Talk:Superstring theory

Define Variables

Sorry I don't have a degree in physics, but even if I did I would still like my variables to all be defined before you put up an equation, in that way it could actually mean something to someone. It would also be nice for people to put their units of measurement too.

EM and gravity - be concsistent with other articles

excerpt from the article: "...which describes gravitation and applies to large-scale structures (stars, galaxies, super clusters), with quantum mechanics which describes the other three fundamental forces acting on the microscopic scale."

Classical electromagnetism, not just gravity, affects large-scale (macro) structures (according to several Wiki entries: Quantum_Mechanics and Classical_Mechanics, and even Maxwell's Equations {see Electromagnetism, which is also a page that describes electromagnetism as a macro, or Classical, science}: The fact that Maxwell's equations pre-date Quantum Mechanics shows that Electromagnetism was observed on the macro scale, prior to the 20th century when QuantMechs was first explored).

The above quote from this article contradicts those Wiki entries (and my engineering professors) by placing *only* gravity on the macro (Classical) scale, and then placing electromag only on the quantum scale; so can someone edit this? (I have my mind on something else and am not too good with describing concepts in words (instead of schematics or other "pictures" (-: ) even on a good day, so I have a brainfart that precludes me from editing it. (-: )

It's made clear that "large-scale structure refers to astronomical scales, so has a different meaning to "macroscopic structure". On the scale of stars/galaxies etc. objects tend to have approximately zero net charge, so the only relevant force for describing their motion relative to each other is gravity.

Shambolic Entity 04:27, 30 June 2006 (UTC)

There can be more space dimensions

Although some scientists say that there can be upwards of four spacetime dimensions, this is untrue. There can only be more space dimensions. This is proven through simple reasoning. If more time dimensions were to exist, and they were curled up and small like the extra space dimensions, we would circumnavigate the time dimension very quickly, due to its size. This would mean that we would return to a previous instant in time. Obviously, this is beyond our experience and comprehension, so there is no reason to believe we should ever experience it.

"Proven through simple reasoning," huh? Firstly, logicians have recognized two principles which you are trying to violate above when you say (to paraphrase you, not quote you), "There can NOT be a second time dimension": the "not" being "the negative," and you are trying to "prove the negative" [there are exceptions to the rule, but they don't apply to your paragraph above]; also, you are using an Argument from Lack of Imagination. For all 2500 years, or so, that "logic" (the Latin word for "reason") has existed as a formal science, this has been recognized as invalid (fallacious) reasoning. Since logic is a word synonymous with "reason," you cannot prove your statement above "with simple reasoning," you 'proved' it with Sophistry (i.e. a false/invalid proof).

Secondly, if there is a second time dimension, it isn't necessarily subject to the Laws of physics as we know it, since a Law BECOMES a "Law" by being obsevable within the 4 dimensions we have observed, i.e. within the range of telescopes (e.g. Hubble). Who knows what lies inside a Black Hole or beyond the edge of the Universe (i.e. where dark matter/energy are thought to dominate), for example (places we can't observe), and what type(s) of physics occur in those areas? And not even as far away as the above examples, the Second Law of Thermodynamics was shown, about 2 years ago, to be warped (for lack of a better word) slightly over long distances. Just as there are PLACES we haven't visited (nor can even observe yet), there are also TIMES we haven't visited: This is the nature of time itself, that we have not time-traveled to the future, correct? Therefore, a second time dimension also, for example, could be linear like the "time" we experience, not looped as you described; the time we experience could end and another time-dimension could start -- one which subjects the other 3 dimensions to different Laws of physics, for example -- we do not know whether this will occur (because it hasn't occurred yet and we cannot tell the future). Nothing is impossible, and unless you're God (e.g. prescient), something in the future absolutely CAN shock us. It is possible (and here you shine: there indeed is no REASON to believe any of these possibilities; but, OTOH, there's currently no reason to disbelieve them as POSSIBLE), and although as a scientist, I concentrate on what's PROBABLE/observable, not merely "possible," I think your analysis above is a bit...presumptuous and closed-minded when you say "this is proven" (because you proved squat) rather than at the end where you say "this is beyond our comprehension".

String theory is separate from superstring theory

Maveric - I know this much about the topic: String theory and Superstring theory are different enough to be written separately - I just read the "Elegant Universe" which discusses the differences in depth over several chapters. I am, unfortunately, far too ignorant to attempt to explain the difference adeqautely. - User:MMGB

I'll try to explain it soon.

---

String theory is about strings. But strings of what? As an answer to that question, I like to think 'strings of energy'. After all, we know that

1. energy is a fundamental concept in string theory (which makes it a possible answer)
2. dimension is a derived concept in string theory (which nixes it as a possible answer)
3. information is just wrong since strings are continuous while information is discrete

So there's only one possible answer as far as I can see. Plus,

1. energy is distributed on the string's world-sheet. Isn't it?

Can we have some expert explain in comprehensible terms why this is completely wrong?

From my understanding, it's not really a meaningful question. In the

Standard Model we don't ask what electrons are made of, because they're

supposed to be fundamental particles. Likewise, string theory says that

strings are fundamental. Being the fundamental building block means that

there isn't anything for it to be made of. But I could be wrong.

--Stuart Presnell 29/11/2002

Ambiguity

Please clarify the following statement in the article:

Heterotic SO(32) is slightly inaccurate since among the SO(32) Lie groups,

string theory singles out a different Spin(32)/Z2.

Does this mean merely that the name is inaccurate? Inclusion of the words a different has not helped much! --yoyo 12:54, 8 December 2005 (UTC)

The answer may be hard to understand if you don't know a bit about the theory of Lie groups. An overly short article on spin groups does exist, but it may not mean much to people who don't know the subject already. In brief, the group Spin(n) is a "double cover" of SO(n): every point in SO(n) corresponds to two points in Spin(n). So if you start with Spin(32) and create a smaller group by identifying each of those pairs as a single point, you get SO(32).

That process can be described mathematically as "Spin(32)/Z₂" (the Z₂ refers to the operation that switches from one point in each pair to the other). But this notation is imprecise, because there are multiple distinct ways of pairing up the points in Spin(32) to make a smaller group. Only one of these results in SO(32). The statement in the article means that string theory picks out a pairing that doesn't give SO(32).

Now, if you can come up with a way to summarize all that in just a sentence or so, so that it will fit into the article, more power to you! : ) --Steuard 18:40, 8 December 2005 (UTC)

Extra Dimensions

I read with interest the theory that extra spatial dimensions exist. However, this view is at variance with one expressed by Professor Stephen Hawking who remarked that " if there were more that three spatial dimensions, the orbits of planets around the sun or electrons around a nucleus would be unstable and they would tend to spiral inward."

                                       Derek R Crawford.

See an answer here.

I was under the impression that that particular problem had been worked around as of 2005. Is that incorrect?

Personally, I thought that this particular problem had been worked around as of Oskar Klein's work in 1926, or thereabouts. As long as the size of the extra dimensions is small relative to the solar system, planetary orbits will only "see" the gravitational effects of three spatial dimensions. Conversely, there wouldn't be stable gravitational orbits whose radius was smaller than the size of an extra dimension. (And similarly for electromagnetism.)

Very roughly speaking, the gravitational (or electromegnetic) field of a small mass (or charge) expands out evenly in all dimensions at first. But if a dimension is "small", the field will eventually "fill it up" and run out of new space to expand into in that direction. Past that point, the physics of the "large" dimensions is all that is relevant. Hawking's comment (assuming he's the original source) was presumably in the context of more than three "large" spatial dimensions, which would be bad exactly as he describes.--Steuard 19:48, 12 June 2006 (UTC)

How does an hydrogen atom look in superstring theory?

i'm new to all these, and i'm just wondering how an atom, say an hydrogen atom look in superstring theory? in Quantum mechanics, for example, atoms are made up of electrons, protons are further defined into its sub particles and quarks and anti- quarks(?) have been added in the elements composition or "soup of elements".

For the record, this isn't really the place to discuss string theory itself; the talk page is intended for discussions on improving the article itself.

Having said that, my first answer to your question is "really big": the typical size of string vibrations is as much smaller than an atomic nucleus as an atomic nucleus is smaller than us. More to the point, string theory doesn't argue with the model of an atom as a nucleus of quarks (which lump together into nucleons like the proton) orbited by electrons. The string idea is simply that the quarks and the electrons are (when viewed on a very small scale) actually vibrating bits of "string". Different vibrational modes correspond to different particles.--Steuard 19:16, 12 June 2006 (UTC)

Tension of the strings

from the article: The tension of a string (8.9×10⁴² newtons) is about 10⁴¹ times the tension of an average piano string (735 newtons).'

Using the number 10⁴¹ as a comparison of order is less than useful. I, and probably many others, can't really grasp a number that large, especially in relation to piano strings. My suggestion is to change the comparison to something larger, such as the sun. According to the List of solar system objects by mass, the sun weighs in at 2 x 10³⁰ kg. To me, it would be more meaningful if the article instead compared the string's tension to 400 billion Suns (4×10¹¹) on the end of a string -- at least that would emphasize the shear magnitude of the number.

I realize that there are some problems with this (i.e. do we need to specify that it is 400 billion Suns in earth's gravity that we are talking about?), but to a lay person, this is a more approachable comparison.

(as evidence I told a friend about the 10⁴² number without reaction while the 400 billion number got a "jeez!") --22:22, 6 July 2006 (UTC)

The tension of a string (8.9×10⁴² newtons) is about 400 billion (4×10¹¹) times the weight of the Sun.

As it now reads the text confuses mass with force—a stupid mistake for a physics article. Also, I don't see a need for such sensationalist comparisons: an encyclopedia's purpose is to inform, not to evoke "jeez!" reactions. I'll rewrite this.
—Herbee 19:39, 3 January 2007 (UTC)

Soft suggestion from Jean-Pierre Petit, 69, Phd, astrophysicist, France

I put this sketch on september 22. This was cancelled ten minutes later.

Considering the current situation about superstring theory I suggest the creation of a humour section

Criticism

I just deleted a paragrgaph that was critical of super-string theory. I did this because it was incoherent, didn't lay down a logical basis and incorporated diatribe like "if men of science don't...". This though was with a view to a replacement criticism paragraph/section. I feel any appraisal of Super String Theory must comment on the lack of falsifiable predictions made, but I am not eloquent or informed enough to do a commentary any justice. —The preceding unsigned comment was added by 124.101.149.170 (talk) 01:36, 12 March 2007 (UTC).

Plagiarism

Plagiarism

The table of superstring theories is plagiarized from http://superstringtheory.com/basics/basic5.html

Verin 22:49, 8 April 2007 (UTC)

...and that explain the lack of 11th dimension from the table, too :); it was mentioned in the first paragraph for 'extra dimensions'...

Princeton physicists connect string theory with established physics

This seems like major news which should be reported within the article:

...Princeton researchers have found new mathematical evidence that some of string theory's predictions mesh closely with those of a well-respected body of physics called "gauge theory," which has been demonstrated to underlie the interactions among quarks and gluons, the vanishingly small objects that combine to form protons, neutrons and other, more exotic subatomic particles. The discovery, say the physicists, could open up a host of uses for string theory in attacking practical physics problems....

...The team's paper appears in the March 30 issue of the scientific journal Physical Review Letters. Klebanov's co-authors include graduate student Marcus Benna and postdoctoral fellows Sergio Benvenuti and Antonello Scardicchio.

...In the 1970s, physicists posited that when gauge theory loses its power to describe particle behavior as quarks bond together, string theory might be able to step in and handle the job. What string theorists needed was some indication that both theories were headed in the same direction. The lucky break came in 1997 and early 1998 when a precise relation between the two was conjectured in the work of Princeton physicists Alexander Polyakov, Steven Gubser and Klebanov, as well as the Institute for Advanced Study's Juan Maldacena and Edward Witten....

...String theory, for all its mathematical beauty, once again seemed too difficult to test -- until Niklas Beisert, an assistant professor of physics at Princeton, published a paper in late October of last year containing an equation that turned out to be a crucial piece of the puzzle. "Beisert and his collaborators made an inspired guess based on sophisticated notions of gauge theory behavior," said Curtis Callan, the James S. McDonnell Distinguished University Professor of Physics at Princeton. "Their equation allowed Igor and his colleagues to work out the 'transition' between the two regimes. They demonstrated that it exactly matched string theory's predictions at the strong interaction limit....

See these websites [1]

[2]

RK