Posts Tagged string theory


Posted by on Wednesday, 1 June, 2011


I try to keep my writing reasonably lively so as to keep my readers awake. This time, however, you’re kinda on your own to keep your head off the pillow. Sorry. My blog, my (sometimes deadly dull) topics.


Dr. Brian Greene:

The Elegant Universe is my favorite book. It describes string theory. My copy’s old and I don’t “get” it all. But each time I read it, I learn something.

Readers of my blog should be as lucky.

Here’s what bothers me, Brian Greene. You say strings are one dimensional . Most of them are so tiny (.000000000000000000000000000000000001 meters) that they’re as small as anything can get – the “Planck length”. Nothing physical gets to be smaller than the Planck length.  Not everyone’s on board with the idea that space is “granular” (things have a minimum size) but it’s gaining acceptance.

Anyway, I’m kinda stumped. I’m a three dimensional guy in a multidimensional world. Strings don’t have width. Or depth. They have a volume of zero, right?  Nothing to grab on to. More like thought experiments. Vibrate them in the right modes, and they “real up”, each becoming a particle or a force. One of these strings accounts for each particle in the universe.

But how does a one dimensional string trick itself out with additional dimensions? Is  it the “moving around” thing?  And aren’t strings long in one dimension and skinny in the others? Isn’t that the idea behind calling them strings? Except they don’t HAVE other dimensions. And if they DID have such things, they wouldn’t be any smaller than the Planck length, right? So a “string” would be a cube?

My poor head!

Another thing. Strings, you say, are being pulled apart by a tension force of 1,000,000,000,000,000,000,000,000,000,000,000,000,000  tons. As a former structural engineer,  I worry about them breaking.

So, dividing 1,000,000,000,000,000,000,000,000,000,000,000,000,000 tons of force by the non existent cross section of a string, I arrive at something more-or-less like an infinite tensile stress.

This is bad.

In The Elegant Universe, you emphasize the superior nature of string theory over the prevailing “Standard Model” of physics which,  you say, suffers from too many infinities (like when the denominator of a fraction is zero?) I realize that strings, which are saved from being infinitely small by the Planck length, are also saved from “midriff bulge” (thickness across the middle) by their one dimensional nature. Maybe this vaccinates them against having to worry about internal stresses. But there’s still a big-force, small-object thing going on here that’s a little confusing, okay?

Elegant Universe

I do think I’ve answered one of my own questions which is how this tension force manages to maintain itself. After all, why doesn’t the string just  shrink till it doesn’t HAVE to shrink anymore, relieving its own internal tension?  It’s not like it’s tied to anything.  However, the string seems to be “Plancked out”. It can’t get smaller than that stupid Planck limit.

What a world!

Strings are distinguished from one another (I gather) by their modes of vibration and the way they wrap (open or closed). Except that 1,000,000,000,000,000,000,000,000,000,000,000,000,000 tons isn’t a small  force. It’s what  a rock  with mass equivalent to  hundreds of billions of stars  would weigh here on earth. Those pictures in your book of strings wrapped around things? Or vibrating, away in different “modes”? How do they stay so curvy with that kind of tension trying to snap them straight?

All I’ve got. And thanks for your patience,

MISTER ScienceAintSoBad


Credit, once again, to xkcd, it’s fine and funny drawings (top).
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