String Theory Says We Have at Least 10 Dimensions, but That's Not the Weirdest Thing About It

physics is weird. As soon as you think you understand it, you find five more
reasons you don't. Take this, for example: the Standard Model of quantum
physics says that everything is made up of elementary particles, including
things like quarks, electrons, and protons. But string theory says nope, not


All of these
different particles? They're just strings, each vibrating in their own way.
That might sound like it adds unnecessary complexity, but it could solve a
problem that has plagued quantum physics for decades.

As you can
see in the chart below, the Standard Model says that there are 12 basic
building blocks to the universe: six quarks, and six leptons. Bundled up with
this are the four fundamental forces: gravity, electromagnetism, and the weak
and strong nuclear forces. Surprisingly, it's the most familiar of these—gravity—that
has scientists the most puzzled. Why?

Well, the
three other forces each arise from the exchange of an elementary particle:
photons impart the attraction of electromagnetism, gluons are the
"glue" that binds the strong nuclear force, and the W and Z bosons
whip the weak nuclear force together. 

Scientists have proposed a particle that
could be responsible for gravity, called the graviton, but we're not sure if it

That's where
string theory comes in. String theory proposes that each elementary particle is
just a different version of a very tiny loop of string. Just like a guitar
string vibrates at different frequencies to create an A or an F#, these strings
oscillate in certain ways to create the different kinds of particles. Oscillate
in one way, and we see an electron; oscillate in some other way, and we may see
a photon or a strange quark. Once you accept that everything is just
oscillating strings, it's pretty simple to accept that there's a kind of
oscillation that creates a graviton. Boom: the mystery of gravitation is
solved, and the four forces of nature are united at last.

Okay, well,
maybe string theory isn't all that simple. For one thing, it requires the
universe to have at least 10 dimensions to work (and some versions require as
many as 26). So how is it we only perceive four dimensions: up-down,
right-left, forward-backward, and time? There are a few explanations.

One is
compactification, or the idea that the other dimensions are folded down in a
way that keeps us from perceiving them. It's kind of like looking at a piece of
paper directly from the side makes you see just a line, even though that paper
has a lot of surface area you aren't seeing. Other theories invoke the
existence of higher-dimensional objects called branes. Unfortunately, all these
possibilities and explanations have yet to come up with that big shiny unifying
theory that physicists are chasing. Still, that won't keep them from trying.