Gerardus 't Hooft

Supertheories


Abstract

The Universe appears to be controlled by laws of physics that can be deduced from observation and have consequences that can be derived and understood. The first discoveries concerning these laws date from antiquity, but only in the last few centuries the rate of discoveries accelerated so much that we are now arriving at a picture that is remarkably complete.

Physical phenomena that we experience in our daily lives can be attributed to great precision to laws that are universally valid: the laws of motion are often described by "classical mechanics", in some cases refinements due to "relativistic mechanics" are needed, and in others "quantum mechanics", sometimes both, as in the particles out of which atoms are built.

Then, there are "forces" influencing this motion, which come in several categories: the "weak force", "electro-magnetism", the "strong force", and finally the "gravitational force". These forces only show up in their full complexity when sub-atomic particles collide against one another at tremendous energies, which is why large particle collider machines, tens of kilometres in size, were required to arrive at the present picture.

What is revealed is that the forces known at present originate in sub-atomic structures a thousand times smaller than the sub-atomic particles themselves; these are the smallest structures that presently can be analyzed.

But, underneath that, there must be even smaller features. They will be associated with forces and particles that we do not know about. These forces and particles play no role in our ordinary lives, but they must be responsible for the very nature of the particles and forces that we do observe, which is why we do desire to know about them. These sub-sub-atomic structures must once also have been decisive in the evolution process of the Universe at the very beginning. Futuristic machines of still larger dimensions will be needed for experimental observations of the new expected phenomena. In the mean time, theoreticians speculate about them.

If developments in the past give us any hint, it is that the physical laws controlling the smallest structures will be even more universal, elegant and beautiful than what we have presently. In fact, we have sound reasons to believe that there will be an ultimate limit, a universal law that will not require any further refinements because there is an end to the scale, due to curvature of space and time. To find this law is the ultimate challenge for many physicists.

Will we ever succeed? Some theoreticians claim that they already have it. Their theories started off as "superstring theory", but now evolved in what is called "M-theory". Indeed, these theories appear to be unambiguous, universal and complete. Not only do they determine the ultimate Laws of Nature, they also address the shape and the history of the entire Universe. But some of us have doubts. Quite a few embarrassing difficulties are still standing in our way, and as long as that is the case, the discussions continue.


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