[Bored chemist]

So why the one-generational back-step to grandfather?  Has it any significance?

Good question.
And you can take it a stage further; you could go and kill your younger self.

[maria123]

The question of whether time travel is possible or not has been asked for many years and there is still no exact answer. In my opinion, nowadays science and technology are so advanced that there can be no device that transports us even a little back in time. Probably even if I'm right and have such a device, it is not shown to a very large audience of people.
Probably even if I am right and have such a device, it is not shown to many
The question is very broad and mine to be considered from many streans and many points of view. Even if it is not yet fully created and invented, its invention is certainly being worked on.

[maria123]

Is there a universal moral standard? This would only be possible if we were all the same. Everyone has different principles and different views on things and we cannot have the same moral principles. It is connected and depends on the origin of a person - both from which country and from which family. Each of us grew up and grew up differently, had different friends, different families, and faced different things to have the same views on things.
If we all had a standard and universal moral model, there would be no prisons, no police, no lawyers, no courts, and so on.

[yor_on]

No, not to the past. And even if it would be it would need to bifurcate (split) 'world lines' to keep the history known by the time traveler intact. It becomes a paradox if treated otherwise.

[TommyJ]

Relativity theory shows that travelling forward in time is possible. It may be a spaceship travelling with near to light speed, though we don't have such a technology yet.

Travelling back in time have several known tries to get scientific approach. Still it implies travelling faster than light constant.
- Kurt Godel found a solution to Einstein's equation (e.g. new structure of space-time, but with different starting and ending point). That accepts travelling back in time but in a different Universe;
- Wormholes;
- Feynman sees anti-body as a body moving back in time (but it is only micro, not macro level);

There are no requisites in the relativity theory that there is not any same time measure for every observance, and also not any sequence of observation occurrences.