What Every Fantasy Writer Needs To Know About Quantum Physics

 

 

I have a Ph.D. in Electrical Engineering, which in itself doesn’tqualify me to talk about quantum physics, but I did my thesis research onsuperconducting quantum computation.  Inother words, I investigated ways to use superconductors to make a computerbased on quantum states.  I was alwaysmore of an experimentalist than a theorist, so I’ll be the first to admit thatthere’s a lot that I don’t understand, but I can at least talk about thebasics.

 

The first thing to realize is that quantum physics iscounterintuitive.  It doesn’t work theway we expect, because it doesn’t work the way that we observe the world to bein our daily experience.  The way that weinteract with the world is not on a quantum level (at least as far as we canobserve it), and therefore quantum physics seems strange and mysterious tous.  Sometimes quantum physics is citedas proof that the universe is magical, or that human consciousness is special,et cetera.  In reality, quantum physicsis proof only that the universe is strange and mysterious to ourexperience.  It may also be magical;human consciousness may be special.  Inmy admittedly anecdotal experience, different scientists believe differentthings about the whole metaphysics of the universe, but that is usually basedon reasons other than their knowledge of quantum physics.

 

Rather than focusing on the wave particle duality, or the Heisenberguncertainty principle, or quantum entanglement, or any of a hundred otherstrange things about quantum physics, I’ll focus on the fundamental issue thatcauses so much consternation and so many interpretations.

 

In quantum physics, it’s possible to have a superposition ofstates.  For example, imagine that youhave two metal plates.  You can placecharge on one, which affects charge on the other, and you have a capacitor,which there’s really nothing quantum about. However, suppose that instead of millions of electrons, you have acharge of one electron, which you place on one plate.  If you place your electron on the firstplate, your system is in one state, let’s call it state 0.  If you place your electron on the secondplate, your system is in state 1.  Sowhat happens if you place your electron on both plates?

 

Wait a second, you say.  It’sonly one electron, you can only place it on a single plate.  And here’s where quantum physics getsstrange.  In quantum physics, you can placeyour electron on both plates.  In thiscase, it’s called a superposition of states, because it’s in both state 0 andstate 1.  However, when you measure thesuperposition, it collapses.  It becomeseither state 0 or state 1, not both. Wait, you say again.  If everytime you measure it, it’s only in one or the other state, how do you know thatit’s ever in a superposition of states? We can tell because of certain measurements which can characterize thestate as a superposition rather than one or the other, but that would requiremore detail than I can give here.  Youcan read here for more information. 

 

The bottom line is that the system is in both states until you measureit, and then it becomes one.  Which oneit becomes when measured is a matter of statistics.  The weight of each state in the superpositioncan vary—it can be equal amounts of state 0 and state 1, mostly 0 with a little1, or vice versa.  When it is measured,the chance of finding it in one state or another is dependent on the weightingof each state.  If the superposition isweighted to 75% of state 1 and 25% of state 0, there is a 3 in 4 chance ofmeasuring it in state 1 and a 1 in 4 chance of measuring it in state 0.

 

And this is one of the fundamental issues with quantum physics.  What does it mean that the superpositioncollapses when you measure it?  There area number of explanations.

 

The Copenhagen interpretation says that observation is what causes itto collapse.  This is sometimesinterpreted as proof that consciousness is real, that there is somethingspecial about people, since their observation causes a real, physical change toa system, but the Copenhagen interpretation was never meant to encompass suchphilosophical considerations.  Instead,it was proposed as an empirical explanation. That quantum superpositions collapse when they are observed is whathappens, and the reasons behind it are not a concern of the interpretation.  The idea that it’s our conscious knowledgethat causes it to collapse is actually called the von Neumann/Wignerinterpretation, which doesn’t have that much of a following. The most popularidea as to the reason for the collapse is decoherence, which I’ll discuss morein a moment.

 

Another interpretation, especially popular among sci fi and fantasywriters, is the “many worlds” interpretation. This is much more popular in fiction than in physics, although it doeshave its adherents among physicists.  Themany worlds theory states simply that the quantum superposition does notcollapse.  It’s still in a superposition,only now, so are you.  There are now twoof you, one of which observes the system in state 0, the other of whichobserves the system in state 1.  Now thisconcept, of coexisting worlds based on coexisting quantum states is often mergedwith the idea of alternate dimensions with alternate timelines—despite the factthat there’s no dimensional element to the many worlds theory.  The many worlds would co-exist in the samespace and time.  The other issue withmany worlds, at least as it corresponds to alternate timelines, is that eventswhich change history are, for the most part, not quantum.  They’re on the large scale compared toquantum physics.  Physicists would saythey’re based on classical physics.  It’shard to see how the state of an atom would affect whether Booth shotLincoln, for example.  Oh, it’s notimpossible that if there was a change in a large enough number of atomic statesthat would have an effect, but it would have to be a huge number in aggregate,meaning that alternate history events would be very low probabilityevents.  In a many worlds interpretation,that would not mean it didn’t exist, but it would be a very small weight in thesuperposition.   In an infinite number ofworlds, most of them would be indistinguishable from our own.

 

Adherents of either interpretation are familiar with the concept of decoherence.  That’s the idea that any time you measure asystem, you introduce noise into it. This noise determines how quickly the superposition collapses, ordecoheres.  This means that noise can becontrolled for, feedback decreased, and coherence times lengthened.  If you can get quantum states to last longerdespite interacting with them, you can do things with them.  Now measuring a state without collapsing itmay be out of the question, but you can probably manipulate it, which allowsyou to do quantum computation with it—which was my field.  Decoherence works.  You can test in the lab how long it takes aquantum state to decohere, and increase it or decrease it, according to howmuch noise you couple into the system. That doesn’t necessarily mean that there’s nothing to the otherinterpretations—you still can’t measure a state without collapsing it, which isthe question the interpretations were dealing with in the first place—but inrecent years, physics has focused on the mechanism causing them to collapse.

 

What does all this mean for the fantasy writer?  Should he stay away from alternate worlds,decry the existence of consciousness as a force which can influence systems,and the like?  No, of course not.  The fun of fantasy is that you can play withreality, rather than abide by it.  Butmany writers, when they want their characters to justify the existence of magicor the supernatural or alternate worlds, appeal to quantum physics as proof ofthe soul or multiple worlds.  Theseappeals are hardly necessary, and in fact can be quite damaging to thesuspension of disbelief for those who know something about quantum physics. 

 

I used the Wikipedia article on the interpretation of quantum physics to review, and as a starting point, for writing this.