Questions about string theory's extra dimensions.

[tgoolsby2]

They say that these extra dimensions are so small that we don't experience them. So what is the dividing line (in terms of size) between what makes a particle stop interacting with the extra dimensions; in other terms, how much smaller is a string than a quark? Can anyone put that into perspective? What would that look like?

I was wondering how big the strings are because I wanted to know if they are smaller than the Plank Length. If they are then would that mean that the extra dimensions can only exist for lengths less than the Plank Length?

[Cougar]

So what is the dividing line...

Detectability.

[John Jaksich]

Detectability.

To
tgoolsby2 :
I agree---as with any mathematically involved theory---this one is so thick with proofs, that many people are dismayed by the fact that it has been no real apps yet---

I don't really know your background---but check out the two following websites for opposing views by two prominent theoreticians:

in the next post---

[John Jaksich]

Interview at Caltech:

Dr. Edward Witten

http://www.superstringtheory.com/people/witten.html

[John Jaksich]

The other leading opponent is Dr. Lee Smollen---

I, currently, don't have a website for lectures---

but here is the Wikipedia linK

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

[Cougar]

The other leading opponent is Dr. Lee Smollen...

I'm not sure that Smolin deserves to be even in the same thread as Witten. From wiki:

Witten is a leading researcher in superstring theory, a theory of quantum gravity, supersymmetric quantum field theories and other areas of mathematical physics. He is regarded by some of his peers as one of the greatest living physicists, perhaps even a successor to Albert Einstein.

He has also made seminal contributions in mathematics and helped bridge gaps between fundamental physics and various areas of mathematics. In 1990 he was awarded a Fields Medal by the International Union of Mathematics, which is the highest honor in mathematics and often regarded as the Nobel Prize equivalent for mathematics. He is the only physicist to have received this honor.

On the other hand....

"Almost all of the reviews of [Smolin's] book by the theoretical physics community have been very negative."

[WayneFrancis]

They say that these extra dimensions are so small that we don't experience them. So what is the dividing line (in terms of size) between what makes a particle stop interacting with the extra dimensions; in other terms, how much smaller is a string than a quark? Can anyone put that into perspective? What would that look like?

I was wondering how big the strings are because I wanted to know if they are smaller than the Plank Length. If they are then would that mean that the extra dimensions can only exist for lengths less than the Plank Length?

From my understanding the dimensions are equal to the planck length which is why movement in those dimensions doesn't matter. Nothing to our knowledge would ever be able to probe movement of even close to the planck length. .

[John Jaksich]

I'm not sure that Smolin deserves to be even in the same thread as Witten. From wiki:

Witten is a leading researcher in superstring theory, a theory of quantum gravity, supersymmetric quantum field theories and other areas of mathematical physics. He is regarded by some of his peers as one of the greatest living physicists, perhaps even a successor to Albert Einstein.

He has also made seminal contributions in mathematics and helped bridge gaps between fundamental physics and various areas of mathematics. In 1990 he was awarded a Fields Medal by the International Union of Mathematics, which is the highest honor in mathematics and often regarded as the Nobel Prize equivalent for mathematics. He is the only physicist to have received this honor.

On the other hand....

"Almost all of the reviews of [Smolin's] book by the theoretical physics community have been very negative."

I don't necessarily disagree with your point ---but it is normally instructive for some dissent

[Cougar]

I don't necessarily disagree with your point ---but it is normally instructive for some dissent

Yes, and there is some dissent. Peter Woit's view was certainly one of dissent: Not Even Wrong, the failure of string theory and the search for unity in physical law (2006). Other than at the end when he "went Arp"*, at least he gives a fair introduction to some of the math going on in the higher reaches of today's physics. Better than Smolin.

Then for something completely different, there's Nobelist Robert B. Laughlin with his view of A Different Universe: Reinventing Physics from the Bottom Down (2005), followed by Nobelist Frank Wilczek describing The Lightness of Being, Mass, ether, and the unification of forces (2008). Eye openers.

_____________________
* The old Seeing Red funding complaint.

[EigenState]

Greetings,

The following page at the Perimeter Institute for Theoretical Physics might prove useful regarding the question initially posed: Superstring Theory. Approximately half way down the page there is a subsection entitled Where are the Extra Dimensions? which discusses the possibilities of both small and large extra dimensions.

Best regards,
EigenState

[trinitree88]

And in all fairness, there remains as yet no viable experimental test for string theory after 25 years. It has certainly produced mathematical advances by its' proponents and has occupied an immense presence in theoretical physics, but in the real world the proof is in the pudding....the experiment that confirms or denies the prediction. Here, string theory fails.

Wilcek has managed to account for the great majority of the mass of the proton using Standard Model-based QCD.

So to the original post, there is as yet no viable affirmation of hidden dimensions all rolled up in either branes or strings, even though the theory has as many as 10⁵⁰⁰ viable solutions.
That means Minkowski spacetime still looks pretty good. pete