David M. Brown's Blog

September 16, 2009

What are the “dimensions” posited in string theory?

Filed under: Science — davidmbrowndotcom @ 6:51 am
Tags: , ,

I’m not sure I understand even what it means to have four dimensions, but I gather it has to do with space+time. What would it mean to posit 26 or 4+n dimensions? What is the definition of a dimension here? I understand what it means in science fiction. It’s the alternate reality that somehow exists alongside our own and where the evil Captain Kirk and other wonders live. But I assume that this is not what physicists mean by a dimension. From a Wikipedia science article (like many of its science articles, full of passages helpfully unintelligible to the layman):

String theory builds on the notion that the “universe is wiggly” and hypothesizes that matter and energy are composed of tiny vibrating strings of various types, most of which are embedded in dimensions that exist only on a scale no larger than the Planck length. Hence N=3 and T=1 do not characterize string theory, which embeds vibrating strings in coordinate grids having 10, even 26, dimensions.

My question was occasioned by an article in Science News published a few years back, but which recently came to my notice, reporting on skepticism about string theory.

I can explain string theory to you. String theory is a theory of physics purporting to integrate quantum mechanics and relativity which builds on the notion that the “universe is wiggly” and hypothesizes that matter and energy are composed of tiny vibrating strings of various types, most of which are embedded in dimensions that exist only on a scale no larger than the Planck length. Hence N=3 and T=1 do not characterize string theory, which embeds vibrating strings in coordinate grids having 10, even 26, dimensions.

According to the criticism related in the SN piece, the only problem with string theory is that after decades of labor attempting to scrounge up evidence for the theory, none whatever has been produced. Moreover, it is so unintelligible that the only way anybody can explain it is by plagiarizing other non-explanations of it.

Now, at this point, I am sure you will be wanting to ask what a “coordinate grid having 10, even 26, dimensions” might look like, even hypothetically, or, as it were, imaginatively. This is very easy to sketch out. First, descend to the level of quanta…

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