Time Travel paradox = logically equivalent to Russell's Paradox?

Factual Questions
21

Chronos, I agree that those solutions are available theoretically, but right now they are practically unavailable. Building something with negative energy just seems impossible at this point. However, the two solutions I’m talking about both are available with proper amounts of material available to us in the universe (we see it) if arranged in the right fashion. I admit the one I’m more familiar with is the cosmic string model which may seem a bit out in left-field (as no cosmic strings have been seen), but may be conceivably constructed out of materials we do observe. The alternative time-travel to the past solution I’ve seen that involves using only materials available to our universe also seems to indicate that it’s not feasible to go to a point before the solution existed.

These two solutions are resultant from investigations into constraints of actually being able to BUILD the time machine in order to contradict Hawkings hypothesis that nature conspires to prevent time travel to the past. In effect, these two solutions allow for time travel to the past in such a way that the causality ambiguity is still up in the air. The other more commonly quoted solutions for time-travel to the past involving negative energy densities… it is unclear whether they are actually impossible or not. Regardless, the problem of causal ambiguity is independent of whether or not these constraints of having epochs of time-travel to the past available or not and having to use large masses are applied. These were simply mentioned as current constraints that avoid Hawking’s nature forbidding past-time travel.

22

Oh, no offense taken. I’m rather enjoying the threads.

I’m noticing is that the various “paradoxes” under discussion are complicated statements, which have logical, linguistic, semantic, and sometimes even physical componants. People seem to gravitate to particular aspects of the problem, and ignore others. There must be a lesson for life in there somewhere.

Paradoxes do exist, of course. They’re manifestations in people’s mind of conflicts they can’t resolve. They do not represent anything inherently in conflict within physical reality. Putting a name to something does not make it so. Ghosts don’t exist, just because there are ghost stories.

I assume “paradoxes” are of two kinds: problems with reconciling two coherent systems that do not agree (Zeno’s Paradox is an example), and contrived word games (Russell, and the other two “paradoxes” mentioned in the other thread that’s going on.)

Zeno’s Paradox is interesting, important, and legitimate, because it points out problems our perception of the nature of time, space and motion. (It still is not a paradox. It’s an example of a weakness in a particular conception of space and time. As Zeno noted, we move from point A to point B all the same.)

Russell’s sort of “paradox”, being contrived, and corresponding to no actual physical problem, has no value, except that it serves as a platform for people to examine their own thinking processes, and to hash ideas out with like-minded people. That’s actually a good thing.

The logical system which has served so well for computers is a good counterexample to paradox. Computers are based on languages that are complete in themselves, and where all statements are either valid or invalid. Exactly the opposite of the natural language that supports “paradox”.

Russell’s induction into the hall of shame is that he uses sophisticated ambituities in language to make paradoxes to entertain and bemuse his academic collegues.

Certainly, people should not stop discussing paradox. It’s encouraging people to think very hard about logic and language. Can’t fault that.

23

Which is addressed in the definative time travel movie “Bill and Ted’s Excellent Adventure”. Bill and Ted find themselves locked out of somewhere they need to be, and only Ted’s dad has the key. Bill swears to himself that, when they get out, he’s going to steal the key from Ted’s dad and then go back in time and hide it under a rock nearby or something (I forget the details). Then he picks up the rock and gets the key. After they get in, he says to Ted, “Dude, we need to remember to go back in time and hide this key under the rock, or else we’ll never get in here”

24

I don’t see a direct connection between the time travel paradox and Russell’s, but frankly I know just enough about Russell’s to declare it much more significant and difficult than to dismiss it as a verbal trick.

Frege who Russell originally addressed the paradox to was reported to be quite disturbed by it and so have many of the best minds in logical theory and mathematics since.

25

This concept has been exploited to great effect in fiction. Two notable examples are a story by Robert Heinlein (the name of which escapes me at the moment) where a man goes back in time and procreates with a woman and returns. In the future he has a sex change operation which allows full reproductive function, goes back in time again and procreates with his male self. So he is both of his own parents (IIRC).

The other is the B movie Timerider, written and produced by ex-Monkee, Michael Nesmith. The main character travels back in time, meets a woman. She asks him about the amulet around his neck. It was given to him by his father, who said his own mother (the character’s grandmother) had given it to him. She had stolen it off his grandfather after she got pregnant with him as the despicable grandfather escaped her. Of course, he had sex with this woman. Just as he was about to return to the future, she grabbed his amulet. So he’s his own grandpa.

26

Good. I’m glad I didn’t offend you. In fact, it sounds as if we’re much more on the same page than I thought.

I suppose I’m a bit of a “Russell-phile”, but I won’t bore you by trying to change your mind about him (not in this thread, at any rate!). I suppose we can “agree to disagree” for the time being :wink: