3d? Why not 10D?
Um, OK. Sorry, you guys, I know this is going to be, like, the LEAST fascinating post ever, but, I read something in my "physics update" email tonight that, as usual, by reading it myself, I have to file it in under the "dog watching television" department:
WHY DO WE RESIDE IN A THREE-DIMENSIONAL UNIVERSE? Andreas Karch (University of Washington) and Lisa Randall (Harvard) propose to explain why we live in three dimensions and not some other number.Currently, the popular string theory of matter holds that our universe is actually ten-dimensional, including, first of all, the dimension of time, then the three "large" dimensions we perceive as "space," plus six more dimensions that are difficult to see, perhaps because they are hidden in some way. There is reason to believe, therefore, that our common 3D space is but a portion of some membrane or "brane" within a much more complicated higher-dimensional reality. Specifically, Karch and Randall address themselves to the behavior of three-dimensional force laws, including the force of gravity. Having several dimensions rolled up is one way to explain why gravity if so weak. Another view, pioneered by Randall and Raman Sundrum, holds that if gravity is localized on a 3D defect in the larger multi-dimensional universe and if spacetime is sufficiently warped, then the other spatial dimensions might be large after all. But why is our "local gravity"apparently a 3D defect in a 10D universe? Why not a 4D defect or some other dimensionality? In the present paper, Karch(email@example.com) and Randall show that the cosmic evolution of the 10D universe, involving a steady dilution of matter, results in spacetime being populated chiefly by 3D and 7D branes. Several versions of string theories require the existence of 3D and 7D branes; indeed, the particles that constitute matter---such as quarks and electrons---can be considered open strings with one end planted on a 3D brane and the other end planted on a 7D brane.
OH. So that's it.
OK. So... why am I posting this? Just so you can enjoy the same thrill I felt. And what is that? It's why I like having an FTP sever on my PC. Or a screen saver that resolves protein strings to fight cancer or search for extra-terrestrial life (still waiting for the one that'll locate terrestrial life, but let's not quibble). It's all about the idea that my PC is DOING something while I'm not there, something, presumably, to benefit humanity. And what does 10D space have to do with anything? Well, I suppose-- no, I'd bet you a million dollars-- that these yahoos thinking about and working on all this amazing physics stuff are supported by MY-- er, correction: YOUR-- tax dollars. While 98% of all your tax dollars are going to line the pockets of Bush cronies or fight the war in Iraq, isn't it nice to know that somewhere, a small percentage of it goes to support dreamers-- guys who could REALLY change the world, I mean-- like these guys?