BartSimpson BartSimpson:
Proculation Proculation:
Exactly. That's why IF you can go back, you could not arrive in your own timeline. Like Hawking says, if you kill your grand parents, that only means you eliminate your future double in that spacetime, not you since it's impossible.
The other notion is that when you travel into the past you're originating in a meta-timeline and if you then travel into the past and kill your grandparents there is no paradox because they did exist in the meta-timeline you came from.
So while you could alter your past, you could not then return to the same present.
Proculation Proculation:
For the Twin paradox, it's no longer that paradoxical. It's quite easily explained by relativity. But I guess for people who does not understand relativity, it's still paradoxical.
I understand relativity and, to me, there is no paradox.
It brings to me an anecdote:
In my last ADVANCED (yes, you've read well) english class in CEGEP (it's 2 years between high school and university in Quebec), we had to take a free subject, write something like 10 pages on the subject and do an oral exam on that subject.
I had NO IDEA what to choose. I hate free subject exams
The night before, I decided to do my exams on special relativity with powerpoints and all. Since I was quite easy with that subject, I did everything in like 4 hours. Two hours of that on those damn powerpoints.
The day after, I was in class listening to my group oral exams. Subjects: wolves, skateboards, cats, cooking, etc. Mine was special relativity...
I was the last one to pass. My oral exam was supposed to be 10 minutes. I did 20 minutes

I got 96%

My only mistake was how I used the 'ch' as in 'chemistry' and the 'k' in 'kinetics' (in french it's 'cinétique' like 'see-nay-tik'. I used the 'ch' like 'chimney'.
Sorry, nostalgia ....
