Quantum physics, time travel, and Kate & Leopold

Factual Questions
1

Well, I know I haven’t completely tortured my husband with a sappy, romantic comedy when we have a quantum physics/time travel debate afterwards. While the debate ended that night with us both going “huh?”, I have continued to wonder how well time travel was portrayed in Kate & Leopold.

Here is a simplified summary:

1876 - Leopold, Lord of Albany sees a man in his home during a party using a spy camera to take pictures. Cornering him, and after a small exchange, the man runs out of the house with Leopold hot on his heels. Chasing him all the way to an early version of the Brooklyn Bridge, the man jumps off into the East River. However, Leopold reaches out to “save” him just in the nick of time. Ultimately, they both fall into the East River together.

2001 - We then learn the man, Stuart, has found an opening in “time” which is located in the East River. To enter this “portal” you must leap off the Brooklyn Bridge and achieve a velocity equal to gravity, thus passing into 1876. Since Leopold took the leap with Stuart, he is now in present day New York. As the inventor of the elevator, all elevators begin to malfunction.

Of course Leopold falls in love with Kate. Blah de blah blah. And of course, he has to return to his own time in order to get all the elevators working again. And of course, Kate goes back after seeing herself in a picture that Stuart took while at the party in 1876.

Now here is the debate:

When Leopold goes back, he relives a few events that have already happened before he left 1876 (while chasing Stuart). Leopold walks back into his house. He sees Stuart again, but, of course, doesn’t chase him. Later, Kate begs her way into the house. He sees her, and she sees him, and they are going to get married.

My husband was upset that there wasn’t two Leopolds. He felt that Leopold should have waited until he saw himself chase Stuart out of the house, and then walked in the house like, “I got rid of that scoundrel.” That way Leopold #1 disappears into the future, while Leopold #2 is back where he should be.

I argued that the whole premise of the movie was that he got complete sucked out of 1876, and that’s why all the elevators quit working because he wasn’t there to invent them. And that’s why there weren’t 2 Leopolds.

Despite other things that didn’t quite work like how did Stuart take a picture of Kate standing inside the house, when he ran out of the house (chased by Leopold) just as she appears to come in? (You only see her in 1876 in the beginning of the director’s cut.)

SO! Are there general rules concerning time travel? General theories that are already in place? Would you be completely sucked out of your own time or would you see yourself again if you went back before you originally left? (Just like in Back to the Future, when Marty sees himself being chased by the Libyans before reaching 88 miles per hour.)

Please tell me! And be gentle, I’m a Lit major. I’m sure all have more questions.

2

If the man who invented the elevator didn’t, one of two things would happen:

  1. Elevators never came into existance. That means no elevator shafts in skyscrapers (so they wouldn’t just stop working, they wouldn’t be there at all).And no one would think that was odd- just like we don’t think it’s odd that every home doesn’t have it’s own fusion power supply, even though it’s possible that someone was supposed to invent it, but (s)he was taken out of time in a similar manner to Stewart, and so never invented it. The absence of elevators would also mean that skyscrapers probably never would’ve been built (a 50 story building is impractical if you have to take the stairs all the time). Since cities couldn’t grow upwards, they’d have no choice but to grow outwards. This would probably greatly impact land prices. Not to mention the NYC skyline would look quite different.

  2. Some other person invents the elevator. Events proceed much like they are supposed to.

3

You can’t deduce logic from from a sci-fi movie that stars Meg Ryan.

Think about it, if no one had invented the elevator they wouldn’t stop because they wouldn’t exist in the first place.

4

Despite the fact that the movie stars a very lippy-looking Meg Ryan, I’m more interest in the time travel. (Should you see yourself if you go back to the time before you first left?)

Now as far as the elevators go, even though Leopold leaves 1876 before he invents the elevator, he does go back to 1876 to live his life and invent them. So wouldn’t the elevators be there in the present cuz the past has already happened? Now whether or not they would begin to malfunction when he leaves 1876 is other story…

5

RR, my point was that with such a huge logical inconsistency you have no expectation that time travel depicted in the movie follows any rules. Think about it for a second; the man who would invent elevators is snatched away before he can invent them. If the resulting world was one where no elevators existed that might make some sense. If someone else invented the same thing that would make more sense. Instead someone else invented elevators that don’t work and every tall building has one.

Architecht 1: Damn, these non-evator systems cost a lot and they don’t add any value. I mean they might be useful if they could be used to carry people and freight to all the different floors.
Architecht 2: Doesn’t matter, building code says we have to install them. The mayor’s brother-in-law gets a kickback.
Architecht 1: Then it makes perfect sense. Never mind.
K&L a mushy, romance chick-flick that was not intended for your left brain, don’t force it to fit.

6

If the past is changed, you’ve got two potential timelines thereafter - most hard sf I’ve seen has one or the other, but lots of soft sf has one slowly merging into the other in some ill-defined and anthropomorphic way. I can’t make it make sense, but go with it.

Jumping into the past and replacing your original body? Again, it’s a standard, but I can’t think of any way whatsoever it can make sense.

7

Ok, well K&L just got me thinking about time travel, and my only exposure to how time travel might work has been through movies. Leopold and elevators aside, my general question for this general question forum is: what are the basic theories concerning time travel?

What is needed to accomplish it? What happens if you change history? Are there paraell time lines? How do you make sure you are traveling back and forth between the ones you want?

Are there even generally accepted theories for these questions? Help!

I’m sorry if it seemed like K&L was my sole focus.

8

Scientists are divided as to whether time travel is possible. Some physicists think that future supercivilizations manipulating rotating black holes, or cosmic strings, (if they exist) or wormholes (again, if they exist) may be able to create time travel according to general relativity. Others say that time travel is totally impossible.

Given that noone can even whether time travel is possible even in principle, there is no accepted general rules of time travel. However, it would seem that the “many worlds” interpretation of quantum mechanics is the only way to solve the paradoxes that time travel would create. According to this, you would time travel however much you wanted, but it wouldn’t affect the past you know. It would merely create new universes in which the consequences of your actions were felt. So if you killed your father for instance, you would create an entire new universe where your father (and you) never existed. This would not affect you in the slightest, and avoid any possible paradoxes.

9

The drawback to this form of time travel is that you can never go back to your original timeline. So from their point of view, you just disappear forever. Even if you went back to the present, it would be a different present.

Since the physical methods of time travel are way beyond modern engineering capabilities, if it’s even possible, we’re stuck with just coming up with the logic of how it would work. The grandfather paradox of course is a big deal, with only 3 solutions:

  1. You kill your grandfather, therefore you’re never born, so you never kill your grandfather…logical inconsistency tears hole in universe and destroys time.
  2. The very fact that you are alive means that you have already failed to kill your grandfather, meaning there is one time line and it is stagnant. This also messes with our ideas of free will and predetermination.
  3. You kill your grandfather and create an alternate universe in which your grandfather is dead, and you’re never born (but you as yourself still exist because you travelled from the other timeline). In fact, just the act of travelling back in time and displacing atoms and whatnot would create new timelines.

There’s also another weird product of time travel. Say, for example, you go into the future and read about the invention of fusion power. You swipe a generator, come back to the present, and claim to have invented it. So the timeline is changed to you inventing fusion power instead of the other guy. But then, in this timeline, where did the information about fusion come from? The future guy didn’t invent it, because you changed history so you invented it. But you didn’t invent it, you swiped it from the future guy. So this information seemed to have just popped out of nowhere.

Alternate timelines can explain away many of the logical paradoxes. Actually, because the quantum world is governed by probability, there could be new universes created for every quantum reaction, and time travel would just be a method of travelling to one of them.

10

Interestingly enough, the converse “grandfather paradox” isn’t even inconsistent with classical GR. I’ll illustrate with an inanimate object, the McGuffin Tablet.

Scientists at the McGuffin Institute of Technology one day see a strange metal slab appear in an engineering lab. They name it after the institute (of course), the “McGuffin Tablet”. After analyzing it, they determine it to encode the secret to building a time machine with current materials and, say, ten years worth of work. Ten years later, the time machine is ready for its first field test. What better object for a test than the original McGuffin Tablet (these are postmodern scientists)? So, they set the dial for -10 years and throw the McGuffin Tablet in…

11

Are you sure? What if, and I realise this is a long and convoluted if, you (1) went back in time (2) killed your grandfather (3) went back to the future either by ‘time travel’ or cold sleep (4) didn’t like it (5) went back to the past to just before you time traveled (8) explained why killing your father is a bad idea (9) your previous self aborts the mission (10) you return to a future put back on the original timeline. OK, it might not be really the same, but it would look exactly the same, so does it make sense to say it isn’t.

To be nitpicky, you’d have to remember that if you do go back, it’s possible anything will change the future significantly; not just stepping on a butterfly, but moving the air… Also, it’s posisble you’d have to persuade your previous self in addtion to not altering the past to go back in time and deliver the warning you just delivered to himself, else I sense unstability…

12

All this would do is create another timeline. So you’d have the original one where your grandfather lives and eventually produces you, another one where he is killed, and another one where he lives. You’d be in the third one, which may be very similar to your original one, but it still wouldn’t be the same. Truly random events like atom decay etc would be different, if nothing else.

Another point about time travel is that all the time travel machines that have been proposed have one thing in common - they don’t allow you to travel back before the time machine is created. So the fact that we don’t see time travellers doesn’t say anything about the possibility of time travel.

13

Time travel is debatable, classical physics is less so. Gravity doesnt give you a constant velocity, it accelerates you downwards. A nitpick I realize, but you can chalk it up to more evidence that Meg Ryan and Co. may not have ran the script by a scientific advisor before filming.

14

Make it a transcription of the Tablet, and you’ve got yourself a deal. But if they send back the original, then it’ll be subject to an infinite amount of wear and tear.

Incidentally, as a general rule of thumb, most of the books and almost all of the movies you’ll ever see or read about time travel are completely nonsensical. The only movie I’ve ever seen with a good depiction of time travel was Twelve Monkeys… Most movies seem content with a slipshod partial changing of the timeline, like the aforementioned nonworking elevators (which, presumably, everyone remembers as working), or people fading out of pictures (one body part at a time!), or the like.

One important point to consider is that people are physically no different than any other objects. This means, first of all, that if a timeline “changes”, nobody would remember the “old” timeline (it’s very debateable whether it’s meaningful to talk about a timeline “changing” in the first place). Human brains are no more “special” than anything else which can remember the past. Secondly, you see some movies where, when the time traveller goes to the past, all the people are gone, because they’ve all moved into the present, but inanimate objects remain in the past. This is clearly ridiculous.

15

Suggested reading for Ritzy (and any others not familiar with time travel):

The Theory and Practice of Time Travel by Larry Niven (available in the “All the Myriad Ways” collection and possibly other places)
By His Bootstraps by Robert Heinlein (in the collection “The Menace from Earth”)
All You Zombies also by Heinlein (in “The Unpleasant Profession of Jonathan Hoag”)–creepier but easier to follow than “Bootstraps” IMHO