Dear Carmen,

what precisely do you mean by "making changes"? Is what you have in mind similar to the famous (paradoxical) thought experiment of killing your great-grandfather in order to prevent your own birth, do you envisage very small physical "alterations" such as making changes to a microscopic object or do you - on a grand scale - even think of making changes to the "flow" (i.e., speed and/or direction) of time and/or to spacetime itself, e.g. by exerting extreme gravitational forces (provided that was possible to your imaginary time traveller...)?

Thanks,

Julius

Julius Riese Your counter question does not address the actual problem and therefore diverts the discussion rather than continuing it.

The type of change plays no role in the original question. The point is whether any action affects the universe as a whole or only a part of it. The answer depends on the underlying physical and metaphysical laws of the universe.

In movies, the effects affect everything, but I would say it depends on the action. If it's preventing Hitler from being born, the effects should be universe-like. If it's going back in time to spend time with grandma, the effects should be local.

Marharyta Ratushniak What does "universe-like" mean?

Carmen Wrede, Well, you asked whether travel back in time can impact the whole universe or the local parts. So, some effects of travel in time can have an impact on the whole universe, similar to the butterfly effect. Let us continue with the travel back in time to eradicate hitler from history. Such an action changes the course of history, the number of people alive at the 20th century and potentially changes the level of scientific developments. Perhaps, the interspace travel would be possible in 21st century due to the survival of the scientist due to lack of war. If there is inter-space travel, it can literally affect the whole universe, because of the balance at the very least.

Marharyta Ratushniak Sounds reasonable, but it also assumes that inter-space travel is technological possible, which is something we do not know for sure. So perhaps it isn't. Then killing Hitler would just be a local phenomenon.