String Theory
The Multiverse Solution
Horizon - small Universe
On our journey to find the smallest thing in the universe, things have indeed become deeply strange. We have dived down a rabbit hole into a bizarre
wonderland where extra dimensions may lie curled and hidden from our view. But that's just the beginning of the weirdness. As you look even smaller, beyond
even the reach of the Large Hadron Collider, we have to rely on theory alone.
Michael Green
Professor Michael Green is a founding father of one of the strangest theories in physics. A theory that tells us that the universe is made of
strings. String theory starts off simply enough, but it leads to some mind-boggling conclusions.
Michael Green "The fundamental particles, instead of being point-like objects are now thought of as being string-like objects."
Instead of the 17 particles in the standard model, everything is made from a single object – an incredibly tiny loop of string.
Michael Green "The characteristic feature of a string, which makes it different from a point is that it can vibrate and the different modes of
vibration, the different notes, if you like, are seen as different kinds of particles. So there's this very appealing, almost poetic way in which
string theory describes all the particles in terms of different notes on a string. It's like the music of the spheres almost."
String Loops
It's a beautifully neat idea. Each note from the vibrating string produces a different particle. There are, however, one or two problems. These
strings are so small that no-one has ever seen anything remotely stringy.
Michael Green "Depending on one's viewpoint, the size of these strings can vary an awful lot, from scales, which are sort of a millionth of a
millionth of the size of a nucleus to scales, which are much, much smaller than that."
If string theory turned out to be true, then a string would be the smallest thing in the universe. The trouble is, once we get this small,
the whole notion of small and big may get turned completely upside down.
Universe Seed
Universe Expanded
Michael Green "Supposing these are quarks and electrons, photons, the particles that constitute the standard model. Now we've got a problem because
if you believe that they're made of something smaller, that's fine. You will find something smaller inside. But if you believe a theory like string
theory, then the notion of smallness no longer means the same. But then of course when you're down to this scale, you may have the whole universe in
your hand, because the, the universe itself started from something this scale and expanded into everything we know. So this thing, which you think
is the smallest constituent, may in fact be the thing that contains all of us. So the notion, the difference between… the notion that this is the
smallest constituent is paradoxically not at odds with the statement that it may also be the whole universe."
String theory is underpinned by some fiendishly complex maths. But to make it work out, the theory invokes not just one new dimension, but
says that we live in 11 dimensional hyperspace. If you could describe exactly how these extra dimensions are curled up, you'd be able to describe
the exact nature of everything in the universe.
The trouble is, there's more than one way to curl them up.
Michael Green "So the equations of string theory of very large numbers of solutions, a humungously large number, any one of which might
describe a possible universe with its own laws of physics, its own kinds of particles and its own kinds of forces. This whole body of solutions
of string theory has been called the landscape string theory."
Each peak in the landscape represents a different solution – a different possible universe. With each one just as likely to exist as the next.
Cable Car
Michael Green "Most of these solutions would describe universes which are completely absurd. The typical ones would be the ones, which came
into being and either ceased to exist after a very, very short time or exploded in such a way that matter exploded apart and never formed
galaxies in the first place. The fact that our universe has existed for long enough for the galaxies to form and evolve and planets to form
and for life to form and us to exist tells us that we are living in a very untypical universe."
If they could find the right solution – the right one out of 1 followed by 500 zeros, we'd have a neat explanation for everything in the universe.
Michael Green "So the fascinating thing is the multiverse idea has been around for some time in astrophysics, but they didn't have a
theoretical way of understanding it. And then along came string theory and then the two got wedded."
Whichever way you look – whether up to the largest scale or down to the very smallest, our universe may not be alone. But for now, string
theory remains a theory, with no experimental evidence for any of its mind-boggling predictions.
