Superstring theories take this idea and build the entire universe from the bottom up. And yes, it's as challenging a task as it sounds. That's why we speak of string theories in the plural, because there are several different string theories that attempt to make it all work. Oh, and at least 10 dimensions are called for, too, just for all the math involved.
Physicists propose that any dimensions beyond time and visible space are folded up and out of sight. As you probably guessed, superstring theory is still developing, meaning that physicists continue to work out kinks in the individual string theories.
Eventually they're aiming to fulfill Einstein's unrealized goal of unifying general relativity with quantum theory. That's why string theory also is sometimes called a theory of everything , because it could serve someday as a foundation for all future scientific discovery and innovation. In the meantime, the next time you look in the mirror or feel the heat of a noonday sun, remember: All of that universal activity may depend on the vibration of incredibly small loops of string.
Strings, and only strings, can collide and rebound cleanly without implying physically impossible infinities. String theory turns the page on the standard description of the universe by replacing all matter and force particles with just one element: Tiny vibrating strings that twist and turn in complicated ways that, from our perspective, look like particles. A string of a particular length striking a particular note gains the properties of a photon, and another string folded and vibrating with a different frequency plays the role of a quark , and so on.
In addition to taming gravity, the framework proved attractive for its potential to explain so-called fundamental constants like the electron's mass. The next step is to find the right way to describe the folding and movement of strings, theorists hope, and everything else will follow.
But that initial simplicity turned out to come at the cost of unexpected complexity — string math didn't work in the familiar four dimensions three of space and one of time. It needed six additional dimensions for a total of 10 visible only to the little strings , much as a powerline looks like a 1D line to birds flying far overhead but a 3D cylinder to an ant crawling on the wire.
Adding to the conundrum, physicists had come up with five conflicting string theories by the mids. The theory of everything was fractured. Over the next decade, scientists exploring the relationships between the five theories began to find unexpected connections, which Edward Witten, a theorist at the Institute for Advanced Study in Princeton, New Jersey, gathered up and presented at a string theory conference at the University of Southern California.
The novel theory is called M-theory, although to this day no one knows what mathematical form it might take. The "M" is likely inspired by higher-dimensional objects called membranes, Taylor said, but since the theory has no concrete mathematical equations, the "M" remains a placeholder with no official meaning.
String theory is one of the proposed methods for producing a theory of everything , a model that describes all known particles and forces and that would supersede the Standard Model of physics, which can explain everything except gravity. Many scientists believe in string theory because of its mathematical beauty.
The equations of string theory are described as elegant , and its descriptions of the physical world are considered extremely satisfying. The theory explains gravity via a particular vibrating string whose properties correspond to that of the hypothetical graviton, a quantum mechanical particle that would carry the gravitational force.
That the theory bizarrely requires 11 dimensions to work — rather than the three of space and one of time we normally experience — has not dissuaded physicists who advocate it. Researchers have used string theory to try to answer fundamental questions about the universe, such as what goes on inside a black hole, or to simulate cosmic processes like the Big Bang.
Some scientists have even attempted to use string theory to get a handle on dark energy , the mysterious force accelerating the expansion of space and time.
In string theory we have this nice feature that everything comes in discrete numbers, so we can count how many solutions there are. What we show is that, yes, the standard model is special, but within string theory it has the potential to be realized in many different ways. What are the challenges of your work, and where do you go next? Cvetic: For consistency, the constructions from string theory rely on something called supersymmetry.
If someone builds a new detector and finds these additional particles, associated with supersymmetry, at some higher energies than what we are currently reaching in experiments, that would be an advance on the experimental side which could help us a lot. On the other hand, not observing supersymmetry in the near future does not mean that string theory is wrong. It just means that we need to develop new frameworks and methods to improve our toolkit.
In terms of what to do with these quadrillion examples, these are not just something to be put in a museum, but you can actually use these examples to test new conceptual frameworks and computational methods in string theory. What continues to excite you and inspire you about this area of research?
Cvetic: I think one of the strengths of the Penn effort is that we ask questions from theory that are relevant to our colleagues in experimental high energy physics. So on one side, the questions we are asking are questions related to things that high energy experimentalists are testing in colliders, and on the other hand we are using techniques of formal string theory that tie us closely to our math department colleagues. Lin: What I find interesting about what we do, and more broadly what string theory provides, is the idea of dual descriptions for the same phenomena that suddenly makes certain aspects much easier to grasp.
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