state (so 4 states, not just 3) in which they both annihilate and don't go through.

If they are both the same type of particle, I guess by Pauli's exclusion principle they can't be at the same point in the same quantum state.

But if they are just two photons, why can't they both go through the same slit at the same time?

[RainaRamsay]

“Sometimes the universe just is weird” has been added to my list of life mottos

[andrewaukerman]

Hey, I know that pop science loves to present quantum mechanics as 'weird', 'odd', and use things like 'cat being both alive and dead' or 'going through slits" and all that, but it's been nearly 100 years since quantum mechanics became established science; it's no longer supposed to be weird and odd. It is only (and should only be presented as such) as very, very successful way of describing and thinking about certain phenomena. Cats don't display observable wave-like properties through double slits, particles do. That's sort of it. I'm not even sure why we still talk about particles in the classical sense - electrons are never "particles" as being like little balls. They only act like it in certain circumstances (like being absorbed by a screen). "Particle is in a super position" is more accurately, "The amplitude describing a particle is in a super position".

[corneliugoea]

Cat darkness? My cat is a darkness blob whenever it wants

[satishbhoos]

Honestly I don't understand any one of those cats

[ScienceClicEN]

Good video as always! I particularly like that you emphasize the accuracy of quantum mechanics. Usually people seem to mystify this theory, leading others to think it's really blurry, even for scientists. In reality it's actually a very rigorous mathematical model which describes reality with an astounding precision.

[LookingGlassUniverse]

I love this video. I was grinning through the entire thing :D

[deepdata]

To everyone saying "The cat metaphor didn't help": It's not a metaphor, it's a pun. A joke for quantum physics insiders. The symbols denoted with <a| are called "bra" and thos denoted with |b> are called "ket". So he when in de video it sounds like he says "cat", he is actually saying "ket". And he drew a cat in the ket, because that is the pun.

[feynstein]

1:36 Um why isn't there a possibility where the bottom cat goes through the top slit and vice versa? Don't Feynman's path integrals prove that particles take all possible paths?

[tutohar]

As a non physicist and after watching lots of videos about quantum mechanics and believing that I can atleast conprehend videos on minute physics... I get these cats ... and I am like...boy I have to start all over again