Gregory (Scotland Yard detective): “Is there any other point to which you would wish to draw my attention?”
Holmes: “To the curious incident of the dog in the night-time.”
Gregory: “The dog did nothing in the night-time.”
Holmes: “That was the curious incident.”
Silver Blaze, Sir Arthur Conan Doyle 1892
This week a science news story appeared that must have seemed to many like ‘non-news’: Two large experiments at CERN’s Large Hadron Collider reported that they didn’t discover a new particle.
If scientific experiments were reported in the press every time they didn’t make a new discovery, then newspapers would be far thicker than they are.
So what gives? Well, as the epigraph from Sherlock Holmes above makes clear, sometimes observing nothing is quite significant. In this case, had the LHC confirmed the existence of a tentative ‘bump’ that had been seen in data obtained last year, which suggested the existence of a totally unanticipated new elementary particle six times heavier than the recently discovered Higgs particle, it would have been the most important discovery in particle physics in a half-century.
For four decades every experiment ever performed at particle accelerators confirmed, with increasing accuracy, all the predictions of theoretical physicists made during a remarkable decade of discovery from the mid 1960’s to the mid 1970’s during which we built what appeared to be a complete understanding, at the quantum mechanical level, of three of the four known forces in nature—with gravity remaining the sole outlier.
The so-called Standard Model built on the foundation of all of the key developments of the 19th and 20th centuries, from our understanding of electromagnetism to relativity and quantum mechanics, and relies on a mathematical framework that has guided physicists in their search to unify all of the known forces in a single theory. It can just be described as the greatest theoretical edifice science has ever produced.
One missing ingredient of the Standard Model was a new particle that had been predicted to exist, but had never been observed. To find it, scientists had to build the most complicated device ever constructed, the Large Hadron Collider, and on July 4, 2012, the Higgs particle was discovered.
While a cause for great celebration—the vindication that nature actually obeyed the mathematical descriptions developed by theorists to describe a strange and exotic fundamental reality underlying all observed phenomena—the discovery of the Higgs also presented science with a new dilemma.
While confirmation of theories is wonderful, what science needs in order to progress are experimental discoveries that can guide theorists as they attempt to discern whether ideas that seem beautiful to physicists are actually true. For that is the beauty of science. Nature doesn’t care what ideas seem natural or compelling to humans. Science differs fundamentally from religion in that it requires us to force our beliefs to confirm to the evidence of reality, rather than vice versa.
And therein lies the rub. Unless there are new discoveries at the LHC we will have no idea whether the current ideas guiding the models physicists are building to press further in our understanding of nature at its smallest scales are correct. In particular, the fundamental question of why the Standard Model has the form it has, and why the Higgs particle exists in the first place will remain unanswered.
Thus the incredible interest of the physics community in the announcement last year that the two experiments at the LHC that had discovered the Higgs found tentative evidence of yet a new elementary particle. What made the discovery so exciting is that none of the new theories built on the basis of the Standard Model predicted such a particle. If it existed, it appeared to require the existence of yet a new fundamental force in nature, beyond the four known forces.
Physicists have learned to be skeptical however. In spite of the fact that literally hundreds of theoretical papers appeared proposing new ideas that might allow such a revolutionary new particle to exist—many of which required altering conventional wisdom about what laws might govern nature on its fundamental scales—it is a maxim in physics that most revolutionary observations are unlikely to survive further scrutiny. If this weren’t the case, then revolutionary developments would be so common that they would no longer be revolutionary.
Thus, many of us theorists were not surprised when the new, far larger data set unveiled this week at an international meeting of the particle physics community revealed that the tantalizing bump previously observed at the LHC was merely a statistical fluke. As Carl Sagan often repeated, extraordinary claims require extraordinary evidence. And the potential discovery at the LHC was extraordinary beyond anything that I have experienced in my lifetime as a physicist.
Still, the news from CERN is bittersweet. While the remarkable intellectual edifice built as part of the Standard Model remains intact, there is nothing as exciting in science as when nature throws us a curve ball, because it means that the cosmos is stranger and more exciting than we ever imagined.
Nevertheless, while the news from CERN this week is less exciting than we might have hoped for we can take solace from something else. While the continued success of the Standard Model provides testimony to the power of human imagination, if history is any guide, the imagination of nature is greater still. The LHC is still running strong, and I for one will be very surprised if one day soon I am not surprised.
Lawrence Krauss's new book "The Greatest Story Ever Told...So Far" covers this topic and more. It will be released in March, 2017