TWO mysteries – what makes up the universe, and how did it come into existence – have driven scientific inquiry since the dawn of civilization. Within the last 20 years or so, those mysteries have been, if not exactly resolved, at least placed in a context where their solution is inevitable.
As far as where the universe came from, it is generally accepted that it began as a zero-dimensional point of infinite mass and energy, which began expanding (13.799±0.021)×109 years ago in what is referred to somewhat misleadingly as the “Big Bang.” While it might be intellectually amusing to consider where the seed of the universe came from, it is probably also futile; we have no frame of reference from which we can consider it externally, and thus, as Hawking and Mlodinow put it in their 2010 book The Grand Design, “…it would make no sense to create a model that encompasses time before the big bang, because what existed then would have no observable consequences for the present, and so we might as well stick with the idea that the big bang was the creation of the world.”
What the universe is made of has been a little harder to pin down, but science seems to have finally gotten itself on the right track to figuring it out with something called M-Theory, which was introduced to the world in 1995 by a physicist named Edward Witten.
At this point I should offer a disclaimer that what follows will likely make any real physicist reading it cringe at its simplicity, but the beauty of nature is that the horribly complex concepts we use to describe it actually can be distilled to simple terms normal humans (a large subset of our species that even some physicists would agree doesn’t include them) can understand.
If our understanding of nature is correct, the science we use to describe it should be consistent at any scale, from the very smallest particles that make up everything in the universe to the universe itself as a single object. The biggest problem in physics is that our science doesn’t do that, yet.
We know that everything in our four-dimensional universe (three dimensions of space and one of time, all bound up in one medium we call spacetime) interacts through four fundamental forces: The strong force, which is responsible for holding atoms together; the weak force, which is responsible for radioactive decay; electromagnetism, which is responsible for, among other things, my ability to sit at a computer and type this and your ability to read it on the device of your choice; and gravity, which holds everything together in the nice, orderly way we perceive when we step outside and look up at the stars at night, or pour a cup of coffee with the certainty the liquid will stay there until we do something with it.
Quantum mechanics, which, when combined with Einstein’s special theory of relativity, becomes relativistic quantum field theory, describes the action and relationships of three of the four forces, but ignores gravity. Gravity is a bit weird when compared to the other three fundamental forces; it is extremely weak, but works over extremely large distances. Einstein’s general theory of relativity – the application of his special theory to Newton’s theory of gravitation – describes gravity very well on a cosmic scale. A theory that would connect all the forces together would close that big gap and give us a Theory of Everything, one set of rules that describes our entire reality. Witten’s M-Theory (only Witten knows what “M” means – others have suggested it might mean “magic,” “mother,” “membrane,” “muffin,” “matrix,” “mystery,” or maybe “Mets”) might be that Theory of Everything, but more likely is just a solid step in that direction.
M-Theory is an evolution of string theory, which established that elementary particles are not “particles” at all, but small, one-dimensional strings that differentiate themselves into the different kinds of particles by their form (whether or not they are strings or little loops) and the way in which they vibrate. String theory answered a couple of big questions: First of all, it provided an answer to the question, “What are fundamental particles made of?” and most importantly, it provided a potential solution to the problem of including gravity in the Standard Model of particle physics. In the Standard Model, particles can interact at zero distance, but gravity cannot – the math that should describe the graviton, the theoretical particle that transmits gravitational force, becomes a complete mess. If the particle is actually a vibrating string, there is a small distance between the particles, and the graviton works.
String theory was gradually refined into superstring theory, which resolved some problems by establishing that every particle (fermions, which transmit matter, and bosons, which transmit force) has a massive partner of the opposite type – in other words every fermion has a complementary boson, and vice versa. The only problem was, there were five superstring theories, all somewhat incomplete, but as far as anyone could tell, all equally valid despite expanding the realm of quantum physics into 10 dimensions – the four we know, plus 6 more dimensions of space.
By adding one extra dimension and including a previously abandoned idea called 11D Supergravity (the “D” is for “dimensions”), Witten found a way to show that all five theories were simply different ways of looking at the same thing; they were in effect just special cases of one unifying theory – a practical, although extremely complex, example of overlapping, valid world-pictures in Hawking’s and Mlodinow’s model-based realism.
M-Theory has its critics, and even its proponents acknowledge that large parts of it are, as they say, topics for further study – for one thing, it is far more complex than most scientists, philosophers, or philosophical scientists think a good theory should be. But so far, no one has been able to definitively dismiss it, nor string theory in general, which has been evolving for close to half a century at this point. Whether M-Theory has got the mechanics quite right or not is something the “further study” of several thousand physicists will determine, but for whatever comfort the knowledge might bring, we can say with a fair degree of confidence that everything that exists – us, our world, the stars, the very fabric of the universe – is nothing more, or less, than a collection of little wiggly bits of string, arranged and interacting among themselves in ways we are quickly coming to understand, which leaves us with just one really bothersome question:
What’s a string?