What can Schrödinger's cat teach us about quantum mechanics? - Josh Samani

Summary

This script explores the quantum world's peculiarities, contrasting everyday physics with quantum mechanics. It uses Schrödinger's cat to illustrate quantum superposition and entanglement, where outcomes are undetermined until observed. Quantum entanglement's strangeness is highlighted by the instantaneous correlation of distant particles, a phenomenon confirmed by lab experiments. The script suggests quantum mechanics' potential applications in secure communication and computing, hinting at a future where quantum phenomena might become part of everyday life.

Takeaways

• 📝 Classical mechanics governs the motion of macroscopic objects, whereas quantum mechanics rules the behavior of atomic-scale systems.
• 📚 The motion of an electron in a hydrogen atom is not like throwing a ball; it's described by probabilities rather than definite orbits.
• 📝 Quantum physics introduces the concept of superposition, where particles like electrons can exist in multiple states simultaneously until measured.
• 📚 Schrödinger's cat is a thought experiment illustrating quantum superposition, where a cat in a box with a bomb is both alive and dead until observed.
• 📝 Quantum entanglement is a phenomenon where the states of two or more particles are interconnected, affecting each other regardless of distance.
• 📚 In an entangled system, the outcome of one particle's state can instantly affect the state of another, even across vast distances.
• 📝 Quantum entanglement has been experimentally confirmed, showing that entangled particles maintain their connection even when separated.
• 📚 Quantum information science explores applications of quantum mechanics, such as quantum cryptography and computing.
• 📝 Quantum cryptography uses entanglement to create secure communication channels, while quantum computing leverages quantum states for powerful computation.
• 📚 The script suggests that as quantum technology advances, everyday applications may become more intertwined with quantum phenomena.

Q & A

What is the difference between classical mechanics and quantum mechanics?

Classical mechanics governs the behavior of large, everyday objects, while quantum mechanics describes the behavior of systems at atomic and subatomic scales. The laws of physics in these realms are very different.

Why can’t we predict the behavior of electrons based on our experience with everyday physics?

Because electrons, as quantum particles, follow the laws of quantum mechanics, which are vastly different from classical mechanics that govern everyday objects. The quantum world operates with probabilities and superpositions, unlike the deterministic nature of classical physics.

What is Schrödinger’s cat thought experiment, and what does it illustrate about quantum mechanics?

Schrödinger's cat is a thought experiment where a cat is placed in a box with a bomb that has a 50% chance of exploding. Until the box is opened, the cat is considered to be in a superposition—both alive and dead. It illustrates how quantum particles exist in multiple states until measured.

What is quantum superposition?

Quantum superposition refers to a system, like an electron or Schrödinger's cat, being in multiple states simultaneously. For example, an electron can be in different positions at once, and only upon measurement does it collapse into a single state.

How does quantum entanglement differ from classical mechanics interactions?

Quantum entanglement allows particles to be linked in such a way that the state of one particle instantaneously determines the state of the other, even across vast distances. This defies classical mechanics, where information transfer is limited by the speed of light.

In the context of quantum entanglement, what does it mean when two cats are in an entangled state?

In an entangled state, if one cat is alive, the other must be dead, and vice versa. The two cats' states are linked, even if the boxes are at opposite ends of the universe, ensuring that one is always alive and the other is dead upon measurement.

What makes quantum entanglement 'mindblowing' according to the script?

Quantum entanglement is mindblowing because even if two particles or cats are separated by vast distances, measuring one immediately affects the state of the other. This happens without any communication between them, seemingly defying classical ideas of time and space.

What real-world evidence exists to support quantum entanglement?

Quantum entanglement has been confirmed in real-world lab experiments. For instance, two entangled particles will spin in opposite directions, even when separated by large distances, and there is no way for information to pass between them.

What practical applications does quantum entanglement have?

Quantum entanglement has potential applications in quantum cryptography, for secure communication, and quantum computing, where it can be used to solve complex problems like cracking codes.

How might the strange behavior of quantum mechanics impact the macroscopic world in the future?

As quantum technologies develop, phenomena like quantum teleportation could become more prevalent in the macroscopic world, enabling advancements such as secure communication or even teleportation across galaxies, as speculated in the script.

Outlines

00:00

🔬 Everyday Physics vs Quantum Mechanics

The paragraph introduces the predictability of everyday physics, exemplified by a ball thrown into the air, and contrasts it with the unpredictable nature of quantum mechanics governing atomic scales. It explains that while we are familiar with the laws of classical mechanics that govern macroscopic objects, quantum mechanics rules the behavior of atoms, creating a strange and different reality. The thought experiment of Schrödinger's cat is introduced to illustrate quantum superposition, where the cat is neither alive nor dead until observed, similar to an electron in a hydrogen atom that is not in a fixed orbit but exists in a probability cloud.

Keywords

💡Classical Mechanics

Classical Mechanics refers to the branch of physics that deals with the motion of bodies under the influence of forces. It is based on principles such as Newton's laws of motion. In the video, classical mechanics is contrasted with quantum mechanics to illustrate the difference in behavior between macroscopic objects and atomic-scale systems. The video implies that while we can predict the motion of a thrown ball using classical mechanics, this approach fails when trying to understand atomic phenomena.

💡Quantum Mechanics

Quantum Mechanics is the branch of physics that explains the behavior of matter and energy at the atomic and subatomic level. It is characterized by phenomena such as superposition and entanglement, which are not explainable by classical mechanics. The video emphasizes that quantum mechanics governs the behavior of systems at small scales, like electrons in a hydrogen atom, and introduces the concept of superposition with the example of Schrödinger's cat.

💡Superposition

In quantum mechanics, superposition is the concept where a particle exists in all its theoretically possible states simultaneously until it is observed or measured. The video uses Schrödinger's cat thought experiment to illustrate superposition, where the cat is considered to be both alive and dead until the box is opened, highlighting the probabilistic nature of quantum states.

💡Schrödinger's Cat

Schrödinger's Cat is a thought experiment in quantum mechanics, involving a cat that is simultaneously alive and dead due to being linked to a random event (the explosion of a bomb). The video uses this thought experiment to explain the concept of superposition and to demonstrate how quantum mechanics can lead to seemingly paradoxical outcomes.

💡Electron

An electron is a subatomic particle that orbits the nucleus of an atom and is responsible for chemical reactions and electrical conductivity. The video mentions electrons to discuss their behavior in a hydrogen atom, contrasting the classical view of orbiting with the quantum mechanical view of existing in a cloud of probabilities.

💡Hydrogen Atom

A hydrogen atom is the simplest atomic structure, consisting of one proton and one electron. The video uses the hydrogen atom as an example to explain how quantum mechanics describes the electron's behavior differently from the classical view of planets orbiting the sun.

💡Probability

In the context of quantum mechanics, probability refers to the likelihood of finding a particle in a particular state or location. The video explains that electrons in a hydrogen atom are not in a fixed orbit but are instead found in various locations according to a probability distribution, which is a fundamental aspect of quantum mechanics.

💡Quantum Entanglement

Quantum entanglement is a phenomenon where the state of one particle becomes dependent on the state of another, no matter the distance between them. The video describes entanglement using the modified Schrödinger's cat experiment with two cats, suggesting that the fate of one cat is instantly connected to the other, even when separated by vast distances.

💡Observation

In quantum mechanics, observation or measurement is crucial as it causes a quantum system to 'collapse' into a definite state. The video mentions that until a measurement is made, such as opening the box in Schrödinger's cat experiment, the system remains in a superposition of all possible outcomes.

💡Macroscopic World

The macroscopic world refers to the world of large-scale objects and phenomena that we can observe with the naked eye. The video contrasts the macroscopic world, which follows classical mechanics, with the quantum world, emphasizing that everyday experiences do not prepare us for the strange behavior of particles at the atomic level.

💡Quantum Cryptography

Quantum Cryptography is a method of secure communication that uses the principles of quantum mechanics to encrypt and decrypt messages. The video mentions quantum cryptography as an application of quantum mechanics in the macroscopic world, suggesting that the strange rules of the quantum world can be harnessed for practical purposes.

💡Quantum Teleportation

Quantum teleportation is a process by which the quantum state of one particle is transferred to another particle at a different location. The video humorously suggests that quantum teleportation could one day be used to move objects, like a cat, to a safer place, illustrating the potential future applications of quantum mechanics.

Highlights

Predicting the motion of a thrown ball is easy due to everyday experience with physics.

The motion of an electron in a hydrogen atom cannot be predicted by everyday physics.

Physics at small scales, like atoms, is governed by quantum mechanics, not classical mechanics.

The quantum world is very different and strange compared to the macroscopic world.

Schrödinger's cat thought experiment illustrates quantum superposition.

In quantum physics, before observation, the cat is in a superposition of being alive and dead.

Electrons in a hydrogen atom are not orbiting but exist in a probability cloud.

Quantum measurement pinpoints the electron's position, similar to knowing the cat's state.

Quantum entanglement involves two systems that affect each other's states regardless of distance.

Entangled cats will always have opposite states: one alive and the other dead.

Quantum entanglement has been experimentally confirmed in real-world lab settings.

Entangled particles behave in correlated ways even when separated by large distances.

Quantum entanglement is central to quantum information science.

Quantum cryptography uses entanglement for secure communication.

Quantum computing leverages entanglement to solve complex problems.

Everyday physics may increasingly incorporate quantum phenomena.

Quantum teleportation could potentially transfer objects to distant locations.

Transcripts

Consider throwing a ball straight into the air.

Can you predict the motion of the ball after it leaves your hand?

Sure, that's easy.

The ball will move upward until it gets to some highest point,

then it will come back down and land in your hand again.

Of course, that's what happens,

and you know this because you have witnessed events like this countless times.

You've been observing the physics of everyday phenomena your entire life.

But suppose we explore a question about the physics of atoms,

like what does the motion of an electron

around the nucleus of a hydrogen atom look like?

Could we answer that question based on our experience with everyday physics?

Definietly not. Why?

Because the physics that governs the behavior of systems at such small scales

is much different than the physics of the macroscopic objects

you see around you all the time.

The everyday world you know and love

behaves according to the laws of classical mechanics.

But systems on the scale of atoms

behave according to the laws of quantum mechanics.

This quantum world turns out to be a very strange place.

An illustration of quantum strangeness is given by a famous thought experiment:

Schrödinger's cat.

A physicist, who doesn't particularly like cats, puts a cat in a box,

along with a bomb that has a 50% chance of blowing up after the lid is closed.

Until we reopen the lid, there is no way of knowing

whether the bomb exploded or not,

and thus, no way of knowing if the cat is alive or dead.

In quantum physics, we could say that before our observation

the cat was in a superposition state.

It was neither alive nor dead but rather in a mixture of both possibilities,

with a 50% chance for each.

The same sort of thing happens to physical systems at quantum scales,

like an electron orbiting in a hydrogen atom.

The electron isn't really orbiting at all.

It's sort of everywhere in space, all at once,

with more of a probability of being at some places than others,

and it's only after we measure its position

that we can pinpoint where it is at that moment.

A lot like how we didn't know whether the cat was alive or dead

until we opened the box.

This brings us to the strange and beautiful phenomenon

of quantum entanglement.

Suppose that instead of one cat in a box, we have two cats in two different boxes.

If we repeat the Schrödinger's cat experiment with this pair of cats,

the outcome of the experiment can be one of four possibilities.

Either both cats will be alive, or both will be dead,

or one will be alive and the other dead, or vice versa.

The system of both cats is again in a superposition state,

with each outcome having a 25% chance rather than 50%.

But here's the cool thing:

quantum mechanics tells us it's possible to erase

the both cats alive and both cats dead outcomes from the superposition state.

In other words, there can be a two cat system,

such that the outcome will always be one cat alive and the other cat dead.

The technical term for this is that the states of the cats are entangled.

But there's something truly mindblowing about quantum entanglement.

If you prepare the system of two cats in boxes in this entangled state,

then move the boxes to opposite ends of the universe,

the outcome of the experiment will still always be the same.

One cat will always come out alive, and the other cat will always end up dead,

even though which particular cat lives or dies is completely undetermined

before we measure the outcome.

How is this possible?

How is it that the states of cats on opposite sides of the universe

can be entangled in this way?

They're too far away to communicate with each other in time,

so how do the two bombs always conspire such that

one blows up and the other doesn't?

You might be thinking,

"This is just some theoretical mumbo jumbo.

This sort of thing can't happen in the real world."

But it turns out that quantum entanglement

has been confirmed in real world lab experiments.

Two subatomic particles entangled in a superposition state,

where if one spins one way then the other must spin the other way,

will do just that, even when there's no way

for information to pass from one particle to the other

indicating which way to spin to obey the rules of entanglement.

It's not surprising then that entanglement is at the core

of quantum information science,

a growing field studying how to use the laws of the strange quantum world

in our macroscopic world,

like in quantum cryptography, so spies can send secure messages to each other,

or quantum computing, for cracking secret codes.

Everyday physics may start to look a bit more like the strange quantum world.

Quantum teleportation may even progress so far,

that one day your cat will escape to a safer galaxy,

where there are no physicists and no boxes.