SPEAKER_02: TED Audio Collective. It's TED Talks Daily.I'm your host, Elise Hu.Why is the universe the way it is?And what is it made of?It turns out we only know about 5% of what the universe is composed of.And the standard model for understanding particle physics has hit a limit.It doesn't help us understand the three big mysteries facing scientists today. about where we live.Now there's a new tool to explain the mysteries.
They're called muons and you're about to learn more about them and how they work from particle physicist Alex Keshavarsi in a talk recorded at TEDx Manchester 2023. Support for TED Talks Daily comes from Capital One Bank.With no fees or minimums, banking with Capital One is the easiest decision in the history of decisions.Even easier than deciding to listen to another episode of your favorite podcast.And with no overdraft fees, is it even a decision?That's banking reimagined.What's in your wallet?Terms apply.See CapitalOne.com slash Bank.Capital One N.A.
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SPEAKER_01: Welcome to the Canva guided meditation for stress at work.Impending deadline?Generate Canva presentations in seconds.So So today, I'm really here to talk to you all about one thing.The universe.
SPEAKER_00: In the world of particle physics, the ultimate goal is to be able to describe all the particles and forces that make up our universe.And while we've made an extraordinary amount of progress in this over the past hundred years, we're doing it still because there are big mysteries about what the universe is made of and how we came to be here.So let me start by introducing you to three of the big mysteries about our universe. First, we know that the universe is expanding.So astrophysical evidence suggests that the universe started as a very dense, very hot Big Bang and has since been expanding outwards from that point. However, as a complete shock in the late 90s, physicists discovered that the expansion of the universe isn't slowing down, as you might expect, it's actually accelerating.And we have absolutely no idea as to why this is.All that we know is that some unknown source or force of nature is stretching the universe out in every direction at an ever-increasing rate.And because we don't know what that source is, we've just called it dark energy. Now, what we do know about dark energy is that it makes up roughly 74% of the energy content of our universe.
So straight off the bat, that 74% of our universe that we know absolutely nothing about.Second, we know that 85% of all the matter in our universe is made up of something called dark matter. Now, we have no idea what dark matter is, and we've never observed it in experiments here on Earth, but we know from several corroborating astrophysical observations that it has to be there.Importantly, another thing that we know about dark matter is it makes up another 21% of the energy content of our universe.So that, coupled with the dark energy problem, means that we only know what 5% of our universe is made of, and the rest is totally dark to us. The third problem concerns how we've come to exist at all.Now, fundamental particles of matter have their own antimatter particles, which are the same as their normal matter counterparts, except they have opposite positive or negative charge, just like the two ends of a normal everyday battery. Now, together, this charge is equal and balanced.The electron, for example, which we're a bit more familiar with and gives us electricity in our homes, is negatively charged.But it has an antimatter partner called the positron, which is positively charged.
Now, to ensure this balance, matter and antimatter are always created and destroyed equally and in pairs.This is what all of our theories predict, and this is what we observe in all of our experiments.And so in the Big Bang, we would have expected that matter and antimatter would have been created in equal amounts, and so we would expect to see equal amounts of matter and antimatter in the universe today. However, nearly every structure of matter, every natural structure of matter in our universe, you, me, the Earth, the stars, are made almost entirely of normal matter, leaving a lot of antimatter missing from the balanced equation.For all you Marvel and Avengers fans out there, it's a bit like someone's just snapped their fingers and half of all the natural stuff in the universe has disappeared.There literally should be another universe's worth of stuff all around us, but somehow it's not there. One of the greatest challenges in particle physics today is to figure out what happened to all the antimatter and why we see an asymmetry between matter and antimatter at all. So those are three of the big mysteries about our universe, and that's a lot of what we don't know.Now, what this means is our current understanding of the universe up until this point can't tell us why the universe is the way it is or what 95% of it is made of.But importantly, each of these mysteries, what is dark energy, what is dark matter, and the matter-antimatter asymmetry in the universe could all be solved by finding a new particle or a new force of nature.
So now let me introduce you to our current understanding of the universe.The standard model of particle physics, the mathematical equation, which I'm sure you're all very used to, which describes how our universe works.You can think of it as the recipe for how all the particles and forces in the universe interact and result in the structures of matter that we see around us.Now, this equation represents a huge level of achievement over the past 100 years, and in its full form, it's much longer.But simplified like this, you see a very elegant, I think elegant, representation of the structure of matter. And then if that equation is the recipe, then these are the ingredients.Just 17 ingredients, 17 fundamental particles, where fundamental here means they're not known to have a substructure.They're not known to be composed of any smaller particles. Together with the equation, they make up the standard model of particle physics.
It is our best, most tested and globally accepted theory of all the known particles and forces in the universe.It's given rise to much of what we take granted for in the modern world today. A good example would be our ability now to harness the energy from the sun, where our ability to use solar power and our moves towards nuclear fusion couldn't be possible without understanding the particles and forces of the Standard Model.Now, whilst the Standard Model has been so successful at testing the phenomena that we can test here on Earth, it cannot accommodate and has no explanation for those big mysteries about our universe. And so it's at this point that I'd like to introduce you to a particular particle and the hero of our story, the muon.Now, muons may seem unfamiliar to you all, but actually they're around us all the time.Cosmic rays that hit the Earth's atmosphere result in showers of muons that constantly bombard the Earth.You may be surprised to learn, for example, that there are on average 30 muons traveling through each and every one of you every second. Now, muons can be thought of quite simply as the heavy cousin of the electron.But importantly, they're an ideal tool for physicists to use to search and look for new particles and forces to explain those big mysteries.
And so why is that?Well, let's assume for a second that we can represent the muon by this gyroscope.When you spin a gyroscope, it wobbles around its axis.And muons have an identical behavior when you place them in a magnetic field.They spin and they wobble. Now, whilst they're doing this, the muon will come into contact with any and all other particles in the universe, standard model or otherwise.And in fact, it's the interaction of the muon with those other particles that defines how fast it wobbles.In essence, the more different particles that bounce off the muon whilst it's wobbling, the faster it will wobble.And so then, this is what we want to measure.
How fast muons wobble in a magnetic field due to their interaction with all the particles and forces in the universe.Now, so far, no new particle or force outside of the standard model that could explain those big mysteries about our universe has ever been discovered.But the point to re-emphasize is that the rate or the speed by which muons wobble when we place them in a magnetic field is directly defined by all the particles and forces in the universe that it comes into contact with. And so, if we can measure very precisely how fast they wobble, we can then compare that to the theoretical prediction of how fast they should wobble from just the particles and forces of the Standard Model.And then, if the measurement was found to be different and larger and disagree, then there would be an indication of new particles or forces outside of the Standard Model that could explain those big mysteries about our universe. An experiment I work on has done just that.This is the Muon g-2 experiment located at Fermilab on the outskirts of Chicago. Now, this experiment released its first result in April of 2021.And the take-home message of this talk is that the result I'm presenting you here today from the muon g-2 experiment is the closest glimpse that we've had to seeing a new particle or force here in a laboratory on Earth.
When muons are placed in a magnetic field, they wobble faster than what the theory predicts.So all the known particles and forces of the standard model have failed to predict how fast muons have wobbled. And what does this suggest?Well, it suggests that there are new particles or forces that aren't part of that globally accepted theory interacting with the muon and causing them to wobble faster. Now, a reason why physicists are so excited about this result is that the chance that this result is a fluke statistically is 1 in 40,000.So that's the same as saying that there's a 99.9975% chance that we've seen the influence of a new particle or force here in a laboratory on Earth.But a word of caution. Physicists actually set a much stricter threshold by which they can claim a discovery, and that is the chance the result is a fluke cannot be more than one in 3.5 million.And so we haven't reached that discovery threshold yet, and so we can't definitively say that we've seen the influence of a new particle or force.And the reality is that to reach that one in 3.5 million threshold, there's a lot of work to be done.
But that work is being done right now and will continue to be done over the coming years. So what does this all mean?Well, first, any result from the muon g1s2 experiment, even the result that said there were no new particles or forces, would be a good result.That is science, right?Sometimes it's not discovering new things.Sometimes it's just confirming old things.And even if that were the case, the byproducts of particle physics experiments have been advanced in human civilization for much of the past hundred years.Modern electronics, the internet, satellite navigation, these are all byproducts of particle physics experiments or endeavors.There's no telling what experiments like the muon g1s2 experiment could do for us in the future.
But if that were the case and we found no new particle or force, then we wouldn't be able to explain those big mysteries about our universe.What is dark energy?What is dark matter?And where did all the answer matter go? Whatever the outcome, the Muon G1S2 experiment will keep releasing results in the next few years that will continue to test our understanding of the fabric of reality.I, for one, am really excited about it, and I really hope you stay tuned with us to find out if we've definitively discovered a new particle or force for the first time.Thank you very much.
