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Oct 03 2009

Schrodinger’s flippin’ cat!

There comes a time in a blogs life when a bit of a rant is called for, here’s mine or at least the first one. To be honest it’s a fairly discrete, civilised rant – because that’s the sort of chap I am. It’s about cliches in science.

Quite some years ago, Stephen Jay Gould wrote an essay entitled “The case of the creeping fox-terrier clone”, published in “Bully for Brontosaurus“. In it he describes how he was writing a piece on evolution using the time-worn example of the horse, and in particular an animal named hyracotherium also known as eohippus or “The Dawn Horse”. The problem for Professor Gould was that he found himself on the point of typing that eohippus was “the size of a fox-terrier”, the thing is he had no idea how big a fox-terrier was! That’s right, Prof Gould (who I think writes very nicely) was about to commit a cliche to paper, and rather admirably he stopped and had a bit of a think instead. Now the reason he was about to write this was that he’d read it many times before, it’s a very standard story in evolution. He wasn’t alone, many writers have written how “eohippus was the size of a fox-terrier”, and doubtless many of them had no idea how big a fox-terrier was. Many readers have, no doubt, read those words, nodded sagely to themselves and said “All is well, I know that eohippus was the size of a fox-terrier”. It’s not really the cliche that’s the problem, the problem is that we’ve gone through the motions of communicating an idea, but sort of failed. Just in case it was bothering you, a fox-terrier is about the same size as eohippus, or roughly 40cm at the shoulder ;-)  I reckon that’s about the same size as a large lamb.

This isn’t an isolated example, science writing (and education) is riddled with cliche, not just cliche in word, but cliche in thought. My own bugbear is Schrödingers cat, of whom surely everyone must have heard. Erwin Schrödinger was one of the fathers of quantum mechanics.

IM IN UR QUANTUM BOX � MAYBE.
 (I have a bit of a weakness for lolcats)

Briefly, Schrödingers “thought experiment” is as follows: take one quantum mechanical system (a radioactively decaying material is common), one cat, one diabolical system to kill the cat based on a random event from the quantum mechanical system and one opaque, cat-proof box. Combine ingredients and wait…now open the box. The argument put is that prior to opening the box the cat is in an uncertain state between dead and alive (which is true of the quantum system, atoms in the radioactive material could be said to be decayed and undecayed simultaneously). 

However, Schrödinger prefaces this thought experiment thusly: “One can even set up quite ridiculous cases.” Schrödinger didn’t think his cat was genuinely in some weird half-way house between dead and alive he was quite clear that it was very definitely one or the other and the problem was that for systems obeying quantum mechanical rules this wasn’t the case. That’s the useful point in this thought experiment: “There’s something weird that goes on between the quantum and the classical and we don’t know what it is”. Yet time after time you see this experiment described without the critical proviso. People go away with the false impression that undead cats exist!

oh dear I can feel my self getting a bit incoherent now… special relativity, I’ve taught special relativity, it’s genuinely a marvelous intellectual leap that solved a couple of serious problems in physics. It has some real world applications (understanding my old friend the synchrotron, GPS satellites, lifetimes for relativistic muons in the atmosphere etc). But the text book examples we give to students are rather worn, nope, “worn” is the wrong word. “flippin’ ridiculous” gets a bit closer. Here’s one:

“You have a 10 meter long ladder, and a 5 meter long shed. How fast must the ladder enter the shed in order for it to appear to fit inside to a stationary observer?”

I can tell you the answer: it’s “really fast” – some large fraction of the the speed of light. To put it another way, a ladder travelling at the requiste speed could travel the length of the equator in something under quarter of a second, that’s probably a little faster than your reaction time and I’m sure you have an intuitive feel for the length of the equator. My point here is that (1) You’re going to struggle to get your ladder going that fast (2) if that ladder’s going past you that fast, the absolute last thing on your mind is going to be “ooo…look, the 10m ladder is fitting into the 5m shed”. If your shed is in a vacuum then you won’t get killed by massive plasma shockwave, but how many sheds have you seen in a vacuum? For part 2 of this experiment one may find some halfwit has placed a concrete block at the back of the shed to check the ladder really is fitting into the shed by bringing the ladder to an instant standstill inside the shed. Once again, when ladder hits concrete whether ladder fits into shed is the least of your worries. Assuming that you were in a vacuum, your ladder/concrete collision is going to release “absolutely loads” of energy – fusion bomb scale. There you go, I’ve lost it completely now. Special relativity teaching is full of everyday objects (trains and rulers are typical) traveling at implausible speeds, and it really winds me up!

Don’t get me started on “Alice and Bob“, the quantum cryptographers and if one more string theorist tells me that all the extra dimensions are “curled up very small”, there’s going to be some hurtin’.

And relax… I feel better now that I’ve written it down.

2 comments

  1. Jim

    Cathartic isn't it?

    I like to tag my rants as 'rants' and mirthfully re-read them every so often, quietly shaking my head at myself.

    …then of course, two days later I'm up in arms again!

  2. SomeBeans

    Yes, I feel much better for that!

    And as a bonus I've discovered I still have "Bully for Brontosaurus" and Stephen Jay Gould's book on the precambrian fossils in the Burgess shale (A Wonderful Life).

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