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A Cosmic Quest for Dark Matter

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Scientists are hunting one of the biggest prizes in physics: tiny particles called wimps that could unlock some of the universe’s oldest secrets

Gautam Naik writes: A mile under Italy’s Gran Sasso mountain, scientists are seeking one of the smallest objects in the universe—and one of the biggest prizes in physics: a wimp.

A wimp—a weakly interacting massive particle—is thought to be the stuff of dark matter, an invisible substance that makes up about a quarter of the universe but has never been seen by humans.

Gravity is the force that holds things together, and the vast majority of it emanates from dark matter. Ever since the big bang, this mystery material has been the universe’s prime architect, giving it shape and structure. Without dark matter, there would be no galaxies, no stars, no planets. Solving its mystery is crucial to understanding what the universe is made of.

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“If we don’t assume that 85% of the matter in the universe is this unknown material, the laws of relativity and gravity would have to be modified. That would be significant,” says physicist Giuliana Fiorillo, a member of the 150-strong team searching for the particles at the Gran Sasso National Laboratory, 80 miles east of Rome.

The quest for dark matter has intensified since the discovery of the Higgs boson particle two years ago, which helped to narrow the field in which wimps might be hiding. Today, more than 20 different teams of researchers are hunting for the elusive stuff, using some of the most elaborate and delicate experiments ever devised.

Dark-matter detectors have been installed on the sea bed nearly 8,200 feet beneath the surface. Others operate deep inside mines. There is one on the International Space Station. China’s new dark-matter experiment sits 1.5 miles beneath a marble mountain. When it restarts later this year, the Large Hadron Collider will look for wimps, too, by smashing together subatomic particles.

Scientists estimate that visible matter makes up just 4% of the universe, while dark matter makes up 23%. The remaining 73% is an even bigger puzzle, a repulsive force known as “dark energy.”

Dark matter neither emits nor absorbs light. We know it is out there, because scientists can measure the immense gravitational force it exerts on stars, galaxies and other cosmic bodies. The best candidate for what dark matter consists of is the wimp: an ethereal being that barely interacts with normal matter. Every second, billions of wimps flow through the Earth without hitting anything. Read the rest of this entry »

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James Kakalios: Finally, Science Explains Why No One Can Lift Thor’s Hammer

James Kakalios writes: These are exciting days for physics, with several recent experimental observations providing important information on some of the most important mysteries of nature. The Large Hadron Collider at CERN has found the Higgs boson, the last missing particle in the Standard Model, advancing our understanding of the origin of the mass of fundamental particles. The discovery by astrophysicists that the expansion of the universe is accelerating implies that 75% of the universe is composed of “dark energy.” And a recent trailer for Avengers: Age of Ultron suggests an explanation for the long-standing open question: can the Hulk lift Thor’s hammer?61uU2GVaAJL._SL250_

[Order James Kakalios’ book “The Physics of Superheroes: Spectacular Second Edition” from Amazon]

The scene in question aired Oct. 28 during an episode of Marvel’s Agents of S.H.I.E.L.D. on ABC. In this clip, the Avengers are relaxing in their street clothes in Tony Stark’s penthouse apartment, and are discussing the “enchantment” on Thor’s hammer, Mjolnir, which stipulates that it can only be lifted by those “deemed worthy,” and whoever does so will “possess the power of Thor.” Thor places his hammer on a coffee table (actually, as shown below, it is resting partially on some books on the table), and various heroes attempt to pick up the hammer, to no avail. Thor then hefts the hammer and casually flips it into the air.

YouTube/Screengrab

YouTube/Screengrab

And thus one proposal for why the hammer is unliftable is put to rest. Astrophysicist and Director of the Hayden Planetarium, Dr. Neil deGrasse Tyson, has speculated that, if Mjolnir is composed of neutron star matter, the densest material in the universe outside of a black hole, then it would weigh as much as three hundred billion 51Ozfu+0xrL._SL250_elephants.

[Check out James Kakalios‘ other book “The Amazing Story of Quantum Mechanics: A Math-Free Exploration of the Science That Made Our World” at Amazon]

Water has a density of one gram per cubic centimeter, and lead has a density of eleven grams per cubic centimeter, but they pale compared to neutron star matter, which has a density of one hundred million million grams per cubic centimeter. In this case Mjolnir would weigh roughly twelve thousand trillion pounds. I know Tony Stark is rich, but even if he could buy a coffee table that could support such a weight, I can’t imagine any book, even an impenetrable physics text, that could bear up under this force. No, we must look elsewhere for an explanation as to why only Thor (and a few select others—more on this in a moment) can raise Mjolnir. Read the rest of this entry »