Wednesday, September 9, 2009

Interview on

An interview with me by Betsy Mason has been published on

High Energy Particle Physics Demystified

Sunday, September 6, 2009

Galileo's Legacy

By Paul Halpern

Four hundred years ago last week, Italian astronomer Galileo Galilei announced the invention of what would be the world’s first astronomical telescope. Although the Dutch had pioneered the telescope, his instrument would be powerful enough to discover the mountains of the moon, four of the largest satellites of Jupiter, the phases of Venus, sunspots and other evidence of the magnificent diversity of the solar system. In short, it would prove most the most cutting-edge instrument of its era—as particle-smashers such as the Large Hadron Collider (LHC) in Europe are today. On August 25, 1609, Galileo presented one of his prototypes to the Venetian legislature, pointed out its military applications, and was promptly rewarded with a lifetime professorship and a substantial bonus.

After months of stargazing and taking careful notes about the features he observed, Galileo arrived at the astonishing conclusion that, contrary to age-old beliefs, there are other worlds in space besides Earth. If people could travel to the moon, he surmised, they could walk upon its surface too. He also verified the Copernican hypothesis that all planets in the solar system, including Earth, revolve around the Sun. By maintaining his belief in the non-uniqueness of Earth, and the capability of science to reveal new facts that supersede prior religious tenets, Galileo was eventually charged with heresy. History has vindicated Galileo, however, and established him as one of the founders of the modern scientific method. The Apollo mission of 1969, celebrated last month for its 40th anniversary, offered tangible proof that Galileo was amazingly prescient in his view of the universe.

The past century has revealed that the solar system and all the stars that speckle the sky are part of an incredibly vast spiral galaxy, itself but a minute part of an immense universe. As the noted American astronomer Edwin Hubble demonstrated in the 1920s with a huge optical instrument atop Mt. Wilson in California, the galaxies, by and large, are moving apart from each other. This discovery revealed the expansion of the universe. Further evidence gathered from the 1960s until the present day has indicated that the cosmos began in a hot, dense state known as the Big Bang. The wealth of cosmic knowledge gathered through variations of Galileo’s device is truly astounding.

Despite the amazing progress in astronomy our understanding of space is far from complete. In fact, observations made in the mid-to-late 20th century revealed that the visible content of the universe is but a small fraction of all that is out there. In the mid-1960s, astronomers Vera Rubin and Kent Ford engaged in a detailed study of the outermost stars in the Andromeda galaxy and found these to be moving much faster than expected. They arrived at the startling conclusion that invisible material, now known as “dark matter,” was exerting an extra gravitational tug on the stars—like hidden reigns pulling mechanical horses around a merry-go-round.

The situation became even trickier in the late 1990s, when two teams of astronomers, studying the energy profiles of exploding stars, or supernovae, in very distant galaxies, determined their distances and speeds, and discovered that the universe has been expanding at an increasingly rapid pace. Gravity alone could not explain such cosmic acceleration. Rather, some invisible dynamo, dubbed “dark energy” must be pushing all the galaxies away from each other at a faster and faster rate. Some models predict that the universe will eventually be torn apart, like a sheet stretched beyond its limits and ripped into tatters. Such a “Big Rip” would mean the complete fragmentation of space itself.

Dark matter and dark energy are mysteries that scientists cannot ignore. Around 72 percent of the known content of the universe is estimated to be dark energy, and another 23 percent dark matter. Only 5 percent is ordinary visible material, composed of the atoms that make up all things on Earth, the stars, planets and everything familiar.

Just as it took Galileo’s extraordinary new instrument to vanquish misconceptions about the solar system, it will take a fantastic new device to unravel the mysteries of dark matter and dark energy. One of the principal missions of the LHC, the largest particle collider ever completed, is to create massive particles that could potentially represent a component of the invisible substances in the cosmos. Although the LHC was shut down for repair soon after its opening in September 2008, it is scheduled to restart this November. By winter, if all goes well, physicists will begin collecting data that could further our understanding of the natural world in unprecedented ways. As we commemorate Galileo’s legacy, let’s hope that the LHC will revolutionize our vision of nature in the way the telescope did four centuries ago.

Paul Halpern is Professor of Physics at the University of the Sciences in Philadelphia
He is the author of Collider: The Search for the World’s Smallest Particles