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!
Of course, there's the level 3 Ozma problem.
If those aliens made of anti-matter are moving in the opposite direction of time, then you again end up not being able to know what's left (unless you know that they are traveling backwards in time).
For anyone unfamiliar with what I'm talking about, I really do think Neil Turok's concept on a CPT symmetric universe in negative time relative to the Big Bang is at least worth a read. (Popsci article, Source work).
What about right handed magnetic field around moving charge?
Love minute physics!
I'm a bit confused. what is meant by the mirror [image?] of a particle?
Wow k-on is such a cool show i cant believe that it can even tell left from right thank you japan
minutephysics anime sparkling eyes
I read obama, could not understand the image
But is there an ELI5 explanation for what makes the weak force so special?
Crazy, I was just listening to a podcast similar to this yesterday that was discussing left and right hand spin with CP violation and some other ideas.