Question:
String Theory and Graviton questions?
You'veBeenHitBy**
2008-06-21 20:12:14 UTC
I watched some interesting video documentaries on String Theory. I have a basic understanding of it but some famous guy once said something like: "if you think you understand physics you dont understand anything"

How do we even know that these strings exist if they are billions of times smaller than atoms and even quarks?

Do these strings create gravity?

I remember the physicists in the video saying that strings create the properties that the certain particles have.

If you yourself want to watch it to see what I'm talking about (hopefuly you can understand more that I do)

Part 1:
http://www.youtube.com/watch?v=E7FV9aaiwKQ

After watching that your gonna want to watch it all just like me.

But if you ARE physicist then maybe you can answer my question right away.

Simple terms and explanation please
Four answers:
answerman
2008-06-21 20:22:49 UTC
Strings are a mathematical probability that exists on paper. M theory has "beauty" and symmetry which has too many answers that seem to work in physics and is hard to ignore. The theory may never be proved since the energy required to generate observable data would be enormous.



Strings do not create gravity according to the theory, gravity leaks out of another dimension therefore making it weak.
.
2008-06-22 02:23:47 UTC
String theory arose about thirty or so years ago but has come into the 'fore' during the last decade or so as physicists have attempted to search for a unified theory of the four forces of nature. Please allow me to explain why string theory has provided such a good starting point for a possible unification of the four forces!



Grand Unification Theory or GUT for short is an attempt by theoretical physicists to provide a single unified theory of the four forces of nature.



These four forces are: the strong nuclear force, a short ranged powerful force responsible for the binding together of nuclei; the weak nuclear force, a short ranged less powerful force responsible for radioactive decay processes; the electromagnetic force, a infinite ranged force of moderate strength responsible for chemical and electromagnetic wave phenomena; and last of all, the gravitational force, which governs the universe as a infinite ranged force that is only powerful when it results from massive bodies such as stars.



During the nineteen-sixties, the theoretical physicists Glashow, Salam and Weinberg developed a theory which unified the electromagnetic and the weak nuclear forces. This theory is known as the ‘electroweak’ theory, it predicted the neutral vector boson Z0, and weak nuclear force reactions arising from its exchange, in what are known as neutral current reactions. The theory also accounted for the heavy charged bosons W+ and W-, required for the mediation of all observed weak interactions, known as charged current reactions. These particles were discovered in 1983.This unified theory is a ‘gauge invariance’ theory, which means that if the components of its underlying equations are transformed, in position or potential, they still predict exactly the same physics. Because the force carrying particles (Z0, W+ and W-), of this theory, are massive spin-1 bosons a spin-0 boson is required to complete the theory. This spin-0 boson is the as yet unobserved ‘Higgs’ boson.



The discovery of the Higgs at CERN's LHC will help complete the standard model of elementary particle physics. This model deals with the quarks and their strong nuclear force interactions, along with weak nuclear force interactions and electromagnetic interactions among the leptons. However, the standard model doses not sit comfortably with Einstein's General Theory of Relativity (1915). This theory describes gravity as a geometrical distortion of space-time due to the presence of mass energy within it. Thus, even when the Higg's boson has been discovered, as surely it will, there will still exist a disparity between the force of gravity and particle theory.



The strong nuclear and gravitational forces have yet to be unified with the weak and electromagnetic. This is where string theory comes in.



A string is one of the main objects of study in string theory, a branch of theoretical physics. There are different string theories, many of which are unified by M-theory. A string is an object with a one-dimensional spatial extent, unlike an elementary particle which is zero-dimensional, or point-like.



By postulating this one-dimensional structure, many desirable features of a more fundamental theory of physics automatically emerge. Most notably, almost any theory of strings consistent with quantum mechanics must also contain quantum gravity, which had not been described consistently prior to string theory.



The characteristic length scale of strings is thought to be on the order of the Planck length, the scale at which the effects of quantum gravity are believed to become significant:





On much larger length scales, such as the scales visible in physics laboratories, such objects would be indistinguishable from zero-dimensional point particles. However, the vibrational modes and structure of the tiny string would be manifested as different elementary particles in the standard model of quantum field theory. For example, one state of the string would be associated with a photon, and another state with a quark. This unifying feature of string theory is among its greatest strengths, however no known solution of string theory exactly reproduces the particle content of the standard model.



This, then, is where the problem lies with the development of a GUT based upon string theory(s). There are at present five competing versions of super-string theory - none of which truly represent the physical world we see and measure.





I hope this helps, although I concede that it is a very brief survey, which requires a textbook level of coverage to do it justice!
wtjui
2008-06-21 20:26:55 UTC
we dont know they exist, since there hasn't been any experiments to prove or disprove the theory. thats why string theory has been under fire for some time now as to call it abstract math rather than physics.



its certainly true that ALL sciences require a theory to be falsifiable by definition, its too early to presume that there will NEVER be a experiment conceived to test the theory.
2008-06-21 20:17:08 UTC
String Theory is NOT science and not physics.



It is a clever idea but it has never been tested and probably never can be tested.



Is it incorrect to call it "string THEORY". It should be called "string idea".


This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.
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