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How to Tell Matter From Antimatter | CP Violation & The Ozma Problem

How to Tell Matter From Antimatter | CP Violation & The Ozma Problem


Most everyday phenomena happen equivalently
in a mirror as they do normally – at least, from a physics perspective. Unlike when you play a video backwards in
time (where it’s pretty obvious that something weird is going on), when compared with a normal
video, motion in a mirrored video still looks totally physically normal – just mirrored. In fact, without outside context, there’s
no way to tell which was the original and which was mirrored! Which is why horizontally flopped shots are
used in movies all the time. In fact, as far as we know, everything in
the universe governed by electromagnetism and gravity and the strong nuclear force behaves
this way – if you set up two experiments that are mirror images of one another, they’ll
produce results that look like mirror images of each other. Which presents a problem if we ever need to
communicate with aliens from afar: if all physics is mirror-symmetric, that would mean
left handed and right handed are relative – from a physics perspective they’re interchangeable,
just like up and down and forward and back – so if we were simply talking to aliens and
didn’t have any shared reference objects, we’d we have no way of explaining what we
mean by left-handed and right-handed using physics. . This Left/Right ambiguity is called “the
Ozma Problem.” . And the distinction between left and right
IS important, because earth-based life mostly relies on sugars with right-handed symmetry
and amino acids with left-handed symmetry. This isn’t a physics constraint – it just
as easily could have been the other way around – but the point is, the molecules in our food
and our bodies DO have a specific orientation, so not knowing left from right could impair
intergalactic culinary relations. However, there is a solution: the weak nuclear
force doesn’t always play nicely when mirrored . For example, when uranium nuclei beta decay
they emit (mostly?) electrons spinning like left-handed corkscrews, but if you perform
the mirror image of the experiment using a mirror-image uranium nucleus, the nucleus
still emits electrons spinning like left-handed corkscrews (rather than right-handed, as they
would in a mirror) . It turns out that in our universe, the mirror-image of a physical
process doesn’t always result in the mirror image of the outcome – uranium always decays
more into left-handed electrons, no matter how you look at it. So we’d tell the aliens “you know how
electrons spin when uranium decays? That direction is what we call ‘left’”. Which would solve the Ozma problem – except,
there’s a problem with this solution. Because what if the distant aliens were made
entirely of antimatter? I mean, in principle they could be and we
wouldn’t know. Antimatter interacting with itself behaves
exactly like matter interacting with itself: antihydrogen has the same atomic spectrum
as hydrogen, and antimatter-you looks and behaves exactly like matter-you (until it
interacts with matter). And here’s the problem: while the matter
version of a uranium nucleus decays into left-handed electrons whether it’s in a mirror or not,
the anti-matter version always decays into… right-handed anti-electrons whether it’s in
a mirror or not. So if we told the aliens “look at the beta
decay of the nucleus with atomic weight 239 – that’s always the orientation we call
left-handed” we’d be wrong: for aliens made of antimatter, it would in fact be what
we call right handed. And you definitely don’t want to shake either
hand of an alien made of antimatter. So how can you figure out, from afar, if a
distant alien is made of antimatter? This is the Ozma problem, level 2. Essentially, antimatter is another kind of
mirror we can hold up to the universe, which combined with the possibility of regular mirroring
means we can’t use beta decay to define left vs right. But luckily, there’s a next level solution,
again thanks to the weak nuclear force. Enter the Kaon, a fast-decaying subatomic
particle. Whether they’re mirrored or not, around
20.3% of the time Kaons decay into right-handed anti-electrons , while around 20.1% of the
time – slightly less often – they decay into left-handed electrons. And the key is this : if you instead take
antimatter Kaons, whether mirrored or not, they still decay slightly less often into
left-handed electrons, rather than right-handed anti-electrons as you might have expected
from the way antimatter-uranium decays. That is, normal kaons – whether mirrored or
not – and anti-kaons – whether mirrored or not – both decay less often into left-handed
electrons. And this is how distant aliens could figure
out if they’re made of matter or antimatter and whether or not they’re using the same
concept of “left” as us: simply build a particle accelerator and look at the decays
of neutral kaon particles; the electron-like thing that they decay into slightly less frequently
is made of what we call matter, and it’ll be moving in what we call a left-handed way. The universe doesn’t distinguish between
left and right or antimatter for electromagnetism, for gravity, and for the strong nuclear force. But for some reason, the weak force allows
us to tell the difference. This video was made with the generous support
of the Heising Simons foundation, which also supports research into the violation of antimatter-mirror
symmetry in our universe. Processes that violate antimatter-mirror symmetry
(which is called “CP Violation”) are necessary to explain why there’s so much more matter
in universe than antimatter, and while the weak nuclear force does violate that symmetry,
it doesn’t come anywhere close to accounting for the observed imbalance between matter
and antimatter in the universe. So physicists around the world (among them
researchers supported by the Heising Simons foundation) are searching for other possible
processes that might break antimatter-mirror symmetry to help explain how the universe
ended up made mostly of matter, and thus, why it was possible for us to exist. Thanks Heising Simons!


Reader Comments

  1. Maybe the universe isn't mostly made of matter, but matter and antimatter that are just very far apart. Who knows, maybe some of the stars in the night sky are antimatter, how would you know?

  2. Sure, but if an alien made of anti-matter were to ever meet us normal matter folks, wouldn't they believe we are made of anti-matter, and that they are normal matter?

  3. How do we know whether Kaon decay probabilities are influenced by mainly matter surrounding the experiment – in the detector, particle accelerator and Earth? We really ought to commission building an anti-detector and anti-(particle accelerator) on an anti-planet to make sure.

  4. Aren't kaons both matter and antimatter? A down quark and a strange antiquark, or the opposite? Which counts as an "antimatter" kaon?

  5. that's one way to do it…
    But if we're able to communicate with aliens on that level, all it would need is 3 galactical objects (point of reference, center point, object orbiting it) to explain clock- and counterclockwise. Since up and down are relatively easily explained due to objects sticking to the celestial body they inhabit, left and right could very well be derived from those two.

  6. When my Mum was at School the Nuns would strike a Left hand with the edge of a wooden ruler if caught using it to write with…. I say we send Nuns to make First Contact 🖖

  7. Fun fact anti matter is most of the universe. Not the other way around. Matter occurs less often therefore less of it exists…..simple logic

  8. "Simply build a particle accelerator" Can I get one at Ikea? And how many part(ticle)s does it consist of? Must be one hell of manual.

  9. The Ozma problem is that it keeps casting Meteor for ten hits of random damage so it always has a chance of wiping out your whole party in one turn no matter how well you prepare

  10. I find it amusing that this video avoids words like chirality and positrons when that is exactly what it is talking about.

  11. Of course the anti-me is a thought experiment, but going further, say if anti-me exists, could we even communicate with it? Would me photons interact anti-me?

  12. Scientist A: "Do you know what's the difference between Matter and Anti-matter?"
    Scientist B: *shrugs *
    Scientist A: "Neither do I, but it doesn't matter."

  13. Whenever I feel burnt out and feel like science has become tiring, minute physics seems to always pull me back in

    His explanation and his videos make me feel at home (at my sciencey home)

    Just sharing

  14. L and R symmetry in those things is even more arbitrary than the left and right we think of in the Marco world. There is nothing specifically right or left about them, they are just turned in one way vs turns in the other. If you flipped them over you could just call them Left and Right the other way, we picked on and called a 3d object left and another 3d object right and then said all objects that are twisted in this way are left and all the others in the other way are right.

    Left and right have always been stupid away to look at things. Far better to talk about something turning a direction vs turning another. Clockwise and anti-clockwise make far more physical and less arbitrary sense and we can point at a physical object, and tell them it's spinning clockwise, vs anti-clockwise from their perspective. Even if they turned themselves upside down to look at it, that thing would still be spinning that way. while if they did the same for left and right it would be backward. The problem here and the one that has always made me made about this 'problem' is that it's so simple to skip over it you just stop thinking about Left and Right being important and use terms we can easily define instead.

  15. Are the decay properties of antiuranium really known with certainty? We've obviously never observed the stuff itself (even antihydrogen is incredibly difficult to make and study), and I thought uranium was too large and complex to model precisely at the quantum level.

  16. Perfect. Now that I know how to tell matter from antimatter, I'll never run the risk of accidentally annihilating myself, so long as I have a FRIKIN PARTICLE ACCELERATOR IN MY POCKET!

  17. "you definitely dont wanna shake EITHER hand of an alien made of anti matter"…. love it dude, love it i can stop laughing🤣

  18. btw how the hell do you even wanna comunicate with antis? legit question in my opinion since i dont know how theyd at all be able to receive our messages + they must be heckin far off just cause their home-planet would also have to be made of anti matter and that would kind of reck anyttikg that gets in contact with em right?

  19. I am pretty sure I recently read and watched about how we don't know how antimatter behaves under gravity because we've never produced enough of it and cold enough to observe whether it falls.

  20. How do we tell that an alien from a far isn't made of anti-matter? They, and/or their stuff, don't just simply explode when in this universe

  21. This isn't true, K0's decay into leptons 100% of the time decays into e+, and K0~ (antiparticle) decay into leptons 100% of the time decays into e-. K0 and K0~ behave exactly as you would expect, you can just flip all the decay particles from matter to antimatter. i.e. K0->pi-ve+ has the exact same probability as K0~->pi+v~e-. Judging from the branching fractions of 20.3% and 20.1% I think this is meant to be about K-long's decays which is correct, K-long decays more often into e+ than e-, but K-long doesn't have an antiparticle.

  22. Left is where the thumb is right…
    Pff
    Left is towards the spin dircetion of the less often K_0 decay product.
    I think I can remember the latter better :D.

  23. Wait. Wait. Wait. Nuclei are chiral??! @1:42 it describes a mirror image uranium nucleus. THAT is my learning from this video. Pretty cool. [My google research finds that you need an unpaired nucleon for this, similar to an unpaired electron.]

  24. Evil chirality is a geometric attribute in which an object can have two images: one on the right and one on the left, irreplaceable; that is, they differ spatially, even if the rest of their properties are identical. An object that exhibits chirality is simply called 'chirus'.

  25. Theoretical physics is likely the only place where you can "simply build a particle accelerator and look at the decays of neutral kaons", and telling which left isn't right is the real problem.

    I fucking love science <3

  26. "Touch something to an object in our solar system. If it goes kaboom, let's just stay radio pals."

    But wait. Wouldn't these also be anti-radio-waves that we would get? Aren't they made of anti-photons? We'd know what their world would be made of from that. Or they could polarize their transmission and then we could tell them what we call that polarization, or we could engage in the same kind of exchange with them.

  27. Or could it be something like "God put some of the other stuff into this universe as a laboratory curiosity for us, but not to build anything that actually matters (pun intended) to us." The Big Bang had right hand English on the ball, and that's it, we can't see past it.

  28. If anti-matter and matter act the same way with their like particles, then how do we know we are not part of the anti-matter universe? Or is that relative to our perspective of anti-matter?

  29. Idk why, but when i first saw the title for the first time i somehow read the ozama problem. Triggered me and now i feel like a retard xD

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