I.at 12:00 o'clock Mr.Hopkins(1) enters a building without any thoughts in his mind. as he enters he notices enoughh equipment to build a time machine. he plans to build the time machine and come back in time to 12:00 o'clock of the same day. he immediately starts building the machine. but 5 min later he stops, because if he is to be successful, Hopkins(2) should have been visiting himself already. but if he stops, he can never build the time machine to come back in time to 12:00 o'clock. why he should continue building? II. as Mr. Hopkins(1) is about to reach for the door , Hopkins(2) opens it. Hopkins (2) says he came from the future and offers Hopkins(1) a drink at a nearby cafe. if Hopkins(1) accepts the offer, should Hopkins(2) suddenly disappear? how can we explain his presence ? well, here are two cheesy relativity paradoxes
Normally I don't even read an original post that has not already collected several comments, but I happen to have just read your intelligent comments about light going in straight lines, even if "bending" when space itself is "bent" by gravity in another thread {I.e. not the mass of the photon being attracted by the mass bending space-time, although it is probably possible to consider space time as "unbent" and the photon being attracted by the mass. - just not as consistent with a modern view (essentailly Einstein's) of space-time.} Thus I read this post and am responding. Your "Hopkins" agrument aginst time travel is an interesting variation on the well know version of "returning to the past and killing your grandmother." (There by preventing your very existence to do the killing etc. Same type of logical conflict you suggest for Mr. Hopkins returnig to 12Noon; however the traditional agrument is a little stronger. If one wanted to refute your Mr. hopkins argument, they could claim that Hopkins1 and Hopkins2 are the same - I.e. when Hopkins2 returns from the not too distant future, he is exactly co-located with Hopkins1. (Hence it is not surprizing that Hopkins1 sees no Hopkins2 anywhere in the room. In the traditional "Kill your grandmother return", one usually assumes there is a large age and sex difference between the time traveler and the grandmother. ( Addition evidence of a male bias among people discussing this subject.) Thus, I think the "grandmother killed" argument is stronger than the "Mr. Hopkins " argument, but your version is an interesting twist.
Time paradoxes do not require such complex explanations. As I see it there are the following possibilities. The paradox possibility constitutes a proof that a time machine cannot exist. This seems like a very good explanation. There are parallel universes. When the time traveler goes back in time, changes something, and returns to the future, he is returning to a different future than the one he left. If he manages to kill his grandfather, his counterpart in the parallel universe was never born. In his original universe, he no longer exists because he has traveled via the past to a different universe. I do not like this concept because I just do not believe in the possibility of parallel universes which are almost duplicates of our own universe. The explanation I like best has a relativistic limit on time travel. If you travel 100 years backward in time, you cannot be within100 light years of Earth. It becomes impossible for you to interact with any event in your past. Similarly, if you travel 100 years into the future, you will be at least 100 light years from Earth, making it impossible for you to get information useful to you when you return. You will not be able to get information about the stock market or sporting events usable for financial gain when you return to your own time. Isaac Asimov (I think) wrote a SciFi story in which tinkering with the past results in a universe without a time machine. In the story, the Catholic church controlled the entire world, including access to the time machine. The only person with a memory of the universe with a time machine was in transit from the past, and ended up in a universe which had the history familiar to us. and no time machine.
Hm...Time travel ?. Annother way of looking at it would be; if Mr hopkins travelled back 100 years in time (which I dont beleive for a minute will ever be possible) he could'nt kill his grandma because he himself have'nt been born yet in 1905. He simply did'nt exist. The only way this scenario can be visualized is; if Mr Hopkins had a dream that he was back in 1905 and he killed his granma. But anybody who may decide to kill somebody in a dream, whether it's your grandma or the current prime minnister will find when they wake up that no harm has been done. REGARDS APOLO
I think it relies upon probability ( Quantum behaviour) of all the possibilities that one could do to ones past there is a sort of `feedback` loop that reduces the possibilities to just one (state) and uncertainty is eliminated. “So, if you know the present, you cannot change it.” There is only one path or time line that can exists (ie for that guy)
