Uncertainty from close

2009/06/01 Roa Zubia, Guillermo - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Fisika

It does not seem serious that one of the foundations of science is uncertainty. But yes. It seems like a disgrace from scientists: instead of solving something difficult to solve, it seems that scientists prefer to say that it is one of the pillars of science. But it is not so. Uncertainty is a characteristic of nature.

It is one of the principles of physics, that is, something broader than a theory. The principle says that man cannot be sure by measuring all the magnitudes associated with a system. It is possible to measure the energy, time, speed, position and many other magnitudes of a physical system. But not all at the same time and with great precision.

It is a principle of physics, but it is difficult to understand, because in that intuition does not help us. How can we not measure the speed of a car and where it is exactly and at the same time?

The truth is that uncertainty is not very evident in the physics of 'big' things; to detect this effect it is necessary to work at microscopic size or, rather, at nanoscopic size. It has to be taken into account by those who work with smaller atoms and particles.

For example, a physicist can determine where an atom is. But as the accuracy of this measure increases, it loses the possibility of saying what the speed of this atom is. And if you try to measure speed, you lose the certainty of the position of the atom.

This is one of the best known examples, but it is not the only one; besides the position-speed pair, there are other pairs of magnitudes. When energy and time are measured simultaneously, precision is lost (or the accuracy of one magnitude is lost for the benefit of the other).

The scientist cannot be sure and the uncertainty is not his, that is, the problem is not that a good technology is missing to make the two measurements accurately. No one will ever invent wonderful devices or methods that solve this measurement problem. Not that. The principle of uncertainty is that by itself all things cannot be measured accurately. It makes no physical sense. It is very rare and, as we have said, it is a principle of physics.

Photo Machine

To understand with intuition we can compare it with the photography of small things. Taking a very close picture of a flower, key, or insect is a similar problem.

The problem is that the rays of light reaching the camera of a very close thing come from very different angles. To photograph an insect you may be about fifteen centimeters from the target. At this distance the lens is very wide compared to the insect, which makes it very difficult to focus the image. The lens conducts the rays into the camera and its focus means concentrating all the rays that come from the same place of the insect at a specific point inside the camera.

For example, if in the end we concentrate the rays that come from the eyes of the insect inside the camera, those that come from the legs of the insect will not concentrate on one point and we will see them without focusing.

This technique is more complex because it works with special targets called macros, and closing the diaphragm of the camera reduces the problem of angles, among others. However, regardless of the technique, width, depth of field, of the focused area is limited and the photographer must choose what will be focused, knowing that the other will not be focused.

To focus one thing it is essential to leave without focusing on everyone else. Like the uncertainty of physics. If laboratory instruments are manipulated to accurately measure a magnitude --to get out focused -, they will not necessarily accurately measure the other magnitudes --they will be left unfocused.

Physicist Werner Heissenberg discovered that he was developing the mathematical basis of quantum mechanics. And since then there have been contrary opinions. Many do not accept that uncertainty is a characteristic of nature. Albert Einstein himself did not accept it. But all the experiments carried out so far have made Heissenberg right. In physics, the measures of many magnitudes represent a loss of focus.