Advertisement

String theory arrived
in the public field in 1988 when a BBC radio series Desperately Seeking
Superstrings was aired. Thanks to good marketing and its naturally curious name
and characteristics, it is now part of popular discourse, mentioned in TV’s Big
Bang Theory, Woody Allen stories, and countless science documentaries.

But what is string
theory and why does it find itself covered in controversy?

##
__Life, the universe
and the theory of everything:__

__Life, the universe and the theory of everything:__

Today we think of
string theory in two ways. It’s understood as a theory of everything – that is,
a theory that purposes to explain all four forces of nature within a single hypothetical
scheme.

These forces are:

- Electromagnetic force
- Gravitational force
- Weak nuclear force
- Strong nuclear force.

Electromagnetism
and gravity are acquainted to most people. The nuclear forces happen at a
subatomic level, and are invisible to the naked eye. String theory is also utilized
to explain quantum gravity, a theory that joins Einstein’s theory of gravity
and the principles of quantum theory.

##
__Tangled
beginnings:__

__Tangled beginnings:__

But string theory started
life more humbly, as a way to define strongly interacting particles called
hadrons. Hadrons are now known to be made of quarks linked with gluons but
string theory observed them as quarks joined by strings (tubes of energy).

Understood this
way, string theory buckled under both new experimental proof (leading to the highest
of quantum chromodynamics which describes the connections of quarks and gluons)
and also internal problems. String theory involved too many particles, as well
as a massless particle with so-called spin 2 – spin being the name used for the
angular momentum of particles. As it occurs, this is precisely the property
possessed by the graviton – the transporter of gravitational force in the
particle physics picture of the world.

##
__Beyond four
dimensions:__

__Beyond four dimensions:__

This finding meant
that with a bit of skilful rebranding (and rescaling the energy of the strings
to contest the strength of gravitation), string theory shed its hadronic past
and was born-again as a quantum theory of gravity. All those other particles
that were also difficult for the original string theory were capable of
capturing the remaining non-gravitational forces too. This is how string theory
took on its present role as describing all four forces together: a theory of
everything.

But it could not
shed many of its curious features. One such feature was the need of many more
space-time dimensions than are really seen.

In a “bosonic” form
of string theory (i.e. without matter or fermions, there would have to be 21
dimensions – 20 space dimensions and one time dimension. In a theory with
fermions, there would have to be nine space dimensions and one temporal, ten
dimensions all together. The problem is that we only observe four dimensions:
height, width, depth (all spatial) and time (temporal).

##
__Supersizing symmetry,
downsizing dimensions:__

__Supersizing symmetry, downsizing dimensions:__

The “super” in
“superstring theory” refers to symmetry, known as supersymmetry, connecting bosons
and fermions. There are five probable theories that include matter in ten
dimensions. This was formerly taken as a problem since it was projected that a
theory of everything should be unique. The six hidden dimensions (ten minus the
four dimensions of everyday life) are made too small to be seen, using a
process known as compactification.

##
__Beautiful Maths:__

__Beautiful Maths:__

It is from this
process that much of the extremely beautiful (and cruelly difficult)
mathematics involved in string theory stems. We have no problem thinking of
each occasion in the world as labelled by four numbers or coordinates (e.g.,
x,y,z,t). A string-theoretic world adds another six coordinates, only they are wrinkled
into a tiny space of radius related to the string length, so we do not see
them.

But, according to
string theory, their influence can be observed indirectly by the way strings
moving through spacetime will wrap around those crumpled, curled up directions.
There are very many ways of concealing those six dimensions, yielding more probable
stringy worlds (possibly as many as 10500!).

##
__How long is a
piece of string?__

__How long is a piece of string?__

This is why string
theory is so controversial. It apparently loses all predictive power since we
have no way of separating our world between this plenitude. And what good is a
scientific theory if it cannot make predictions?

One response is to
say that these numerous theories are not in fact so different. In fact there
are all sorts of strict relations known as dualities connecting them. More current
progresses based on these dualities include a new type of object with higher dimensions
– so called Dp-branes. These too can wrap around the dense dimensions to make possibly
visible effects.

Most outstandingly,
they can also deliver boundaries on which endpoints of strings sit. Just to confuse
things more, a new kind of theory has been found, this time in 11 dimensions:
11 dimensional supergravity - it is also very attractive mathematically.

##
__Dial M for
Multiverse:__

__Dial M for Multiverse:__

String theorists
are fond of saying that these six theories are features (special limits) of a
deeper fundamental theory, known as M-theory. In this way, individuality is
restored.

Or is it?

We still have the
spectre of the 10500 solutions or worlds. The great hope is that the numeral solutions
with features like our own world’s (with its four noticeable dimensions,
particles of numerous types interacting with particular strengths, conscious
observers, and so on) will be small enough to be capable of extracting testable
predictions.

So far, though,
the only actual way of getting our world out of the theory includes the use of
a multiverse (a realistically interpreted ensemble of string theoretic worlds
with differing physical properties) joint with the anthropic principle (only
some of these worlds have what it takes to support humans).

Unnecessary to
say, this does not completely sit easy with critics of string theory!

But string theory
has been making strides in other areas of physics, remarkably in the physics of
plasmas and of superconductors. Whether this success can be repeated within its
proper realm (fundamental physics) remains to be seen.

## Post A Comment:

## 0 comments: