String Theory

[Ufology_Exobiology]

The physical idea is utterly simple. Instead of many types of elementary point-like particles, we postulate that in nature there is a single variety of string-like object. The string is not ``made up of anything'', rather, it is basic and other things are made up of it. As with musical strings, this basic string can vibrate, and each vibrational mode can be viewed as a point-like elementary particle, just as the modes of a musical string are perceived as distinct notes!

Thus string theory certainly is a model of elementary particles. The great surprise is that mathematical equations describing strings are highly constrained by consistency. In some sense, most of the equations we would think of writing down turn out to be inconsistent, only a few appear to be allowed. Indeed, it looks most likely that (unlike particle theories) there is only one unique string theory! If so, what does it predict, and is it the promised unified theory?

Surprises from Strings.

Researchers studying the equations of string theory soon discovered a wealth of surprises. First of all, among the particles arising as vibrations of the string, we find some which are very similar to electrons, muons, neutrinos and quarks -- the known matter particles. There are others similar to photons, W and Z bosons and gluons -- the known force carriers. And there is one particle similar to the graviton, the elusive fourth force carrier.

Now since the structure of the theory is unique, we can work out (not postulate) what are the types of interaction between these particles. Astonishingly, at low energies the interactions are precisely of the type appearing in the Standard Model, and as a welcome bonus, we also get the gravitational interaction that Einstein originally discovered. So string theory predicts, roughly speaking, the right types of particles and the right types of interactions among them. The famous mathematical inconsistency -- which for decades made it impossible to incorporate quantum gravity in a theory along with the other interactions -- is conspicuous by its absence in string theory. It is almost as if gravity needs strings in order to exist!

More Surprises, and Some Hopes.

Besides these surprises, there are many others that we have stumbled upon in the last decade. In string theory, the fact that there are three space dimensions in our world might also be predicted rather than assumed. The dimension of ``space-time'' is variable in string theory, in the sense that we have to understand and solve string equations to determine it. This has not been done yet, because of the great complexity of the theory. If the answer comes out to be four (three space and one time) then we would have ``explained'' one of the most deep and abiding mysteries since the dawn of civilization: why does our world have the dimensionality that it has? If the answer is something else then string theory may be the wrong theory of nature, though we may still learn something about the right theory. Only successful comparison with experiment can give us convincing proof that string theory is correct.

[Buffy]

Are you Sunhil Mukhi? Otherwise you should have referenced him as this entire piece is lifted directly from his page on the topic.

Please respond to this or we will be required to remove this post.

Thanks,
Buffy

[Ufology_Exobiology]

Originally Posted by Buffy

Are you Sunhil Mukhi? Otherwise you should have referenced him as this entire piece is lifted directly from his page on the topic.

Please respond to this or we will be required to remove this post.

Thanks,
Buffy

The pervious compostion is by Sunhil Mukhi.

I apologize for my error.

[InfiniteNow]

Also, that paper was last edited in 2000, now 7 years ago. Many changes have been made since then, as well as a move away from ST into brane theory. The sense is generally that ST is not living up to its promise and offers no testable hypotheses.

Here’s a nifty debate between Brian Greene and Lee Smolin which I enjoyed, and others may as well:

NPR : Physicists Debate the Merits of String Theory


IMO, as it stands right now, this is not a theory bringing us greater understanding.