Lex FridmanBiggest Mysteries in Physics: Antimatter, Dark Energy & ToE - Don Lincoln | Lex Fridman Podcast #497
Lex Fridman
Introducing Don Lincoln 0:00
The conversation features Don Lincoln, a particle physicist at Fermilab who has spent decades working at the frontier of high energy physics. The host introduces him as someone with a rare gift, similar to Richard Feynman, for explaining complicated physics ideas simply without losing their essential brilliance.
Unification as the Story of Physics 1:01
Don Lincoln frames the entire history of physics as a long quest for unification, where scientists show that seemingly unrelated phenomena are actually governed by the same underlying principles. He starts around 1650, when the laws of celestial gravity, the gravity that governs planets and stars, and terrestrial gravity, the gravity you feel when you trip and fall, seemed completely unrelated. Newton realized the moon is essentially falling toward the earth but continually missing it, which meant celestial and terrestrial gravity were the same force. This is why Newton's work is called the law of universal gravity, and Lincoln calls Newton one of the most brilliant humans he is aware of.
Democritus and Early Atomism 3:30
Lincoln notes that ideas about the smallest building blocks of matter go back even further, to Democritus, who imagined atoms of oil as smooth because oil feels smooth, and atoms of vinegar as sharp and pointy because vinegar pricks the tongue. Democritus was wrong about the details, but the core idea that matter is made of small indivisible particles turned out to be right, even though our modern concept of atoms is very different from his.
Maxwell Unifies Electricity and Magnetism 4:30
Around 1830, electricity and magnetism looked like unrelated phenomena, a magnet sticking to steel versus a spark or a lightning bolt. Decades of experiments, including the discovery that running electricity through a wire creates a magnetic field, led James Clerk Maxwell to write his laws of electromagnetism around the 1860s. These equations essentially say that electricity equals magnetism, unifying the two. Lincoln points out that applying calculus to Maxwell's equations produces a wave equation showing that electric and magnetic fields oscillate together, and the speed of that wave turns out to be the speed of light, a result that convinced people of the theory's power. Electromagnetism also underlies chemistry, since atoms are held together by electromagnetic forces, and it underlies modern technology, since electricity powers computers and the internet. Lincoln uses this to argue that curiosity-driven digging into fundamental, seemingly impractical questions can transform the world decades or centuries later, just as nuclear physics research eventually led to nuclear power.
Future Payoffs From Fundamental Physics 12:31
Lex Fridman extends this point, suggesting that unresolved mysteries like dark energy and antimatter could eventually unlock new energy sources or even propulsion systems for space travel, even though such applications currently seem far-fetched. Both agree that such breakthroughs are a double-edged sword, since the same fundamental knowledge that powers civilization can also be turned into dangerous weapons, much like fire can cook a meal or burn down a house. They conclude that because scientists uncover how nature works, society as a whole must decide how that knowledge gets used.
Einstein, Time, and Spacetime 15:32
The discussion turns to Einstein's 1905 special relativity, which showed that time is not universal, contrary to Newton's assumption, and that people moving at different speeds experience time differently. Lincoln credits the specific insight that space and time are unified into a single spacetime not to Einstein himself but to his teacher Hermann Minkowski, who in 1908 recognized this structure in Einstein's equations. Special relativity rested on two premises, that the laws of nature are the same for everyone, and that everyone measures the speed of light as the same number regardless of their own motion. Lincoln describes how particle physicists have confirmed this second premise experimentally by measuring light emitted from subatomic particles decaying at nearly the speed of light and finding the light still travels at exactly the speed of light, not faster. He argues that this speed limit becomes far less strange once you view it as the speed of light through spacetime itself, a property of space rather than an arbitrary rule.
General Relativity and the Nature of Genius 24:00
Lincoln compares the difficulty of grasping unification to the way sodium, an explosive metal, and chlorine, a deadly gas, combine into ordinary table salt, something necessary for life despite each ingredient being dangerous alone. He then turns to general relativity, explaining that Einstein realized acceleration and gravity feel identical, which led him to describe gravity itself as the bending of spacetime. Lincoln calls the failure to give Einstein a Nobel Prize for general relativity a crime against humanity. Reflecting on how such ideas arise, Lincoln says genius requires more than a spark of intuition, it also requires deep knowledge of prior work, mathematical skill, and the discipline to critique one's own ideas, since most new ideas turn out to be wrong. He notes that Einstein, despite his own creative brilliance, struggled to accept quantum mechanics, remaining one of its most valuable and persistent critics even though he understood it fully.
Critique as Part of Discovery 30:31
Don Lincoln explains that Einstein's role in the development of quantum mechanics was not always about generating new ideas but about testing them. He would take someone else's spark of an idea and push it to its logical conclusion, saying essentially, if you're right, then this must follow, which let others go test it. This combative, critical process, where ideas get challenged and sometimes killed, is uncomfortable but essential to how science actually advances and confirms what is true.
Four Forces Before Unification 33:01
By the 1930s, physicists had identified four separate forces in nature: gravity, electromagnetism, the strong nuclear force that holds atomic nuclei together, and the weak nuclear force responsible for certain kinds of radioactivity. Recognizing these four distinct forces was itself a major achievement, even though the deeper goal of physics has always been to find out whether they are really just different faces of one underlying force.
Merging Electromagnetism and the Weak Force 34:32
In the late 1950s and 1960s, physicists began exploring whether electromagnetism and the weak nuclear force were secretly the same thing. In 1967, Sheldon Glashow, Abdus Salam, and Steven Weinberg showed that at high energies these two forces merge into a single electroweak force. The catch was that electromagnetism has infinite range, visible in starlight traveling millions of light years, while the weak force barely reaches beyond the size of a proton, so calling them the same force seemed absurd until the Higgs idea explained the difference.
How the Higgs Field Gives Mass 37:02
The resolution came from papers written in 1964 proposing a field, now called the Higgs field, that fills all of space. Some particles interact with this field and gain mass, while others, like the photon, pass through it unaffected and stay massless. Lincoln compares this to a gravitational field: an object with mass falls when dropped, while a hypothetical massless object would just float, showing that mass is really about how strongly a particle couples to the field around it. In the very hot, high energy conditions right after the Big Bang, the Higgs field's strength was zero, so nothing had mass and the weak force particles moved at light speed just like photons. As the universe cooled, about 10 to the minus 12 seconds after the Big Bang, the Higgs field switched on, giving mass to the weak force particles but not to photons, an event called electroweak symmetry breaking.
Detecting the Higgs Boson 43:01
Fields themselves are never seen directly, only their effects, and the Higgs field is no exception. Because quantum fields can vibrate like a drumhead, a localized vibration in the Higgs field shows up as a particle, the Higgs boson, just as a vibration in the electromagnetic field shows up as a photon. Predicted in 1964 and made scientifically useful by 1967, the Higgs boson was finally hunted for using particle accelerators, starting with the Tevatron at Fermilab outside Chicago, which had already discovered the top quark in 1995 and was later upgraded with ten times more collisions per second in the search for the Higgs.
Turning Energy Into Matter 48:00
Particle accelerators work because energy and matter are equivalent, a fact predicted around 1928 and used routinely ever since. When two particles collide with their momentum canceled out, the energy has nowhere to go but into creating new particles, always alongside an antimatter partner. The antimatter electron was discovered in 1932 and the antimatter proton in 1955 at the Berkeley Bevatron. Fermilab produced antiprotons as a byproduct of its collisions, though at a steep cost, needing about 100,000 protons smashed to yield just one antiproton, and it stopped making them in 2011 when it shifted focus to neutrino physics.
Comparing Fermilab and CERN 51:30
CERN's Large Hadron Collider is now the world's highest energy proton collider, roughly seven times more powerful per collision and about a hundred times more frequent in collisions than Fermilab's old Tevatron. Yet CERN makes antiprotons using a smaller, lower energy stage of its accelerator complex, only 26 GeV compared to Fermilab's 120 GeV, because antiproton production was never its main goal. The extra power at CERN means particles once painstaking to find, like the top quark, which took Lincoln's team six months to a year to gather just 38 candidate events in 1995, are now produced roughly once per second, turning them from a prized discovery into background noise physicists have to filter out.
Inside the Giant Detectors 56:00
At the LHC, beams of protons resemble thin strands of spaghetti moving in opposite directions, colliding about a billion times per second across roughly 40 million crossing moments, each containing up to 20 collisions. Two massive detectors capture these events, CMS, which Lincoln works on, weighing 14,000 tons and standing five stories tall, and Atlas, which is larger in size but lighter at 7,000 tons, big enough that four of them could fit on a football field. Since most collisions involve well understood physics that no longer interests researchers, fast electronic triggers filter the 40 million snapshots per second down to about 100,000 promising ones, which are then passed to computer processors for a quicker analysis that narrows the selection down to roughly a thousand collisions worth keeping.
Petabytes of Data, Handful of Discoveries 1:01:30
You learn how the Large Hadron Collider handles fifty million possible collisions per second, with fast electronics and computers narrowing that down to about a thousand events worth recording. Those get passed through analysis software to graduate students, who sift through them looking for the rare handful that could be the next Nobel Prize. Don Lincoln expresses genuine admiration for the accelerator builders, detector builders, and software engineers who make petabytes of data flow seamlessly around the world.
Racing Toward the Higgs Discovery 1:02:30
Lincoln describes the strange position of working at Fermilab while knowing CERN's Large Hadron Collider was coming online with far greater power, ten times the collision rate and three and a half times the energy. Both labs could either find or definitively rule out the Higgs boson, since the theory made precise predictions for every possible mass value. Fermilab narrowed the possible Higgs mass down to a range between roughly 120 and 145 before running out of time, and with two or three more years of data it would have made the discovery itself. Instead, after a rocky start in 2008 and repairs, the LHC turned on fully in 2012 and announced the discovery on July 4th, just two days after Fermilab's own measurement had narrowed the remaining possibilities.
What the Discovery Actually Confirmed 1:07:30
Lincoln stresses that finding the particle in 2012 only showed something consistent with the Higgs boson, not full confirmation, since rival theories like supersymmetry predicted five Higgs bosons rather than one. Fourteen years of further study have since validated the particle's mass, its zero spin, and its predicted decay patterns into bottom quarks, W and Z particles, and photons, all matching the original 1964 theory by Peter Higgs, Robert Brout, and François Englert. He also explains the "God particle" nickname came from Leon Lederman's publisher wanting better book sales, not from any religious meaning, joking that Lederman actually wanted to call it the "goddamn particle" for how hard it was to find. The Higgs boson mattered as the last unvalidated piece of the Standard Model, closing a fifty-year chapter of discovery, though Lincoln ranks its significance below Einstein's shifts in how we understand the world.
Grand Unified Theories and Their Limits 1:13:00
Lincoln explains the Grand Unified Theory, or GUT, as the hoped-for merger of the electroweak force with the strong force, leaving gravity to be folded in later by a full theory of everything. He sees no fast progress toward this, partly because attempts from the early 1980s failed to pan out.
Why a Final Theory Is Distant 1:14:30
Lincoln believes real rules govern matter, energy, and spacetime, and that a true theory of everything is achievable in principle, but not within his lifetime, his grandchildren's, or even their grandchildren's. He notes it took two hundred years to unify gravity and electromagnetism conceptually, then a hundred years to unify electromagnetism with the weak force, while the next unification scale sits at ten to the fifteenth times higher energy than today's accelerators, a quadrillion-fold leap that outpaces even optimistic projections of accelerator progress.
Superstrings and the Problem of Testability 1:17:30
Lincoln admires string theory's idea of tiny vibrating strings at the Planck scale but does not believe it, insisting no idea should be trusted until tested. He points out string theorists have worked since the 1980s without producing solvable equations that predict measurable quantities like the electron's mass, leaving the theory still built on approximate solutions to approximate equations.
The Australopithecus Analogy 1:23:00
Lincoln compares humanity's attempt to extrapolate physics a quadrillion times beyond current measurement to an early human in Kenya trying to predict the Alps, penguins, or the ocean floor from local experience. Just as that person's best theory would never anticipate such distant realities, he argues it is arrogant to expect today's physics to correctly predict conditions at the Planck scale.
Practical Progress Over Grand Leaps 1:26:00
Lincoln argues real progress means tackling open questions close at hand, such as whether something exists smaller than quarks, what dark matter and dark energy actually are, and the nature of space and time. He compares this to how chemistry alone could never have predicted nuclear physics, suggesting some undiscovered physics, not human limitation, stands between us and a final theory. He cites dark matter models like "dark atoms" forming a whole hidden sector, and the idea of gravity leaking into extra dimensions to explain its weakness, as intriguing ideas that mostly failed testing, underscoring that experiment, not elegant theory alone, is what validates real progress.
Dark Matter as a Clue 1:31:30
Progress in physics often starts with a puzzling observation rather than a finished theory. Vera Rubin measured how fast galaxies rotate, a calculation simple enough for high school physics, and found the answer did not match what was observed. That mismatch became the clue that led to the hypothesis of dark matter, which is not itself a theory of everything but a strong hint that something in the current picture either needs a small fix or a much bigger rethink.
Is String Theory Dead 1:32:31
String theory relies on extra dimensions that have never been observed, and it allows for an enormous landscape of possible universes, which makes it hard to use for actual predictions. Don Lincoln argues the theory is very difficult to truly kill, since killing a theory means making a prediction that fails, and string theory has not failed so much as stalled. After roughly fifty years of work without solving the problem, many physicists are choosing not to spend their careers on a question that may not be answered in their lifetime, much as some researchers once avoided deep interpretive questions in quantum mechanics for the same reason.
Loop Quantum Gravity Explained 1:36:32
Unlike string theory, loop quantum gravity does not try to unify all the forces. It only tries to quantize gravity itself, treating space as possibly having a smallest indivisible unit rather than being smooth and endlessly divisible as in Einstein's general relativity. String theory originally emerged as a competitor to quantum chromodynamics for explaining the strong force, and only became a theory of everything candidate once it was noticed that it predicted a massless spin-two particle, which is a signature of the graviton. Loop quantum gravity once predicted that light of different frequencies would travel at slightly different speeds, but observations of gamma-ray bursts showed no such difference, and the theory's developers later revised it so that this old prediction no longer applies.
Gravity Travels at Light Speed 1:41:02
A striking confirmation came from two colliding neutron stars 140 million light years away, which produced both gravitational waves and a bright flash of light. Astronomers detected the light and the gravitational ripples arriving within 1.7 seconds of each other, proving that gravity travels at the speed of light.
Empty Space Is Not Empty 1:42:30
Quantum field theory holds that space contains a field for every kind of particle, and that these fields can vibrate in ways that are not quite full particles, producing what are called virtual particles that flicker in and out of existence. Two experiments confirm this strange picture. The Casimir effect shows that two close metal plates get pushed together because more virtual particles can exist outside the gap than inside it. Separately, the magnetic properties of the electron and muon, measured to twelve significant figures, match quantum electrodynamics predictions for ten of those figures, a level of agreement Lincoln calls staggering.
Antimatter From Prediction to Reality 1:49:30
Paul Dirac predicted antimatter in 1928 while merging quantum mechanics with relativity, and the positron was discovered in 1932. Antimatter protons followed in 1956, antimatter neutrons a year later, and scientists have since made antimatter helium nuclei and even antimatter hydrogen atoms at CERN, whose light spectrum matches ordinary hydrogen exactly. In 2023 the ALPHA experiment released antimatter hydrogen from a bottle and found it fell downward, with a measured strength about seventy five percent that of ordinary matter, though the uncertainty is large enough to be consistent with normal gravity.
The Staggering Cost of Antimatter 1:55:32
Producing antimatter is extremely hard. Fermilab, once the world's most powerful antiproton facility, needed to smash one hundred thousand protons into a target just to get a single antiproton, yielding roughly a nanogram of antimatter per year. At that rate it would take a billion years to produce a single gram, and combining a gram of antimatter with a gram of matter releases energy equal to the combined Hiroshima and Nagasaki explosions. NASA estimates put the cost of antimatter around sixty two to sixty three trillion dollars per gram, compared to ten to fifty million dollars for an equally powerful nuclear warhead.
Antimatter for Propulsion 1:59:31
Despite the cost, antimatter's compactness makes it appealing for propulsion, with one gram theoretically able to help a craft reach Alpha Centauri in twenty years at a fraction of light speed. Lincoln calls this an engineering problem rather than a physics one, since the real challenge is containment: any loss of containment for even a millionth of a second would be catastrophic. He does not expect future physics breakthroughs to make antimatter easier to produce, since making it simply requires concentrating energy, and any method of doing that would work the same way.
Concentrating Energy to Make Antimatter 2:03:00
Making antimatter requires squeezing energy into a volume as small as a proton, not just having a lot of energy spread out. That is why particle accelerators, which smash protons together in a tiny space, are the best tool available. If someone found a cheap way to create that same density of energy, making antimatter would become easy, but doing so without spending trillions of dollars remains the real obstacle.
The Missing Antimatter Puzzle 2:04:02
After the Big Bang, energy should have produced equal amounts of matter and antimatter, yet the universe we observe is made almost entirely of matter. By counting protons in galaxies and photons in the cosmic microwave background, physicists calculate that for every billion billion antimatter particles there was one extra matter particle. Everything you see is the leftover from that tiny imbalance, and why it happened is still unknown. One idea, baryogenesis, suggests matter and antimatter can oscillate into each other with a slight asymmetry, though the known effect is too small to explain everything. Fermilab is testing a related idea called leptogenesis, using neutrinos, which are known to oscillate between three types, to see if neutrinos and antineutrinos oscillate at different rates, a difference that could help explain the imbalance, with Fermilab and a Japanese team racing to measure it first.
Discovering Dark Energy 2:10:31
Dark energy is best described as the energy of space itself, acting like a repulsive form of gravity. In the late 1990s, astronomers measuring the universe's expansion expected it to be slowing down because matter's gravity pulls things together, but instead found the expansion speeding up, revealing a repulsive force. Einstein had once proposed something similar, the cosmological constant, to keep his equations from predicting a collapsing universe, then abandoned it once Edwin Hubble showed the universe was expanding, only for the idea to return in 1998 once acceleration was confirmed.
The Worst Prediction in Physics 2:14:30
Quantum field theory's calculation of vacuum energy, done by adding up contributions from every possible wavelength, gives a number about 10 to the 120th power larger than what is actually observed for dark energy. Even assuming new physics appears well before reaching the theoretical maximum energy scale, the mismatch only shrinks to about 10 to the 60th power, still enormous. This suggests some unknown field may be canceling most of the energy, but not perfectly, since a small leftover amount of dark energy remains, and figuring out why that cancellation is imperfect is itself a major puzzle.
Is Dark Energy Constant or Changing 2:23:00
Dark energy is usually described as having a constant density, but since energy equals density times volume, a constant density in an expanding universe actually means the total amount of dark energy is increasing over time. A recent, unconfirmed measurement hints that dark energy might actually be decreasing, which would be a significant shift if it holds up. One speculative idea is that space itself is quantized, so as the universe expands, new tiny units of space keep appearing, each carrying a fixed amount of dark energy, which would explain the constant density without requiring space to stretch continuously. Testing whether gravity itself is quantized, potentially through experiments with quantum-entangled particles affecting each other gravitationally, could offer clues, since confirming quantized gravity would push thinking toward quantized space as well.
Evidence for Dark Matter 2:27:30
Dark matter is considered even more mysterious than dark energy, and the case for it starts with galaxies spinning faster than the visible matter's gravity can explain, along with galaxy clusters moving too quickly and distant light bending more than expected. Since the physics equation linking gravity and motion could be wrong in either its gravity term, its motion term, or the assumption that they are equal, searches ruled out ordinary missing matter like hidden hydrogen gas or extra black holes. The bullet cluster, where two galaxy clusters passed through each other, showed gravitational distortion following the galaxies rather than the hot gas clouds in the middle, strong evidence that unseen dark matter, not a flaw in gravity's laws, is responsible. A newer example, the Dragonfly 2 and Dragonfly 4 galaxies, rotate exactly as Newton's laws predict, suggesting these particular galaxies may lack dark matter altogether.
Dark Matter Ruled Out As Ordinary Objects 2:33:30
Don explains that observations of galaxies like DF2 and DF4, which appear to lack dark matter, actually strengthen the case that dark matter is real, since finding galaxies without it shows it can be present or absent independently of visible matter. He notes that thorough searches have already ruled out black holes and rogue planets as candidates across nearly every mass range, so if dark matter exists, it must take the form of a particle rather than a compact object.
Three Ways To Hunt For Particles 2:35:32
He lays out the three main strategies for finding a dark matter particle, often called a WIMP for weakly interacting massive particle. The first is direct detection, placing underground detectors to catch dark matter passing through Earth like a wind, which has so far found nothing. The second is looking for annihilation signatures such as gamma rays at galactic centers, a method complicated by other sources like neutron stars. The third, which is Don's own approach, is smashing particles together at high energy and looking for missing momentum that suggests an escaping dark matter particle, similar to how neutrinos are inferred.
A Vast, Mostly Unsearched Mass Range 2:37:30
Don stresses that viable dark matter particle masses could range from something as heavy as an asteroid down to far lighter than an electron, and experiments have only ruled out small slices of that range. He describes microlensing searches, where a massive object passing in front of a distant star briefly brightens it, as the main way to search for heavier candidates, though sensitivity bottoms out around a third of the Moon's mass. Dark matter is now estimated to be five times more prevalent than ordinary matter, which is part of why Don finds it such a compelling open problem, even though he does not work on it directly because any single experiment can only probe one narrow slice of the possible mass range.
Childhood Curiosity And A Love Of Reading 2:43:30
Don describes growing up poor without academically involved parents, but with strong emotional support, and reading science fiction voraciously as a child, sometimes finishing a book a day. Popular science writers of the 1970s like Isaac Asimov, Carl Sagan, and George Gamow gave him an early taste of real science, and his naturally curious, quasi-philosophical mind drew him toward big questions about how the universe began and why its laws are what they are.
Choosing Particle Physics Over Cosmology 2:46:01
In college Don studied philosophy and religion alongside science, hoping history might illuminate his big questions, but concluded those answers lay elsewhere. Deciding between cosmology and particle physics in the mid-1980s, he chose particle physics because it offered the chance to actually run experiments and get answers rather than just theorize.
Writing Books To Reach Other Kids 2:47:00
Don explains that he writes books and makes videos partly because he imagines another kid somewhere in a small town without access to educated mentors, hoping his work might help them find their own path the way early science writers helped him. He mentions that interns have told him they came to the lab because of his videos or books, which he sees as evidence of a small but real impact.
Working Eight A M To Midnight 2:48:31
Don recalls working at Fermilab from 8 a.m. to midnight six days a week as a graduate student, and from 8 to 5 on Sundays, simply because he loved the work and had no other obligations at the time. He argues that grit and an inability to tolerate an unsolved problem separate dedicated scientists from merely smart people, and that this drive, not just intelligence, is what sustains a real scientific career.
Closing Thoughts And A Quote From Marie Curie 2:52:01
The conversation closes with reflections on hard work as fulfilling when directed at something you love, comparing it to the dedication of artists or musicians. Lex thanks Don for his work at Fermilab and for public science communication, and ends the episode with a quote from Marie Curie, a two-time Nobel laureate in physics and chemistry, saying that nothing in life is to be feared, only understood.
AI-generated summary. It can be wrong or incomplete - check anything that matters against the original.
