Episode 3: Ted makes the call (superposition of states and Schrödinger´s cat)


So far, Ted´s attempts to find himself a date have led us through the ideas of probability and that light comes in individual lumps known as photons. We left him as he was about to make a call to a girl he had met the night before…

Having finally worked up the courage following his lighting-related procrastination, Ted decided it was time to bite the bullet and make a call to the girl he had met the night before. He knows that confidence is everything, but still it takes him a good fifteen minutes or so of sitting with his phone in hand, thumb hovering over the small green dial button.

He can feel the adrenaline rising with his heart rate, and for some reason his bladder feels much more full than it actually is. He went to empty it anyway, then went back to the phone, took a deep breath, and pressed dial…

There´s so much he doesn´t know. He doesn´t know if she´ll remember him from the night before, whether she´ll regret having given away her number, whether she´s actually interested. To calm his nerves, Ted simplified the problem in the drawn out seconds while the phone rang at the other end.

He decided there were two possible outcomes- success or failure, sucess being her agreeing to meet him at a specific time and place. This would depend upon her existing attitude towards him, which he has no way of knowing without calling her to find out. But it also depends to some extent on how he talks to her on the phone- he wants to be confident without being arrogant, and interested without being needy.

The phone keeps ringing… Ted thinks of an analogy with quantum mechanics, where electrons, the tiny particles responsible for electricity, or photons, can be in two states at the same time, until you do some kind of experiment to find out what state they are in. Both might be equally likely, but by doing an experiment there has to be some kind of interaction which forces the quantum particle into one state or another.

In a classic experiment involving firing single photons (like from Ted´s dimmer switch) or single electrons at a screen with two holes, each particle seems to go through both holes at the same time. That is unless you put a detector directly behind each of them to find out which way it goes, in which case it seems to be very distinctly one or the other. By trying to find out the path each one takes, you affect the very thing you are trying to find out.

In some ways it´s like the anology of Scrodinger´s cat, which in an imaginary experiment was locked in a box with a nasty little setup involving a radioactive lump of material, and a vial of deadly gas (with at least 9 times the lethal dose for cats). Over a certain amount of time, the radioactive element has a 50/50 chance of decaying. This could happen at any time during the experiment, and is only predicatble in terms of probability over time. If it does decay, a mechanism detects it and releases the gas.

To the observer outside the box, there is no way of knowing whether the cat is dead or alive without opening the box, so it´s said that the cat is both dead and alive at the same time. Ted never liked this analogy, despite its fame. It´s too much like a “tree falling in the woods” kind of explanation, and was actually first proposed to show how daft quantum mechanics is. And besides, the cat would know if it was still alive, or you could put a window in the box and see the cat without affecting the experiment.

Ted though, has to interact with the girl in order to find out if she´s interested, but by doing so he is affecting the outcome. If she is undecided as to whether she likes him, the phonecall will likely be the deciding factor one way or the other.

However, Ted´s analogy broke down when a third possibility came up; one he was totally unprepared for … the answerphone.

Explore posts in the same categories: Explaining nano, Quantum Disco

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