Oct 08

Reported by Adam Mann, in Wired Science, 8th October 2013.

Data from the CMS experiment, one of the main Higgs-searching experiments at the Large Hadron Collider. Image: CERN

More than a year ago, scientists found the Higgs boson. This morning, two physicists who 50 years ago theorized the existence of this particle, which is responsible for conferring mass to all other known particles in the universe, got the Nobel, the highest prize in science.

For all the excitement the award has already generated, finding the Higgs — arguably the most important discovery in more than a generation — has left physicists without a clear roadmap of where to go next. While popular articles often describe how the Higgs might help theorists investigating the weird worlds of string theory, multiple universes, or supersymmetry, the truth is that evidence for these ideas is scant to nonexistent.

No one is sure which of these models, if any, will eventually describe reality. The current picture of the universe, the Standard Model, is supposed to account for all known particles and their interactions. But scientists know that it’s incomplete. Its problems need fixing, and researchers could use some help figuring out how. Some of them look at the data and say that we need to throw out speculative ideas such as supersymmetry and the multiverse, models that look elegant mathematically but are unprovable from an experimental perspective. Others look at the exact same data and come to the opposite conclusion.

“Physics is at a crossroads,” said cosmologist Neil Turok, speaking to a class of young scientists in September at the Perimeter Institute, which he directs. “In a sense we’ve entered a very deep crisis.”

The word “crisis” is a charged one within the physics community, invoking eras such as the early 20th century, when new observations were overturning long-held beliefs about how the universe works. Eventually, a group of young researchers showed that quantum mechanics was the best way to describe reality. Now, as then, many troubling observations leave physicists scratching their heads. Chief among them is the “Hierarchy Problem,” which in its simplest form asks why gravity is approximately 10 quadrillion times weaker than the three other fundamental forces in the universe. Another issue is the existence of dark matter, the unseen, mysterious mass thought to be responsible for strange observations in the rotation of galaxies.

The solution to both these problems might come from the discovery of new particles beyond the Higgs. One theory, supersymmetry, goes beyond the Standard Model to say that every subatomic particle — quarks, electrons, neutrinos, and so on — also has a heavier twin. Some of these new particles might have the right characteristics to account for the influence of dark matter. Engineers built the Large Hadron Collider to see if such new particles exist (and may yet see them once it reaches higher energy in 2014), but so far it hasn’t turned up anything other than the Higgs.

In fact, the Higgs itself has turned out to be part of the issue. The particle was the final piece in the Standard Model puzzle. When scientists discovered it at the LHC, it had a mass of 125 GeV, about 125 times heavier than a proton — exactly what standard physics expected. That was kind of a buzzkill. Though happy to know the Higgs was there, many scientists had hoped it would turn out to be strange, to defy their predictions in some way and give a hint as to which models beyond the Standard Model were correct. Instead, it’s ordinary, perhaps even boring.

All this means that confidence in supersymmetry is dropping like a stone, according to Tommaso Dorigo, a particle physicist at the LHC. In one blog post, he shared a rather pornographic plot showing how the findings of the LHC eliminated part of the evidence for supersymmetry. Later, he wrote that many physicists would have previously bet their reproductive organs on the idea that supersymmetric particles would appear at the LHC. That the accelerator’s experiments have failed to find anything yet “has significantly cooled everybody down,” he wrote.

In fact, when the organizers of a Higgs workshop in Madrid last month asked physicists there if they thought the LHC would eventually find new physics other than the Higgs boson, 41 percent said no. As to how to solve the known problems of the Standard Model, respondents were all over the map. String theory fared the worst, with three-quarters of those polled saying they did not think it is the ultimate answer to a unified physics.

One possibility has been brought up that even physicists don’t like to think about. Maybe the universe is even stranger than they think. Like, so strange that even post-Standard Model models can’t account for it. Some physicists are starting to question whether or not our universe is natural. This cuts to the heart of why our reality has the features that it does: that is, full of quarks and electricity and a particular speed of light.

This problem, the naturalness or unnaturalness of our universe, can be likened to a weird thought experiment. Suppose you walk into a room and find a pencil balanced perfectly vertical on its sharp tip. That would be a fairly unnatural state for the pencil to be in because any small deviation would have caused it to fall down. This is how physicists have found the universe: a bunch of rather well-tuned fundamental constants have been discovered that produce the reality that we see.

A natural explanation would show why the pencil is standing on its end. Perhaps there is a very thin string holding the pencil to the ceiling that you never noticed until you got up close. Supersymmetry is a natural explanation in this regard – it explains the structure of universe through as-yet-unseen particles.

But suppose that infinite rooms exist with infinite numbers of pencils. While most of the rooms would have pencils that have fallen over, it is almost certain that in at least one room, the pencil would be perfectly balanced. This is the idea behind the multiverse. Our universe is but one of many and it happens to be the one where the laws of physics happen to be in the right state to make stars burn hydrogen, planets form round spheres, and creatures like us evolve on their surface.

The multiverse idea has two strikes against it, though. First, physicists would refer to it as an unnatural explanation because it simply happened by chance. And second, no real evidence for it exists and we have no experiment that could currently test for it.

As of yet, physicists are still in the dark. We can see vague outlines ahead of us but no one knows what form they will take when we reach them. Finding the Higgs has provided the tiniest bit of light. But until more data appears, it won’t be enough.

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