Time Travel Confusion
 

Hi, I don't think a post has been made about this, but has anyone read the short story, 'All You Zombies' by Robert Heinlein? It's about a person who becomes his/her own mother and father, so essentially this person gives birth to himself/herself. Maybe I think too much about these things, but how is such a thing possible in time travel? Where did the person come from? From nothing? How is it possible for the person to be here? How was the person here before without the use of time travel? Any thoughts, ideas? Because stories like that make my head spin.

Re: Time Travel Confusion
 

I would have to say that that would not be possible. I mean, this goes back to an episode of Star Trek Deep Space Nine where the crew are thrown back in time and encounter Captain Kirk, Spock, etc... One of the crew ponders the fact that his great grandmother is on the ship and has flirted with him. Could it be that he is destined to be his Grandfather's father????? I believe they called this a pre-destination paradox. I found this little blurb on the subject via google:
"A predestination paradox, also called a causal loop, is a paradox of time travel. The idea is that when one travels back in time, one may influence events while in the past.

Suppose a man travels back in time and impregnates his great-great grandmother. The grandmother would thus give birth to one of the man's great grandparents, who would then give birth to his grandmother or father, who would then be able to give birth to one of the man's parents, and finally to the man himself. As a result, the man's very existence would be pre-determined by his time traveling adventure, and therein lies the paradox.

The Predestination paradox is very closely related to the Grandfather paradox. "

I myself don't buy this theory. It's just too out there to theorize that your traveling through time was your destiny and it was enevitable that you would travel back in time to become your own mother or father. It leaves no room for error or chance. You HAVE to travel through time at some point, or otherwise, you wouldn't exist now. It's interesting to think about, but like I said, too out there. Assuming this theory is solid, if you are your own mother, grandmother, great grandmother, etc... you MUST travel through time, and nothing or no one can prevent it even if they try. If they do, it would cause a paradox, which could by Doc's theory, destroy the entire Universe, or just be limited to our own galaxy. Okay, I'm rambling... it's late.

Re: Time Travel Confusion
 

It's perfectly possible. It's called a closed time-like curve. Asking where does the person come from is a null question. The person exists because the person exists.

Look at this another way. Let's say there's a Bill & Ted style time machine (i.e. a phone booth). One day, you walk past the phone booth. Here are 2 possible scenarios. One is that you simply walk past the phone booth, nothing happens, and you continue on your way. Another possibility is that you are jumped by somebody from the phone booth. The person knocks you out and encloses you in the booth. While you are in the booth, you time travel to the past. When you wake up, you are confused. But from inside, you see the person who jumped you walking past the phone booth. So you leap out, jump this person before s/he sees you, enclose him/her in the phone booth, and then run off.

Both of these possibilities are perfectly possible and consistent. But option 2 begs further explanation. Why did this complicated scenario happen instead of the much simpler option 1? The answer is that option 2 had a far lesser chance of happening, but quantum mechanics has shown that both possibilities can be assigned a non-zero chance of happening. In fact, ANY physically possible scenario is has a chance of happening.

Thus while somebody becoming his/her own father or mother (or even both!) through time travel may not be entirely likely, it is not ruled out at all.

volveralfuturo, there doesn't need to be room for error. Because there is no error! If it happens a certain way, it happens a certain way. Period! A common misconception here is that the scenario has to be replicated in some manner because the person is caught in a time loop of sorts. This is faulty reasoning. The events happen *once.* Your objection is similar to saying that it is impossible to kick a 60 yard field goal because it is very hard to do and there is very little room for error. Moreover, if the person kicks the field goal, he or she must have willed the attempt, but who's to say the person could have done something else instead (like left and gone to mcDonalds)? Well, all of that that may be true. But if somebody does it, it happened!

Re: Time Travel Confusion
 

There is also a short story about a guy who travels into the future, takes a knife from a destroyed museum, and brings back to the past. Now it is on display in the very same museum that someone will take it from in the future and bring it back.

Or another story about a guy who travels back to the past to give himself the plans to build a time machine. So sometime in the future, when he is done, he goes abck to the past and gives himself the plans to build a time machine. In both cases, the objects just 'are' and have no origin really. They have always existed.

Re: Time Travel Confusion
 

Of course, this one only works if the proton doesn't decay. ;)