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• Is it possible for an electron to be in two places at once?

• Or for a cat to be both alive and dead at the same time?

• According to quantum mechanics, both scenarios are possible

• and at the heart of this conceptual dilemma lies the wave function,

• the mathematical formula that we use to describe quantum objects.

• To see the wave function at work, let's take the case of an electron

• shooting out of the back of a cathode ray tube,

• a device found in the back of old fashioned TVs.

• The wave function for this electron is just the description

• of where the electron is and what it's doing.

• For example, how fast it's going.

• To predict where the electron will be in the future,

• you just plug the wave function into Schroedinger's wave equation,

• the quantum equivalent of Newton's laws of motion.

• But here's where it gets tricky:

• The wave function isn't a regular number.

• It's a complex function that relies on imaginary numbers,

• such as the square root of negative one.

• And it gets even worse...

• The wave function can only give you a statistical prediction

• about where the electron will be in the future.

• It's a statement about probabilities, nothing more.

• If you took two electrons with the exact same wave function

• and looked to see where they are, you might find that one is over here

• and the other is over here.

• And worse yet, once you observe an electron, detecting it in this place

• and not in this place,

• the wave function immediately and irreversibly changes.

• Physicists say that it collapses from a broad range of possibilities

• to one specific answer.

• Think about that for a second.

• The act of measuring the electron is what gives it its position.

• And this brings us back to the cat

• that's both alive and dead at the same time.

• As it's usually told,

• a cat and a vial of poison are sealed into a box.

• Then a quantum event happens with a probability of 50 percent

• that breaks or does not break the vial of poison

• and kills or does not kill the cat.

• So, is the cat still breathing?

• The wave function reflects both possibilities.

• In the standard interpretation of quantum mechanics,

• both possibilities are real.

• The cat is truly both alive and dead

• until an observer opens up the box.

• At this point, the kitty collapses

• into either an alive or a dead state.

• This is absurd, of course.

• Cats can't both be alive and dead at the same time.

• So how do we get out of this paradox?

• One of two ways:

• Either the wave function doesn't really exist,

• it's just a reflection of our knowledge.

• Or the cats are both alive and dead, but in two parallel universes.

• For Scientific American's Instant Egghead, I'm Michael Moyer.

Is it possible for an electron to be in two places at once?

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What Is the Wave Function? - Instant Egghead #50

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葉大 谷翔平 posted on 2017/06/08
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