String Theory?

Question

I don't get string theory at all. Could some one explain it to me, or give a link to a website that does?

Answer 1

A string is an infinitely thin thing that is 1 Planck length (10^-33 cm) long. It exists in our universe and in higher dimensions...higher than the four of our own space-time. How a string appears in our 4D space depends solely on the frequency the string vibrates at.

For example, at one frequency, a string will look and act like a photon in our 4D space-time. At another frequency, another string will look and act like a graviton (the gravity particle string theory predicts). Still another frequency will give us fundamental particles that have mass...like hadrons. Everything in this universe, both mass and energy, is made up of these strings.

There are several string theories (and associated theories). They all have something in common...the higher dimensions. Some say 10 dimensions, some say 11, and there are some that say there are more than 20 dimensions. The most commonly accepted guess as to where these dimensions are is that they are tightly wound; so small we cannot see them.

Brian Greene [See source.] uses the ant on a rope to illustrate the higher dimensions as tightly wound very small ones. Consider you see an ant crossing a rope strung between two trees. You can see the length of the rope, but you can't see it's width because you are too far away. And the ant cannot travel on the rope except fore and aft along the length of it; it would fall off otherwise.

OK, then, the diameter/width of the rope is the higher dimension of the one dimensional rope. The ant is totally unaware that the rope has width and it is content to go back and forth along the length. And that's what we do...bo back and forth through 3D space and 1D time...without sensing the other, higher dimensions the strings also exist in.

In fact, what we see of strings is strictly how they appear in 4D ordinary space-time. We have no clue how they appear or if they are observable in the higher dimensions.

As another answer mentioned, string theory is not a theory. A true theory is testable and can be validated through experimentation. The theory of relativity, for example, is a true theory because a number of experiments have validated its premises (like increasing mass or time dilation at close to light speed for example). There have been no validating experiments for string theory. So, at best, it is a hypothesis; not a theory.

Answer 2

String theory is a model of fundamental physics, whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point particles that form the basis for the standard model of particle physics. The phrase is often used as shorthand for superstring theory, as well as related theories such as M-theory. By replacing the point-like particles with strings, an apparently consistent quantum theory of gravity emerges. Moreover, it may be possible to "unify" the known natural forces (gravitational, electromagnetic, weak nuclear and strong nuclear) by describing them with the same set of equations, as described in the theory of everything.

For a scientific theory to be valid it must be verified empirically, i.e. through experiment or observation. Few avenues for such contact with experiment have been claimed. With the construction of the Large Hadron Collider in CERN some scientists hope to produce relevant data, though it is widely believed that any theory of quantum gravity would require much higher energies to probe directly. Moreover, string theory as it is currently understood has a huge number of equally possible solutions.Thus it has been claimed by some scientists that string theory may not be falsifiable and may have no predictive power.
Studies of string theory have revealed that it predicts higher-dimensional objects called branes. String theory strongly suggests the existence of ten or eleven (in M-theory) spacetime dimensions, as opposed to the usual four (three spatial and one temporal) used in relativity theory; however, the theory can describe universes with four effective (observable) spacetime dimensions by a variety of methods.

Answer 3

There was a great show on PBS a few years back about it.

Answer 4

it is too hard for most people to understand.
there is an excelent article in wikipedia.

Answer 5

http://en.wikipedia.org/wiki/String_theory