We have seen in previous episodes the grand scientific quest to come up with a single unifying theory of everything, as well as the repeated historical failures to achieve this goal, from Newton to Einstein to quantum mechanics. One of the major obstacles to explain has been not only the relationship between gravity and the other three fundamental forces but the very nature of gravity, that force with which we are so familiar, but whose nature we do not yet understand in any meaningful sense. Then we saw that string theory provided an elegant mathematical model theoretically capable of unifying relativity and quantum mechanics, the very large with the very small. The problem, however, was that as elegant as string theory is, the fact that there are various versions of it, each incompatible with one another, implies that at most only one of them can be true. If they all produce the same observational consequences, however, then how can we tell which, if any, is the right theory of the universe?

This is where the genius of Edward Witten comes in. In a conference on string theory years ago, Witten revolutionized the intellectual world and showed mathematically how all the different, seemingly incompatible versions of string theory can actually be embedded in a grander unifying theory, now called M Theory. As beautiful as the mathematics of the theory are, the only problem left to solve is to show empirical evidence for this theory. This would not be such a big deal if some of these 'empirical' consequences were not things like multiple dimensions, parallel universes, worm-holes and quantum membranes, consequences mathematically entailed by the theory, but which may seem impossible to ever observe, perhaps even in principle.

Of course, if M Theory can't be confirmed or refuted empirically, that is, if it can't be falsified through observation, can it be considered a scientific theory or just beautiful mathematics and metaphysics?

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