How would the world work if time travel was possible?

If time travel was possible and the public could go back in time, then could they alter the things that happened in the past? And if so, then wouldn't some ppl with bad intentions try to do something like for example: bring an iPhone to the Roman era?
( or something like that ) and if that happened, then wouldn't the technology nowadays be more sophisticated than it already is? If people could really alter the past, then how would the world be governed? Could only specific people access the time machine?
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I know I'm asking a lot of questions, but this is a really interesting topic and I'm really curious to know what will happen

Well how do you know that that hasn't already happened?

This is the interesting thing about time travel - how would you know that it changed?

Hyperthetically - someone goes back to 1990 and drops someone off the plans for a cell phone - he then "invents it" - but then when it gets to the future - how would the guy know to go back in time and drop one off because they would have already had them? COnfusing? Quite

And because of all that time travel is not possible, at least not in that sense of the word.

The only real answer to this is: we don't know. Until someone can actually demonstrate time travel working, we can't say for sure how it would work and what effects it would have. Right now, it's looking increasingly as though time travel just isn't possible, so that might just be it. We can never know how it would affect things, because it doesn't.

There have, however, been a few proposed explanations:

* The "Novikov" principle (named after the person who proposed it): this one suggests that time travel doesn't allow you to alter the past. The past is already affected by time travellers, so nothing is being "changed" by them going there. So to use your example with the Romans: even if someone did go back in time with an iPhone, they clearly didn't have any long-term effects; if they had, technology now would already be even more sophisticated like you said. Because it isn't, we already know going back with an iPhone would have no effect.

* The "many universes" answer: this one suggests that if you go back in time, you create a new timeline and the effects carry on there. So in this case, maybe someone does go back to ancient Rome with an iPhone, and Rome goes on to become far more advanced and the world subsequently changes- but only in the new timeline you created, not the existing one.

* Time travel may also just be too difficult to have any significant effects. We usually think about it as you can just get in a time machine and go wherever you want. If it is possible, it's probably going to be much harder and may well involve just sending information back to a receiver in the past (which would require a receiver to already be there).

All those, though, are just possibilities. We don't know, and until someone develops time travel, we'll never know. We may never be able to develop it.

Supposedly only travel to the future is possible as it disallows for certain paradoxes to happen but then retruning to the present follows that any travel to the future can't follow with memories that are viable which poses problems. Experiments with this have actually been done by the CIA and other facilities of the government back in the 90s (supposedly) and their findings showed that data transfer between time periods are foulable and do not withstand the pressures of what was expected of the experiment. (if indeed it happened at all) ( I personally don't doubt it happened)

Time travel will never be possible. It is logically impossible. The reason is because there's no way around paradoxes. For example, say I traveled back in time before I was born and killed my father. I could never have been born, and therefore never existed to go back in time in the first place.

You could take an iPhone to Ancient Rome but you might have trouble finding a service provider or a cafe which has Wi-Fi.

Causation would not be taught. Or maybe it would… But after you already knew it.

The world would not work well.

If time travel were possible, it would likely be be multi-directional so the past, present, AND future
could all be accessed. Given that ability, anyone could create a future where the present would never end
and we could all become stuck in a loop made up from somebody's daydream… Never to see a future again.

Ever see the movie Edge Of Tomorrow?

Time Travel is already possible.

The present would definitely be affected if the past were changed; it is a simple concept. If one brought any type of modern technology to the Roman Era, we don't know how humans would be affected technologically. It could possibly slow the technological advancements of humans.