String theory seems to me to have failed to deliver what it had promised in the ’80s, and is one of the many ‘nice-idea-but-nature-is-not-like-that’ that dot the history of science. “It is possible that the two theories could be parts of a common solution … but I myself think it is unlikely.
“The string planet is infinitely less arrogant than ten years ago, especially after the bitter disappointment of the non-appearance of supersymmetric particles,” he said. Carlo Rovelli, a physicist at the University of Marseille and a founding father of LQG, believes his field ascendant. Not everyone on the LQG side expects the two will merge either. “But the methods are what people normally care about, and these are similar enough the mathematical methods could have some overlap.” “I don’t think that there is any likelihood that string theory and LQG are going to converge to some middle ground,” he said. “If your approach does not respect the symmetries of special relativity from the outset, then you basically need a miracle to happen at one of your intermediate steps.” Still, Rozali said, some of the mathematical tools developed in LQG might come in handy. Moshe Rozali, a string theorist at the University of British Columbia, remains skeptical of LQG: “The reason why I personally don’t work on LQG is the issue with special relativity,” he said. It’s a method that string theorists can use and are actually using. It’s a method to think of quantum mechanics and geometry. “It’s more sociological than scientific, unfortunately.” He doesn’t think the two approaches are in conflict: “I’ve always viewed as parts of the same description. “The biggest difference is in how we define our questions,” said Verlinde. They are very interested what is going on at the interface.” “But younger people in string theory, they are very open-minded. “On some occasions I’ve had the impression that string theorists knew very little about LQG and didn’t want to talk about it,” he said. Bodendorfer feels that the former chasm between string theory and LQG is fading away.
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He argues that LQG can be useful for the AdS/CFT duality in situations where string theorists don’t know how to perform gravitational computations. More recently, Norbert Bodendorfer, a former student of Thiemann’s who is now at the University of Warsaw, has applied methods of LQG’s loop quantization to anti-de Sitter space. A group around Thomas Thiemann at Friedrich-Alexander University in Erlangen, Germany, has extended LQG to higher dimensions and included supersymmetry, both of which were formerly the territory of string theory.
Meanwhile, in a development that went unnoted by much of the string community, the barrier once posed by supersymmetry and extra dimensions has fallen as well. Quantum Supergravity Could Explain Weirdness of Black Holes Arrow We just don’t inhabit the mathematical construct that is AdS space. But even having successfully combined LQG methods with string theory to make headway in anti-de Sitter space, the question remains: How useful is that combination? Anti-de Sitter space-times have a negative cosmological constant (a number that describes the large-scale geometry of the universe) our universe has a positive one. It’s much more intellectually forward-looking,” he said. “Loop quantum gravity has been seen too narrowly. Verlinde hopes to generalize the model to higher dimensions.
Even though the construction presently only works in 2+1, it offers a new way to think about gravity. He found that the AdS space can be described by a network like those used in LQG. In a recent paper, Verlinde looked at AdS/CFT in a simplified model with only two dimensions of space and one of time, or “2+1” as physicists say. Herman Verlinde, a theoretical physicist at Princeton University who frequently works on string theory, finds it plausible that methods from LQG can help illuminate the gravity side of the duality. If we were to zoom out, quantum details would disappear, and space-time would begin to resemble the smooth, continuous geometry of classical physics. The video shows the behavior of space-time at the Planck scale, the smallest possible area.
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In this artist’s conception, the network underlying space-time in loop quantum gravity is shown as a series of colored faces. This content can also be viewed on the site it originates from.ĭavid Kaplan, Petr Stepanek and MK12 for Quanta Magazine Music by Steven Gutheinz
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