by James Patrick Kelly
On June 28, 2009, the celebrated physicist and cosmologist Stephen Hawking threw a party www.youtube.com/watch?v=elah3i_WiFI. It was a catered affair, complete with champagne and hors d’oeuvres. Hawking was meticulous in creating his invitations, giving not only the address of the hall at Cambridge University, but its exact coordinates in hyperspace. He distributed these invitations throughout the world; over the years they’ve become something of a collectors’ item. You can find them on the internet, and for £39.00 you can own an authorized reproduction www.kiteprint.com/collections/frontpage/products/stephen-hawkings-time-travellers-invitation-open-edition. Despite all his efforts, however, Hawking failed utterly as a host. “I sat there a long time,” he reports, “no one came.”
Perhaps this was because Hawking didn’t send invitations out until after the party took place. Or perhaps it was because the guests he invited didn’t exist. You see, the invites read, “You are cordially invited to a reception for Time Travelers. Hosted by Stephen Hawking.”
Anyone who thinks that Hawking doesn’t have a sense of humor just hasn’t been paying attention. But when Hawking documented this party in his television series www.dailymotion.com/video/x1lvfi0_into-the-universe-time-travel_tv, it was not only as a jape but also as an experiment. He did all that he could to ensure that his invitations would last a long, long time in the hope that someone in the (perhaps distant) future who had mastered time travel would jump at the chance for a convivial glass or two with him in the twenty-first century. It was a win-win proposition for Hawking, who famously declared in his 1992 paper “Chronology protection conjecture” www.thelifeofpsi.com/wp-content/uploads/2014/09/Hawking-1992.pdf that time travel into the past was impossible. “It seems,” he wrote then, “that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians.” On the other hand, if someone from the future had shown up, think of the hot stock tips he could have passed along!
The apparent scarcity of tourists from the year 802,701 is reminiscent of the Fermi Paradox www.seti.org/seti-institute/project/details/fermi-paradox, which observes a similar scarcity of alien astronauts from TRAPPIST-1e http://en.wikipedia.org/wiki/TRAPPIST-1e and the myriad other Goldilocks worlds www.nationalgeographic.com/astrobiology/goldilocks-worlds/ in our universe. Where the hell is everybody?
Is the chronology protection conjecture right? I’m just an English major and can’t begin to explain the prediction that radiation feedback would almost certainly collapse any wormhole a time traveler could conjure up in order to zip into the past. But since a gap—to put it mildly—exists at present in our understanding of wormhole engineering, might there not be other explanations for why Hawking got no takers?
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One is that time travel might be possible, but it’s way too hard to accomplish. Special relativity http://www.einstein-online.info/elementary/specialRT tells us that any subluminal particle with mass would need infinite energy to accelerate to the speed of light. So, galactic empires? No way! Except various workarounds involving space warps have been proposed, notably the Alcubierre Drive http://en.wikipedia.org/wiki/Alcubierre_drive and traversable wormholes www.space.com/27845-interstellar-movie-wormhole-travel-feasibility.html. And if we could break the speed limit of the universe, that might also give us access to time travel. However, warping spacetime will require a tsunami of new science and the harnessing of energy sources that we are most likely centuries, if not millennia, from achieving.
Returning for a moment to the Fermi Paradox, let’s consider some of the variables in the famous Drake Equation www.seti.org/drakeequation, which weighs the probability that there might be aliens out there capable of contacting us. The last three variables in the Drake Equation are fi, the fraction of planets on which intelligent life emerges; fc, the fraction of these civilizations that develop technology capable of sending signals; and L, how long those civilizations last. While we are an instance of fc in the Drake Equation, in that we have been sending radio signals to the stars since 1906 www.quora.com/How-far-has-the-first-radio-signal-data-transmission-to-space-traveled-to-date, we are not yet counted in the fc of what I’ll call the Hawking Equation, which might estimate how likely time travel is to be developed—if it is possible. And what is our L in either equation? Will our fragile civilization survive long enough to leap all the daunting technological hurdles? Maybe our descendants will never get the chance to develop time travel?
Another explanation is that perhaps the time machine can only go back in time to the point where it was switched on. Since one hasn’t been invented yet, much less activated, 2009 (and for that matter 2017) was not accessible from the future. But if at some point a working time machine was turned on, it would create a closed timelike curve (CTC) www.scientificamerican.com/article/time-travel-simulation-resolves-grandfather-paradox/. The CTC would loop from the coordinates of its startup through other spacetime coordinates in the future and then back to the original coordinates. But no further back!
Still another explanation is that future generations may be too responsible to use time travel technology, since they’ll have read the countless—if somewhat quaint —science fiction stories from our era warning of the paradoxes that arise from travel to the past. For an excellent brief look at such hoary tropes as the Grandfather Paradox www.timetravelphilosophy.net/topics/grandfather, the Bootstrap Paradox www.astronomytrek.com/the-bootstrap-paradox-explained, the Meet Yourself Paradox www.timetravelphilosophy.net/topics/double and others, check out 5 Bizarre Paradoxes of Time Travel Explained www.astronomytrek.com/5-bizarre-paradoxes-of-time-travel-explained. For a more comprehensive and logic-twisting survey, try the excellent Time Travel Philosophy www.timetravelphilosophy.net website.
As a side note, a fannish reading of Stephen Hawking’s passing mention of a “Chronology Protection Agency” in his 1992 paper suggests that he was familiar with at least some of SF’s Time Police subgenre http://www.sf-encyclopedia.com/entry/time_police in which responsible citizens from the future patrol the time lines to prevent evildoers from changing history. Indeed, no less an authority than SFWA Grandmaster Frederik Pohl www.thewaythefutureblogs.com asserts that Hawking has always been an SF fan. “Stephen Hawking said he spent most of his first couple of years at Cambridge reading science fiction (and I believe that, because his grades weren’t all that great).” And did you know that Hawking and his daughter Lucy have written a science fiction series for young readers, beginning with George’s Secret Key to the Universe http://en.wikipedia.org/wiki/George’s_Secret_Key_to_the_Universe?
One final explanation for why Hawking failed to attract any guests might be that we inhabit the original timeline that existed before time travel was invented. Suppose that whenever time travelers switch on their devices and traipse off into the past or the future, they remove themselves to a different timeline in a parallel universe and are therefore unable to return to ours, the universe of their origin. Thus whatever mischief they wreak and whatever wrongs they right would have no impact on us.
We Asimov’s readers know all about the long tradition of flipping historical turning points into alternate histories. For “What if the Nazis had won WWII?” see The Man in the High Castle http://en.wikipedia.org/wiki/The_Man_in_the_High_Castle by Philip K. Dick www.philipkdickfans.com or for “What if the Spanish Armada had defeated the English?” see Ruled Britannia http://en.wikipedia.org/wiki/Ruled_Britannia by Harry Turtledove www.sfsite.com/~silverag/turtledove.html. For some time these tales have occupied contested ground in the genre. Are they fantasy or science fiction? Critics still disagree.
In a ground-breaking doctoral thesis published in 1957, physicist Hugh Everett III http://en.wikipedia.org/wiki/Hugh_Everett_III showed (among other things!) how these alternate histories might actually be SF. His proposed interpretation of quantum mechanics was at odds with accepted theory at the time, the Copenhagen interpretation http://plato.stanford.edu/entries/qm-copenhagen championed by Neils Bohr www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html. To understand the disagreement, recall the famous Schrödinger’s Cat thought experiment www.youtube.com/watch?v=OkVpMAbNOAo. It was designed so that, due to a probabilistic quantum process, a vial of cyanide might or might not be smashed, thus poisoning a cat sealed with the vial in a box. The equations tell us that something must happen, but that there’s no way to know what until someone opens the box and looks. Bohr’s Copenhagen interpretation says that the cat exists in a state of superposition, that it is at once alive and dead until someone opens the box and by observing collapses the quantum wave function, settling the cat’s fate. Everett’s take is that the microscale quantum event that determines whether the vial is smashed or not happens at the macroscale as well. Two universes diverge from the defining moment; one in which the cat is alive and one in which the cat is dead. Everett’s mind-boggling idea is known today as the Many Worlds Interpretation www.youtube.com/watch?v=dzKWfw68M5U. While originally dismissed with scorn, it has garnered more and more adherents, although majority opinion among physicists still lies elsewhere. If you don’t mind losing your grip on reality, click over to io9 www.io9.gizmodo.com/the-9-weirdest-implications-of-the-many-worlds-interpre-1692618056, for an exploration of what the many worlds interpretation might mean to you personally.
But for our purposes, the Many Worlds Interpretation offers an explanation of how all time travelers would have to pass out of our universe, never to return. This would leave our world as the pristine one in which time travel does work, but in which it appears not to.
For an amusing video recap of these explanations of why our most famous cosmologist was stood up by the future, click over to Stephen Hawking Invites You To His Time Travel Party http://journalofthingsblog.wordpress.com/2017/02/17/stephenhawking. In fact, let me recommend the entire Journal of Things Blog http://journalofthingsblog.wordpress.com “a weekly essay series on topics ranging from films, politics to science and spirituality” created by Sudharsanan Sampathkumar www.sudharsanansampath.com. His concise and clever videos cover a range of topics of interest to readers of this column.
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I’m afraid I have to agree with Stephen Hawking’s chronology protection conjecture, alas. The arguments against it, while fun to explore and well-suited for storifying by up-and-coming SF writers, do not pass the Occam’s Razor www.youtube.com/watch?v=skcCu4RUkAg test. So sorry, no time travel into the past for the likes of us!
Time travel into the future, on the other hand. . . .
Meanwhile, if it’s any consolation, Hawking was not the first to come up with the tongue-in-cheek idea of a “Chronology Protection Agency . . . which makes history safe for historians.” As James Gleick www.around.com points out in Time Travel www.nytimes.com/2016/10/02/books/review/james-gleick-time-travel.html?_r=0, the book that was in part the inspiration for this and my previous column:
Ray Bradbury, for example, stated it in his 1952 story about time-traveling dinosaur hunters: ‘Time doesn’t permit that sort of mess—a man meeting himself. When such occasions threaten, Time steps aside. Like an airplane hitting an air pocket.’ Notice that time has agency here; time doesn’t permit and time steps aside.
Hey, if you haven’t read Ray Bradbury’s www.raybradbury.com “A Sound of Thunder” http://en.wikipedia.org/wiki/A_Sound_of_Thunder go find a copy to cheer yourself up. One of the best time travel yarns ever!
And on a personal note, I was reminded when I went to save this file that my first “On The Net,” entitled “Experiment,” appeared in the August 1998 issue of this magazine. I’m proud, if a little bemused, to report that this is my one hundredth column. Thank you, dear readers, for your attention and support over the years!
Copyright © 2017 James Patrick Kelly