String theory, which came to the fore some 30 years ago with its own perfection, aimed at solving thorny problems in fundamental physics, including reconciling the contradictions between relativity and quantum mechanics.
In general relativity, events are continuous and deterministic, meaning that each cause matches a specific, local effect. In quantum mechanics, the events produced by the interaction of subatomic particles occur in a jumping fashion (quantum transitions) and the results are probabilistic, not deterministic.
Simply replacing infinitesimal particles with tiny vibrating chord rings, to borrow michael Faraday's words, seems too wonderful to be unreal. These vibrations produce quarks, electrons, gluons, and photons. Quantum uncertainty cannot tear space-time to pieces, and it seems that there is finally a viable theory of quantum gravity.
Even more beautiful than the text description is the mathematics behind it, which has ecstatic some physicists. To be sure, string theory has had troubling effects. These strings are too small for experiments to detect, and exist in spaces of up to 11 dimensions. These dimensions are folded into complex shapes. No one knows how these dimensions fold, but it's safe to say that certain configurations will eventually produce forces and particles that we are familiar with.
Many physicists believe that string theory would unify quantum mechanics and gravity.
Later physicists realized that the dream of a single (unified) theory was just an illusion. After completing the powerful "Standard Model" of particle physics in the 1970s, they hoped the story would be repeated in string theory. Like many mature theories, string theory has become rich, complex, difficult to handle, and has a wide range of influences in some ways. Its tentacles have penetrated into many areas of theoretical physics.
The mathematics of string theory has been applied to fields such as cosmology and condensed matter physics. Today's string theory looks almost fractal. The closer people get to any corner, the more structures they find. Some dig deep in specific "cracks"; others zoom in on the field of view in an attempt to understand larger patterns. As a result, today's string theory contains a lot of things that don't seem to be strings anymore. Those tiny chord rings are thought to penetrate into every particle and force known to nature.
Even when the mathematical tools of string theory were adopted by the physical sciences, physicists struggled to deal with the central tension of string theory: Could it give researchers an idea of how gravity and quantum mechanics reconcile?
"The problem is that string theory exists in the realm of theoretical physics," said Juan Maldacena, a mathematical physicist at the International IAS who is perhaps the most prominent figure in the field today. "But we still don't know how, as a theory of gravity, it relates to nature."
<h1 class="pgc-h-arrow-right" data-track="71" > burst of quantum fields</h1>
String theory emerged as a culmination of the theory of everything in the late 1990s, when Maldasena revealed that string theory containing five-dimensional gravity was equivalent to four-dimensional quantum field theory. This "AdS/CFT" duality seems to provide a map to grasp gravity, the most difficult object in physics, by linking it to the ancient, well-understood theory of quantum fields.
This connection was never considered a perfect model of reality. The five-dimensional space in which it is located has an "anti-de Sitter" geometry, which is not at all like our universe.
But they were surprised when the researchers delved into the other side of this duality. Most people take for granted that quantum field theory is well understood. It turns out that our understanding of them is very limited.
These quantum field theories were developed in the 1950s to unify special relativity and quantum mechanics. They worked very well for a long time. But today, when physicists revisit "the part you thought you understood 60 years ago," IAS physicists say you'll find "shocking results," which is completely unexpected. "Every aspect of quantum field theory as we understand it is wrong."
Researchers have developed a large number of quantum field theories over the past decade or so, each of which is used to study different physical systems. The explosion of this new quantum field theory is reminiscent of physics in the 1930s, when the unexpected appearance of a new type of particle, the meson, made a frustrated rabbi ask, "Who discovered this?" By the 1950s, the proliferation of new particles had Enrico Fermi complaining: "If I could remember the names of all these particles, I would be a botanist." ”
It was only when physicists discovered more fundamental particles, such as quarks and gluons, that they began to see their way in the jungle of new particles. Now many physicists are trying to do the same with quantum field theory.
Conformal field theory is a starting point. You can start with a simplified theory of quantum fields that behaves the same way over distances large and small. If these particular types of field theories can be fully understood, the answers to esoteric questions will become clear.
<h1 class="pgc-h-arrow-right" data-track="86" > string theory mathematics</h1>
Perhaps the area that has benefited the most from the boom in string theory is mathematics itself. The IAS researchers explain how some seemingly tricky mathematical problems can be solved by imagining a string. For example, how many spheres can a calabi-chu manifold (a complex folded shape used to describe space-time) hold?
Mathematicians are trapped. A two-dimensional string can swing in such a complex space that when it twists, it acquires new insights, like a mathematical multidimensional lasso. This is Einstein's famous physical way of thinking: a thought experiment flying with a beam of light revealed E=mc^2. The imagination of falling from the upper floor gave him a flash of inspiration: gravity is not a force, it is the property of space-time.
Using the physical intuition provided by strings, physicists have come up with a powerful formula to solve the problem of embedded balls. They came up with these formulas using tools that mathematicians did not allow. Then, after string theorists found the answer, the mathematicians proved it in their own terminology.
String theory has also made important contributions to cosmology. The role played by string theory in thinking about the mechanisms behind the expansion of the universe — the quantum effects and gravitational force met head-on in the moments after the Big Bang — was "astonishingly powerful."
Inflation models are entangled in a number of ways in string theory, notably the multiverse (the concept of a multiverse is that our universe may be one of an infinite number of universes), each created by the same mechanism that gave rise to our own universe. Between string theory and cosmology, the idea of an infinitely possible universe was not only accepted, but even taken for granted by many physicists. The selection effect will be a very natural explanation of why our world is the way it is, in a very different universe, and we won't be talking about this article here.
This effect may be the answer to a big problem that string theory is supposed to solve. As Gross puts it: "What picks this particular theory (the Standard Model) out of infinite possibilities?" ”
<h1 class="pgc-h-arrow-right" data-track="97" > construct a new picture</h1>
At the very least, a mature version of string theory offers powerful new ways to observe how seemingly incompatible descriptions of nature are simultaneously correct. The discovery of a double description of the same phenomenon largely sums up the history of physics. A century and a half ago, James Clark Maxwell discovered that electricity and magnetism are two sides of the same coin. Quantum theory reveals the connection between particles and waves. Now physicists have string theory.
Once we probe space with strings instead of particles, the angle of seeing things is different. If it's too difficult to get from point A to point B with quantum field theory, rethink the problem in string theory. In cosmology, string theory "wraps up physical models in a way that is easier to think about, and it may take centuries to piece together all these clues into a coherent picture."
Einstein also tried to find a theory of everything, but also failed, which did not detract from his genius. Maybe the real situation is more like a map in an atlas, each with very different information, and different. Using atlases will require physicists to be proficient in multiple languages and methods at the same time. Their work will come from many different directions.
We are in the most exciting era of physics since quantum mechanics emerged in the 1920s. But nothing will happen anytime soon.
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