The Science of Science Fiction

Transcription

1 Week 2: Back in Time The Science of Science Fiction OLLI at UNCA, Winter 2017 Mark Whipple

2 The Science of Science Fiction Course Outline 1: Size Does Matter 2: Time Travel 3: Beaming Us Up 4: Aliens Among Us 5: Warp Speed 6: Grab Bag From Back to the Future

3 Assuming it were possible, is time travel into the past a good idea? From 1978 s Superman: The Movie

4 What is Time? No, not the magazine. Everyone knows what time is, but this is one of those concepts, like distance that has no real definition.

5 Are we all time travelers? It is a trivial point, but worth mentioning: yes, we all travel in time every day. It would be truly extraordinary if we were not; in fact, if time suddenly stopped, we would have no way of knowing it. Maybe it just did. Additionally, if time were to suddenly go faster or slower we would have no way of knowing it either in fact, to say that time is going faster or slower is truly meaningless, unless we are comparing it to some other frame of reference.

6 In a very real sense, time travel is science, not science fiction According to the theory of relativity, and confirmed by numerous experiments, the rate at which time passes can vary between one frame of reference and another. This means that it is only limitations in our technology that prevents us from visiting the distant future. The catch: the theory does not explain how (or if it is indeed possible) to return to your original time. You can vary the rate at which you go forward in time, but going backwards in time is another matter entirely.

7 How does one change the rate that time passes? According to relativity theory, there are two ways to do this. (Relativity actually says that these two ways are equivalent to being the same thing, but that is not the point here.) One way is to travel close to the speed of light (we shall say relative to the Earth) and then return. In such a case, you would find that much more time has passed on Earth than it has for you, perhaps centuries or millenia. The other way is to spend time in a very strong gravitational field, such as near a black hole.

8 What about those scenes where characters can walk around while time is stopped for everyone else? Yes, I know they are even doing it in TV commercials now. There are several reasons why this is absurd; let s mention a few of them.

9 The Grandfather Paradox This argument proposes that a time traveler goes back in time and kills his own grandfather as a child, which means that the birth of the time traveler never happened so how could he have ever made the trip in the first place? (For obvious reasons, it is not called the Mother Paradox although logically that would make a lot more sense.) Any time travel story that does not deal with the GFP is hardly even worth discussing in this course except that so many of them do not. So if a time traveler does go into the past, interacts with it, and then returns to his/her original time, what happens? There seem to be three possibilities:

10 Grandfather Paradox, Scenario A You can t change the past; whatever happened is still going to happen no matter what you do. A time traveler is locked into events in the past, which make it impossible to change what has already occurred. In this version, it frequently turns out that the visitor was part of the previous events all along, even if this was not realized at the time. This version has been used frequently in SF stories. Back There The Twilight Zone, 1961

11 Grandfather Paradox, Scenario B Timeless, NBC-TV, 2016 As long as the traveler stays out of the mainstream of major events, the return trip comes back to a present that is only minimally different from the original. This version also often appears in many science fiction stories, notably in Star Trek. It is also nonsense.

12 Grandfather Paradox, Scenario C In this version, any visit into the past makes significant differences to the present, even if you keep out of the way of history. A new timeline is created which differs fundamentally from what it was before. Although this version is not often used in SF stories, it is the one which is most likely to be scientifically accurate. The Butterfly Effect, 2004

13 H. G. Wells This man literally did invent the time machine in 1895: the term did not exist until then. Since then, three motion pictures (1949, 1960, 2002) plus two TV versions of the story have been filmed and released. How does the grandfather of all time travel tales deal with the GFP?

14 Let s pause the timeline and take a break.

15 The Butterfly Effect and Chaos Theory

16 The origins of chaos theory The extraordinary French mathematician Henri Poincaré is often credited as the founder of chaos theory, even though it seems that he made the discovery partly by accident. He found that he had made a critical error in his partial solution to the famous three body problem in physics, and that a miniscule difference in initial conditions could make a large difference in the final outcome of a system. Henri Poincaré

17 So what does chaos theory suggest about going back in time and the GFP? Everything we have learned about chaos theory indicates that there is no way to avoid interfering with the course of history if you go back in time. The Butterfly Effect means that even seemingly insignificant changes in the past could have great and catastrophic effects on the future. The farther back you go, the greater and more unforeseen the changes.

18 Example of disturbing the timeline: Back to the Future In this movie (actually three movies), Marty McFly goes back in time and interacts with his parents before they were married. Chaos theory virtually guarantees that because of this meeting, Marty will never be born. This creates the paradox: if he is never born, how can he go back in time and prevent his own birth?

19 So if going back in time creates a whole new timeline, what happens to the original one? (This all depends on the idea that going back in time is even possible, which may not be true.) But given that assumption, the result (which is taken seriously by many in the physics world including myself), is that there would be an infinite number of parallel universes with more being created all the time.

20 Not a Universe, but a Multiverse This notion is based on quantum mechanics, which states that some events on the atomic scale are purely probabilistic, and that in fact all possible outcomes should (and do) occur, but each in their own separate timeline. This cosmos must have enough extra dimensions so that all these universes could fit together like very thin pages in a very large book. If this is true, then its implications for time travel into the past (and the GFP) are truly enormous so let s consider some of them.

21 Returning to the original question, in light of what we have now seen, is time travel a good idea?

22 The other side of time travel: A temporal cold war?

23 Star Trek s Prime Directive And eventually, a Temporal Prime Directive: a timetraveling alien with knowledge of the past could resolve a dilemma for the captain

24 1. Back to the Future (I, II, III) 2. The Terminator (I, II, not III) 3. La Jetée 4. Twelve Monkeys 5. Groundhog Day 6. Primer 7. Looper 8. Source Code 9. Edge of Tomorrow 10. Time Bandits Top Ten Time Travel Tickets (according to one internet list)

25 Famous fiction featuring time travel The Time Machine (H. G. Wells) 11/22/63 (Stephen King) A Wrinkle in Time (Madeleine L Engle) Timeline (Michael Crichton) Slaughterhouse-Five (Kurt Vonnegut) A Connecticut Yankee in King Arthur s Court (Mark Twain) The Door into Summer (Robert Heinlein) The End of Eternity (Isaac Asimov) The Time Traveler s Wife (Audrey Niffenegger)

26 Highly recommended. Next week: Whatever you do, don t beam me up.