S4F: If You are Uncertain—Call a Quantum Mechanic for a Fix

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by David Siegel Bernstein, PhD

The only thing that makes life possible is permanent, intolerable uncertainty; not knowing what comes next. – Ursula K. LeGuin

In honor of Halloween I’m writing about a spooky topic: quantum mechanics (QM). Don’t run away!  I promise this post won’t be too scary. But I warn you, although it will sound like fiction, it really is science.

QM is a lot like Alice’s Wonderland so I’m going to ask you to believe at least one impossible thing before breakfast: The Heisenberg uncertainty principle—the lynchpin of quantum theory. It states it is impossible to simultaneously measure both the momentum and position of a particle with certainty. More importantly, these two uncertainties cannot be reduced to zero together. Of particular interest to science fiction writers, there is also a minimum for the product of the uncertainties of energy and time. More on that in a future post.

These simple statements, proven by experiment, describe the absolute limit to what can ever be known! No matter how much we struggle against it, there will always be uncertainty in the quantum Wonderland.

But why?

In classical physics, whatever is measured always has definite, well defined, properties so any possible uncertainty must come from perturbation (a change) that occurs from the act of measuring. Let’s assume that in the QM Wonderland the Mad Hatter is the size of an electron. Yes, I know it’s impossible to shrink smaller than your constituent parts—atoms, but go with me on this. To observe the little guy, we need light. When a photon (a discrete bundle of light) hits him, it perturbs him enough to make him run off. Photons have large wavelengths, giving him a lot of running room, so the chances of finding him are smaller than the chances of finding Alice after she’s unwisely drank from an unidentified flask. Now if instead we use high frequency gamma rays, small wavelength, they will hit the Mad Hatter like missiles. The point of impact gives us a good idea of where he was, but we’ve knocked him away unpredictably.

However in quantum physics (the study of the very small) there are no definite values to measure, only fuzziness.

“Fuzziness?” you ask.

Yes! That is the impossible thing I want you to believe. It’s all fuzzy in the QM wonderland because particles can also be waves. In fact anything with mass, including you, can be described as a wave with a frequency.  In QM, size matters, because the larger the wave relative to size, the greater the uncertainty and fuzziness. This wave-particle duality was first described by DeBroglie in 1924.

The reason you don’t have (much) uncertainty in your location or how you journeyed to your computer to read this post is because your velocity is too slow and mass too large to overwhelm your practical certainty. So if we tumble down the rabbit hole, shrinking until we’re the size of the subatomic Mad Hatter, our wavelength relative to our size will become larger and larger, making us fuzzy to anyone trying to find us. This fuzzy probability cloud is similar to what an electron is while orbiting an atomic nucleus.

So, it is not the measuring that changes the state of a system—it’s the fact that position and momentum are undefined (fuzzy) until measured. Spooky.  In fact Heisenberg claimed it made no sense to talk about where an electron was or what it was doing between measurements. If you take this thinking to the extreme, measuring something creates the reality we observe. Past behavior does not exist until measurement is made and future paths can’t be predicted either. So observing changes what is observed.  This interpretation is known as the Copenhagen interpretation of QM.

Einstein and Schrödinger did not like this interpretation. Schrödinger attempted to demonstrate its absurdity with his famous thought experiment. Allow me to paraphrase it: consider a Cheshire cat in a box with a device connected to a hammer and a glass tube of cyanide. The device contains an atomic isotope that has a 50% chance of decaying within an hour. If it does decay, the hammer will drop, breaking the glass tube, killing the Cheshire cat. Note, because the isotope is atomic, it is subject to the spookiness of QM.

After an hour, the question is whether the Cheshire cat is dead or alive. What happens if you don’t check?

According to Schrödinger, the Copenhagen interpretation would conclude that, as long as the box remains closed, the Cheshire cat is both dead and alive, a state called superposition.  Only when the cat is observed as being either dead or alive does it actually become dead or alive. Put that in your caterpillar’s hookah and smoke it!

Now that I think about it, we might not exist if no one is looking for us while we are in the QM Wonderland. Or—worse—we may never have existed to fall in the rabbit hole in the first place.

Ponder this: do we exist if no one friends us on Facebook?

In a story I wrote titled, Chronology, I ratcheted up the fuzziest of the uncertainty principle to the point where I kept my protagonist in superposition, trapped in many different states (each state being a different character). I kept the reader guessing which of my characters would be left when finally observed; all the other characters vanished along with their histories (all unremembered). The big lie of my story was taking QM weirdness and applying it to the macro-world, which can’t be done outside of fiction. In order to maintain a semblance of plausibility, I kept all the other science in my story as accurate as possible.

Have a happy Halloween and if you are planning on trick-or-treating as Alice, please avoid any holes into quantum reality and don’t drink from unlabeled flasks.

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3 Responses to “S4F: What’s the Matter with Antimatter?”

  1. William Haloupek Says:
    March 8th, 2012 at 6:43 pm

    Interesting article!

    Stealth is easier than cloaking, and we already have the technology.

  2. David Siegel Bernstein Says:
    March 30th, 2012 at 7:41 am

    William you are absolutely correct. Invisibility (a descendant of Stealth) is not only easier to achieve, but a future topic. I thought I’d go over invisibility first to please those who enjoy Harry Potter, but want to write hard science fiction.

  3. donnagalanti Says:
    April 5th, 2012 at 5:39 am

    Fascinating post. We are so much empty space and mostly water. Amazing to think how we can be beings of intelligence and creativity.

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