AMASE: Schrodinger's Cat

[Orbax appears from below his desk in his office. There is a box on his desk.]

Orbax: Hello! I'm the great Orbax. 

Or am I ??? 

And welcome, to Ask Me Anything Science Edition! 

Or is it?

[Cut to Guelph Physics logo. Sound.]

[Cut back to Orbax.]

Orbax: You may have noticed for my incredible intro that there's a degree of uncertainty in today's video.

Or is there?

Yes, there is. Our question today comes from one of our Instagram followers who wants Schrodinger's Cat explained. Well as our resident departmental catistician....

[A cats jumps on and off of the desk.]

Orbax: I volunteered for the job!

To begin we need to discuss uncertainty and why we're so uncertain. When I look at large objects, I can tell you a few things. I know where they are.

[ A cat appears on Orbax’s shoulder. It jumps off.]

Orbax: Often, I know how fast they're moving or at least something that I can measure.

I would say I don't see uncertainty in large objects. I'm pretty sure my cat is here, right now.

[Orbax tips the box to show a cat in it.]

Orbax: Or is it?

[A cat jumps out of the box and runs away.]

Orbax: So, when do we become uncertain? Consider this, when a particle is massive, and by that I mean macroscopic, I can measure it. I can tell you where it is. I can measure how fast it moves. I can use different techniques like a ruler, or a laser, and get you very, very, accurate numbers. 

In this state, I have a low level of uncertainty. In fact you'd say I was fairly certain and physics would behave classically. Well mass and uncertainty are inversely proportional. When masses are very, very tiny the uncertainty increases so think about measuring an atomic particle.

Everything we have that can measure that particle will inherently affect its position or its speed. Like a ruler.

[A cat appears on the desk. Orbax plays with the cat using a tape measure.]

[Orbax plays with the cat using a laser.]

Orbax: Or a laser!

All these things will affect that particle and that makes our measurements uncertain. In this case we would say that the particle no longer behaves classically, that it behaves according to quantum mechanics.

Quantum mechanics was formulated in the early 1900',s as a way to being actually able to deal with this uncertainty. As you can imagine not being able to know or measure a particle's position or its speed at a given moment in time actually changes the way in which we do physics... and this is where Schrodinger's cat comes into play!

Schrodinger was an Austrian physicist who formulated something called Schrodinger's equation which is an equation which mathematically treated the uncertainty we talked about as if it was a wave but when you do that you run into some problems... let's call them paradoxes, like this one that was conceived of by Schrodinger.

Let's say we have two items one which is macroscopic and can be treated with classical mechanics like this cat.

[Orbax opens a box and shows a cat inside.]

Orbax: And let's take another item one that's on the atomic level and should be treated with quantum mechanics... like this radioactive atom. 

[Orbax grabs at the air.]

Orbax: So, here's the thought experiment. We take the radioactive atom and if the atom decays the decay is detected by a device. The device releases a hammer which breaks a vial of poison we've placed this inside the box with the cat and we seal it all up.

[Orbax puts cat back in the box and closes it.]

Orbax: Now, there's a chance that the atom will decay within a given time frame but there's an uncertainty as to whether it will or not. See there's a chance that the atom decays and the poison kills the cat and there's also a chance that it didn't decay and the cat is fine, but the box sealed!

So how do we know what happened?

Well, the easiest thing to do is open the box and we discover... 

[Orbax opens the box and the cat jumps out. He hits the box off of the desk.] 

Orbax: Our cat's okay! But was the cat always okay? 

[Orbax picks up a box from the floor.]

Orbax: Well, that's where quantum mechanics takes over. You see we don't know that the cat's okay until we observe it. Until we measure it by opening the box.

[The cat is okay! Orbax laughs.]

Orbax: So, what quantum mechanics says is that when the box is sealed this cat's in a state of
quantum superposition, both alive and dead, until we make the active measurement of opening that box and that's not until we open the box that we discover that it's been in that state the entire time.

[Orbax spins the box and shows the cat. The cat jumps out of the box and off the desk.]

Orbax: Or has it?

Sounds weird right? Well, that's what Schrodinger's point was. He was actually so disillusioned with the philosophical implications of quantum mechanics that he abandoned it all together. 

Now today there are two popular interpretations of quantum mechanics. The first is the Copenhagen interpretation. This one says that all possibilities exist prior to our observation. At the moment of observation the wavefunction collapses to the most probable outcome and life goes on. 

[Orbax puts the cat back in the box.]

Orbax: Having always been the most probable state from the moment that we measured and before. 

[Orbax takes the cat out of the box.]

Orbax: But there's also the many-worlds interpretation where all the possibilities exist but upon observation we continue to live in the world where what we observed happened. 

[Orbax takes the cat out of the box again.]

Orbax: But then so does another version of us in another world and another version in another world. As a matter of fact, since there are infinite possibilities in terms of the outcomes of our experiment. 

[Cat jumps out of the box.]

Orbax: There are infinite worlds where each one is a result of one of those possibilities. Now that's strange.

[Orbax takes a cat out of the box again.]

Orbax: And I'm not talking about the quark.

[Orbax hits the box off of the desk.]

Orbax: For more or Ask Me Anything Science Edition click the links.

[Pointing around the screen.]

Orbax: And if you have a question, go ahead and just post in the comments below. Stay safe and stay Science.