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I will admit that this topic has nothing to do with Einstein's theories of relativity, but it does pop up occasionally in time-travel fiction. I'm talking about time travel as a genetic disorder or mutant trait. This is not science. There are no scientific theories of time being dependent on an individual's genetics (perception of time is another matter). That doesn't mean we can't enjoy it as fantasy fiction. Examples include The Time Traveler's Wife (chrono displacement) and Hiro from the television series Heroes.

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

  —Ursula K. Le Guin

  He lies here, somewhere.

  —Werner Heisenberg's epitaph

  Welcome to the spooky world of quantum mechanics. Don't run away! I promise this chapter won't be too scary. But I warn you, although it will sound like fiction, it really is science.

  Quantum mechanics is a lot like Alice's Wonderland, so I'm going to ask you to believe at least one impossible thing before breakfast. That impossible thing is the Heisenberg uncertainty principle, the lynchpin of quantum theory. The principle states that it is impossible to simultaneously know for certain both the current location of a subatomic particle and the path it has taken to get there.

  More importantly, these two uncertainties cannot be reduced to zero together, meaning that the more you learn about one, the less you know about the other. This uncertainty is not from flaws in measurement but from quantum fuzziness due to the wave nature of particles (more on waves in a moment). This principle has been proven by experiment and describes 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. In 1927, Werner Heisenberg published his work on this principle,1 and in 1932—with certainty—he won the Nobel Prize in Physics.

  Joke: Werner Heisenberg was pulled over for speeding. The officer asked him if he knew how fast he was going. Heisenberg replied, “No, but I know where I am.”

  The reason for all the fuzziness is that particles can also be waves. This is the so-called wave-particle duality. In fact, anything with mass, including you, can be described as a wave with a frequency. Frequency is the number of cycles of an oscillation. Think of frequency as the number of waves that pass a fixed place in a given amount of time.

  In quantum mechanics, size matters. The larger the wave relative to the size of an object, the greater the uncertainty and fuzziness. The reason you don't have (much) uncertainty in your location or how you journeyed to your favorite coffee shop to read this book is because your velocity is too slow and your mass is too large to overwhelm your practical certainty.

  However, as 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. A wavelength is defined as the distance between successive peaks of a wave (think of water in a lake). Because our wavelength increases (relative to our size), we become fuzzy to anyone trying to find us.

  This fuzzy probability cloud is similar to where an electron is as it orbits an atomic nucleus. In fact, Heisenberg (allegedly) claimed that it made no sense to talk about where an electron was or what it was doing between measurements.

  For the record, it is impossible to shrink smaller than your constituent parts (atoms), but go with me on the whole Mad Hatter thing. I believe it will help you conceptually. Inside that fuzzy haze, where is the Mad Hatter? I know he has to be somewhere because I sent him down the hole. I will have to guess. I want it to be an educated guess, so I will search in the place where he is most likely to be.

  The best way to do this is to use the Schrödinger wave equation.2 This equation describes reality in terms of probability. Although this is not a perfect analogy, imagine that I flip a subatomic-sized coin. While it is spinning, I don't know whether it will land heads up or tails up, but I do know the probability. There is a 50 percent chance of it landing heads up. If this were a true quantum-level event, we could say that the coin is simultaneously in a state of both heads and tails while it is spinning, a state called superposition.

  In quantum physics, superposition is defined as the total of all possible states in which an object can exist. When the coin settles on the ground, the probability cloud evaporates and there is only one result: either a head or a tail faces up. Scientists call this the collapsing of the wave function. Probability fades into the deterministic world in which we live. This is true for all subatomic particles like electrons.

  More generally, the wave function describes a probability wave where the peak is the highest probability of an outcome. Think of a bell curve with its rounded peak and, on either side of the peak, descending tails associated with lower probability. A particle can be found anywhere in the wave, and, at the quantum level, the particle is in all locations in the wave (superposition). Only when the wave function comes crashing down after an observation does all uncertainty fade. Presto! We have a classical particle with a known position and path.

  So the measuring doesn't cause the uncertainty; rather, the uncertainty is because the position and momentum are undefined (fuzzy) until measured. The act of observing changes what is observed. Spooky. This interpretation is known as the Copenhagen interpretation of quantum mechanics. If you take this thinking to the extreme, then measuring things creates the reality we observe along with all past behavior.

  This interpretation did not sit well with Einstein and Schrödinger. Schrödinger attempted to demonstrate its absurdity with his famous cat thought experiment.3 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 percent chance of decaying within an hour. If it does decay, the hammer will drop, breaking the glass tube and killing the Cheshire cat. Because the isotope is atomic, it is subject to the spookiness (probabilistic nature) of quantum mechanics.

  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 in superposition, both dead and alive. Only when the cat is observed as being either dead or alive does it actually become dead or alive.

  WHAT IS A QUANTUM LEAP?

  Imagine you have drawn a series of bouncing ball pictures in a flip tablet. As you flip through your book from back to front, the ball should appear to be continuously moving. But we know better. Each page is a discrete (meaning noncontinuous) moment of the ball's path. The movement from one page to the next is analogous to a quantum leap, a discrete movement from one spot to the next. The whole might appear continuous, but deep down at the moment level, it is not.

  A quantum leap refers to an abrupt movement from one state to another. In the quantum universe, there is no in-between transition. For example, an electron is fuzzy (remember to think of it as a wave) in its orbit around an atomic nucleus. When it changes to a different energy state, it leaps from one orbit to another rather than move in a continuous fashion.

  Whereas chapter 1's theories on relativity view the universe as continuous, quantum mechanics treats it as granular (the technical term is quantized). Here is another way to think about it. If you keep zooming in closer and closer on a picture, it will begin to look pixelated. The same is true for time. If you slow time down enough, movement might no longer appear to be continuous but rather would leap from one moment to another. No smooth transitions.

  THAT SPECIAL MOMENT…WHEN YOU JUST KNOW

  Decoherence is the term scientists use for the initial interaction of a quantum particle with its environment. This is the moment when its position, location, and other traits can be measured. In other words, you go from an undecided superposition to an ordinary position. It is the instant we open the box and observe the Cheshire cat, and she goes from superposition to her fate. Decoherence is not the cause of the collapse (that may
be due to observation); rather it is the decay of coherence of the wave function as it leaks into our classical environment.

  In the 2013 movie Coherence, a loss of decoherence leads to parallel versions of the characters leaking out into the story.4 This is a cool use of quantum mechanics as a plot device.

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

  In a story I wrote for M-Brand SF titled “Chronology,” I ratcheted up the fuzziness of the uncertainty principle to the point where my human protagonist stayed in superposition, trapped in many different states (each state being a different character). I kept the reader guessing which character would be left when finally observed, and once observed, all the other characters vanished along with their histories. The big lie came from applying quantum mechanical weirdness to the macroworld, which can't be done outside of fiction. To maintain a semblance of plausibility, I kept all the other science in the story as accurate as possible.

  In the Copenhagen interpretation, our measurements cause the decoherence, but other interpretations are available. One such alternative is the many-worlds interpretation, originally suggested by Hugh Everett in 1957.5 It can be a fun way to invoke quantum physics in science fiction.

  Remember Schrödinger's cat? Now imagine it's possible for both states (dead/alive) to continue after the box is opened. Each state causes the universe to branch.

  Joke: Schrödinger's cat walks into a bar…and doesn't.

  The many-worlds interpretation doesn't explicitly rely on decoherence, so there is no need for an observer. In this interpretation, every quantum event causes our universe to split into parallel universes. Each nonzero probable outcome is realized. When I flip my quantum coin, both outcomes occur. The universe has branched into two: one in which the coin comes up heads, and another where it lands tails up.

  In the many-worlds interpretation, there is no wave function collapse. The wave is always standing, and the particle can be found in all locations, each in a different universe. Every outcome for every subatomic particle has occurred, meaning every possible atomic reaction has occurred, meaning every possible formation of molecules has occurred, meaning every possible you has occurred.

  If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.

  —Niels Bohr

  Now that you know all about fuzziness, uncertainty, and the wave-particle duality—all of which, technically, are three sides of the same quantum coin—there is another feature of quantum mechanics that is popular in science fiction: quantum entanglement.

  Quantum entanglement is when two particles are said to share the same quantum state despite their locations. Notice, I did not write similar states—I wrote the same state, and I meant it. Any change in one particle instantaneously translates into a change for its entwined partner no matter how much distance separates the particles. They can be apart the distance of a universe or the width of a strand of hair. This entanglement is what Einstein described as a “spooky action at a distance.”6

  REAL SCIENCE AND SCIENCE FICTION

  Two practical applications for entanglement can and should be exploited more in science fiction: quantum communication and quantum computing.

  1.Quantum communication

  Theoretically (which is good enough for science fiction), quantum communication allows for instantaneous communication anywhere in the universe. The important idea here is that instantaneous implies faster-than-light (FTL) communication.

  Wait. In chapter 1, didn't I write that the speed of light was the absolute speed limit? I did, and that is why this quantum application is so extraordinary.

  Measurement is the key to a functional quantum communication system. The act of measuring one entangled particle will force the wave functions of both particles to collapse. The spin of the measured particle instantaneously makes the other particle spin the same way. Now you have a quantum communication system translating spin into language.

  2.Quantum computing

  Quantum computing also exploits the spookiness of quantum entanglement. The computers we are currently enslaved to rely on byte-sized strings of binary data. A byte is the smallest unit of working memory used to encode a single character of text or number. Bytes are traditionally made up of eight binary digits called bits. A bit can have a value of either one or zero.

  All of which is old school because a quantum computer uses quantum bits, commonly called (by computer geeks) qubits. The qubit is described in terms of probability, until it is observed. The values of one and zero are in superposition, and the probabilities of being either one or the other rise and fall with time. Sometimes the probability of a one is higher than zero, and sometimes it is less.

  So now you have a qubit representing a value of one or/and zero, and everything in between. The entanglements between qubits allow their probabilities to mix. This is quite a big deal because quantum computers can perform operations while the qubits are in this state of superposition and entanglement.

  Why is all this helpful? After an inputted problem is broken down into small parts, massive amounts of calculations can run in parallel (all the parts are run simultaneously) where the sum of qubit probabilities can be used to determine the most likely answer to the problem. Quantum computers can solve very complicated problems relatively quickly, ones that today's computers would need hundreds of years to solve.

  Finally, let's get crazy for a moment and mix quantum computing with the many-worlds interpretation. What about quantum computing between parallel universes, or using the computing power of other universes to solve complex problems in our own?

  MIND-BLOWING QUANTUM TRIVIA

  In quantum mechanics, particles don't have definite positions or velocities unless they are observed. To get weirder, in some cases, particles only exist as part of an ensemble of many particles. None have any existence on their own.

  According to quantum mechanics, the past and future are indefinite and might exist as a continuum of possibilities.

  PARTING COMMENTS

  The Heisenberg uncertainty principle does not mean that accurate quantum measurements cannot be taken. It means that they come at a cost—the increase in uncertainty of something else. Wave equations in quantum physics capture both the wave(ness) and particle(ness) of a subatomic particle. The size of the wavelength dictates the range of possibilities for a particle's position. This has been proven by experiment, but there are different interpretations of what it all means. Two major interpretations:

  The Copenhagen interpretation states that a subatomic particle can be anywhere along the wave front but collapses to a single point when observed.

  The many-worlds interpretation considers a never-collapsing (standing) wave that holds many branches, wherein each spike (an area of high probability) is perceived with 100 percent probability by some observer.

  Examples of practical applications of quantum mechanics in science fiction:

  Quantum communication relies on particle entanglement for instantaneous communication independent of distance.

  Quantum computers take advantage of both entanglement and superposition to increase their computing power.

  CHAPTER 2 BONUS MATERIALS

  BONUS 1: A TIME-TRAVEL PARADOX

  This is the so-called grandfather paradox thought up by French journalist René Barjavel in his 1943 novel Le Voyageur Imprudent to show how traveling back in time is impossible.7

  Imagine that you kill your grandfather at a time before your father was conceived. Does this mean you wouldn't have been born? And if you weren't born, how could you have gone back in time to off your grandfather in the first place? According to Barjavel, you exist right now because everything in the past happened the way it did. By going back in time to change events, you are preventing your own existence. Ouch.

  In science-consistent science fiction, an author
can avoid the paradox by accepting the many-worlds interpretation. Each time a character travels to the past, he generates a new timeline. The original timeline of the character's birth, the one where his grandfather has not faced his grand-patricidal doom, still exists. But now there is a new timeline in which the character was never born. Paradox avoided.

  In a story I cowrote with Dr. Susanne Shay titled “Mirror, Mirror,” published in Tales from Elsewhere, we used a version of this branching theory. The story included gender swapping and a very confused protagonist.

  There is a bit of good news, or possibly bad, depending on your point of view. The reasoning does mean there has to be branching if you travel into the future. This means there is no problem with a grandfather zipping into the future to off his grandson.

  BONUS 2: PHOTOSYNTHESIS AND QUANTUM MECHANICS

  Photosynthesis is the process by which plants take in sunlight and carbon dioxide and churn out oxygen and glucose. This process has a remarkable 95 percent efficiency rate. Researchers have calculated that the efficiency rate should be closer to 50 percent.8 How did it get so high?

  It is possible that the conversion energy is in a quantum superposition state and travels along all molecular pathways simultaneously. Once the quickest, most efficient path is found, the probabilities collapse and take that path. The best path is always taken, so efficiency is boosted.9

  If this is truly due to quantum superposition then the question for scientists is, how are biomolecules able to exploit this quantum effect, and how can we copy it and make super energy efficient solar cells (our current versions operate at about 20 percent efficiency)?

  BONUS 3: WHAT ARE QUANTUM SUICIDE AND QUANTUM IMMORTALITY?