Читать книгу String Theory For Dummies - Andrew Zimmerman Jones - Страница 93

Physicists believe that the laws of the universe used to be even more symmetric but have gone through a process called spontaneous symmetry breaking, where the symmetry falls apart in the universe we observe.

If everything were perfectly symmetric, the universe would be a very boring place. The slight differences in the universe — the broken symmetries — are what make the natural world so interesting, but when physicists look at the physical laws, they tend to find that the differences are fairly small in comparison to the similarities.

To understand spontaneous symmetry breaking, consider a pencil perfectly balanced on its tip. The pencil is in a state of perfect balance, of equilibrium, but it’s unstable. Any tiny disturbance will cause it to fall over. However, no law of physics says which way the pencil will fall. The situation is perfectly symmetrical because all directions are equal.

As soon as the pencil starts to fall, however, definite laws of physics dictate the direction it will continue to fall. The symmetrical situation spontaneously (and, for all intents and purposes, randomly) begins to collapse into one definite, asymmetrical form. As the system collapses, the other options are no longer available to the system.

The Standard Model of particle physics, as well as string theory (which includes the Standard Model in an appropriate limit), predicts that some properties of the universe were once highly symmetrical but have undergone spontaneous symmetry breaking into the universe we observe now.