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cdaveI recently read "The Fabric of the Cosmos" by Brian Greene. It contained a rather brilliant description of the Delayed Choice Double Slit experiment, in which effect precedes cause. Rather damaging to the notion of free will I thought.
This led to me think about an Asimov story where such an experiment takes place. They wait until the experiment says that water was/will be poured on this in 24 hours, and then seal the container. They find that the universe conspires to ensure that there always was/will be someone to do just that. Be it a Janitor spilling something, or a junior lab technician not understanding, or something more.
I was wondering what would happen if the same thing was done with this Delayed Choice test. So I started writing it up as popular science essay, that I was aiming at being understood by anyone without a science background.
I was comparing this to the Bell's inequality experiment, when I finally realised what I'd missed. In the Bell's inequality tests, non-local quantum entanglement cannot be used to send information faster than light because it involves random processes, and you need to combine information from detectors on both sides of the experiment before you can see the non-local connection.
Similarly, there is no way to send information back in time using the Delayed Choice test, as the only way to show that effect has preceded cause is to combine information from both detectors at the cause and effect time of the experiment before you can see the non-temporal connection.
{ETA} This makes the weirdness of quantum mechanics really clear to me. I knew that entanglement meant that entangled particles have some faster-than-light spacial connection, but hadn't made the obvious connection that they therefore must have some faster-than-light chronological connection.
I think this implies that all events must be predetermined.
This led to me think about an Asimov story where such an experiment takes place. They wait until the experiment says that water was/will be poured on this in 24 hours, and then seal the container. They find that the universe conspires to ensure that there always was/will be someone to do just that. Be it a Janitor spilling something, or a junior lab technician not understanding, or something more.
I was wondering what would happen if the same thing was done with this Delayed Choice test. So I started writing it up as popular science essay, that I was aiming at being understood by anyone without a science background.
I was comparing this to the Bell's inequality experiment, when I finally realised what I'd missed. In the Bell's inequality tests, non-local quantum entanglement cannot be used to send information faster than light because it involves random processes, and you need to combine information from detectors on both sides of the experiment before you can see the non-local connection.
Similarly, there is no way to send information back in time using the Delayed Choice test, as the only way to show that effect has preceded cause is to combine information from both detectors at the cause and effect time of the experiment before you can see the non-temporal connection.
{ETA} This makes the weirdness of quantum mechanics really clear to me. I knew that entanglement meant that entangled particles have some faster-than-light spacial connection, but hadn't made the obvious connection that they therefore must have some faster-than-light chronological connection.
I think this implies that all events must be predetermined.
no subject
Date: 2009-07-02 08:00 am (UTC)As I understood it the point of Bell's inequality is that it proves that 'hidden variables' are not enough and that there must be non-locality.
no subject
Date: 2009-07-02 08:45 am (UTC)no subject
Date: 2009-07-02 08:58 am (UTC)Maybe the universe is like a violin string. There's an infinite number of modes of vibration, but they almost all destructively interfere leaving you with only a few harmonics. That doesn't mean that any of those notes actually existed. It's just a mathematical trick. The laws of physics allow for many things that could happen, but most of them never will.
no subject
Date: 2009-07-02 10:04 am (UTC)no subject
Date: 2009-07-02 12:41 pm (UTC)That was awesome and got awesomer all the way through. I don't understand why people didn't understand the ending.
no subject
Date: 2009-07-02 01:11 pm (UTC)Firstly there were the people who we're'nt clear with which way round the implications would be if envelope had contained an interference pattern or a diffuse spread. That's understandable, apparently the magazine had diagrams at the appropriate point in the exposition.
The last line: "a series of shaded semi-circles" put me (and all but 1 of the other commenters) in mind of an interference pattern. Which implies one of at least three things happen next.
However the author apparently meant the opposite, and the envelope contained only a diffuse pattern, which only has a single, depressing, meaning.