# Only 90’s kids

Nineties kids and younger millennial hipsters will have fond memories of Boo, the lovable ghost character introduced in Super Mario Bros. 3, the greatest video game of all time. If you are not familiar with Boo, you can see the game mechanics in this video:

# Quantum Mario Bros.

Disclaimer: if Boo obeyed quantum physics, we would not be able to see it do much of anything interesting on a screen because a screen displays classical information. The purpose here is to give you an intuition for some aspect of quantum physics. For a deeper understanding of quantum physics, you have to read this book.

# Quantum Power-ups

Uh oh! Quantum Boo seems unstoppable. But wait! Mario has the power of observation — the power of quantum measurement. Whenever Mario looks toward Quantum Boo, Boo is only either found on top of Mario or at Boo’s starting position. If timed correctly, Mario can force Quantum Boo back to its starting position with a 0% chance of catching him. Of course, Mario could get unlucky and turn to find Boo on top of him as well — it all comes down to a quantum coin toss!

# A ghostly state

In classical physics, the state of Boo is a list of all the important properties it possesses. Boo has a location, direction, speed, and whether or not it is hiding. Boo’s position can be anywhere, which means the possible states are continuous. Continuous means any small change is another allowed state. You can’t count the number of possible states in classical physics — it’s uncountably infinite. In quantum physics, the possible states Quantum Boo can be found in are discrete and finite — you can count them.

# Super Position Bros.

Yet, Quantum Boo does somehow move continuously between the two locations in an ephemeral way. The probability of being in one location or the other changes continuously. An instant after Mario turns his head away from Quantum Boo, Boo ceases to be in the starting position. Boo is also not at Mario’s position either at this point. In fact, Boo is in no definite position at all! This new state is called superposition. It’s not here or there, and it’s not both here and there. It is something entirely new.

# Quantum Boo gets a classical scare

Mario cannot “see” the quantum superposition state of Boo. Boo only occupies a superposition when Mario is not looking. There is no answer to what quantum superposition “looks like”. As soon as Mario looks, Boo is either found on top of him or way back at Boo’s starting location. Boo is never found in the space between. In quantum physics, Boo is said to have collapsed into the state it is found in.

# Intermission: who the hell is Zeno?

Zeno was the dictator of the galactic confederacy who brought billions of Teegeeack to Earth in a souped-up jumbo jet 75 million years ago only to kill them with hydrogen bombs releasing thetans which now stick to humans and cause spiritual harm. Wait. No. Wrong book. That was Xenu, not Zeno. My bad.

# Quantum Zeno

Would you believe me if I told you that now you have all the knowledge and intuition to explain the quantum Zeno effect to your friends? (Maybe don’t though unless quantum physics naturally comes up in conversation.)

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## More from Chris Ferrie

Quantum theorist by day, father by night. Occasionally moonlighting as a author. csferrie.com

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## Chris Ferrie

Quantum theorist by day, father by night. Occasionally moonlighting as a author. csferrie.com