How to Make an Apple Pie from Scratch

by Harry Cliff

  But ALPHA has another, potentially even more exciting measurement in the offing. Just to the side of the original experiment, Jeffrey pointed me to a tall metal structure rising several meters up from the factory floor. Inside was another version of ALPHA, this time mounted on its side so that it pointed vertically toward the roof. This, Jeffrey told me, is ALPHA-g, and its mission is to check whether antimatter falls up.

  Considering that antimatter was discovered almost a century ago, it’s amazing that we still don’t know whether it’s repelled by the gravity of ordinary matter. Again, most theorists think this is vanishingly unlikely, but until someone actually measures it, we can’t be certain. The idea of ALPHA-g (where “g” stands for “gravity”) is to produce antihydrogen and then release it and see which way it falls.

  If antimatter did turn out to be repelled by ordinary matter it would have profound implications for our understanding of the universe. “There’s a lunatic fringe out there who claim that repulsive gravitation would solve everything: antimatter asymmetry, dark energy, dark matter. If that actually happens you could explain everything that we’re missing,” Jeffrey told me as we stood staring up at the tank. Indeed, if antimatter is repelled by ordinary matter it would explain why we don’t see any antimatter in the universe around us, as it would all have been forced to distant parts of the cosmos, removing the need to find a recipe for making more matter than antimatter in the big bang. “There are a lot of guys that have an article under their mattress waiting for this measurement.”

  In 2018, Jeffrey and the team were in a desperate race against time to get ALPHA-g ready to collect data before the CERN accelerator complex went into a two-year shutdown at the end of the year to allow for upgrade work on the LHC and its experiments. The ALPHA team knew that if they could just get the experiment switched on they would find out almost immediately whether antimatter falls up or down. “I worked the hardest I’ve ever worked, from May to November, seven days a week, twelve-, fifteen-hour days, trying to make that measurement before the shutdown. We really wanted to nail that measurement. If I’d had an extra month, I’d have made it.”

  In the end, they got agonizingly close but didn’t quite get over the line, and so now they’re working hard to get both ALPHAs into tip-top working order for the restart. Jeffrey and his colleagues are forever looking for ways to improve their experiment; “If it works, fix it” is his motto.

  Besides, the ALPHA team don’t have the field to themselves. They share the Antimatter Factory with several other experiments, including two that are racing to measure the effect of gravity on antimatter. But Jeffrey is in no doubt about who is going to get there first: “I’m really confident that we’ll win.” After all, they were the first to trap antihydrogen and then the first to measure a quantum jump. You certainly wouldn’t want to bet against them.

  As an experimental physicist, I find ALPHA’s approach to science really inspiring. Not only are the measurements they are making extraordinarily difficult, they are also testing principles that most respectable theorists would tell you are bound to be true. Jeffrey clearly takes the view that until a principle is put to the test, you can never be sure that it’s right. As Richard Feynman, doyen of quantum field theory famously said, “It doesn’t make a difference how beautiful your [theory] is, it doesn’t matter how smart you are…If it disagrees with experiment, it’s wrong.”

  ALPHA is experimental physics at its purest: grabbing hold of the physical world and studying its most basic principles in the lab. It’s the endless pursuit of precision, the joy of solving difficult problems, and the determination to be first. Jeffrey is clearly a man in love with his work. As he showed me blinking back into the bright summer sunshine, he told me, “There’s no other place like this. I have the only job in the world that I’m qualified for; it’s either this or I’m playing guitar on the street. I got no choice. I remember that every day, I better not screw up.”

  Skip Notes

  *1 Wu had performed her experiment with meticulous skill, although, rather disgracefully in my view, she did not receive the Nobel Prize for her discovery, which instead went to the two theorists who had first suggested that the weak force might violate mirror symmetry.

  *2 No one has yet managed to make such a large anti-atom. The heaviest so far is anti-helium, which was detected in the collisions produced by RHIC at Brookhaven in 2011.

  *3 Baryo- refers to baryons, the class of particles made from three quarks that includes protons and neutrons, and -genesis meaning “origin.”

  *4 Guilty as charged.

  *5 In 1999, NASA estimated that a single gram of antihydrogen (which is about what you’d need for a city-destroying bomb) would take the age of the universe to make and set you back around $62.5 trillion, so it would be more efficient for the Illuminati to buy the Vatican outright and then hire an army of builders to take it apart brick by brick.

  CHAPTER 12

  The Missing Ingredients

  “With these record-shattering collision energies, the LHC experiments are propelled into a vast region to explore, and the hunt begins for dark matter, new forces, new dimensions, and the Higgs boson.”

  It was with these words that Fabiola Gianotti, spokesperson of the ATLAS experiment, had fired the starting gun on the search for new particles at the Large Hadron Collider, as the first high-energy protons smashed into one another on March 30, 2010. That day, the ten-thousand-strong CERN community was buzzing with optimism and anticipation, while theorists around the world waited impatiently for answers to questions that many had spent their careers puzzling over. After a very, very long wait, the greatest scientific instrument ever built had fired up, a once-in-a-generation opportunity to explore a new subatomic landscape where all kinds of strange and exotic objects were surely waiting to be discovered.

  As Gianotti suggested, the Higgs boson was just one of them. In fact, for many particle physicists, perhaps even the majority, it was one of the new machine’s less exciting quarries. The Higgs belonged to the old, established story of particle physics, the last missing piece of a standard model that had remained more or less unchanged since the late 1970s. Nima Arkani-Hamed, one of the world’s leading particle theorists, was so confident that the Higgs would be found at the LHC that he had offered a year’s salary to anyone willing to bet against it. Even many experimentalists saw finding the Higgs as a tick-the-box exercise, a bit of unfinished business from the twentieth century before the real journey into terra incognita could begin.

  Despite all its successes—explaining the structure of matter, quantum fields, the forces of nature, and the origin of mass—we know that the standard model is at best incomplete, an echo of a deeper, more fundamental theory that we have yet to glimpse. For starters, many physicists regard the standard model as ad hoc, ungainly, even ugly. Take the forces. There are three in the standard model—the electromagnetic, weak, and strong—but why those three? We don’t know. The electromagnetic and weak forces are unified, but the strong force is left hanging out on its own. Do all the forces unify at high energy? Again, we don’t know. Perhaps most significantly of all, gravity is left out completely.

  Things get even worse when you look at the matter particles. We are made of electrons, up quarks, and down quarks, which along with the electron neutrino form a quartet known as the “first generation” of matter. We do not know why these four particles exist, we just observe that they do and put them into the theory by hand, like a botanist collecting flowers in a field. Why couldn’t there have just been one? Or five? Or a hundred? On top of this, nature decided to include heavier, unstable copies of these four particles. There’s a second generation of matter, which includes the muon, the muon neutrino, the charm quark, and the strange quark, and then a third set of even heavier and more short-lived particles: the tau, the tau neutrino, the top quark, and the bottom quark. Why three generations and not f
our, or a thousand? Again, we don’t know.

  Since the standard model was first put together, many have yearned for a deeper, more elegant theory, where all its apparent arbitrariness would be explained by some single, unifying principle. As we saw a couple of chapters back, the forces appear to arise because of symmetries in the laws of nature. Perhaps the standard model is only a corner of a larger, more symmetrical structure, like fragments of glass fallen from a great stained-glass window in some medieval cathedral. Only by finding other missing pieces will the full beauty and majesty of nature’s fundamental laws be revealed. Of course, nature doesn’t have to abide by our sense of what is beautiful. The desire for a more unified theory is really just an aesthetic one, even if unification and simplicity have been powerful guides in the past. But aesthetics aside, there are solid, observational reasons for believing that we are missing something big.

  We’ve already seen that new quantum fields are needed to explain how matter got made in the fearsome heat of the big bang, but some of the greatest challenges to the standard model come not from particle physics, but from astronomy. During the twentieth century, observations of the heavens began to hint that there is far more to our universe than meets the eye. In the 1930s, the Swiss astronomer Fritz Zwicky found that galaxies in a giant group of more than a thousand known as the Coma Cluster were moving so fast that the gravity of the visible stuff shouldn’t be strong enough to hold the cluster together. He suggested that the cluster must contain some invisible matter, which he called “dunkle Materie,” German for “dark matter,” which was generating an extra gravitational pull and binding the cluster together.

  The existence of dark matter remained controversial for the best part of forty years until a series of exquisite measurements made by the American astronomer Vera Rubin in the 1970s. Rubin showed that stars orbiting in spiral galaxies, including our nearest galactic neighbor, Andromeda, were moving so fast that they should break free and fly off into intergalactic space. Again, there simply didn’t appear to be enough matter in the galaxies to generate the gravity needed to hold the stars in orbit.

  Although Rubin’s observations were received with skepticism at first, over the coming years it became clear that the effect was real. One possibility, still explored by a fringe group of physicists today, was that Newton and Einstein had gotten their theories of gravity wrong, and that gravity was stronger at long distances than first supposed. However, by far the more popular explanation is that almost every galaxy, including our own Milky Way, sits at the center of a vast cloud of invisible dark matter, whose gravitational pull keeps the stars on their orbits. This unseen material is known as dark matter because it doesn’t emit, absorb, or reflect light, making it completely invisible to our telescopes. However, astronomers can infer its presence by the way its gravity pulls on stars, galaxies, and light as they move through the cosmos, a bit like a poltergeist moving the furniture about in a haunted house.

  The astronomical evidence for dark matter is now overwhelming, with multiple different types of observations allowing astronomers to map its influence throughout the cosmos. Our best estimates now indicate that there is more than five times more dark matter in the universe than all the visible atomic matter, including every star, planet, and speck of dust.

  Even more mysterious is a form of repulsive gravity known as dark energy, which is thought to be responsible for causing the expansion of the universe to accelerate. Between them, dark matter and dark energy are thought to make up 95 percent of the total energy content of the universe. We, and everything we see in the night sky, are just a tiny fraction of a mostly unseen, unknown, and unexplored universe, sparkling froth on the surface of a dark ocean.

  There are no particles or quantum fields in the standard model that could be dark matter*1 or dark energy. This is both a huge challenge for particle physicists and a huge opportunity. While we’re highly unlikely to learn about dark energy from particle physics experiments, there is a chance that a dark matter could be found, either in collisions at the LHC or by experiments deep underground that watch for the rare occasions when a dark matter particle bumps into ordinary matter. If we could find such a particle, it could not only explain the motions of stars and galaxies but would give us a clue to whatever larger, more symmetrical picture lies beyond the standard model.

  The prospect of creating dark matter was certainly a big motivation for building the LHC, but, surprisingly perhaps, it wasn’t the main reason physicists expected to see something new at the collider. There is another mystery, one that has implications that go far beyond just adding another bunch of particles to nature’s list of ingredients. It is a mystery that challenges our basic conceptions of the laws of nature and makes us doubt our ability to explain the universe as we find it. It is a problem with the Higgs field, and the strange fact that atoms, people, and apple pies can exist at all.

  LIKE A KITE IN A HURRICANE

  About halfway into Monty Python’s comedy movie masterpiece Life of Brian we find the eponymous hero, Brian of Nazareth, on the run from a troop of Roman centurions. As he scarpers through the streets of first-century Jerusalem, Brian takes a wrong turn up an unfinished spiral staircase, falling with a shriek to what should be his death on the streets far below. However, in a bit of classic Pythonesque surrealism, just before he hits the ground, he falls through the roof of a passing alien spaceship, which is on the run from a second alien craft. After a dramatic chase around the Moon, Brian’s ship receives a direct hit from its pursuer and plummets to Earth, crashing at the foot of the same tower that he had just fallen from. As Brian emerges from the smoking wreck unscathed, a bystander who witnessed the whole strange episode exclaims, “Ooooooh, you lucky bastard!”

  “Lucky” is a bit of an understatement. I mean, what are the chances that just at the moment Brian is falling an alien spaceship should just happen to be passing by the Earth, and not just the Earth, but that specific bit of air just above the streets of Jerusalem? Then multiply that bit of amazing luck by the incredible improbability that when the craft is shot down, it crashes back at the very same spot, and what’s more that Brian survives the impact. And that’s before we get into considerations of the likelihood of intelligent life evolving near enough to the Earth to be able to pop over for a day trip, or the difficult-to-account-for fact that this particular spaceship presumably had a sunroof, which its pilots must have absentmindedly left open.

  Yes, “lucky” doesn’t quite cover it. But if we take the standard model at face value, then atoms and therefore anything made of atoms, from stars to human beings, only exist because of an equally ludicrous set of coincidences.

  These coincidences relate to the Higgs field, the all-pervading cosmic energy field that is responsible for giving mass to fundamental particles. As we’ve already discussed, around a trillionth of a second after the big bang, the Higgs field turned on throughout the universe, rising to a nonzero value everywhere. It’s this nonzero value that gives fundamental particles mass and basically sets up the ingredients of the universe (and thus our apple pie) as we know them.

  With the discovery of the Higgs boson, we know that this field exists, and based on the masses of the W and Z bosons, we can calculate that it settled at a value of around 246 GeV. Now for the important bit. The specific value of the Higgs field is what determines the masses of the fundamental particles. If it helps, you can imagine it like a great cosmic dial, like the kind you use to set the temperature in your house. Reduce it a little bit and the particles of the standard model get lighter; increase it and they get heavier. The trouble is that it seems to be incredibly, fantastically, ridiculously (I’m running out of adverbs here) unlikely that the Higgs field should have settled at what turns out to be a suspiciously perfect Goldilocks value.

  Our theories suggest that there should be only two likely values for the Higgs field: 0 GeV or 10,000,000,000,000,000,000 GeV. We’ll get to why in a
bit, but what you should appreciate first is that either of these two scenarios would be really, really bad if you like existing. If the Higgs field had a value of 0 GeV—that is, switched off—electrons wouldn’t have a mass and therefore wouldn’t stick to atoms, which alongside a bunch of other bizarre consequences would mean we would not exist. The second scenario, where the Higgs field is turned on all the way, would give fundamental particles such enormous masses that no structures could form without immediately collapsing into black holes. Again, we could not live in such a universe.

  On the other hand, 246 GeV is just right to give particles finite but not stupidly big masses, creating a universe full of interesting stuff instead of a haze of massless particles or a load of black holes. However, to get such a pleasant Goldilocks value requires an incredible set of coincidences in the laws of nature, no less improbable than Brian Cohen being saved from death by an alien spaceship.

  Ultimately, the origin of this problem lies in the way the Higgs field is affected by empty space, or what physicists call “the vacuum.” As we’ve seen, there isn’t really such a thing as empty space thanks to the existence of quantum fields, which are always there even when there are no particles sloshing about in them. We saw too that these quantum fields can affect the properties of a particle like an electron—by gathering around it and altering its shape, for example. Well, the quantum fields present in the vacuum should also affect the strength of the Higgs field, and in a catastrophic way.