Schrödinger’s Cat is a thought experiment devised by the Austrian physicist Erwin Schrödinger, which he designed to illustrate a paradox of quantum superposition wherein a hypothetical cat may be considered both alive and dead simultaneously because its fate is linked to a random event that may (or may not) occur.
What Is Schrödinger’s Cat in Simple Terms?
Schrödinger’s Cat, as a thought experiment, states that if you seal a cat in a box with something that can eventually kill it, you won’t know if the cat is alive or dead until you open the box. So, until you open the box and observe the cat, the cat is simultaneously dead and alive.
How Does Schrödinger’s Cat Work?
We often use Schrödinger’s thought experiment to explain the concept of superposition. The experiment states that a hypothetical cat is locked in a box with some radioactive substance controlling a vial of poison. When the substance decays, it triggers a Geiger counter that causes the poison to be released, thereby killing the cat.
Since the box is locked — and we on the outside don’t know whether or not the radioactive substance has decayed and released the poison — we can’t tell if the cat is dead or alive. So, until we open the box to know for sure, the cat is both dead and alive. Mathematically speaking, there’s a 50 percent chance the cat is dead and a 50 percent chance the cat is alive.
How Is Schrödinger’s Cat Both Alive and Dead?
In quantum mechanics terms, the cat’s ability to be in an ambiguous state of both alive and dead until it’s observed (i.e. when someone opens the box) is referred to as quantum indeterminacy or the observer’s paradox. The paradox states that an event or an experiment’s observer affects its outcome. In this case, whoever is performing this hypothetical experiment can affect whether the cat remains in an unknown state or they can open the box and know if the cat is dead or alive with 100 percent certainty.
The experiment also points out when the resolution of possibilities occurs. The experiment is intended to make people ask themselves if it was logical for the observation to trigger the answer. After all, wouldn’t the cat be either dead or alive even if we never open the box?
Schrödinger’s Cat and the Role of the Observer
In quantum mechanics, the observer (the person conducting the experiment) has a role in the results of the experiment. In this case, we are unaware of the cat’s state until the observer opens the box. Until the observer opens the box, the cat exists in a superposition state; that is, the cat is both alive and dead. Only by opening the box and looking at what’s inside (i.e., observing it) is the cat’s state confirmed to be one of the two states. This is called The Copenhagen interpretation of quantum mechanics, which basically explains that a quantum system exists in all of its possible states at the same time. Only when we make an observation can we confirm the true state of the system.
Interpretations of Schrödinger’s Cat
Quantum reality and the Schrödinger’s Cat experiment can be interpreted in various manners. Here’s a few different interpretations for these concepts and how they are measured:
Copenhagen Interpretation
The Copenhagen interpretation proposes that a quantum system exists in a superposition of all possible quantum states simultaneously until it is measured or observed. In the Copenhagen interpretation, the quantum state’s wave function (a mathematical description of the quantum state of a quantum system) collapses into a single, definite state once the state is observed.
Developed in the 1920s, the Copenhagen interpretation is one of the earliest and most widely taught interpretations of quantum mechanics, and is often the interpretation referenced in relation to Schrödinger’s Cat.
Many-Worlds Interpretation
The many-worlds interpretation proposes that all possible outcomes of a quantum event actually do occur, but in separate, parallel universes. When applied to Schrödinger’s Cat, the universe would split upon the quantum event occurring, where in one split universe the cat is alive, and in the other the cat is dead. Here, no collapse of wave function occurs, but instead reality continuously branches into multiple versions based on a possible outcome the cat could be in.
Objective Collapse Theories
Objective collapse theories or interpretations, such as the Ghirardi-Rimini-Weber (GRW) model, propose that wave function collapse is an objective physical process, and not something that is directly triggered by observation of the quantum state. Collapse is thought to occur spontaneously once a system reaches a certain level of mass or complexity, meaning the cat in Schrödinger’s Cat would end up definitively alive or dead independently to the action of an observer.
Relational Quantum Mechanics Interpretation
The relational quantum mechanics interpretation proposes that the state of a quantum system is relative to the observer. In the case of Schrödinger’s Cat, one observer might see the cat in superposition, while another observer who has opened the box sees a definite outcome (of the cat being either alive or dead). Both observer perspectives are true within their own relational frameworks, emphasizing the idea that there may not be a singular, absolute version or truth to reality.
Experimental Developments and Further Research of Schrödinger’s Cat
Modern experimental physics has begun to explore quantum mechanics further in ways that directly relate to the Schrödinger’s Cat thought experiment. In particular, scientists are working with systems large enough to explore the divide between classical and quantum physics — here’s how:
Wigner’s Friend Experiment
The Wigner’s friend experiment goes beyond the basis of Schrödinger’s Cat by including an observer (a “friend”) inside the box with the cat. The inside observer measures the cat and sees a definite outcome (dead or alive), but for an outside observer who hasn’t opened the box, both the cat and friend are in a superposition.
Experiments following this concept suggest that different observers may record different realities, leading to questions about truth and objectivity in quantum mechanics.
Macroscopic Superposition Experiments
Today, scientists have succeeded in creating macroscopic superpositions in quantum systems involving thousands of atoms, pushing the boundaries of how large a quantum system can be. These experiments demonstrate that quantum behavior can expand beyond just the microscopic level, which reinforces Schrödinger’s questioning of where quantum indeterminacy stops and classical reality begins.
Why Do We Use Schrödinger’s Cat?
We still use this thought experiment today to explain quantum physics concepts in an easy-to-understand way. Some people also use Schrödinger’s Cat to talk more philosophically about how the thought experiment can be extended to other situations in life. For example, let’s say you meet your friend for a night out and you’re both unsure about what to have for dinner; until you reach an agreement or one of you decides for the group, the possible food option is “every option that can exist where you and your friend are.” Looking at things from this perspective has led many people to think of everything in life as “quantum” because until the future is here, it technically (according to Schrödinger) exists in a state of superposition of all possible scenarios.
History of Schrödinger’s Cat
The Schrödinger’s Cat thought experiment was introduced in 1935 by Austrian physicist Erwin Schrödinger to challenge the Copenhagen interpretation of quantum mechanics. Copenhagen’s interpretation suggests that quantum systems exist in all possible states until they are observed. Schrödinger applied this idea to the scenario where a cat is placed in a sealed box with a radioactive atom that could release poison, making the cat both alive and dead — according to quantum rules — until someone opens the box.
With this in mind, Schrödinger did not intend this scenario to be taken literally. Instead, he used it to highlight the chaos or absurdity of extending quantum principles to everyday, macroscopic objects. In his view, applying superposition to something like a living being (such as a cat) worked to question how quantum mechanics was being interpreted, especially in regards to the boundary between quantum and classical physics.
Schrödinger’s Cat is meant as a critique — not an endorsement — of the idea that observation determines reality. The thought experiment has since become a notable example in discussions about quantum theory, sparking ongoing debates about the measurement, limits and objectivity of quantum mechanics. Today, it remains as a teaching tool and philosophical concept used to challenge and invoke discussions about modern physics ideas.
Frequently Asked Questions
What is Schrödinger's Cat in simple terms?
Schrödinger’s Cat is a famous thought experiment that demonstrates the idea in quantum physics that tiny particles can be in two states at once until they’re observed. It asks you to imagine a cat in a box with a mechanism that might kill it. Until you look inside, the cat is both alive and dead at the same time.
Is Schrödinger’s Cat a metaphor?
Schrödinger’s Cat is a thought experiment and is also considered a metaphor or a paradox.
Is Schrödinger’s Cat literal?
Schrödinger’s Cat is not meant to be taken literally, but as a thought experiment designed to show the counterintuitive idea of quantum superposition.
Is there an answer to Schrödinger’s Cat?
No, there isn't (and isn’t meant to be) a single, universally accepted answer to Schrödinger’s Cat. Schrödinger designed the thought experiment to highlight unresolved questions in quantum mechanics, especially about how and when a quantum system transitions into a definite, observable state. It continues to be a tool for exploring observation in physics and quantum systems.
