The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World (38 page)

It might seem that such a scheme gives up on any pretense of making testable predictions. It’s certainly difficult, but advocates of the multiverse argue that there is still hope. In many parts of the multiverse, they argue, conditions are so inhospitable that no intelligent life can possibly arise. Maybe there are no appropriate forces, or the vacuum energy could be so high that individual atoms would be torn apart by the expansion of the universe. One problem is that we don’t have a very good understanding of the conditions under which life can form. If we can overcome such mundane considerations, however, optimists hold out hope that they can make predictions for what typical observers in the multiverse would actually observe. In other words, even if we don’t see other “universes” directly, we might be able to use the idea of the multiverse to make testable predictions. The “anthropic principle” is the idea that there is a strong selection effect that limits the conditions we can possibly observe to those that are compatible with our existence.

It’s an ambitious plan, and possibly doomed to failure. But people try, and in particular they have applied this idea to properties of the Higgs boson. These are treacherous waters; back in 1990, Mikhail Shaposhnikov and Igor Tkachev tried to predict the value of the Higgs mass under certain anthropic assumptions and came up with the answer 45 GeV. That’s clearly incompatible with the data as we now understand it, so something was wrong about those assumptions. Under different assumptions, in 2006, another group predicted a value of 106 GeV; closer, but still no cigar. Now that we have a Higgs boson at 125 GeV, it is unlikely that many predictions will be published that don’t somehow manage to reach that value.

To be fair, we need to mention the most impressive success of anthropic reasoning: predicting the value of the vacuum energy. In 1987, more than ten years before the discovery of the acceleration of the universe, Steven Weinberg pointed out that a very high (or large and negative) vacuum energy would inhibit the formation of galaxies. Therefore, most observers in a multiverse should see small but nonzero values of the vacuum energy. (Zero is allowed, but there are more nonzero numbers than numbers equal to zero.) The value we think we have observed is perfectly consistent with Weinberg’s prediction. Granted, Weinberg was implicitly imagining a multiverse in which only the value of the vacuum energy changed from place to place; if we let other parameters change, the agreement becomes much less impressive.

Despite the pessimistic, even curmudgeonly tone of this section, I believe the multiverse scenario is actually quite plausible. (In
From Eternity to Here
, I suggested that it might be helpful in explaining the low entropy of the early universe.) If string theory or some other theory of quantum gravity allows for different manifestations of local laws of physics in different regions of spacetime, the multiverse might be real, whether we can observe it or not; I’m always an advocate for taking seriously things that might be real. At the current state of the art, however, we are very far from being able to turn the multiverse into a predictive theory for particle physics. We can’t let our personal distaste color our judgment of cosmological scenarios, but neither can we let our enthusiasm get in the way of our critical faculties.

Venturing forth

There is much more to be discovered in the realm of the very small, and there are many aspects to particle physics beyond the Standard Model. Why is there more matter than antimatter in the universe? Several scenarios for generating such an asymmetry involve the cosmological evolution of the Higgs field, so it’s plausible that a better understanding of its properties will lead to new insights on this problem. There are also interesting “technicolor” models, according to which the Higgs is a composite particle like the proton rather than something fundamental. Current versions of technicolor tend to be disfavored by other particle-physics data, but studying the actual Higgs itself might very well lead to surprises.

Discovering the Higgs is not the end of particle physics. The Higgs was the final piece of the Standard Model, but it’s also a window onto physics beyond that theory. In the years to come, we’ll be using the Higgs to search for (and hopefully study) dark matter, supersymmetry, extra dimensions, and whatever other phenomena prove to be needed to fit the new data that is rapidly coming in. The Higgs discovery is the end of one era and the beginning of another.

THIRTEEN

MAKING IT WORTH DEFENDING

In which we ask ourselves why particle physics is worth pursuing, and wonder what comes next.

R
obert Wilson, the physicist who was in charge of building Fermilab, was dragged before the Congressional Joint Committee on Atomic Energy in 1969 to help senators and representatives understand the motivation behind the multimillion-dollar project. It was a turning point in the history of particle physics in the United States; the Manhattan Project had given physicists easy access to influence and funding, but it was unclear how the search for new elementary particles was going to lead to anything as immediately valuable as a new kind of weapon. Senator John Pastore of Rhode Island asked Wilson directly: “Is there anything connected with the hopes of this accelerator that in any way involves the security of the country?”

Wilson answered with equal directness: “No, sir, I don’t believe so.”

We can imagine that Pastore was a bit taken aback by this answer; presumably he expected to hear a song and dance about how Fermilab played a crucial role in keeping up with the Soviets, the kind of argument that was trotted out for all kinds of purposes in that era. He asked if there was really nothing at all, to which Wilson simply replied, “Nothing at all.” But you don’t get to be senator without being at least a little stubborn, so Pastore tried a third time, just to ensure he had heard correctly: “It has no value in that respect?”

Wilson was no dummy; he realized he was expected to provide a little bit more if he wanted Congress to fund his ambitious but esoteric endeavor, but he refused to back off from his original point. His answer is one of the most-remembered quotes in the long history of scientists trying to explain why they do what they do:

It has only to do with the respect with which we regard one another, the dignity of man, our love of culture. It has to do with: Are we good painters, good sculptors, great poets? I mean all the things we really venerate in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending.

Big Science is not cheap. The Large Hadron Collider has cost about $9 billion, almost all of which came ultimately from taxes collected in countries around the world. The people who paid that money have a right to know what they are getting for their investment. It’s the duty of the scientific community to be as honest and convincing as possible about the rewards of basic research.

Some of those rewards come in the form of technological breakthroughs. But ultimately, those are not the most important rewards; what matters most is the knowledge that is brought back to us by these extremely ambitious experiments.

Not everyone agrees. Steven Weinberg, who has been a tireless advocate for investment in basic science, recalls a telling anecdote.

During the debate over the SSC, I was on the Larry King radio show with a congressman who opposed it. He said that he wasn’t against spending on science, but that we had to set priorities. I explained that the SSC was going to help us learn the laws of nature, and I asked if that didn’t deserve a high priority. I remember every word of his answer. It was “No.”

It’s not an uncommon attitude. But it’s an impoverished perspective, one that misses the bigger picture. Basic science might not lead to immediate improvements in national defense or a cure for cancer, but it enriches our lives by teaching us something about the universe of which we are a part. That should be a very high priority indeed.

When do I get my jet pack?

None of which is to say that we wouldn’t
like
to have useful technological applications of the work being done in modern particle physics. Scientists are quick to point out that basic research—scientific investigation carried out purely for its own sake, rather than in pursuit of immediate applications—has very often ended up having enormously practical implications, even if they were unanticipated at the time. From electricity to quantum mechanics, the pages of history are strewn with ideas that once were abstract and impractical, only to later become central to technological progress. As a result, whenever new scientific discoveries are made, people want to know: When do I get my jet pack?

Can we imagine that something similar will be the fate of research at the LHC? As Yogi Berra once said, making predictions is hard, especially about the future. However, we can admit that what we find at the LHC might have a very different character from the fundamental physics of previous centuries. It’s possible that any particles we discover at the LHC will literally never be put to good use in practical devices.

That’s not just pessimism; it flows from the particular kinds of things we might hope to discover. When Benjamin Franklin was studying electricity or Heinrich Hertz was producing radio waves, they weren’t creating things that didn’t already exist in the world. Electricity and radio waves are all around us, even if we discount all the artificial sources of them. Scientists in that era were learning to manipulate mysterious features of the readily accessible world, and it’s not surprising that the knowledge they discovered later became technologically useful. At the LHC, by contrast, we are literally creating particles that don’t exist in our everyday environments. There are good reasons for that. The particles are typically very massive, so it requires an enormous amount of energy to make them. And they are either very weakly interacting, so it’s hard to capture or manipulate them (like neutrinos), or they are extremely short-lived, so they decay before they can be put to much good use.

Take the Higgs boson as an example. It’s not easy to make a Higgs boson—the only way we know is to have a particle accelerator several miles long. We can certainly imagine technological improvements that would give you a pocket-size device able to reach such high energies; nobody has any idea how to do it, but it doesn’t violate the laws of physics. But even if you had a handy iHiggs boson producer, what would it be good for? Every Higgs you make decays in less than a zeptosecond. It’s hard to imagine any application of those bosons that wouldn’t be carried out more efficiently by some other kind of particle.

This argument isn’t airtight, of course. Muons are unstable particles, and they have found potential technological applications, from catalyzing nuclear fusion to searching for hidden chambers in pyramids. But the muon has a lifetime of about one millionth of a second, much longer than a Higgs boson. Neutrinos are stable but weakly interacting, and some farsighted folks have imagined using them for communication purposes. If we were feeling especially expansive, we might imagine discovering dark-matter particles that could find similar uses. It’s not a place I would recommend investing a lot of money, however.

Warp drive and levitation

Because the Higgs boson is responsible for giving particles mass, people sometimes wonder whether mastering its properties will allow us to make things lighter or heavier. Or worse. The day after the July 4 announcement of the Higgs discovery, Canada’s
National Journal
printed a bold headline:
HIGGS BOSON FIND COULD MAKE LIGHT-SPEED TRAVEL POSSIBLE, SCIENTISTS SAY.
None of the scientists quoted in the article said anything of the sort, but I suppose it’s possible that some scientists somewhere did say that at some point in time.

Using the Higgs to make things lighter or even massless is pretty much a nonstarter, for a few reasons. Most obvious, the large majority of the mass in ordinary objects doesn’t come from the Higgs; it comes from the strong-interaction energy inside protons and neutrons. But more important, it’s not really the Higgs boson that gives mass to the quarks and charged leptons, it’s the Higgs field lurking in empty space. If you wanted, for example, to change the mass of an electron, it’s not a matter of shooting Higgs bosons at it; you would have to change the value of the background Higgs field.

That’s easier said than done. For one thing, while we can imagine changing the Higgs field, we have no idea how to actually do it. For another, it would require an absurd amount of energy. Let’s imagine that we figured out a way to displace the Higgs field from its regular value (246 GeV) all the way to zero, inside some small but macroscopic volume of space. The usual value the Higgs field has is the state of minimum energy it can be in; pushing it back to zero means that our small volume is now packed with energy. From
E = mc
²
, that means it has mass. A quick calculation reveals that a region the size of a golf ball, inside of which the Higgs field is displaced to zero, would have approximately the same mass as the entire earth. If we were to make it much bigger than that, there would be so much mass inside a small space that the whole volume would collapse to make a black hole.

Finally, even if you somehow managed to turn off the Higgs field in, say, your body, it’s not just that you would suddenly become lighter. Certain elementary particles would become lighter—the electrons and quarks—and the broken symmetry of the weak interaction would be restored. As a result, the atoms and molecules in your body would fall into completely different configurations, mostly just disintegrating altogether and releasing a huge amount of energy. Decreasing the Higgs field wouldn’t put you on a diet; it would make your body explode.

So, don’t be looking forward to Higgs-powered levitation devices anytime soon. On the other hand, it remains entirely possible that new discoveries at the LHC will lay the groundwork for future applications in ways we can’t currently anticipate. Even if that’s not why we pursue them.