Tuesday, 18 January 2011

Demystifying quantum mechanics prologue

Ok it was bound to happen sooner or later I would be provoked by an article or TV program on quantum mechanics claiming that it's all mysterious, no one can understand it, it is totally counterintuitive and so forth. I'm afraid I find all this talk at misleading and at worse really no more than absolute tosh. The culprit in question was last nights Horizon programme shown on BBC2 last night. I can only sketch my objections into what I imagine will be a big theme of these blogs. For now I just want to point out some of the claims that I object to and I will try and provide appropriate references for each of the claims in a series of posts.

1) The two slit experiment implies that particles split in two and then reform before impinging on a screen.

2) Particles after separating from a common source still stay in communication with each other and send signals faster than the speed of light

3) Every time a measurement is made a parallel universe is made

4) Objects are created simply by an act of measurement

and so forth,

Ok to give some clues to more detailed posts, the interpretation I favour, if it can be called an interpretation is the minimal statistical model. It seems to me that much of the so called mystique surrounding the interpretation of quantum mechanics stems from the fact that people refuse to take the probabilistic aspects of quantum mechanics seriously. I will expound more in a later post but let's just take the two slit experiment for example. The facts are that it is only  possible to see the classic interference pattern emerging as a result of a cumulative number of events. Indeed it is only after a statistical significant events have occured that anything like wave like properties can be attributed to a photon or electron. Conversely it makes sense to speak of certain attributes of particles such as their mass or charge as belonging to individual particles. Rather than as some people would have it that particles split in two and then magically reform why not simply admit that the so called interference  pattern is no different from say the way in which other probability distributions emerge from a collection of events eg the binomial distribution. OK the interesting question is why the probability distribution in events like the two slit experiment are not the same as would be classically expected. But please do not try and interpret what is primarily a statistical phenomenon on what is alleged to happen to a single particle.  It has just as much significance as a single  throw of the  dice does or a single roll of a roulette wheel. If particles really did split into when they pass through slits why are we bothering with the Large Hadron collider ?

I will provide a link to a paper which shows how the formalism of quantum mechanics taken for what it is can explain the essential features of the two slit experiment without having to invoke wave particle duality or  the idea that particles split in two when passing through slits. The essential feature is that the slits can be seen as measuring devices the uncertainty in position measurement allows for the uncertainty in momentum arising in an interference pattern.


  1. Chris,

    You mean the BBC Horizon episode 'What is Reality?'. The 'parallel universe'-guy talks about PUs if they are a certainty. Which they are not, of course. Just in his mind because he created that particular niche in physics and is making a living out of it by writing nonsense papers no one can argue with anyway ( it might be true! ) and appear in programs like Horizon. He is competing with Michio Kaku on the number of times his face was on television because scientifically he is -out of ideas-. Just my 0,02c worth of opinion.

    Back to your point. I know that light behaves partially as a wave and otherwise as a particle beam. Are you referring to the experiment that proves this?

  2. Actuallly it was Everrett in 1957 who first thought of this idea, Max Tegmark is just jumping on the bandwagon (along with a lot of other people). Yes I am referring to the 2 slit experiment as explained in the next post the simplest explanation that is available is to concede that the intereference pattern is statisitical but individual particles do not simply split into and magically reform. Nor as the Horizon program seem to indicate in one universe it passes through one slit and in another universe it passes through the other. The paper I give a link to gives the simplest explanation of the two slit experiment I've come across it's a pity that it's not more widely known.

  3. Not even his own idea?! It looks as though it is the only idea he ever had ( =jumped on )! :-)
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