# What keeps strings in their proper “shape” despite their enormous inherent tension?

Here is an extract from a great answer by Luboš Motl to this question: Tension in Strings

Because the string tension is not far from the Planck tension - one Planck energy per one Planck length 10$^{52}$ Newtons or so - it is enough to shrink the string almost immediately to the shortest possible distance whenever it is possible. Unlike the piano strings, strings in string theory have a variable proper length.

Now to balance the level of knowledge, I would like to ask a few extremely naive questions, (and please bear with me as I am trying to transition from pop sci books to Physics for Grown Ups.)

I am not sure what shape means on this scale, and with the extra dimensions included, I am even less sure. It could be that we are working in a completely abstract space.

However, IF the shape is important and if the string is under the huge tension described above, how is the shape maintained?

Somewhere or other, I read it is by the action of quantum fluctuations. I realise the phrase quantum fluctuations is often a byword for misunderstandings, so I read Matt Strassler's Blog first.

Compactification can be used to construct models in which spacetime is effectively four-dimensional. However, not every way of compactifying the extra dimensions produces a model with the right properties to describe nature. In a viable model of particle physics, the compact extra dimensions must be shaped like a Calabi–Yau manifold. A Calabi–Yau manifold is a special space which is typically taken to be six-dimensional in applications to string theory.

• I'm very interested to see what answers come up. +1 – heather Jul 25 '16 at 14:17
• Caveat: any answer to this question would be partially wrong if it did not at least mention that for the most part we don't know the answer to this question. We can't even prove string theory, much less know how physics would work at this scale. If quantum mechanics is any indication, it certainly would not work not as we would expect. – Neil Jul 25 '16 at 14:30
• @Neil understood, I have read Woit and Smolin but obviously I have not got enough background to judge. – user108787 Jul 25 '16 at 14:33