Schrödinger's cat: A thought experiment in quantum mechanics - Chad Orzel

Summary

Erwin Schrödinger's thought experiment, 'Schrödinger's Cat,' illustrates the quantum superposition principle, where a cat in a sealed box with a 50% chance of being killed is considered both alive and dead until observed. This paradox highlights the dual particle-wave nature of quantum objects, essential for modern technology like computers. The script explains how quantum phenomena, such as electrons existing in multiple states simultaneously, underpin the functioning of semiconductors and transistors, ultimately enabling the technology we use today.

Takeaways

• 😺 Erwin Schrödinger, an Austrian physicist, is renowned for his thought experiment involving a cat, which illustrates the concept of superposition in quantum mechanics.
• 🧠 Schrödinger's cat paradox questions the state of a cat in a sealed box with a 50% chance of being alive or dead, suggesting it is both until observed.
• 🌌 Quantum physics posits that particles can exist in multiple states simultaneously, challenging our classical understanding of reality.
• 🤔 Schrödinger found quantum mechanics philosophically unsettling, leading him to shift his focus to biology.
• 💻 The concept of superposition is crucial for modern technology, particularly in the development of computers and semiconductors.
• 🌊 The dual particle-wave nature of quantum objects allows them to exist in multiple positions and states at once, a fundamental aspect of quantum mechanics.
• 🔬 Experiments with electrons and double slits demonstrate wave-particle duality, showing electrons behaving as waves when not observed.
• 🔗 The sharing of electrons between atoms is key to forming chemical bonds and understanding the properties of materials like conductors, insulators, and semiconductors.
• 💾 The ability to control electron sharing in semiconductors is fundamental to the creation of transistors and the technology within computer chips.
• 🌐 The Internet, jokingly attributed to the sharing of cat videos, owes a foundational debt to Schrödinger's work on quantum mechanics and its applications in technology.

Q & A

Who is Erwin Schrödinger and what is his contribution to quantum mechanics?

Erwin Schrödinger is an Austrian physicist and one of the founders of quantum mechanics. He is most famous for proposing the thought experiment known as Schrödinger's cat.

What is Schrödinger's cat thought experiment?

Schrödinger's cat is a thought experiment where a cat is placed in a sealed box with a device that has a 50% chance of killing the cat in an hour. The experiment illustrates the concept of superposition in quantum mechanics, suggesting that the cat is both alive and dead until the box is opened.

What does the cat being 'equal parts alive and dead' signify in quantum physics?

In quantum physics, the cat being 'equal parts alive and dead' signifies the concept of superposition, where a quantum system can be in multiple states simultaneously until it is observed or measured.

Why did Schrödinger find quantum physics philosophically disturbing?

Schrödinger found quantum physics philosophically disturbing because it challenged classical notions of reality and determinism, suggesting that particles could exist in multiple states until observed.

How is the concept of superposition essential to modern technology?

Superposition is essential to modern technology because it underlies the behavior of electrons in materials, which determines their properties as conductors, insulators, or semiconductors. This understanding is crucial for the development of electronic devices like transistors and computer chips.

What is the dual particle and wave nature of quantum objects?

The dual particle and wave nature of quantum objects refers to their ability to exhibit properties of both particles and waves. This means they can be localized in space like particles or spread out over a region like waves, which is key to phenomena like superposition.

Why don't we observe wave-like behavior in everyday objects like a cat?

We don't observe wave-like behavior in everyday objects like a cat because their wavelength is extremely small due to their size and mass. The wave properties become negligible compared to their particle properties.

How does the behavior of electrons in a double-slit experiment demonstrate superposition?

In a double-slit experiment, electrons show wave-like behavior by creating an interference pattern on the far side, indicating that each electron goes through both slits simultaneously. This demonstrates the superposition of states, as the electrons are not choosing one path or the other but both at the same time.

How does the superposition of electrons in atoms lead to the formation of chemical bonds?

The superposition of electrons in atoms allows them to be shared between atoms, leading to the formation of chemical bonds. This is because electrons can exist in a spread-out, wave-like state that extends over multiple atoms, enabling them to contribute to the bonding between them.

What role do semiconductor materials play in modern electronics?

Semiconductor materials play a crucial role in modern electronics because their properties can be precisely controlled to manipulate how electrons are shared among atoms. This allows for the creation of transistors and other components that are essential for devices like computer chips.

How is the existence of the Internet related to Schrödinger's cat thought experiment?

The existence of the Internet is related to Schrödinger's cat thought experiment in a metaphorical sense, as the foundational principles of quantum mechanics, which include superposition and the behavior of electrons, are essential for the technology that powers the Internet and electronic devices.

Outlines

00:00

🧬 Schrödinger's Cat and Quantum Superposition

Erwin Schrödinger, an Austrian physicist and a key figure in quantum mechanics, is renowned for his thought experiment involving a cat. He proposed a scenario where a cat in a sealed box, along with a device that has a 50% chance of killing it within an hour, would be in a superposition of states - both alive and dead - until the box is opened. Schrödinger used this paradox to illustrate the strangeness of quantum mechanics, where particles can exist in multiple states simultaneously. This concept, which he found philosophically unsettling, led him to shift his focus away from quantum theory. Despite its absurdity, the thought experiment is crucial for understanding quantum phenomena like superposition, which is essential for modern technology, including the computer on which this video is being watched.

Keywords

💡Quantum mechanics

Quantum mechanics is a fundamental theory in physics that describes the behavior of particles on an atomic and subatomic level. In the video, it serves as the scientific framework within which Schrödinger's thought experiment, involving the cat, is based. The concept is essential for understanding phenomena like superposition and dual wave-particle nature, which are critical themes in the video.

💡Schrödinger's cat

Schrödinger's cat is a famous thought experiment that illustrates the concept of quantum superposition. In the video, the cat is described as being simultaneously alive and dead until an observation is made, highlighting the counterintuitive nature of quantum physics. This thought experiment serves as an accessible way to explain the strange realities of quantum mechanics.

💡Superposition

Superposition is the ability of a quantum system to exist in multiple states simultaneously. In the video, this concept is used to explain the dual states of Schrödinger's cat and how electrons in semiconductors can occupy multiple positions at once. It’s key to understanding both the behavior of quantum particles and the development of modern technologies like transistors.

💡Wave-particle duality

Wave-particle duality is the principle that quantum objects, such as electrons, can exhibit properties of both particles and waves. In the video, this concept is demonstrated through the behavior of electrons passing through two slits, where they act as both waves and particles. This duality is fundamental to quantum mechanics and underpins the behavior of electrons in semiconductors.

💡Electron

Electrons are subatomic particles with negative charge, crucial in both quantum mechanics and modern electronics. The video explains how electrons exhibit wave-like behavior in superposition, and how this property allows them to be shared between atoms, forming chemical bonds and making technologies like semiconductors possible.

💡Semiconductor

A semiconductor is a material that can conduct electricity under certain conditions, making it essential for modern electronics. In the video, semiconductors are described as materials where electrons exist in a superposition of states. This ability to control electron behavior in semiconductors is the basis for creating transistors, which are foundational components of computer chips.

💡Transistor

A transistor is a tiny electronic device that regulates the flow of electrical current, acting as a switch or amplifier. The video mentions that millions of transistors are packed into a computer chip, and their functioning is reliant on the quantum behavior of electrons in semiconductors. Transistors are fundamental to the operation of modern computers and electronics.

💡Thought experiment

A thought experiment is an imagined scenario used to explore the implications of a theory or concept. Schrödinger's cat is a famous example of such an experiment, illustrating the paradoxes and peculiarities of quantum mechanics. In the video, it helps to explain the complex idea of superposition by using a relatable, everyday object—a cat.

💡Probability

Probability in quantum mechanics refers to the likelihood of a particular outcome in a system that can exist in multiple states. The video discusses how, before observation, Schrödinger's cat is a 'blur of probability'—both alive and dead. This highlights the idea that quantum outcomes are not definite until measured, a core principle in quantum theory.

💡Observation

Observation, in quantum mechanics, refers to the act of measuring or detecting a quantum system, which forces it into a definite state. In the video, Schrödinger's cat is said to be in a superposition of alive and dead until the box is opened and the cat is observed, illustrating how measurement collapses quantum possibilities into a single reality.

Highlights

Erwin Schrödinger, an Austrian physicist, is renowned for his foundational work in quantum mechanics.

Schrödinger is most famous for his thought experiment involving a cat, which illustrates the concept of superposition.

The cat in the sealed box is proposed to be both alive and dead simultaneously until observed, challenging common sense.

Quantum physics suggests that before observation, the cat exists in a superposition of states.

Schrödinger's thought experiment highlights the philosophical discomfort with quantum mechanics.

Despite finding quantum physics disturbing, Schrödinger's work is essential for modern technology.

The phenomenon of superposition is a consequence of the dual particle and wave nature of quantum objects.

For an object to exhibit wave properties, it must occupy many positions at once, which is a feature of superposition.

Everyday objects like a cat do not exhibit wave properties due to their size and momentum.

Electrons, being tiny particles, can demonstrate their dual nature through experiments like the double-slit experiment.

The double-slit experiment shows that electrons can pass through both slits simultaneously, indicating wave-like behavior.

The superposition of states is crucial for understanding how chemical bonds form through electron sharing.

Electrons in a solid can be shared among all atoms, which influences the material's conductivity.

Understanding electron sharing among atoms allows for precise control over semiconductor materials like silicon.

Combining different semiconductors enables the creation of transistors, which are essential for computer chips.

The superposition principle and electron sharing are foundational for the technology that powers computers and the internet.

The Internet, in a profound way, owes its existence to Schrödinger's thought experiment and the principles of quantum mechanics.

Transcripts

Austrian physicist Erwin Schrödinger is one of the founders of quantum mechanics,

but he's most famous for something he never actually did:

a thought experiment involving a cat.

He imagined taking a cat and placing it in a sealed box

with a device that had a 50% chance of killing the cat in the next hour.

At the end of that hour, he asked, "What is the state of the cat?"

Common sense suggests that the cat is either alive or dead,

but Schrödinger pointed out that according to quantum physics,

at the instant before the box is opened, the cat is equal parts alive and dead,

at the same time.

It's only when the box is opened that we see a single definite state.

Until then, the cat is a blur of probability,

half one thing and half the other.

This seems absurd, which was Schrödinger's point.

He found quantum physics so philosophically disturbing,

that he abandoned the theory he had helped make

and turned to writing about biology.

As absurd as it may seem, though, Schrödinger's cat is very real.

In fact, it's essential.

If it weren't possible for quantum objects to be in two states at once,

the computer you're using to watch this couldn't exist.

The quantum phenomenon of superposition

is a consequence of the dual particle and wave nature of everything.

In order for an object to have a wavelength,

it must extend over some region of space,

which means it occupies many positions at the same time.

The wavelength of an object limited to a small region of space

can't be perfectly defined, though.

So it exists in many different wavelengths at the same time.

We don't see these wave properties for everyday objects

because the wavelength decreases as the momentum increases.

And a cat is relatively big and heavy.

If we took a single atom and blew it up to the size of the Solar System,

the wavelength of a cat running from a physicist

would be as small as an atom within that Solar System.

That's far too small to detect, so we'll never see wave behavior from a cat.

A tiny particle, like an electron, though,

can show dramatic evidence of its dual nature.

If we shoot electrons one at a time at a set of two narrow slits cut in a barrier,

each electron on the far side is detected at a single place at a specific instant,

like a particle.

But if you repeat this experiment many times,

keeping track of all the individual detections,

you'll see them trace out a pattern that's characteristic of wave behavior:

a set of stripes - regions with many electrons

separated by regions where there are none at all.

Block one of the slits and the stripes go away.

This shows that the pattern is a result of each electron going through both slits

at the same time.

A single electron isn't choosing to go left or right

but left and right simultaneously.

This superposition of states also leads to modern technology.

An electron near the nucleus of an atom exists in a spread out, wave-like orbit.

Bring two atoms close together,

and the electrons don't need to choose just one atom

but are shared between them.

This is how some chemical bonds form.

An electron in a molecule isn't on just atom A or atom B, but A+ B.

As you add more atoms, the electrons spread out more,

shared between vast numbers of atoms at the same time.

The electrons in a solid aren't bound to a particular atom

but shared among all of them, extending over a large range of space.

This gigantic superposition of states

determines the ways electrons move through the material,

whether it's a conductor or an insulator or a semiconductor.

Understanding how electrons are shared among atoms

allows us to precisely control the properties of semiconductor materials,

like silicon.

Combining different semiconductors in the right way

allows us to make transistors on a tiny scale,

millions on a single computer chip.

Those chips and their spread out electrons

power the computer you're using to watch this video.

An old joke says that the Internet exists to allow the sharing of cat videos.

At a very deep level, though, the Internet owes its existance

to an Austrian physicist and his imaginary cat.