Can scientists build a time machine?

How does time travel work?

This would also raise the worrying question of what would happen to our concepts of cause and effect if time travel into the past were possible. The most famous of these puzzles is the so-called grandfather paradox. Suppose you travel back to the time when your own grandfather was still a young man. He is killed (maybe accidentally), which means either your mother or father will not be born. This in turn means that you are not born yourself and therefore cannot travel through time and kill your own grandfather.

Do multiple timelines exist?

Over the years, physicists and philosophers have pondered different solutions to the grandfather paradox. One possibility is that the paradox simply proves that no such trips are possible. The laws of physics must somehow prevent time travel into the past. That was also the view of the late physicist Stephen Hawking, who made this rule chronology protection conjecture (Eng .: Chronology Protection Hypothesis ”) called. Mind you, he never specified the actual physics behind such a rule.

But there are other, more fascinating, solutions as well. Perhaps time travel to the past is possible, and yet time travelers cannot change the past no matter how hard they try. Effingham, whose book “Time Travel: Probability and Impossibility” was published in early 2020, puts it this way: “You could shoot the wrong person or you could change your mind. Or you shoot the person you think is your grandfather, but it turns out that your grandmother was having an affair with the milkman and that was your grandfather all along. They just didn't know. "

This also means that the much-discussed fantasy of killing Hitler before the outbreak of World War II cannot be implemented. "It's impossible because it didn't happen," says Fabio Costa, a theoretical physicist at the University of Queensland in Australia. “That's not even an option. We know how the story developed. There is no second attempt. "