Stop. Just…stop. A Blast from the Past. (Slightly updated)

I recently saw a blog post over on IO9 about 10 scientific ideas that scientists wish people wouls top using (incorrectly).  They missed my personal pet peeve–the use of quantum theory, badly understood or not understood at all, to supposedly explain new-agey magic (of the wizard and witch kind rather than the stage type) or psychic phenomena.

In quantum mechanics observation changes the thing observed, but that doesn’t mean you can use that to cast spells that do whatever folk claim to do with magic.  Here’s how it works:

Imagine you’re in a dark room.  There are objects in that room.  You have a big pile of baseballs and want to know where the objects are in the room.  You can throw the baseballs in various directions.  In certain directions the baseballs bounce back.  When they do, you know they hit some object.  You can then use things like the speed and direction in which you threw the ball and how long it took to bounce back to tell you in what direction and how far the object is.  Throw enough balls and you can get some idea of the size and shape of the objects.

Now, all the objects in the room are on casters.  When you hit them with a thrown ball, they move.  If they’re big and heavy they don’t move much.  If they’re small and light they move a lot.  Observing them, by throwing these balls at them, is going to affect them.

Consider the balls themselves.  The size of the balls limits what you can “see” with them.  Anything smaller than the ball itself you might see that it’s there, but you won’t be able to tell it’s size and shape.  And when you hit it with that ball it’s more likely to go sailing across the room and you only know where it was, not where it is now (after it got hit).  If you want to see smaller objects, you need smaller balls.  Now, this is the tricky part.  There’s a rule.  The smaller the “ball” the heavier it has to be.  That’s backwards from what we usually think of things, but to describe quantum effects you need that rule.

So you can see smaller objects by using smaller “balls”, but the result is that you’re going to hit the objects harder with those heavier balls and knock them just that much farther and faster away.

This, right here, is “observation changes the thing observed.”  The balls are whatever we use to look at something, whether sound waves, quanta (discrete packets) of light, electrons in an electron microscope, or anything else.  We “shine” the light or whatever on the object we wish to see (throw balls at it) and look at either what’s reflected or what passes through it to “see” the object.

At a basic level, when it comes to light the size of the “balls” (the wavelength of the light) is given by the following formula:

Eλ = hc

E = energy
λ = the wavelength (size of the “balls”)
h = Planck’s Constant a really, really, really small number. (Okay, it’s
6.62606957 × 10−34 joule∙second, but at this level what you need to know is that it’s really small.)
c = the speed of light.

For “particles” like electrons that have mass, the equation is a bit different:

λp = h

Here p = momentum.
You can think of momentum as the ability to impart motion in things.

for the momentum of massless particles (like light) we have (simplified):

p = E/c = h/λ
Note that momentum is inversely related to wavelength, the size of the “balls”.

In both cases, to get a small wavelength (small “balls” to look at small stuff) you need to have either a high energy (light) or high momentum (particles with mass).  Heavier balls that you throw harder.  And, when you throw heavier balls harder at the thing you’re observing, you knock it around more.

That’s “observation affects the thing observed.” It’s not magic.  It’s the simple fact that to observe something you essentially throw balls at it.  They’re just really, really tiny balls (see that Planck’s Constant).  Something like this, if you wanted to “observe” an electron:


And the effect is only important on really, really small things, things like electrons, sometimes atoms themselves.  Electrons and atoms are very small compared to the energies of light, of “photons” and their momentum, that would be small enough, have a short enough wavelength to see them.  Thus, they get moved by that light.  The observation affects the thing observed.

Larger things can be observed by longer wavelengths, by much less energetic photons.  And are not, then, appreciably changed by the observation.  To appreciably affect them, you’d have to throw a whole lot more energy and momentum at them, far far more than necessary for mere observation.

This analogy only scratches the surface.  There’s a lot more I could do. (Quantum tunneling:  the balls are “squishy” and can sometimes get through holes that are nominally too small for them.) But that will be enough for now, I think.


2 thoughts on “Stop. Just…stop. A Blast from the Past. (Slightly updated)”

  1. You describe what is known as “The Observer Principle,” which applies at rather more than a quantum level (Id est, “reality television.” The act of observing people in their “reality” changes their “reality” and behaviour, because they know they’re being watched. (I shan’t dig in to the likely scripting and suchlike that is going on – I don’t watch television from the off, much less “reality” television. It has as much bearing on reality as trying to determine my physical size by examining the little toe of my left foot.)

    However, we don’t fully understand “quantum mechanics – the dreams that stuff is made of.” Quantum entanglement, for instance, may explain tele-psychic phenomena (in “entangling” one mind with another, for instance, allowing emotion or thought transference.) Actual “magic” is another matter entirely, I’d look for explanations for that in higher dimensions rather than quantum mechanics (cf: “Flatland.”)


  2. An imperfect explanation? Perhaps. Still LOADS better than everything else I’ve encountered to date (which includes actually *doing* some – admittedly EXTREMELY* basic quantum computations). This post would be an excellent addition to any (text)book purporting to cover/explain (ha!) Quantum Mechanics.

    * Yes, Ox slow. Slow mean “take time” NOT “never get there.”


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