According to the known laws of physics, my favorite food, tacos, shouldn't exist. But no,
physics isn't specifically against these tortilla treats. Neither you, nor I, should exist, either.
In fact, all of the matter, all of the stuff in our universe, shouldn't exist.
Fortunately my (and hopefully by now, your) favorite little particle the neutrino
just might be a clue to figuring out why it does. Today, we're discussing what teeny tiny
neutrinos have to do with the existence of tacos and everything else in the universe.
[music]
>Wait a second, hold on, what is this? What are you doing?
>I'm hosting this video about matter and antimatter.
>No, no that's my job! >Oh come on, you've done
all of the videos. It's my turn. >Because it's my video series.
And hey, that's my taco. [zap]
>Now look what you've done, we've annihilated each other. [sigh]
>Kirsty, sorry I'm late. I hope I haven't missed anything important. Uh, Kirsty? Are you there?
Oh look, tacos. Okay, well, I'll go ahead as we planted. To understand why the universe exists,
we have to understand the difference between matter and antimatter. A particle and its
anti-particle have the same mass, but all of their other quantum mechanical properties are reversed.
For example, electrons are negatively charged and positrons are positively charged. Properties like
spin and momentum will also be the opposite of its partner particles. Because of this,
if a particle and anti-particle meet each other, they annihilate.
They can turn into photons or other particles as allowed by their energies and by quantum
mechanics. We can calculate this using the famous E=MC squared.
This set us up for possibly the biggest mystery of the universe, the universe itself. We think
that the big bang should have created equal amounts of matter and antimatter, which should
have all annihilated each other leaving the universe full of energy and empty of matter
and antimatter. But if you're watching this video, well, you exist, so clearly that hasn't happened.
>I'm back! Sorry I left you hanging, Pedro. I was
dealing with anti-me, you know how it is. You didn't talk about neutrinos without me, did you?
>Oh no I didn't, I was just explaining how the universe
started with slightly more matter than antimatter.
>Perfect! Yes, there was probably only one extra matter particle per million particle-antiparticle
pairs. But over time, it added up to, well, everything: atoms, galaxies, you, me, tacos.
It seems that this universe likes matter more than antimatter. Why?
Scientists are still searching for an exact answer, but it has
something to do with a wrinkle in the fundamental symmetry of the universe.
Symmetry is seen almost everywhere in the physics world but something in the beginning of
the universe tipped the scales towards matter. The more hints of asymmetry physicists can find at the
most fundamental levels, the more clues we have about why there's more matter than antimatter.
>There's a rule in physics called "CP Symmetry" that essentially means if every particle in the
universe was replaced with its anti-particle and reflected in a mirror, all of the laws of physics
would still work exactly the same. We want to find examples of that symmetry being broken
by finding particles and anti-particles that don't behave quite the same.
>And this is where neutrinos finally come into the picture! Thanks, Pedro. I'll take it from here.
We've discussed how neutrinos can change what flavor they appear as,
just like this ball can rotate from red to blue to yellow. Antineutrinos also change flavors.
If neutrinos obey the symmetry rules then antineutrinos should change in the exact
same way. But current experiments have seen some hints that neutrinos and antineutrinos
might flavor shift differently, which is really exciting. It could be another hint
towards whatever imbalance in the early universe led to all the matter
you see around you today, including your lunch.
While our current results are encouraging,
they don't provide quite enough data for scientists to say for certain that neutrinos
are breaking the symmetry rules. That means we need more neutrinos... a lot more neutrinos.
And that's why I'm working on the Deep Underground Neutrino Experiment, which will see
incredible numbers of neutrinos thanks to huge detectors and an intense new particle beam.
The neutrinos and antineutrinos created at Fermilab will be mostly muon flavor. Once they've
made their 800-mile journey to the DUNE detectors in South Dakota, lots of them will have oscillated
and will interact as the electron flavor. If DUNE measures different numbers of
electron neutrinos and antineutrinos than CP symmetry predicts, that could
be evidence that neutrinos and antineutrinos follow different rules of physics. And that
could point scientists towards an explanation for the origin of tacos, I mean, the universe.
What's your guess, do you think neutrinos will break symmetry rules? Let us know in
the comments. And don't forget to share, like, and subscribe for more quality neutrino content.
Fun fact: Scientists have already measured a difference between matter and antimatter in
quarks. Kaons and B mesons, which are made up of quarks and anti-quarks
decay in a way that slightly breaks CP symmetry. But the mass-antimatter
difference here is far too small to account for all the matter we see around us today.
Theories suggest that neutrinos could violate CP a thousand times more than quarks,
so the search for more symmetry breaking neutrinos continues.
>Wait, where did my taco go?
>Not touching you, not touching you, not touching you. >Don't. Don't do it.