Research is a search through the unknown. If you knew the answer, there would be no need to do the research, and until you do the research, you don’t know the answer. Science is a complex social phenomenon, but certainly its history includes repeated episodes of people having ideas, trying experiments to test those ideas, and using the results to inform the next round of ideas.. When an experimental result indicates that one particular idea is not correct, this is neither a failure of the experiment nor of the original idea itself; it’s an advancement of our understanding of the world around us.
Recently, particle physics has become the target of a strange line of scientific criticism. Articles like Sabine Hossenfelder’s New York Times op-ed questioning the “uncertain future” of particle physics and Vox’s “The $22 Billion Gamble: Why Some Physicists Aren’t Excited About Building a Bigger Particle Collider” raise the specter of failed scientists. To read these articles, you’d think that unless particle physics comes home with a golden ticket in the form of a new particle, it shouldn’t come home at all. Or at least, it shouldn’t get a new shot at exploring the universe’s subatomic terrain. But the proposal that particle physicists are essentially setting money on fire comes with an insidious underlying message: that science is about the glory of discovery, rather than the joy of learning about the world. Finding out that there are no particles where we had hoped tells us about the distance between human imagination and the real world. It can operate as a motivation to expand our vision of what the real world is like at scales that are totally unintuitive. Not finding something is just as informative as finding something.
That’s not to say resources should be infinite or to suggest that community consensus isn’t important. To the contrary, the particle physics community, like the astronomy and planetary science communities, takes the conversation about what our priorities should be so seriously that we have it every half decade or so. Right now, the European particle physics community is in the middle of a “strategy update,” and plans are underway for the U.S. particle physics community to hold the next of its “Snowmass community studies,” which take place approximately every five years. These events are opportunities to take stock of recent developments and to devise a strategy to maximize scientific progress in the field. In fact, we’d wager that they’re exactly what Hossenfelder is asking for when she suggests “it’s time for particle physicists to step back and reflect on the state of the field.”
One of the interesting questions that both of these studies will confront is whether or not the field should prioritize construction of a new high-energy particle accelerator. In past decades, many resources have been directed toward the construction and operation of the Large Hadron Collider, a gigantic device whose tunnel spans two countries and whose budget is in the billions of dollars. Given funding constraints, it is entirely appropriate to ask whether it makes sense to prioritize a future particle accelerator at this moment in history. A new collider is likely to have a price tag measured in tens of billions of dollars and would represent a large investment—though not large compared with the scale of other areas of government spending, and the collider looks even less expensive when spread out over decades and shared by many nations.
The LHC was designed to reach energies of 14 trillion electron volts, about seven times more than its predecessor, the Tevatron at Fermilab in Chicagoland. There was very strong motivation to explore collisions at these energies; up until the LHC began operations, our understanding of the Standard Model of particle physics, the leading theory describing subatomic particles and their interactions, contained a gaping hole. The theory could only consistently describe the massive fundamental particles that are observed in our experiments if one included the Higgs boson—a particle that had yet to be observed. Self-consistency demanded that either the Higgs or something else providing masses would appear at the energies studied by the LHC. There were a host of competing theories, and only experimental data could hope to judge which one was realized in nature.
So we tried it. And because the LHC allowed us to actually observe the Higgs, we now know that the picture in which masses arise from the Higgs is either correct or very close to being correct. The LHC discovered a particle whose interactions with the known particles matches the predictions to within about 10 percent or so. This represents a triumph in our understanding of the fundamental building blocks of nature, one that would have been impossible without both 1) the theoretical projections that defined the characteristics that the Higgs must have to play its role and 2) the experimental design of the accelerator and particle detectors and the analysis of the data that they collected. In order to learn nature’s secrets, theory and experiment must come together.
Some people have labeled the LHC a failure because even though it confirmed the Standard Model’s vision for how particles get their masses, it did not offer any concrete hint of any further new particles besides the Higgs. We understand the disappointment. Given the exciting new possibilities opened up by exploring energy levels we’ve never been privy to here on earth, this feeling is easy to relate to. But it is also selling the accomplishments short and fails to appreciate how research works. Theorists come up with fantastical ideas about what could be. Most of them are wrong, because the laws of physics are unchanging and universal. Experimentalists are taking on the task of actually popping open the hood and looking at what’s underneath it all. Sometimes, they may not find anything new.
A curious species, we are left to ask more questions. Why did we find this and not that? What should we look for next? What a strange and fascinating universe we live in, and how wonderful to have the opportunity to learn about it.