# More at 10 attometers
### Strings and Supersymmetry
There is some pretty heady stuff going on in physics these days. In
universities around the world, scores of physicists and mathematicians
are working on unifying the large and the small into one grand, all-encompassing,
theory of everything. The concept is called string theory.
For the past 70 years or so, two theories have dominated physics --
general relativity and quantum mechanics. They have dominated because
they work so well at describing the universe as it is. Both make predictions
about the universe that have proved to be true as accurately as anyone
can measure. General relativity describes the universe at the largest
scales. Quantum mechanics describes the universe at the smallest scales.
However, there is one inescapable reality: The two theories are mutually
incompatible and cannot both be true as currently formulated.
For most objects in the universe, one can accurately use one theory
while ignoring the effects of the other -- until one considers objects
that combine the extremes of tremendous mass compressed into incredibly
small volume. For black holes and the big bang, both quantum mechanics
and general relativity apply -- and the answers don't make sense.
### Enter string theory
The theory and equations of general relativity assume that particles
can be considered true points -- that there is no limit to the minimum
size of matter (electrons, quarks) or force (photons, gluons) particles.
This assumption creates problems when attempting to solve problems involving
large mass in a small volume. One gets infinite densities, infinite
pressures, and infinite temperatures. Essentially the equations return
answers that can't be interpreted.
String theory puts a lower limit on the size of particles. In string theory,
particles are one dimensional, vibrating strings with a minimum size of
a planck length, or 10^{-35} meters. When considered in this way,
the combined equations from quantum mechanics and general relativity produce
answers that have changed the way physicists think about the universe.
Kevin Green has written an excellent book on string theory called The
Theory of Strings.
*Copyright © 2016 by Bruce Bryson* |