Four Fundamental Forces
As the inflaton field decayed it produced the four fundamental forces we find in the world today. I will examine them each in turn.
Perhaps the first force to become manifest in the young Universe was the weakest of all four forces: the force of gravity. Gravity is a force of attraction between every of matter in the Universe and every other particle.
Yet, despite its weakness, it is the only force that we humans are familiar with in our everyday lives. It is the force which holds us on to the Earth. Without it none of this story would have been possible.
Gravity holds us on the Earth
So why can we feel gravity when we cannot detect the other, stronger forces which we will see soon?
Because the other three are either very short range, much smaller than a human being, or their attractions cancel out their repulsions. Gravity, on the other hand, is a long-range force and it never cancels itself out. There is no negative gravity in the Universe today (although there probably was negative gravity in the very young Universe, producing the process of inflation).
And there is another very important difference between gravity and the other three fundamental forces. The laws which govern gravity, expressed by Einstein’s theory of General Relativity, are completely different and incompatible from the laws of quantum mechanics which govern the three stronger forces.
Many scientists are sure that this is because we are lacking an even more fundamental theory, one which will eventually unite both of these theories into a single idea. The so-called “Theory of Everything”. Scientists hope that it will be discovered one day, but at present this seems a long way off.
Happily, the effect of gravity is negligible at the scale of particles. So quantum mechanics still works well despite its inability to describe gravity.
One possible way to reconcile relativity with quantum mechanics is string theory. This is the idea that particles are actually made of short lines in space which vibrate. They are called strings. The way they vibrate determines what kind of particle they are. In order to explain how strings work, the theory predicts that there are about 11 extra dimensions of spacetime, curled up very small. The mathematical basis of string theory is very complex and so far it has failed to make any predictions, but some people think it will eventually produce the hoped-for theory of everything.
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