Skeptics with a K: Episode #085


Spirit guides, Korean elephants, theme parks and Challenge 25. Plus Withnail and I, Schrödinger’s cat, Busty Belinda and Kate Middleton. Collapsing the wave function, it’s Skeptics with a K.

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  1. #1 by Marc on November 15, 2012 - 14:01

    After hearing Marsh’s psychic prediction I would like to clarify that I am not actually pregnant I am just fat.

    Otherwise great show as always

  2. #2 by Rupert on November 16, 2012 - 20:48

    Couple of things – Nadine Dorries is still an MP, she’s just suspended from the Conservative Party.

    Also, the situation with quantum physics isn’t exactly as you described it. The issue isn’t that you can’t observe something without shining light on it – although that can be part of the justification of the Heisenberg Uncertainty Principle. After all, you don’t need to shine light on Kate Middleton to see her – you can rely on light that would have been reflected off her even if your camera shutter hadn’t opened on time.

    It’s more to do with the fact that for interference effects to be observable (and for you to, say, get wave-like patterns in the two slits experiment), basically everything other than the interfering particles has to be be identical. When you observe something, the system of differing particles becomes vastly larger, and interference effects become almost impossible to detect.

    I think this is best explained by David Deutsch, in his book, The Fabric of Reality. Bear in mind that he is talking in terms of the Many Worlds Interpretation, rather than Copenhagen. Also, he uses the term “shadow particles” to refer to the parallel universe counterparts of particles in our universe.

    “The reason why interference effects are usually so weak and hard to detect can be found in the quantum-mechanical laws that govern them. Two particular implications of those laws are relevant. First, every subatomic particle has counterparts in other universes, and is interfered with only by those counterparts. It is not directly affected by any other particles in those universes. Therefore interference is observed only in special situations where the paths of a particle and its shadow counterparts separate and then reconverge (as when a photon and shadow photon are heading towards the same point on the screen). Even the timing must be right: if one of the two paths involves a delay, the interference is reduced or prevented. Second, the detection of interference between any two universes requires an interaction between all the particles whose positions and other attributes are not identical in the two universes. In practice this means that interference is strong enough to be detected only between universes that are very alike. For example, in all the experiments I have described, [like the double slit experiment] the interfering universes differ only in the position of one photon. If a photon affects other particles in its travels, and in particular if it is observed, then those particles or the observer will also become differentiated in different universes. If so, subsequent interference involving that photon will be undetectable in practice because the requisite interaction between all the affected particles is too complicated to arrange. I must mention here that the standard phrase for describing this fact, namely ‘observation destroys interference’, is very misleading in three ways. First, it suggests some sort of psychokinetic effect of the conscious ‘observer’ on basic physical phenomena, though there is no such effect. Second, the interference is not ‘destroyed’: it is just (much!) harder to observe because doing so involves controlling the precise behaviour of many more particles. And third, it is not just ‘observation’ but any effect of the photon on its surroundings that depends on which path the photon has taken, that does this.”

    If anyone, in turn, wants to correct me, feel free. I’ll excuse myself if I’m wrong on the grounds that (a) it’s been a few years since I studied this at uni, (b) I was always better at relativity than quantum and (c) I’ve just come back from the pub.

    Cheerio.

  3. #3 by Disagreeable Me on November 19, 2012 - 11:25

    Just to echo Rupert, the explanation of the Heisenberg Uncertainty Principle given by Marsh is incorrect because it implies that there really is a well defined position and velocity of a particle but that we disturb it when we observe it.

    This is not true – there are many experiments whose results are not compatible with this interpretation. It really does seem to be the case that there is no well defined value for a property until you measure it and “collapse the wave function”. The double slit experiment would be the most well-known example.

    This doesn’t have to mean that there is anything spooky about observation and especially consciousness, although explaining why this is the case is tricky. The explanation in this podcast, however, is certainly not the way to resolve the issue.

  4. #4 by Disagreeable Me on November 19, 2012 - 11:50

    Woops, sorry, attributed the quantum mechanics stuff to Marsh instead of Mike by accident.

  5. #5 by Mike on November 19, 2012 - 12:03

    Few points of interest! First, it was me, not Marsh :) Second, I never mentioned the Uncertainty Principle (though Marsh referenced it in the Quantum Land joke).

    Third (and most important) I was not arguing what you seem to think I was arguing. Maybe I wasn’t clear enough on the show, or maybe I just lack the appropriate technical language.

    I’m not arguing, to use the example of Schrödinger’s cat, the cat is definitely, objectively, dead or not dead, but we simply don’t know which until we check. I am fully aware that the evidence suggests there is no real objective answer until a measurement is taken.

    My point on “shining photons in” to see what’s going on wasn’t meant to be taken literally — it was only a description of one method of (pseudo-)passive observation. We collect photons that have reflected off the thing we are observing, and by examining those photons we learn about the thing. We can’t do that on quantum scales, because taking the measurement (even if it were just as simple as throwing photons in and seeing what comes back) changes the system — the Observer Effect.

    The only point I was trying to make is that, on this scale, “observation” is not a passive process. But people are so used to the idea of passive “observation” that they confuse the term “observation” with “information being received by a mind”. They then argue that there must be some special properly of consciousness which allows it to reduce a superposition to a single state — which is not the case. It is the act of measurement which collapses the wave function, not interpretation of that measurement by a conscious mind.

    (Also, Rupert, I know Dorries is still an MP. What was said was “I’m not sure if you can be legally referred to as ‘Nadine Dorries MP’ once you’ve had the whip withdrawn… actually, I think you can. But it was just about getting a dig in to Dorries really” :) )

  6. #6 by Mike on November 19, 2012 - 12:08

    Indeed, the point I was making seems to have been made by David Deutsch in the quote selected by Rupert above:

    “… the standard phrase for describing this fact, namely ‘observation destroys interference’, is very misleading … it suggests some sort of psychokinetic effect of the conscious ‘observer’ on basic physical phenomena, though there is no such effect”

  7. #7 by Heather on December 5, 2012 - 18:19

    What movie are you guys talking about in the opening segment? Sorry for the non-British ear but I just couldn’t suss it out. :-)

  8. #8 by Colin H on December 12, 2012 - 12:16

    That would be ‘Withnail and I’. :)

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