We're still in the dark about what 95 percent of our universe is made of — and the standard model for understanding particle physics has hit a limit. What's the next step forward? Particle physicist Alex Keshavarzi digs into the first results of the Muon g-2 experiment at Fermilab in Chicago, which found compelling evidence of new particles or forces existing in our universe — a finding that could act as a window into the subatomic world and deepen our understanding of the fabric of reality.
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[00:00:00] TED Audio Collective
[00:00:09] We live in a cosmos shrouded in mystery.
[00:00:17] A staggering 95% of the universe eludes our understanding.
[00:00:22] We simply don't know what it is all made of,
[00:00:25] and we haven't had the tools to move forward.
[00:00:28] But this may be changing.
[00:00:30] As the standard model of particle physics confronts its limitations,
[00:00:34] a new dawn emerges in the realm of subatomic exploration.
[00:00:38] I'm Sherelle Dorsey, and this is TED Tech.
[00:00:41] Particle physicist Alex Kejavarzy
[00:00:46] unveils the groundbreaking revelations from a recent experiment.
[00:00:50] And these findings promise to redefine our concept of reality itself.
[00:00:55] Let's listen in as Kejavarzy takes to the TED stage.
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[00:02:48] Hey everybody, I'm Kai Rizdahl, the host of Marketplace,
[00:02:53] your daily download on the economy.
[00:02:56] Money influences so much of what we do and how we live.
[00:02:59] That's why it's essential to understand how this economy works.
[00:03:03] At Marketplace, we break down everything from inflation and student loans
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[00:03:19] So today, I'm really here to talk to you all about one thing, the universe.
[00:03:26] In the world of particle physics, the ultimate goal is to be able to describe
[00:03:30] all the particles and forces that make up our universe.
[00:03:34] And while we've made an extraordinary amount of progress in this over the past hundred years,
[00:03:38] we're doing it still because there are big mysteries about what the universe is made of
[00:03:43] and how we came to be here.
[00:03:45] So let me start by introducing you to three of the big mysteries about our universe.
[00:03:51] First, we know that the universe is expanding.
[00:03:57] So astrophysical evidence suggests that the universe started as a very dense,
[00:04:02] very hot Big Bang, and has since been expanding outwards from that point.
[00:04:07] However, as a complete shock in the late 90s, physicists discovered
[00:04:11] that the expansion of the universe isn't slowing down, as you might expect.
[00:04:14] It's actually accelerating.
[00:04:16] And we have absolutely no idea as to why this is.
[00:04:19] All that we know is that some unknown source or force of nature
[00:04:23] is stretching the universe out in every direction at an ever-increasing rate.
[00:04:28] Because we don't know what that source is, we've just called it dark energy.
[00:04:33] Now what we do know about dark energy is that it makes up roughly 74%
[00:04:38] of the energy content of our universe.
[00:04:40] So straight off the bat, that's 74% of our universe that we know absolutely nothing about.
[00:04:47] Second, we know that 85% of all the matter in our universe
[00:04:51] is made up of something called dark matter.
[00:04:54] Now we have no idea what dark matter is, and we've never observed it in experiments here on Earth.
[00:04:59] But we know from several corroborating astrophysical observations that it has to be there.
[00:05:05] Importantly, another thing that we know about dark matter is that it makes up
[00:05:08] another 21% of the energy content of our universe.
[00:05:12] So that, coupled with the dark energy problem, means that we only know
[00:05:16] what 5% of our universe is made of, and the rest is totally dark to us.
[00:05:23] The third problem concerns how we've come to exist at all.
[00:05:27] Now, fundamental particles of matter have their own antimatter particles,
[00:05:32] which are the same as their normal matter counterparts,
[00:05:35] except they have opposite positive or negative charge,
[00:05:38] just like the two ends of a normal everyday battery.
[00:05:42] Now together, this charge is equal and balanced.
[00:05:45] The electron, for example, which we're a bit more familiar with
[00:05:49] and gives us electricity in our homes, is negatively charged.
[00:05:52] But it has an antimatter partner called the positron, which is positively charged.
[00:05:57] Now to ensure this balance, matter and antimatter are always created
[00:06:01] and destroyed equally and in pairs.
[00:06:04] This is what all of our theories predict, and this is what we observe in all of our experiments.
[00:06:09] And so in the Big Bang, we would have expected that matter and antimatter
[00:06:14] would have been created in equal amounts, and so we would expect to see
[00:06:17] equal amounts of matter and antimatter in the universe today.
[00:06:22] However, nearly every structure of matter, every natural structure of matter in our universe
[00:06:26] you, me, the Earth, the stars, are made almost entirely of normal matter,
[00:06:31] leaving a lot of antimatter missing from the balanced equation.
[00:06:35] For all you Marvel and Avengers fans out there, it's a bit like someone's just snapped their fingers
[00:06:40] and half of all the natural stuff in the universe has disappeared.
[00:06:44] There literally should be another universe's worth of stuff all around us,
[00:06:48] but somehow it's not there.
[00:06:50] One of the greatest challenges in particle physics today is to figure out
[00:06:53] what happened to all the antimatter and why we see an asymmetry between matter and antimatter at all.
[00:06:59] So those are three of the big mysteries about our universe,
[00:07:06] and that's a lot of what we don't know.
[00:07:08] Now what this means is our current understanding of the universe up until this point
[00:07:13] can't tell us why the universe is the way it is or what 95% of it is made of.
[00:07:19] But importantly, each of these mysteries, what is dark energy, what is dark matter,
[00:07:25] and the matter-antimatter asymmetry in the universe could all be solved
[00:07:28] by finding a new particle or a new force of nature.
[00:07:32] So now let me introduce you to our current understanding of the universe.
[00:07:39] The Standard Model of Particle Physics, the mathematical equation,
[00:07:42] which I'm sure you're all very used to, which describes how our universe works.
[00:07:47] You can think of it as the recipe for how all the particles and forces in the universe interact
[00:07:53] and result in the structures of matter that we see around us.
[00:07:56] Now this equation represents a huge level of achievement over the past hundred years,
[00:08:01] and in its full form it's much longer, but simplified like this,
[00:08:05] you see a very elegant, I think elegant, representation of the structure of matter.
[00:08:11] And then if that equation is the recipe, then these are the ingredients.
[00:08:18] Just 17 ingredients, 17 fundamental particles, where fundamental here means
[00:08:24] they're not known to have a substructure, they're not known to be composed of any smaller particles.
[00:08:29] And together with the equation, they make up the Standard Model of Particle Physics,
[00:08:34] and it is our best, most tested, and globally accepted theory
[00:08:38] of all the known particles and forces in the universe.
[00:08:42] And it's given rise to much of what we take granted in the modern world,
[00:08:46] granted for in the modern world today.
[00:08:48] So a good example would be our ability now to harness the energy from the sun,
[00:08:52] where our ability to use solar power and our moves towards nuclear fusion
[00:08:57] couldn't be possible without understanding the particles and forces of the Standard Model.
[00:09:02] Now whilst the Standard Model has been so successful at testing the phenomenon
[00:09:08] that we can test here on Earth, it cannot accommodate
[00:09:11] and has no explanation for those big mysteries about our universe.
[00:09:16] And so it's at this point that I'd like to introduce you to a particular particle
[00:09:20] and the hero of our story, the muon.
[00:09:24] Now, muons may seem unfamiliar to you all, but actually they're around us all the time.
[00:09:30] Cosmic rays that hit the Earth's atmosphere result in showers of muons
[00:09:33] that constantly bombard the Earth.
[00:09:35] You may be surprised to learn, for example, that there are on average 30 muons
[00:09:39] travelling through each and every one of you every second.
[00:09:43] Now, muons can be thought of quite simply as the heavy cousin of the electron,
[00:09:47] but importantly they're an ideal tool for physicists to use
[00:09:51] to search and look for new particles and forces to explain those big mysteries.
[00:09:56] And so why is that?
[00:10:00] Well, let's assume for a second that we can represent the muon by this gyroscope.
[00:10:06] When you spin a gyroscope, it wobbles around its axis
[00:10:10] and muons have an identical behaviour when you place them in a magnetic field.
[00:10:16] They spin and they wobble.
[00:10:18] Now, whilst they're doing this, the muon will come into contact with
[00:10:22] any and all other particles in the universe, standard model or otherwise.
[00:10:27] And in fact, it's the interaction of the muon with those other particles
[00:10:31] that defines how fast it wobbles.
[00:10:34] In essence, the more different particles that bounce off the muon
[00:10:38] whilst it's wobbling, the faster it will wobble.
[00:10:41] And so then, this is what we want to measure.
[00:10:43] How fast muons wobble in a magnetic field due to their interaction
[00:10:47] with all the particles and forces in the universe.
[00:10:53] Now, so far, no new particle or force outside of the standard model
[00:10:57] that could explain those big mysteries about our universe has ever been discovered.
[00:11:02] But the point to re-emphasise is that the rate or the speed by which muons wobble
[00:11:07] when we place them in a magnetic field is directly defined
[00:11:11] by all the particles and forces in the universe that it comes into contact with.
[00:11:15] And so, if we can measure very precisely how fast they wobble,
[00:11:20] we can then compare that to the theoretical prediction of how fast
[00:11:24] they should wobble from just the particles and forces of the standard model.
[00:11:28] And then, if the measurement was found to be different and larger and disagree,
[00:11:32] then it would be an indication of new particles or forces outside of the standard model
[00:11:37] that could explain those big mysteries about our universe.
[00:11:41] And an experiment I work on has done just that.
[00:11:46] This is the Muon G-2 experiment, located at Fermilab on the outskirts of Chicago.
[00:11:53] Now, this experiment released its first result in April of 2021,
[00:11:57] and the take-home message of this talk is that the result I am presenting you here today
[00:12:01] from the Muon G-2 experiment is the closest glimpse that we've had
[00:12:05] to seeing a new particle or force here in a laboratory on Earth.
[00:12:10] When muons are placed in a magnetic field, they wobble faster than what the theory predicts.
[00:12:15] So all the known particles and forces of the standard model
[00:12:18] have failed to predict how fast muons have wobbled.
[00:12:22] And what does this suggest?
[00:12:24] Well, it suggests that there are new particles or forces
[00:12:27] that aren't part of that globally accepted theory interacting with the muon
[00:12:32] and causing them to wobble faster.
[00:12:34] Now, a reason why physicists are so excited about this result
[00:12:38] is that the chance that this result is a fluke statistically is one in 40,000.
[00:12:44] So that's the same as saying that there's a 99.9975% chance
[00:12:48] that we've seen the influence of a new particle or force here in a laboratory on Earth.
[00:12:54] But a word of caution.
[00:12:57] Physicists actually set a much stricter threshold by which they can claim a discovery,
[00:13:01] and that is the chance the result is a fluke cannot be more than one in 3.5 million.
[00:13:07] And so we haven't reached that discovery threshold yet,
[00:13:10] and so we can't definitively say that we've seen the influence of a new particle or force.
[00:13:15] And the reality is that to reach that one in 3.5 million threshold,
[00:13:19] there's a lot of work to be done.
[00:13:21] But that work is being done right now and will continue to be done over the coming years.
[00:13:29] So what does this all mean?
[00:13:31] Well, first, any result from the Muon G1S2 experiment,
[00:13:35] even a result that said there were no new particles or forces, would be a good result.
[00:13:40] That is science, right?
[00:13:42] Sometimes it's not discovering new things.
[00:13:45] Sometimes it's just confirming old things.
[00:13:47] And even if that were the case,
[00:13:49] the byproducts of particle physics experiments have been advancing human civilization for much of the past hundred years.
[00:13:55] Modern electronics, the Internet, satellite navigation,
[00:13:59] these are all byproducts of particle physics experiments or endeavors.
[00:14:02] There's no telling what experiments like the Muon G1S2 experiment could do for us in the future.
[00:14:09] But if that were the case and we found no new particle or force,
[00:14:13] then we wouldn't be able to explain those big mysteries about our universe.
[00:14:17] What is dark energy?
[00:14:18] What is dark matter?
[00:14:20] And where did all the answer matter go?
[00:14:23] Whatever the outcome, the Muon G1S2 experiment will keep releasing results in the next few years
[00:14:28] that will continue to test our understanding of the fabric of reality.
[00:14:32] I for one am really excited about it and I really hope you stay tuned with us
[00:14:36] to find out if we definitively discovered a new particle or force for the first time.
[00:14:40] Thank you very much.
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[00:15:14] Hey TED Tech listeners.
[00:15:16] We're supported by our friends at Working Smarter,
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[00:15:54] That was Alex Keshavarzee at TEDxManchester 2023.
[00:16:04] TED Tech is part of the TED Audio Collective.
[00:16:10] This episode was produced by Nina Lawrence, edited by Alejandra Salazar, and fact-checked by Julia Dickerson.
[00:16:17] Special thanks to Maria Ladius, Farah DeGrange, Corey Hajim, Daniela Balareso, and Michelle Quint.
[00:16:25] I'm Sherelle Dorsey. Thanks for listening and talk to you again next week.
[00:16:45] Support for TED Tech comes from Odoo.
[00:16:47] To put it simply, Odoo is built to save.
[00:16:50] Odoo saves time, Odoo saves money, but most importantly, Odoo saves businesses.
[00:16:55] That's right, Odoo's superhero software rescues companies from the perils of disconnected platforms.
[00:17:01] And Odoo's utility belt of user-friendly applications puts the power of total business management in the palm of your hand.
[00:17:07] Learn more at odoo.com slash TEDtech.
[00:17:10] That's O-D-O-O dot com slash TEDtech.
[00:17:13] Odoo, saving the world one business at a time.