Schrodingers Cat
| Physics: | Quantum Mechanics, Multi-State Theory |
| Grade Range: | Elementary School, Middle School, High School |
| Format: | Stage |
This demonstration is a part of the Quantum Mechanics Show. This demonstration is not typically performed by itself, since it does require background knowledge in the topic to be understood. In the Quantum Mechanics Show, this demonstration is scripted, so although this write-up does not provide a script, one should be aware of the differences that happen between scripted and non-scripted demonstrations.
In order to perform this demonstration, you need two presenters.
Materials
- Schrodinger's Cat Box
- MSU Cat Plush
- Hats
- Large Plastic or Foam Coin
- Black Cloth
- "One Hour Later" Sign
Safety Precautions
Please read the General Safety Precautions section of the Demonstration Safety page before performing this demonstration.
Demonstration
- Set up the box onstage, and have Presenter A briefly introduce the idea of the Schrodinger's Cat Paradox (see "Why This Works"). As they talk about placing a cat in a box, Presenter A should pick up and toss the MSU cat plush into the box.
- Ask for a volunteer from the audience, and explain to them and the audience the purpose of the coin: If it lands heads up, the volunteer can put on a hat (presenter B shows the hats and tosses them into the box). If it lands tails up, then they can put the MSU cat plush on their head.
- Have the volunteer enter the box with the coin, and have them crouch down so the cloth can be put across the top. After the cloth is placed across, tell them to flip the coin and follow the directions.
- Presenter A: Let the audience know that you have to wait an hour now for the experiment to happen. A few seconds later, Presenter B should walk across the front of the stage with the "One Hour Later" sign. Presenter A can then acknowledge that "An hour just passed by".
- Poll the audience to see who thinks the volunteer will be wearing a hat, the cat, or both. Uncover the box and have the volunteer exit it to reveal what they are wearing.
Why This Works
The Schrodinger's Cat Paradox is a classic thought puzzle in Quantum Mechanics. Suppose we put a cat inside of a box which contains a special detector. This detector has a 50% chance of being triggered over the course of an hour. If the detector is triggered, it will open a vial of poison inside the box, instantly killing the cat. If it is not triggered, then the cat will be unharmed. After waiting an hour, before opening the box, is the cat alive or dead? The answer is that the cat would be in both states, alive and dead simultaneously, while the box is still closed.
This thought puzzle may sound silly when applied to living things, but on the atomic scale this theory of being in multiple states is well proven. Multi-State Theory is the tendency for atomic particles to be in multiple energy states simultaneously, without gaining or losing energy. When a particle, such as an electron, is in multiple states, it is said to be in a Superposition between states. This superposition lasts until the particle is observed or measured, since the act of measuring the state of the particle adds energy to the system. This causes the superposition to collapse, and the particle locks into a single state.
When our volunteer is in the covered box, we can pretend that they are in an unobserved state. This means that while they are in there, before we try to observe or measure their state of having a cat or a hat on their head, they would have both the cat and the hat on their head. Our volunteer represents an atomic particle in this respect, since they are unobserved and therefore should be in both states at the same time. However, once we take the cover off and open the lid, we are then observing the system. This collapses the superposition of our volunteer, and so they will end up with either a cat or a hat on their head.
Additional Information
- To see real examples of particles in a superposition, check out this Hyperphysics Double Slit Diffraction Illustration.
- In the scripted version of this demonstration, the background presenters all meow whenever the main presenter says "cat"!
- This demonstration is a part of the Quantum Mechanics Show