If I were to travel back in time and kill my grandfather, what would be the result? I would never be born and, therefore, never able to go back in time and kill my grandfather. But if that were the case, then I would be born as normal and could go back in time to kill him.

Now, I know everyone here has thought about this at one time or another. As far as I can think of, there are two logical answers to this paradox. The boring one, and the one I believe is correct, is that going back in time is impossible.

The other one could be that when a person goes back in time, they create a sort of split in time. I could go back in time to kill my grandfather and that would prevent my parents from ever being born in the new time line. This would also prevent the "second" me from being born as normal. I would still be alive, however. I could either stay in the past and live my life there or go back forward to the time I came from and live life there. From that time-line's perspective, I would have been born without parents. But from my perspective, I had parents up until the time I went back in time.

Note: I am new to posting on this forum, and I was thinking the other day about the possibility of time-travel. It seems like the paradox forum is a little less philosophical (I love philosophy, but don't seem to be as knowledgeable about it as other posters here). So, if this post is off-topic feel free to let me know.

That being said, I'm sure the inquisitive mind of a philosopher is always glad to tackle problems such as this. Have fun.

Some relevant articles: plato.stanford.edu/entries/time-travel-phys/

plato.stanford.edu/entries/time-machine/

If we believe in eternalism and multiverses, than we would travel to parallel universes at earlier histories rather than our own universe in the past. Therefore, we would kill a grandfather of one of our parallel selves.

While this does seem to be more of a physics related problem than philosophy, Einstein was a student of both, so it is not completely foolish that we dabble as well.

Assuming that our existence is solitary and there are no parallels;
If you travel to a time previous than the present and murder your grandfather, then you would not exist. It follows, then, that it is logically impossible to travel to a previous time, or that it is impossible to commit the act of murder towards your grandfather.

Since there is no proof of a force that could physically stay your murderous hand, it must be impossible to travel to a previous time.

If the existence of a multiverse is suggested, then every decision that we make, any and every possible change in our environment creates a different multiverse, in which one singular event occured seperately from our experience in our own, albeit empirical, universe.

Aside from the cause-and-effect paradoxes of killing your parents, etc. here's 2 more things to consider against the possibility of time travel:

First, why suppose that there IS anything in the past? If objects move along the timeline, then they empty out the past as they move, right? If I went into the past, I'd be entering a total vacuum, maybe.

Second, from my perspective, I will have built my time machine before using it and gone into the past after. So in a way, I'm still moving forward along the timeline (the A-series or the B-series, I think, but I don't know which one).

Neither of these points as stated clearly shows that time travel into the past is impossible, but they do intuitively tell against it.

I think.