minutephysics - 2018-12-21
Need a last minute holiday gift idea? Go to https://www.brilliant.org/minutephysics for 20% off a premium subscription to Brilliant (can be given as a gift). Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 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
At some point the cat metaphor actually makes it harder to follow and that point was now
That point was Schroedinger's Cat, TBH. Nearly any other explanation of the same thing without the cat makes so much more sense.
@Ken Mendoza 'Meow' is actually better than a 'Cat', because at least it's a wave ;)
@Grev Agreed. Theres so many unique names for the many hypotheses and new found laws of quantum mechanics that I had to come to the comments to realize that I didnt have to look up this new 'cat particle'
Ostbuggen Thank you! I was JUST about to post a similar comment. Im also tired of the cat metaphor 😁
I got lost as soon as he said cat
Cat analogy did not help much...it would have been much better with electrons🙁
Vince Caso Im not a quantum scientist but im pretty SURE all matter can behave like waves.
Matter waves are reffered to as „De Broigle” waves and are described by the equation λ=h/mv, where h is the plancks constant.
the constant is 6,62x10^(-34) and you can easily substitute the m and v with your own mass and speed and get the resulting wavelength.
You will quickly notice why we cant really observe interference between cats but it doesnt mean it DOESNT EXIST, wave-particle duality doesnt just stop existing if you get big enoug.
Thank you and sorry if i sound rude, I never meant to, I just wanted to clarify sth many people here knew but were to lazy to explain.
Ken is correct, as can be read in any introductory college physics textbooks. The wave character of macro objects has been measured and is consistant with theory. In fact it must be taken into account in silicon chip circuit design, and chips are most certsinly macro objects. The wave character simply gets too small to detect with current instruments at larger scales. Note that lessening wave character
Note that ledsening wave character with increasing size is a simple prediction of quantum theory ie thr DeBroglie wavelength.
@Mikołaj Macroscopic objects in superpositions is incredibly unstable and will never be possible on the scale of a cat
There's no difference I think... the main content is the same
I'm worried about your obsession with cats.
Schrödinger was obsessed too it must be a physicist thing.
toxoplasmosis
even bartonella
CALL PETA
Stop using innocent cats in those quantum experiments!
Did they launch them at the slits using cat-apults?
No, because nobody likes cats.
Those are Shrodinger's cats, there are simultaneously innocent and not and the same time.
@Marik Zilberman you know, I was going to make a dumb catspiracy joke, but now I feel dumb for making a dumber joke...
1:17 you lost your chance to make the anti-cat be a dog... whole video ruined there lol
He didnt want to be that dogmatic 😏
No. Is like saying a proton is the anti electron.
@Doug Rosengard Indeed. A pair o' dogs would annihilate one another.
Would be cataclysmic
Try as I mutt, but, to say the leashed, these comments are too ruff for me to understand. (Are my jokes too corgi for you? I’m sure they’ll hound you for days.)
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.
- " you can't express quantum mechanics in a single phrase ! "
- " 3:39 "
"I understand quantum mechanics perfectly and if you can't, you're stupid" - Tesla
@James McCloskey "Cyka blyat" - Also Tesla
@Diepvries I know quantum mechanics
Quantum mechanics:
"The knowledge of being aware that you can't know everything."
- Pandafish 2018
I second that.
Honestly I don't understand any one of those cats
Satish Bhoos in truth nobody understands cats, even the famous cat psychologist Dr. Felix Grimalkin has admitted as such. So when we bring in quantum cats they are bound to behave only in statistically significant ways.
Cat darkness? My cat is a darkness blob whenever it wants
I believe the coming of the anti-cat will spell doom for mankind
In cat darkness where only chaos reigns one man finds a way to bring back light by having the cat and anti cat go through the same slit both blocking the other one but both reaching this world by the power of quantum mechanics.
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.
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?
@BlackIris Code That is certainly true, but I didn't mention it for the sake of brevity and because the main point is that it still effectively prevents any light from passing through the slit (if they are in fact parallel). Essentially, the OP wanted to know if or how this experiment could apply to photons, and I gave him an extreme idealization mainly for the purpose of conceptual understanding and to show that it can in fact apply to light as well.
You are correct that two photons should be able to go through the same slit at the same time (unless you do as Flatgod mentioned and have the two photons out of phase). The condition that two particles can't go through the same slit at the same time is a constraint designed into the experiment by the choice of particles, not a fundamental law. You only observe Hardy's Paradox if you include this constraint.
When he drew the electron experiment he drew an e- and an e+. I think the experiment was with particle and anti-particle pairs, but there should be a term for ”particle met anti-particle”
@Solveig Lindberg you are right and wrong at the same time: anti electron is
written as e+ which is positron, electrons cant have + charge.
Well, he says in the video that it's only a paradox if you don't believe in superposition. So, you are correct, it's not a problem. It's only a problem if you think cats are still cats when not being asked where they are.
This is Hard to understand 😉
@PaganTeapot
He might have failed in trying to simplify his video but, the fact that he tried to help educate the general public says alot about his character. Good man just not so good at communicating his point to the general public.
@v c ya, no shade. I generally follow and enjoy most of this channel's vids. Just sometimes they go over my head :)
@PaganTeapot
I had someone try to explain it to me i think it was him but i dont know anways he tried using cats again lol hahaha i was like hold up no cats please lol then when he explained it normally it all came together. His hart was in the right place. Im just happy to understand more of what he was talking about.
lisa geurrero would confront unsafe lettuce
The paradox is that both cats simultaneously stop each other from going through the middle slit. It seems that both cats and no cats seem to be going through it. It's a pretty weird paradox.
The cat metaphor was so distracting, I kept having to playback every couple of sentences. My mind takes everything literally, so in order to follow, I had to actively replace the word cat every time he said it.
Sounds like u got issues
Log Nature I’m not denying that, lol
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?
Yes, I too cannot see how one can force the cats to pass through only two of three slits
Is there any way in which I can perform this experiment in the lab at school without any hi tech equipment? The main challenge is how can I stop the top "cat" from going through the bottom slit and vice versa physically. Anyone has an ideas?
@Feynstein 100 Yes it does. If you are aware of this, for double slit experiment the intensity of central maxima is maximum and subsequent maximas are dimmer. But as we keep increasing the number of slits, the maximas keep getting brighter. For countably infinite slits all the maximas will be equally lit.
I made a comment about the same thing, looked in the comments and saw this😂
They would both kill each other by crossing path's simultaneously.
A hole too small for cats to fit through? That's just silly.
YOU REALLY LOVE CATS😂
Replacing the word “particle” with “cat” doesn’t make this easier to understand for me
Get used to it
Physicists and Cats: A Love Story
😅 As soon as you switched to ‘cats’ I kept imagining the shear MESS of firing multiple cats at a wall !!!! 😳 😬 🤣
All these flunky YouTube videos on "double-slit" experiments miss the point of the experiment.
The real experiment is that only one photon is sent to a sheet with two slits. The slits are only big enough to allow for one photon.
When not observed they interfere. Meaning it can't be determined which slit the individual photon went through. The single photon behaves like a wave that interferes with itself.
But when a device is placed to observe the slits, then the photon only goes through one of the slits each time. It was the observation that affected the photon to behave like a particle. While not being observed it behaves like a wave (able to interfere with itself).
Talk about the real double-slit experiment. It takes special equipment to do it, not some laser pointer!
We did this in class with a laser pointer
He's covered that. And quantum venn diagrams... And i think the point of this is for people that totally get it and are bored with the classic double slit, and need to get their Freak On ;)
Darling, where’s our cat? Well, gone. Through which slit in our doors I can’t say.
I know I'm late, but I like the cat analogy meow
So is the cat dead or alive?
@Ryan Wilson
Are you a programmer?
When B = !A (dead = not alive) then the question (A or B) (dead or alive) can always be answered with yes :)
+JetPackJan u have a long way boi.....quantum mechanics just violates these laws
Yes
Now I know why he made them cats. For the extra cat memes for people to comment about
It splattered against the wall. So I'm going to say dead.
I read the title as happy...
Because physics makes me feel that way :)
You could have used electrons instead of cats... cat analogy made it harder 2 digest..I😭😭
Replacing quantum particles with catsa actually made me struggle to follow the point 😔 damn you schrodinger.
“Cat-darkness” :) I presume this has been done with electrons?
Why is he describing this in terms of cats when he could be describing the actual thing, light?
I've seen several videos on the subject and this was legit, the most difficult to follow.
I don't like cats.
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".
particle just means a tiny piece of matter, i dont think anyone literally thinks there are subatomic golf balls flying around the place
I thought it was “purr-fect “.
Although, there’s an alternate version of me posting canine centric pun at this very moment
#Question
Hi minutephysics! I’m involved in an argument with a classmate of mine. He proposes that if there were a steady stream of visible light coming through a double-slit apparatus, and that if all of the photons were observed, then you would be able to see, with your own eyes, 2 bands of light on the screen. I disagree - my thinking is that even if all of the photons were observed going through whichever slit they entered, the photons would still interfere with each other and create the same interference pattern as in the unobserved double-slit scenario. There are good arguments on both sides (we both have limited knowledge) and I haven’t been able to find any resources which might settle the argument. Do you know which of us is correct? Has this scenario been demonstrated? Perhaps this sort of experiment can’t even be done at this point?
Thanks! And thank you for the videos!
It's science!!! Thank you for the information!!!
Congrats , you made it difficult on whole new level by using cat 😊
Can you experimentally verify cat interference? I'd love to see that...
;)
The cat thing went over my head
Maa! Hey Maaa!
That weird cat is causing a paradox! Maaa! The one that looks like grandma has gotten in the cat free zone! Nonononono...!!!!
“Sometimes the universe just is weird” has been added to my list of life mottos
Btw I loved the scene where you reversed the color scheme!
He said "interfere with yourself" 😂
First Schindler now you...
Leave the Cats alone fgs
Great topic, great elucidation. Thank you. Also dig the bass as your backdrop.
I feel like this is better explained with pilot wave theory, no superposition, just particles riding on waves that interfere with each other. Perfectly understandable...
Yeah exempt pilot wave theory requires you add extra math which means extra assumptions. That and you can't reconcile it with gravity at a quantum level, which is why De Broglie never went over to the pilot wave camp even though he was the first one to first suggest it.
@dead abyss You can't reconcile regular quantum mechanics with gravity either. But regular QM has a special-relativistic version (QFT), while Bohmian mechanics does not
I think the reason people don't try is because one can't. If it was pilot waves instead of superposition, both cats wouldn't go through. Nor can it explain or predict the double slit experiment, or the DCQE, or make a useful prediction for more than one particle at a time. That's why even Einstein didn't care for it; even though it fit better with his beliefs.
@Aaron Curtis Correct me if i'm wrong, but Pilot Wave Theory explains the Double slit experiment. As a (pilot) wave can enter the two slits while the particle only enters one. It still produces the interference pattern, no need for superposition. And as with DCQE, it forgoes any need for the photon to make a "decision" about being either a wave or a particle, and assumes that it was a particle guided by a wave the whole time. The other problems, like no unifying QFT are still valid though. That doesn't mean it can't or will never have a unifying theory with the other forces (including gravity) nor does it mean it can or will. In the past Pilot Wave theory had a problem that it required hidden variables, which was proved impossible by Bell's Theorem. But as it turned out, Bell's Theorem only accounted for local hidden variables while Pilot Wave Theory required global hidden variables. Every interpretation from the Copenhagen to the Many Worlds have problems. It's just that the problems with Pilot Wave hampered its development in its infancy, so it never got to be as developed as the rest of the interpretations.
I like the cat analogy! It's clear and makes the video look more explicit in my opinion. and it's fun, 'coz... cats.
I like cat-darkness :D
"Cool things waves do when they interfere" is a great band name.
your videos are awesome !! could you please talk about Journal of High Energy Physics in your next vid plsssss
Luckily I watched this week an hour long introduction into quantum mechanics so I understood this video but otherwise I would have on idea.
sammy3212321 - 2018-12-21
What.
I don't think the addition of cats helped 😭
Matrixar's music workshop - 2019-02-12
xD
Matrixar's music workshop - 2019-02-12
@v c I hope yall just jk as it was just a funny addition
Parth Katke - 2019-02-23
Yep
Son of a Glitch - 2020-01-25
I know right? I'm more of a dog person & I would probably have understood this with dogs (What an asshole he is for not considering that)... Whereas cats; I (sort of but not quite...) hate them... Almost as if they were cockroach-like creatures that were crudely sculpted from freeze dried shit...(potentially created by a thoroughly lame, z-list pagan-god).
I.M. Zhelev - 2020-04-22
I like how you phrase the what as a statement, not as a question. Af if you are saying "Don't clarify it, I won't understand it either way".