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Why Time Travel Won't Work (Sometimes)

ADD Boy

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I was thinking about this the other day, and I'm very curious if anyone else has thought of this before me. Okay, here goes...

Say you have a person that uses a time machine to go back into time. What he does in the past is he kicks his father in the... family jewels, thus delaying him for a few minutes from arriving home to make love to his wife (okay, bear with me). After they make love, the wife conceives the time travelling person.

Therefore, assuming that sperm are randomly moving around inside of wherever they're stored inside your body prior to... well, you know (sorry, I don't remember much from biology :p ), that would mean that if there was a delay of several minutes between when you were supposed to be conceived, one sperm might come out closer to the egg that another sperm would. This would increase the chances of another sperm causing conception.

Therefore, if the baby that was going to be conceived that night was the person who went back in time, and the sperm that time traveller was conceived from does not make it to the egg, that would make the person never born. So therefore, that person would have never gone back in time to do that (because that person would not have existed) and so therefore, the person would exist, only it would have never happened!

Does this make sense to anyone else?

It seems to raise a lot of questions on free will... I mean, if you're not allowed to go back in time to kick your father in the nether regions, what else are we cosmically prevented from doing?

Furthermore, since there's still a chance that sperm might conceive the person, does that mean that we could only do things back in time sometimes? Like, there's a slight chance it would have never happened?
 
Congratulations, you've discovered the causality loop, the basis for every time-travel story in the history of fiction.

No, no one else ever thought of this. You appear to be the first.

Just curious, can you factor polynomials?
 
This is essentially the classic time-traveler paradox, the time-traveler goes back in time and kills himself. If he's dead, he couldn't have killed himself. If he's not dead, he could go back in time and kill himself.

I myself prefer the 'no time-travelling tourists' proof. If time-travel is possible, it's not just possible a hundred years from now; it's already possible. Time travel wouldn't be invented and all of the sudden time-travelers start showing up; why weren't there time-travelers watching the Revolution or the atomic bomb tests. If even a few people each generation wanted to go back and see the Constitution signed, or hear Einstein's last words [which no one really knows], or whatever, 'extra people' would start piling up pretty quickly.
 
(S) said:
I myself prefer the 'no time-travelling tourists' proof. If time-travel is possible, it's not just possible a hundred years from now; it's already possible. Time travel wouldn't be invented and all of the sudden time-travelers start showing up; why weren't there time-travelers watching the Revolution or the atomic bomb tests. If even a few people each generation wanted to go back and see the Constitution signed, or hear Einstein's last words [which no one really knows], or whatever, 'extra people' would start piling up pretty quickly.
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True, although it may not be possible that we see time travellers tourists, due to the reasons I stated above. If we saw one, or if one bumped into us, there's always the chance it could affect history so drastically that they would have never gone back in time, or at least do
 
It has been thought of and explored very well, the premise is called a "Time Paradox". What that means is that you cannot go back in time and kill your grandfather because you would have never been born to go back...


Theres been an explanation by some of the worlds best Physicists have worked on , in terms of mathematics and the bottom line is that the universe does not allow certain behaviors such as faster then light travel and the grandfather paradox.

edit to add:
I know you didn't ask this but apparently Time flows only in one direction. That is forward, so the issue even considering a Time Paradox , means nothing since the real world does not allow us to travel backwards in time. That's all science fiction.
 
Time travel seems to work just fine for me. I seem to be able to travel into the future at the rate of sixty minutes every hour, reliably and predictably. I could quite easily kill any number of relatives, if I chose.

Do I get the million? :D

(Apologies to C. S. Lewis, for shameless plagiarism of a passage in The Dark Tower.)

Rolfe.
 
I reada good book on this a while back... shame I can't remember the title. Author's name was uh... Rudy... uh, somthing. Okay, I read it in high school. Or maybe middle - that's not the point.

As I recally, Einstein's formulations make this sort of thing a *theoretical* possibility. If you can imagine an Einstein-Rosen bridge in space, then you can imagine the same in time, I've little doubt. After all, isn't it Einstein himself who equated the two?

Anyhow, enough rambling. Go play the new Prince of Persia game. If you like this kind of thinking, the plot of that game will leave you wondering for a good long time.

Or if you want something less involved, you could try Back to the Future I. Or was it II where they did this? Maybe it was III -- I forget.

I think I've heard some arguments that if you went back in time you couldn't possibly move fast enough to end up in a location you are familiar with space-wise. IE: if you went back to when your dad was alive you'd have to do some crazy stuff to even be in the vicinity of Earth.

Another argument has it that you'd be in an alternate timeline. I think this requires a funny interpretation of QM to be valid, however.
 

I know you didn't ask this but apparently Time flows only in one direction. That is forward, so the issue even considering a Time Paradox , means nothing since the real world does not allow us to travel backwards in time. That's all science fiction.
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Oh I know :) I understand that we'd have to travel faster than light or make a wormhole through time to go back through time (although don't ask me to explain the specifics of those!)
 
Rolfe said:
I could quite easily kill any number of relatives, if I chose.

Do I get the million? :D
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I'm sure one relative should be enough to qualify you, but they'll probably want you to off at least three for the million. Statistical chance, and all that.
 
I can't remember which really big name scientists said that time travel isn't a possibility as we have never run into any time travellers in our history. What he was saying was that if it was possible, we would already have known about it.

Made sense to me.
 
ADD Boy said:

Furthermore, since there's still a chance that sperm might conceive the person, does that mean that we could only do things back in time sometimes? Like, there's a slight chance it would have never happened?
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Actually Parallel Universes would mean that there could be no paradox for instance:

In universe A) you build a time machine go back in time to the night of your conception kick your dad in the nuts etc. and go forward in time to find yourself not born (in your frame of reference) however what happened was that when you went back in time you actually exited Universe A) and entered Universe B).

So to inhabitants of a) it would seem that you were born, grew up, built a time machine and vanished never to be seen again, whilst in b) you were never born, suddenly appeared in one night of nut kicking insanity and then disappeared to reappear out of nowhere to live out your days.

As to time travelling tourists, given that they are of such an increased level of tech compared to us, how do we know that they dont have chameleon fields such as in Predator? we are already making strives towards active camouflage now, and if they are just viewing and not wanting to affect the time stream it makes sense to me (the assumption that they would visit different times with sentient beings and then make themselves visible seems odd to me).

Oh I know I understand that we'd have to travel faster than light or make a wormhole through time to go back through time (although don't ask me to explain the specifics of those!)
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Another way suggested by a physicist on a show I saw recently, had him creating a tunnel of lasers which effectively bend the space around it creating a tunnel through which information would be able to be passed to the future or past (although not before the Machine was turned on or after it was turned off).
 
Yes the concepts of the E-R bridge and other constructs allow for so called "Time Travel" but it's all due to time dilation which means forward travel. The major scientists normally named are Hawking Thorne , Visser, Sagan,Gott and others.

Any time the discussion of time travel rears it's head theorists become silent because the general idea is viewed as crackpot or a science fiction escape mechanism at best. There is however a framework based on certain maths that describe time travel ( even backwards, according to Thorne, but later he discounted it ) is possible but the bottom line is causality.. You cannot travel back to a time before the machine you have built existed.
 
shemp said:
Tell you what kid, why don't you go kick your father in the nuts right now and see what happens?
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I'd probably be hit so hard I'd go faster than light, and then you'd see me in paintings of the signing of the Declaration of Independence :D

Wouldn't that be cool... George Washington, Jefferson... and me, poking my head out from behind Ben Franklin :p
 
i thought all you had to due was travel towards a star at a certain warp factor. i guess spock is a liar. but vulcans can't lie, right? :confused:
 
I think the theory about "nature conspiring to make sure causality isn't broken" is a load of BS. It seems to presume some sort of supreme intelligence that watches everything all the time.

An idea I have found that resolves the issue in the OP is the following: The paradox apparently lies in the fact that by killing your father, you would never be born and therefore could not go back in time, and so could not have gone back in time. The solution comes by realizing that time is not like space. You do not have to have "left" sometime in order to "arrive" sometime else. Once you go back in time, you now exist in the past as an adult, never having been born. Here's an example:

Timeline A: Your father is born in 1950. You are born in 1980. In 2000 you invent a time machine and go back to 1960. At this point, time "starts over" from 1960, resulting in timeline B.

Timeline B: Your father is born in 1950. You spontaneously appear in 1960 in a time machine and kill a your father as a 10-year-old. Your father's child is therefore not born in 1980, and no time machine is invented in 2000. You die in your sleep in 2020, at the age of 80.

The paradox is gone. :D

Now, if you kill your father (in timeline B) and return to the year 2000 right away, we get timeline C.

Timeline C: Your father is born in 1950. "You" spontaneously appear in 1960, kill him, then disappear. Nothing relevant happens in 1980. In 2000, "you" spontaneously appear again in your time machine. You live to the ripe old age of 80 and die in 2060.

I realize that the idea of matter appearing out of nowhere and people/machines existing without ever having been born/invented is a strange concept to grasp, but it seems to work if you logically follow the timeline from start to end.

Oh, I just remembered. Here is an amazing site that analyzes all of this in depth and explains it better than I did. It's a fascinating read. :D
 
In his book Flatterland, mathematician Ian Stewart goes into some detail about how, based on Hawking's work, it should be possible to construct a time machine by sticking black and white holes back to back. It's a bit mind bending, especially the bit about having a closed time loop where something just travels round and round without having existed in the past or ever existing in the future.

Stewart's take on the grandfather paradox is that it's not really worth worrying about unless time travel becomes possible, at which time the resolution will probably become obvious.
 
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