How does String Theory compare to Relativity theory?

Answer 1

Essentially, string theory is a kind of extension of relativity. Relativity deals with our universe on a large scale (solar systems, stars, planets, galaxies, etc.,.) String theory attempts to describe features of our universe at a much smaller scale (smaller than 1.6 x 10 minus 35 meters) It's hoped that if/when perfected and verified, string theory will help unite the laws of gravity with the other three fundamental forces of nature (strong and weak nuclear forces, and electrogmagnetism).

Answer 2

Relativity is a classical theory while string theory is a quantum theory.

Relativity applies smoothly at all scales, even down to the very smallest. This means it does not have problems in unusual circumstances like the beginning of the universe or inside black holes, where matter is very compacted and scales are very tiny.

Quantum theories break things other than metrics (measures of space and time) into discrete units called quanta. They do not apply smoothly, but because the quanta are very small they look smooth to us. However, they more or less go to pieces at the beginning of the universe or in black holes. This is very embarassing for quantum theory.

While there is no terribly good reason to favour quantum approaches over relativity, string theory attempts to reconcile these two by starting at the quantum stand point. This is because there is a modern prejudice in favour of quantum theories, even if this leads to unexpected complication.

And unexpected complication is certainly what you get with string theory. In string theory the little point particle quanta that were used in early quantum theory are replaced with little string that vibrate in just one dimension. However, to make this work string theory has to introduce new dimensions - lots of them (as many as 7 new ones!)

Now this is highly embarrasing because it is quite clear that there are only three spatial dimension and one temporal dimension. So string theorists have come up with all sorts of odd explanation for why we cannot observe these extra dimensions, most of which require you to be high on drugs to accept them as even vaguely plausible.

Relativity has none of these problems. It arrives at a set of reference frame invarient tensor equations that describe the universe to the largest and smallest level called the Einstein field equations. But of course relativity is not, nor was ever developed to be, a description of how the building blocks of matter work.

But the biggest difference between the two is that relativity has been well tested, while string theory has made no successfully tested predictions. This is the most embarassing thing, because until it does so it could all be a fairy story.

Answer 3

Ted and epidavros are right on point(s). String theory came about because relativity, assuming dimensionless points at the sub-atomic level, blew apart with something called a singularity.

This is just math talk for a value exploding to infinity because, at the dimensionless point sub-atomic level, relativity equations have to divide by zero. And we all know what N/0 equals. Any number N divided by zero (the singularity) gives us an indeterminant value usually called infinity.

So string theory invented the string, which is one Plank length long (10^-35 cm). Thus, its equations never have to divide by zero since its fundamental particle, the string, has length.

To my way of thinking, string theory is a major reach in its attempt to resolve the relativity infinity issue. First, it delves into eleven dimensions rather than the four we can observe in our real world. It has to do that in order to come up with the right answers (answers that agree with our observable real world universe).

The string theorists tell us we can't see these other dimensions because they are wrapped around and very tiny. The way Brian Greene explains it, its something like the inch worm on a clothes line. The inch worm thinks it is in a one dimensional world...it can go forward or backward along the length of the line. But in fact, if it could see it, the worm could actually go around the clothes line as well.

Second, and this is the biggest failing of all to my way of thinking, in order to rid itself of the relativity infinity problem, string theory turns around and introduces a string that is infinitely thin. Argh. It introduces another infinity to rid an infinity. Note they do not say "zero thickness," but "infinitely thin." Not the same thing. The former is zero; the latter only approaches zero, but never gets there.

There are several experiments proposed to test string theory. But to date, these experiments are infeasible because we lack the technology (mainly energy sources) to carry them out. Until we can test string theory, string theory is more a philosophy than it is a theory.

Answer 4

Comparing the two of them is much like comparing apples and oranges. However, one of the reasons why string theory is so appealing is because it solves some of the problems that prevent quantum mechanics from being united with general relativity.

String Theory posits that the smallest elemental unit of all things is a string. Before string theory, most people thought in terms of points. That is, an electron appears to have no "radius." (or at least a radius much smaller than we can measure) Without string theory, we might assume that an electron exists at an infinitesimally small point in space. However, string theory says that the most fundamental units of all things are not points but are strings instead, and those strings each have a finite length. These strings vibrate. Certain vibrations produce qualities of electrons. Other vibrations produce qualities of quarks. Other vibrations produce qualities of photons. And, perhaps someday, certain vibrations will be shown to produce qualities of something like a "graviton." All particles are actually the result of vibrating strings.

Relativity says nothing about the fundamental physical units. Instead, relativity talks about space and time. Relativity states that all objects exist within a 4 dimensional "spacetime" and movement through this 4 dimensional object has an impact on the laws of physics for the object that is moving. Relativity states that all objects are moving through spacetime at a constant speed, even when sitting still (when sitting still, an object is still moving through the time dimension). As an object starts to move through spatial dimensions, it "trades" some of that constant speed for the spatial speed. This is what causes "time dilation", which is what causes objects in motion to experience "slower time" than objects at rest. Similarly, because all objects are actually always moving at a "constant" speed through this 4 dimensional spacetime, there is only a constant amount of speed that can be "traded" into a spatial speed. This is why an object cannot accelerate passed the speed of light. (this is also why photons do not "age" like slower particles do; they have no speed left to move in the time direction)

Thus, relativity really gives us a way to account for the impact of motion through the universe. It would be nice to combine relativity with quantum mechanics. Quantum mechanics gives us the ability to understand how the most fundamental particles in space appear and interact. However, when you use quantum mechanics to focus on a single infinitesimal point in space, Heisenberg's uncertainty principle forces the allowable momentum possibilities to explode to an infinite spectrum. In other words, you lose all information about the velocity of such particles. Thus, it is not possible to apply relativity in a quantum mechanical world when you collapse your view to a single point in space.

Thus, string theory fixes this problem by making the smallest unit of space a discrete finite length. This keeps velocities under control and thus allows us to connect quantum mechanics and relativity. (note: this is not the only reason why string theory is appealing)

Answer 5

string theory was/is developed after the existance of relativity... At that point relitivity was basicly considered law... So string theory uses relitivity as one of its fundemental postulates

Answer 6

There is an informative program in the freezone, on demand, Discovery Channel (COX digital) that covers it.