02/01/2020

In Folha, the bizarre world of quantum mechanics.

Foto: Coleção particular

Reproduction of Marcelo Viana's column in Folha de S.Paulo.

At the end of the 19th century, it seemed that humanity had discovered all the secrets of the universe. The British physicist Lord Kelvin (1824–1907) stated: “There is nothing more to discover in physics. All that remains is to make ever more precise measurements.”

One thing he tried to measure was the age of the Earth. But his estimate—20 to 40 million years—fell far short of the currently accepted value: 4.5 billion years.

Kelvin erred in not taking into account the role of radioactivity in global warming: radioactivity had not yet been discovered!

Even mathematicians got in on the act. In the famous list of 23 problems that the German David Hilbert (1862–1943) presented to the International Congress of Mathematicians in 1900, the Fridays was "to axiomatize physics".

As if, having discovered all the laws of nature, physics were ready to become a subfield of mathematics.

Ironically, a few decades later the Russian mathematician Vladimir Arnold (1937–2010) would write: “Mathematics is a subfield of physics, one in which experiments are cheap.” This statement remains valid.

The beginning of the 20th century evaporated jingoism, generating two advances that radically changed our perception of the universe: relativity—which revolutionized ideas of space, time, mass, and energy—and quantum mechanics, filled with even more paradoxical conclusions.

19th-century science was based on the principle of determinism: knowing the laws of the universe, and its exact current state, we could predict all future evolution.

The idea of probability would be a mere technical tool to compensate for the fact that we cannot know the exact current state .

Quantum mechanics directly challenged this principle, asserting that the evolution of the universe is fundamentally probabilistic: there is much that we cannot know "simply" because it has not yet been decided.

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