What if space isn’t the final frontier? What if beyond our galaxy, far, far away, there is a whole other universe parallel to ours, perhaps in another dimension? Fans of comic books and science fiction have long fantasized about such possibilities. Remember Superman’s Earth-One and Earth-Two? Or how that transporter malfunction brought us an evil Kirk and Spock?
Turns out such awesomeness could transcend mere fanboy musings. It’s also the stuff of serious and popular science. So much so that one Monday night last month, two lecture halls at the American Museum of Natural History were packed with more than 900 curious New Yorkers, who came to watch five physics professors—and one flat-screen TV—debate the merits of string theory, the scientific “theory of everything.” For nearly 30 years, many in physics circles have believed that string theory might help unlock the secrets of the universe and possibly reveal hidden realities beyond our own. But skeptics have charged that instead of aiding scientific discovery, and helping young physics post-docs get on the path to professorships, string theory has actually become a dead end.
That conflict was reflected in the title of the museum event, the Hayden Planetarium’s 10th annual Isaac Asimov Memorial Debate: “The Theory of Everything . . . Still Searching?” The five professors were introduced and seated, and the TV was turned on. There appeared the head of a sixth professor: Brian Greene of Columbia University, author of several popular science books including The Hidden Reality (which just hit stores and discusses extra dimensions and parallel universes), who joined the panel from out of town via Skype. Planetarium director Neil deGrasse Tyson reminded the crowd that Greene had appeared on the very first Asimov panel back in 2001, which also tangled with string theory. That was shortly after he helped found Columbia’s Institute of Strings, Cosmology and Astroparticle Physics (ISCAP).
Tyson asked Greene to boil string theory down to one sentence. “It will be a long sentence,” Greene replied.
A unified theory is something of a Holy Grail in physics, and a long line of brilliant minds from Einstein on down have failed to craft one that can be proven to work. The trick has been to find a single theory that explains all of physics, from the quantum forces that control subatomic particles to the relativity that holds sway over the greater cosmos.
Consider, for example, black holes. These objects, formed from collapsed stars, are believed to be compressed to a size that reaches the atomic level. But no physical law has ever been devised to explain how gravity works at that scale. Einstein’s laws and those of quantum dynamics each work well in their own realm, explained Greene, but become “fierce antagonists” when you try to meld them.
String theory, first proposed in the mid-1980s, proposed a possible solution. It began, he explained, as a new way to envision the inner structure of the tiniest particles. According to conventional theories of physics, matter can be parsed down to molecules, then atoms, then protons and neutrons, then electrons and quarks, then . . . what? String theory suggests a deeper level of tiny filaments of energy that vibrate in certain patterns. A string vibrates one way, you get a quark. Another way, an electron. Yet another, gravity.
With that, and through fancy mathematical footwork, Greene told the Planetarium panel that “we have united gravity and quantum mechanics—at least on paper.”
String theory produced some unusual side effects. To make the math behind the strings work, theorists needed extra dimensions beyond our four (three for space, one for time). Those dimensions became dubbed “branes,” short for membranes. “Imagine that we live on a giant slice of bread, that all reality is on our slice of bread,” Greene tells the Voice. “Now imagine that our slice is in a giant cosmic loaf. We can see only what’s on our slice, but there could be other slices out there.”
If so, Evil Spock and Earth-Two Superman could live elsewhere in the so-called “multiverse” on one of those cosmic brane slices. But other academics beg to differ. One prominent string-theory skeptic, in fact, resides on Greene’s own campus: Peter Woit, an instructor in Columbia’s mathematics department, who in 2006 published his own popular book called Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law. String theory, Woit believes, is so nebulous that it can’t even be used to make predictions that could be proven or disproven, making it effectively useless.
“String theorists would often talk a good game,” says Woit, but their ideas have consistently failed to produce experimental proof (something that many string theorists themselves have long acknowledged). But, he adds, science comes down to whether you can “actually predict something with your theory, and they just haven’t been able to meet that challenge.” His message: Let’s drop strings and move on to more fruitful areas of research.
Woit says that there’s been a backlash to string theory in academe over the past decade, and that both universities and up-and-coming physics post-docs are starting to lose interest. “I feel bad for young people trying to get jobs,” he says. “It’s hard to get a job doing string theory at this point.”
Theoretical physics is “a tough, competitive place for jobs,” admits David Kagan, a first-year post-doc at ISCAP. Nevertheless, he uses string theory in his research on extra dimensions and the ways in which parts of the universe are configured.
His work speaks to why ISCAP was established, which was to facilitate an interdisciplinary approach to studying the cosmos among astronomers, cosmologists, and physicists. Post-doctoral researchers typically spend two years there before getting onto a more permanent teaching track. Kagan feels his work with string theory stands him in good stead to land one of those jobs down the road.
“I got into string theory research because of my love for fundamental physics and my feeling that ideas we work with in this field are some of the deepest, most exciting, and most beautiful,” Kagan says in an e-mail. “I think that that passion for what I do helps me be a better researcher and educator, and insofar as that is true, it should be helpful for eventually getting a professorship in the future.”
Much of the work involved in string theory is “at the edge of understanding and quite speculative,” says Greene. But criticism that string theory is unproven, he says, misses the point. “Yes, we don’t know if it’s right or wrong,” he says. “That’s real scientific exploration. That’s what science is.”
At the museum debate, after panelists took a diversion into whether we all actually live in “the Matrix,” Tyson asked whether string theorists were just “chasing a ghost.”
“We are ambitious,” said Greene on the screen. He holds out hope that future experiments and technology will be able to provide the proof of strings that has so far eluded everyone.
“Do I believe in string theory?” he said. “No. I only believe in things that are proven. Do I think it’s the best approach? I do.”