Today's Google Logo: Schrödinger's cat

Today's Google homepage features strange equations and a cat. Do you know who it is commemorating? If you have some knowledge of physics, you should be able to guess. Yes, today's Google Doodle is in honor of the 126th anniversary of the birth of theoretical physicist and quantum mechanics pioneer Erwin Schrödinger. Even if you are not interested in physics at all, you have probably heard of Schrödinger's Cat.

Erwin Schrödinger (August 12, 1887 – January 4, 1961), full name Erwin Rudolf Josef Alexander Schrödinger, was born in Vienna, Austria. He was an Austrian theoretical physicist and one of the founders of quantum mechanics. In 1926, he proposed the Schrödinger equation, laying a solid foundation for quantum mechanics. He devised the thought experiment of Schrödinger's Cat to demonstrate the incompleteness of quantum mechanics under macroscopic conditions.

In 1933, because of the "discovery of new forms that are very useful in atomic theory" (i.e., the fundamental equations of quantum mechanics—the Schrödinger equation and the Dirac equation), Schrödinger shared the Nobel Prize in Physics with British physicist Paul Dirac.

In 1926, he proposed the famous Schrödinger equation, which laid a solid foundation for quantum mechanics. This proposal came shortly after Werner Heisenberg's matrix mechanics theory. The Schrödinger equation is still considered an absolute standard, using differential equations, the universal language of physics. This made Schrödinger instantly famous, and he also proved that his wave mechanics were mathematically equivalent to Heisenberg and Born's matrix mechanics in the same year.

In 1937, Schrödinger was awarded the Max Planck Medal.

In 1944, Schrödinger published "What is Life?", where he introduced the concept of negative entropy (Negentropie). He developed molecular biology by describing biological topics in the language of physics. He also published many popular science papers, which remain the best guides to the worlds of general relativity and statistical mechanics.

His most famous thought experiment is "Schrödinger's Cat," also known as "Schrödinger's Cat," which is an ideal experiment about quantum theory. The concept of Schrödinger's Cat was proposed to resolve the grandmother paradox brought about by Einstein's theory of relativity, i.e., the theory of parallel universes.

Place a cat inside an opaque box, then connect this box to an experimental device containing a radioactive nucleus and a container of toxic gas. Imagine that this radioactive nucleus has a 50% chance of decaying within an hour. If decay occurs, it will emit a particle, and this emitted particle will trigger the experimental device, opening the container with the toxic gas and killing the cat. According to quantum mechanics, before observation, the nucleus is in a superposition of decayed and undecayed states. However, if the box is opened after an hour, the observer can only see either "decayed nucleus and dead cat" or "undecayed nucleus and living cat." In 1935, Schrödinger published a paper titled "The Present Situation in Quantum Mechanics," where in Section 5, he described what is often seen as the nightmare-like cat experiment: The Copenhagen school says that without measurement, a particle's state is unclear, existing in a mixture of various possibilities. For example, a radioactive atom's decay timing is entirely probabilistic. As long as there is no observation, it remains in a superposition state of decayed/undecayed, and only when measured does it randomly choose one state to appear. Let us place this atom in an opaque box to maintain its superposition state. Schrödinger imagined a cleverly structured precision device; whenever the atom decays and emits a neutron, it triggers a chain reaction, ultimately breaking a poison bottle in the box, along with a poor cat inside. The situation is clear: if the atom decays, the poison bottle breaks, and the cat dies. If the atom does not decay, the cat remains alive.

The ingenuity of this thought experiment lies in connecting the uranium atom's "decay-undecay superposition state" with the cat's "dead-alive superposition state" through the "detector-atom-poison bottle" causal chain, transforming quantum mechanics' microscopic uncertainty into macroscopic uncertainty; microscopic chaos into macroscopic absurdity — the cat is either dead or alive, one of the two must be true, it cannot be both dead and alive simultaneously! No wonder renowned British scientist Stephen Hawking, upon hearing of Schrödinger's Cat paradox, said, "I'll get a gun to shoot the cat!"