Web edition: October 20, 2009
Soon physicists at the world’s most powerful particle accelerator will exhale — when beams of protons there finally begin to collide, even though those collisions will not at first be as violent as originally planned. Physicists at the Large Hadron Collider outside Geneva remain confident, though, that the collisions will eventually attain sufficient energy to produce the Higgs boson, says Nobel laureate Steven Weinberg of the University of Texas at Austin.
As Weinberg recounted to science writers attending the Council for the Advancement of Science Writing’s annual symposium on October 19, the Higgs would be the crowning achievement of the standard model of particle physics, the equations that precisely describe the known particles of matter and three of nature’s fundamental forces: the strong and weak nuclear forces and electromagnetism. In the most basic version of the standard model, elementary particles such as electrons and quarks have no reason to possess any mass. But clearly they do, a fact explained most conveniently if a currently unknown particle, the Higgs, secretly inhabits the particle zoo.
“It’s not a sure thing that the Higgs will be found, but it’s highly likely,” Weinberg said. “If the Congress had not had the imbecility to cancel the Superconducting Super Collider [in 1993], it would have been discovered long ago here in Texas.”
Discovery of the Higgs at the LHC would not necessarily be a cause for unrestrained celebration, though. “Many of us are terrified that the LHC will discover a Higgs particle and nothing more,” Weinberg said. That would just confirm the standard model, which everybody believes already. It would not point the way to further progress in solving a deeper problem that physics faces — how to add gravity to the unified theory of the other forces.
A clue to solving that mystery might be provided if the LHC’s collisions generate new particles governed by a mathematical constitution known as supersymmetry, or SUSY for short. SUSY math embodies a deep connection between particles that seem unrelated (in physics lingo, their spins differ). Roughly speaking, for each known particle that transmits a force, a partner matterlike particle would exist; each matter particle would have a forcelike partner. These partner particles must be much heavier than those already known to have escaped detection in previous experiments.
If SUSY describes nature correctly, one of the partner particles would very likely be the constituent of dark matter, the unseen mass in the cosmos inferred from observations of gravitational effects not attributable to visible matter. Dark matter cannot be made of ordinary quarks or electrons, Weinberg pointed out; otherwise the recipe of chemical elements cooked up in the early universe would be much different from that now measured. Cosmic observations indicate that about five-sixths of the matter in the universe is made from some form of exotic particle, possibly one predicted by SUSY.
“I can’t imagine anything more exciting and more gratifying than for the Large Hadron Collider to discover particles, artificially created, which in their natural state form the great bulk of the mass of the universe,” said Weinberg. “That would be some headline.”
SUSY’s discovery might also offer a clue to that grander problem of merging gravity into the family of forces. Many physicists believe that the most promising approach to solving that problem involves the hypothetical ultratiny entities known as superstrings. If all nature’s particles are just various vibration modes of these tiny strings, gravity and the other forces fit together nicely. But despite a quarter century of intense effort, superstring theory has not produced a cohesive and clear guide to testing its fit with all the observable features of physical existence.
“It has developed mathematically, but not to the point where there is any one theory, or to the point where if we had one theory, we would know how to do calculations to predict things like the mass of the electron or the masses of the quarks,” Weinberg said. “I would say that although there has been theoretical progress, I find it disappointing.”
It may be that a SUSY discovery at the LHC will help, but Weinberg’s hopes are not high, as any LHC-SUSY clue would be very indirect.
“It’s a pity that superstring theory hasn’t developed better,” he said. “I still think it’s the best hope we have. I don’t know of anything else. My own work very recently has been trying to develop an alternative to superstring theory as a way of making sense out of quantum gravity at very high energies, but even though I’m working on this I still find superstring theory more attractive. But not attractive enough.” —Tom Siegfried
Droughts gave early humans survival skills for later travels
Humankind may have survived after leaving Africa thanks to seasonal droughts — not because they created a time of scarcity, but because they produced a time of plenty.
University of Texas at Austin anthropologist John Kappelman presented this counterintuitive idea in a talk titled “Blue Highways,” which followed his fossil digs along the Blue Nile tributaries in Ethiopia. Early humans are thought to have taken one of two routes out of Africa: along the Red Sea, or along the Nile Valley and out across Eurasia.
But “there’s been very little testing on the ground, recovering fossils and sites that actually permit us to evaluate either one of those two hypothetical migration events,” Kappelman said.
Most fossils found to date come from the rift valley on the eastern side of the continent, where dry, flat, exposed land makes for good fossil hunting. In the late 1990s, Kappelman started exploring the tributaries on the western side of the Nile, where no one had looked for fossils before. The last record of western exploration there was from British naturalist Sir Samuel Baker in the 1860s.
“This area that was a blank slate for Africa is finally starting to fill in,” Kappelman said.
Samuel Barker noticed something key: The rivers are dry for most of the year, but every summer the water rushes back “like freight cars,” Kappelman said. The torrent of water gouged out deep holes that retained water even during the dry season, leaving a necklace of isolated pools.
And the pools were full of fish. “The fish were literally in a bucket,” Kappelman says. If early humans stayed near these water holes, they could feast all through the dry season without working too hard.
“We think of dry seasons as a time of adversity. We’re proposing that these were the easy times,” Kappelman says.
Kappelman and his team found double-edged blades that were probably used as arrow heads and evidence of hearth fires in several sites around the Nile. He thinks using these water holes could have taught early humans crucial skills, like fishing with nets or bow and arrow, that helped them survive seasonal and climate changes after migration to other parts of the world.
“It honed the behavioral foraging habits of early humans, and taught them to exploit a wide range of food,” Kappelman said. —Lisa Grossman
Stuff tells snoops what you're all about
If you have a burning interest in getting to know someone better, maybe you should snoop. You won’t have to look too hard. University of Texas at Austin psychologist Sam Gosling says the books, photos, music playlists, calendars and sports equipment that litter people’s home, offices and even their websites all contribute to the bigger picture of who they really are.
Gosling and his students are researching the way people reveal who they are through their intimate surrounding and their stuff. In their quest, the researchers search bedrooms, bathrooms and office desks looking for three basic types of clues to the occupant’s personality. The first group of clues is what Gosling calls “identity claims,” and consists of posters, photos and other times that make a symbolic statement or are meant to project a specific image. Sometimes these items provide insight into a person’s interests, but other times they say more about what people want others to think of them as opposed to what they're actually like, Gosling said.
Other items, such as music, books and DVDs, are often used as “feeling regulators” to help people mange their emotions and thoughts These feeling regulators can provide important clues to what a person is really like. Even the traces left behind as a result of everyday actions can reveal who you are. Gosling points to piles of garbage, food wrappers and notebooks, calling this “behavioral residue.” Together, these types of clues reveal a person’s pattern of thinking, feeling and behaving, and are consistent over time.
Gosling and his crew use this information to rate people on five personality traits: openness, conscientiousness, extraversion, agreeableness and neuroticism. Architects are using the information to help design homes where people can re-create a feeling of comfort and well being.
So where would Gosling look if limited to only one place? That would be a person’s website. People will tell you explicitly what they’re like, and there are so few restrictions to what can be put online, he said.
“If you live in a tiny apartment in New York, you can’t display your love of hang gliding, but you can do that on a website.” —Susan Gaidos