Present at the Future (10 page)

“One thing we would all probably agree on is that there are deep connections between the elementary particles and the universe,” says Turner. “When we talk about the birth of the universe, we need ideas from the elementary particle physicist, and then we need to turn those ideas around and see how they can be tested with the sky today. And when we look at the solutions to the big questions involving dark matter, we hope to produce [it] at an accelerator. So it’s not just telescopes. It’s also accelerators.”

Unlike theorists who hang out by their equation-filled blackboards and think heavy thoughts, the experimentalists actually do the heavy lifting. They must search for evidence in the cosmos that would back up the repulsive nature that the theorists are predicting. “The observers now have the ability to probe the acceleration of the universe,” says Turner.

Some of the tools astronomers are using are the “way back” machines of astronomy: telescopes. In practical usage, a telescope is really a time machine, says Turner. “It allows you to look out in the universe, and as you look out, you look back in time. And so you can compare what the expansion rate is today with what it was back then.”

But the telescopes they use are not the kind you use in your backyard to look at the moon. “Some of them will use X-ray telescopes.” Some will use telescopes that can see gravity acting as a lens to bend light around galaxies. “Some of them are going to use the microwave background to get at this question of acceleration.”

The microwave background radiation is the “echo” left over from the big bang. A NASA satellite, the WMAP (Wilkinson Microwave Anisotropy Probe), hovering in space between the Earth and the sun, has been able to peer back in time to almost the beginning of our universe, detect this very faint microwave remnant, and produce a detailed picture of its early history. “It amazes me that we can say anything about what transpired within the first trillionth of a second of the universe, but we can,” said Charles L. Bennett, WMAP principal investigator and a professor in the Henry A. Rowland Department of Physics and Astronomy at Johns Hopkins University. “We have never before been able to understand the infant universe with such precision.”

So far, in a world where no one knows just what the dark matter or energy is, Dr. Neta Bahcall, professor of astrophysics at Princeton University, says the observations are “remarkable,” because they are all consistent. “All the different observations from different methods—from weighing the universe to measuring distant supernova, to the microwave background radiation—all of those very different methods yield the same result. They all show that we made dark matter in the same amount as we expected. They all are consistent with having some amount of dark energy,
and that’s why it is so exciting. If you talk to the astronomers, we are just jumping for joy, and really jumping in our seats because it is a very exciting time to see that the data is all getting together so beautifully. What is a dark matter? What is a dark energy? What does it all mean for physics? We’re going to have answers in the next ten years or so.”

DARK MATTER: AXIONS, WIMPS, AND MACHOS?

Some of those answers may come not from looking up into the heavens but from looking down into the basements of giant particle accelerators. In their search for the solutions to the super-big questions of the universe, physicists are probing the super-tiny world of the atom, looking for the particles, about whose existence they can only speculate.

Among the most popular candidates are axions—cold particles predicted to have been created in abundance during the big bang. Axions were named after a laundry product by a copredictor of the particle’s existence, Dr. Frank Wilczek. He believed that their presence would help “clean up” some of the problems in theoretical physics. Wimps are another creative solution to the dark energy problem. The term is short for “weakly interacting massive particles.” Wimps theoretically cannot be seen directly because they do not interact electromagnetically or with atomic nuclei. But because they are cold, massive particles that would tend to clump together, wimps fit the bill for cold dark matter. All we have to do is prove they exist.

Finally, of course, if you have wimps, then you need their alter ego: machos, “massive compact halo objects.” (Those physicists are such cards!) A macho would be a clump of normal atomic matter, such as protons or neutrons, that float unseen through the halos around galaxies. They might be black holes, neutron stars, brown dwarfs…yada yada yada. You get the idea; the possibilities are many.

“With all of the instruments we have, two satellites to map the echo of the big bang, the Hubble Space Telescope, the Chandra X-ray Observatory, and NASA’s next-generation space telescope [the James Webb Space Telescope] that will have ten times the light-collecting power,” Turner thinks that cosmologists will have the riddle of the dark matter and energy solved within a decade. “Some of them will use X-ray telescopes. Some of them will use telescopes in a very intriguing way where they look at how the distribution of matter between us and the distant universe is bent or gravitationally lensed. Some of them are
going to use the microwave background to get at this question of acceleration. I can’t predict the exact date, but in the next ten years we’re actually going to be able to answer these difficult questions.”

“As we use this high technology to zero in on every little detail of the matter in the universe, we’ll see that infrastructure in stunning detail, and that will reflect the type of dark matter,” says Dr. Andreas Albrecht, professor of physics at the University of California, Davis.

“An important point to make is that the problem with dark matter is not a particle physics problem,” says Dr. Bernard Sadoulet, professor of physics and a director of the Center for Particle Astrophysics at the University of California, Berkeley. “It is an astrophysical problem, which may point to questions of deep solutions for the particle physics problem. But it’s really the merging of these two fields, of cosmology and particle physics.”

“Discovering supersymmetry has been the holy grail for a number of years of the particle physicists,” notes Turner, “and it looks like the cosmologists—I’ve got my fingers crossed here—might beat them to it, because it might be that our galaxy is held together by super-symmetric particles, and so I’m putting my money on people like Bernard, that they’re actually going to beat the LHC to finding supersymmetry. But as Sadoulet says, in the end, both the astrophysical evidence and the evidence in the laboratory will make it a much richer picture.”

This is a remarkable idea: that the largest things we can imagine—galaxies stretching millions of light-years—started out as small, subatomic particles. “And even more remarkable than that,” says Turner, is that “we can test it. And the answer seems to be written across the microwave sky that the biggest things did evolve from the smallest things.”

CHAPTER EIGHT

STRING THEORY: WE HAVE A PROBLEM

String theorists don’t make predictions, they make excuses.

—RICHARD FEYNMAN

Sometimes you hear something so often that you think it must be true. You wish it were true because it would solve a lot of problems (does “weapons of mass destruction” sound familiar?). That’s not supposed
to happen in science. Ideas and theories are put to the test, to find out if they can stand up to scrutiny. If they do, they become an accepted part of the way we look at the world, until something better comes along. Relativity theory is one such idea. It expanded on a really nifty theory of gravity put out by a guy named Newton, hundreds of years before it. Reality itself has been under scrutiny and test for more than a hundred years, since a pretty good physicist named Einstein published the first of his many papers about relativity in 1905.

Isaac Newton was the rock star of science in his time. And relativity theory—more accurately, Albert Einstein—was the darling of the media immediately after a famous eclipse of 1919 proved true his revolutionary theory that gravity curved space. The modern equivalent would be string theory. Countless books, papers, articles, and TV shows have sought to explain it to us; it has made media stars out of scientists, such as Brian Greene, professor of physics and mathematics at Columbia University in New York. He’s also the author of several books, including The Elegant Universe and The Fabric of the Cosmos.

STRING THEORY IN A NUTSHELL

According to Greene, “We have two main pillars of understanding in physics that were developed in the twentieth century. One is the general theory of relativity, Einstein’s theory that describes gravity. And gravity is a force that’s relevant mostly when things are big—stars and galaxies and so forth.

“The other major development is quantum mechanics, a theory that describes the other end of the spectrum, the small things—the molecules and the atoms and so forth.

“Now for a long time, we’ve recognized that these two theories have to talk to each other in a sensible way. There are realms, extreme realms, where things are both heavy and small, like black holes or the beginning of the universe. And because those realms exist, you need to use gravity, general relativity, and quantum mechanics all at the same time.

“The problem is that for many decades, any attempt to put the two theories together, to unify them, didn’t work. It gave wrong, nonsensical answers. String theory is an attempt to fix that, to give us a theory that won’t give nonsensical answers, that will give answers that make sense when you put gravity and quantum mechanics together.”

QUANTUM RELATIVITY

In a nutshell, string theory says that instead of tiny little subatomic particles being at the root of all matter and energy, tiny little strings exist instead. And when plucked just the right way, they vibrate to produce the building blocks for everything we see around us. And most importantly for cosmology, string theory, theoretically speaking, can unite the disparate worlds of gravity and quantum mechanics.

Sounds great so far, doesn’t it? But as with anything else in life, string theory comes with a little bit of extra baggage. A few big problems. Because while string theory may look sweet, mathematically speaking, it requires that our world be composed not of the 3 or 4 dimensions familiar to all of us but instead 10 or 11 dimensions, most of which remain hidden from view. “Whether there really are extra dimensions or not, I think, remains to be seen,” says Dr. Lawrence Krauss.

Even Einstein found no way to unite gravity and quantum mechanics. And that’s where some scientists see the problem: String theory is aging, and not elegantly. It has been around long enough to be tested, and we should have found experimental evidence to prove that it works. And because it hasn’t been tested, scientists, in a rapid sequence of speeches, articles, and books, are beginning to openly question its usefulness in physics. They say that it is not living up to its promise, that it’s more hype than science.

Take Lee Smolin, faculty member at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. Smolin, of The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, says he is trying to understand why string
theory, which he has worked on himself, is so problematic. “Why the ideas which seemed at first so beautiful, so natural, were not getting us where we expected to get twenty years ago.”

Smolin points out that just about every 25 to 30 years, new ideas in physics come along to replace the old ones. If you look back over the last 200, he says, it’s very unusual for three decades to pass without a scientific revolution. For example, he writes that “from 1830–1855 Michael Faraday introduced the notion that forces are conveyed by fields, an idea he used to greatly further our understanding of electricity and magnetism.”

In the 25 years that followed, James Clerk Maxwell expanded those ideas into “our modern theory of electromagnetism.” He explained how light was also like radio waves and unlocked other secrets of our natural world. Then came the next dramatic period, 1880 to 1905, in which electrons and X-rays were discovered. In that 25-year period, Smolin continues, Max Planck’s work would “spark the quantum revolution.” Einstein’s era would arrive in 1905, and understanding the impact of relativity would occupy the next two and a half decades. By Einstein’s death in 1955, we would know all about a whole new world of subatomic particles and organize the forces of nature into a family of four.

The next 25 years and the 25 after that would see the creation of a “standard model” of the elementary particles in the universe, and on a larger scale, we’d see Stephen Hawking and other luminaries enlighten our understanding of black holes, the big bang, and dark energy and matter.

But since the 1980s, says Smolin, we have been stymied. String theory is now more than 20 years old and doesn’t seem to be yielding the answers that have been expected of it. “History seems to show that when there’s a good idea about unifying different parts of physics, it works fast if it’s going to work.” Scientists should be able to conduct experiments that either bolster or bat down that new idea. But the problem with string theory is that so far, there are no experiments that
can solidify it. Or, as Smolin puts it, “string theory is not making experimental predictions. There are certainly very beautiful things about it,” but a theory that can’t be tested is nothing more than a theory. In science, you can’t hang on to an idea too long; if it can’t be tested and proven, it’s on to the next big thing.

Krauss agrees. He says string theory has been a failure. “There isn’t a shred of empirical evidence, not only for extra dimensions but essentially also for string theory. They [scientists] haven’t made any predictions that have been tested. And moreover, in fact, to some extent, we’re still just learning what the theories are.”

Greene agrees that the evidence, so far, has been lacking. But as one of string theory’s greatest proponents, he says we have to give the experimentalists a bit more time to find the evidence.