Erwin Schrödinger and the Schrödinger's Cat Thought Experiment

Nobel Prize winning physicist who shaped quantum mechanics

American shorthair cat in a cardboard box

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Erwin Rudolf Josef Alexander Schrödinger (born on August 12, 1887 in Vienna, Austria) was a physicist who conducted groundbreaking work in quantum mechanics, a field which studies how energy and matter behave at very small length scales. In 1926, Schrödinger developed an equation that predicted where an electron would be located in an atom. In 1933, he received a Nobel Prize for this work, along with physicist Paul Dirac.

Schrödinger may be more popularly known for “Schrödinger’s Cat,” a thought experiment he devised in 1935 to illustrate problems with a common interpretation of quantum mechanics.

Early Years and Education

Schrödinger was the only child of Rudolf Schrödinger – a linoleum and oilcloth factory worker who had inherited the business from his father – and Georgine, the daughter of a chemistry professor of Rudolf’s. Schrödinger’s upbringing emphasized cultural appreciation and advancement in both science and art.

Schrödinger was educated by a tutor and by his father at home. At the age of 11, he entered the Akademische Gymnasium in Vienna, a school focused on classical education and training in physics and mathematics. There, he enjoyed learning classical languages, foreign poetry, physics, and mathematics, but hated memorizing what he termed “incidental” dates and facts.

Schrödinger continued his studies at the University of Vienna, which he entered in 1906. He earned his PhD in physics in 1910 under the guidance of Friedrich Hasenöhrl, whom Schrödinger considered to be one of his greatest intellectual influences. Hasenöhrl was a student of physicist Ludwig Boltzmann, a renowned scientist known for his work in statistical mechanics.

After Schrödinger received his PhD, he worked as an assistant to Franz Exner, another student of Boltzmann’s, until being drafted at the beginning of World War I.

Career Beginnings

In 1920, Schrödinger married Annemarie Bertel and moved with her to Jena, Germany to work as the assistant of physicist Max Wien. From there, he became faculty at a number of universities over a short period of time, first becoming a junior professor in Stuttgart, then a full professor at Breslau, before joining the University of Zurich as a professor in 1921. Schrödinger’s subsequent six years at Zurich were some of the most important in his professional career.

At the University of Zurich, Schrödinger developed a theory that significantly advanced the understanding of quantum physics. He published a series of papers – about one per month – on wave mechanics. In particular, the first paper, “Quantization as an Eigenvalue Problem," introduced what would become known as the Schrödinger equation, now a central part of quantum mechanics. Schrödinger was awarded the Nobel Prize for this discovery in 1933.

Schrödinger’s Equation

Schrödinger's equation mathematically described the "wavelike" nature of systems governed by quantum mechanics. With this equation, Schrödinger provided a way to not only study the behaviors of these systems, but also to predict how they behave. Though there was much initial debate about what Schrödinger’s equation meant, scientists eventually interpreted it as the probability of finding an electron somewhere in space.

Schrödinger’s Cat

Schrödinger formulated this thought experiment in response to the Copenhagen interpretation of quantum mechanics, which states that a particle described by quantum mechanics exists in all possible states at the same time, until it is observed and is forced to choose one state. Here's an example: consider a light that can light up either red or green. When we are not looking at the light, we assume that it is both red and green. However, when we look at it, the light must force itself to be either red or green, and that is the color we see.

Schrödinger did not agree with this interpretation. He created a different thought experiment, called Schrödinger's Cat, to illustrate his concerns. In the Schrödinger's Cat experiment, a cat is placed inside a sealed box with a radioactive substance and a poisonous gas. If the radioactive substance decayed, it would release the gas and kill the cat. If not, the cat would be alive.

Because we do not know whether the cat is alive or dead, it is considered both alive and dead until someone opens the box and sees for themselves what the state of the cat is. Thus, simply by looking into the box, someone has magically made the cat alive or dead even though that is impossible.

Influences on Schrödinger’s Work

Schrödinger did not leave much information about the scientists and theories that influenced his own work. However, historians have pieced together some of those influences, which include:

  • Louis de Broglie, a physicist, introduced the concept of “matter waves." Schrödinger had read de Broglie’s thesis as well as a footnote written by Albert Einstein, which spoke positively about de Broglie’s work. Schrödinger was also asked to discuss de Broglie’s work at a seminar hosted by both the University of Zurich and another university, ETH Zurich.
  • Boltzmann. Schrödinger considered Boltzmann’s statistical approach to physics his “first love in science,” and much of his scientific education followed in the tradition of Boltzmann.
  • Schrödinger’s previous work on the quantum theory of gases, which studied gases from the perspective of quantum mechanics. In one of his papers on the quantum theory of gases, “On Einstein’s Gas Theory,” Schrödinger applied de Broglie’s theory on matter waves to help explain the behavior of gases.

Later Career and Death

In 1933, the same year he won the Nobel Prize, Schrödinger resigned his professorship at the University of Berlin, which he had joined in 1927, in response to the Nazi takeover of Germany and the dismissal of Jewish scientists. He subsequently moved to England, and later to Austria. However, in 1938, Hitler invaded Austria, forcing Schrödinger, now an established anti-Nazi, to flee to Rome.

In 1939, Schrödinger moved to Dublin, Ireland, where he remained until his return to Vienna in 1956. Schrödinger died of tuberculosis on January 4, 1961 in Vienna, the city where he was born. He was 73 years old.

Erwin Schrödinger Fast Facts

  • Full Name: Erwin Rudolf Josef Alexander Schrödinger
  • Known For/Occupation: Physicist who developed the Schrödinger equation, which signified a great stride for quantum mechanics. Also developed the thought experiment known as “Schrödinger’s Cat.”
  • Born: August 12, 1887 in Vienna, Austria
  • Died: January 4, 1961 in Vienna, Austria
  • Parents’ Names: Rudolf and Georgine Schrödinger
  • Spouse's Name: Annemarie Bertel
  • Child's Name: Ruth Georgie Erica (b. 1934)