Posted by: venuspcs
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[–] 555432? ago
It all depends, and there hasn't really been any scientific study capable of even planning a method to travel forward or back in time that didn't involve near-light-speed starship travel (and then, mostly just traveling forward in time).
Let's assume that some scientists randomly stumbled onto a device that could send the user forward or back in time.
It would have to send them a good distance forward or back, or else it would just be largely viewed as doing nothing and the scientists writing off the time difference to them not keeping proper track of the clock.
It would also have to be able to change their spatial coordinates to match those of the Earth's, or else they would just die alone to the vacuum of space.
It would also have to work with a somewhat reasonable power source, or else it would either never be able to start up at all or send people on a one-way trip.
Now that we finally have a time travel device like the one often depicted in popular media, let's get into the probable limitations on what you would actually be able to do, assuming that you could only travel to the same timeline you were born in and found/invented/bought the time travel machine in.
You would not be able to do anything that would prevent you from finding the time machine in whatever state you found it in initially, as doing so would mean that you didn't get the time machine at that point, which would mean that you never traveled back in time, which would mean you would cease to exist in the past/future, which would mean that your actions in the past/future would be undone, leading to a paradox.
You would not be able to do anything that would prevent your birth, because doing so would mean that you had never lived, which would mean that you never traveled through time, which would mean that your actions in the past/future would be undone, leading to a paradox.
You would not be able to do anything that would change the world enough to make you use the time machine in a different time/place/way, as doing so would mean that you never traveled back to whatever event changed history, which would mean that history was never changed, which would create a paradox.
Basically, unless you travel to the future (and, once there, don't influence any time travelers who were destined to go to the past), you either have to play the role of a tourist (look, but don't touch, as history is being made), play the role of someone who history largely forgot (a random person who lived a normal life, not earning any mention in the history books and not changing history in any meaningful way), or perfectly play the part of a person important to the events of the past.
However, if the Many Worlds theory is correct, and you go to a different world every time you travel, then all of those paradoxes don't exist, because your history was never changed, and thus you always found the time machine and traveled to the same point in history on your first jump.
Basically, if time travel is ever invented, then that world could never have anyone travel into the past before the invention of time travel, or else the entire multiverse could be thrown into a paradox.
[–] venuspcs [S] ago
"It would also have to be able to change their spatial coordinates to match those of the Earth's, or else they would just die alone to the vacuum of space." What if, like some now believe, that all points in time/space are connected? You wouldn't have to account for Space to travel through time if your destination was the same as it was when you departed. It would also mean that by changing your spacial coordinates you could not only travel through time but space simultaneously (which would mean you traveled faster than light) and thus you could end up in a different time and on a different world.
"It would also have to work with a somewhat reasonable power source, or else it would either never be able to start up at all or send people on a one-way trip." So something like the Watch in "Sliders" or the Tardus on "Doctor Who"?
Your comments about not being able to "change" certain things may be completely incorrect. Postulate this: I invent a time machine, now, in the year 2015. I immediately travel back in time to 1971 and kill my mother the week before she gets pregnant. I would never exist, which means I never invented the time machine and traveled back in time and killed her. I now never exist, but if my mom wound up getting pregnant as she initially would have a week later. I would have been born, invented a time machine 43 years later and traveled back in time and killed her.....now imagine that I did in fact travel back and kill her, yes I would cease to exist (as I would have never been born) but she would also cease to exist (from the time I killed her, forward in time). So yes it may actually be possible to change your future by traveling back in time. Additionally, if I was able to go back and kill her, all evidence of me ever inventing time travel (and using it) would be erased from existence as well which may very well be why we have no proof that anyone has ever time traveled. The same goes for all your other theories on "changing anything". Anything you change would most likely erase you from existence and erase any evidence you ever time traveled, or that time travel was ever invented.
Now traveling into the future is a little more straight forward.....at least until you return to your time.....If you travel into the future from 2015 to 2115 and do anything it will not affect the past, yours or anyone's.....or will it? If however, you travel to 2115 and bring back anything (disease, technology, etc) to 2015 it would change the past for everyone that lives between 2015 and 2115 as well as anyone who exists after 2115. Which means that those alive in 2115 would never know that time travel existed either....there whole reality would change and they would never been any the wiser. Now let's assume that time isn't linear but that all points in time exist in the same space....if that is correct, as many now theorize, anything in you change in the future would also affect your past....most likely to the point that you cease to exist, thereby erasing any trace (in any time) that you ever time traveled.
Sadly I have next to no knowledge of the "Many Worlds Theory"....which I should probably read up on. But in my opinion if there are thousands or even millions of other dimensions and time travel is nothing more than a doorway to an alternate dimension (at a different point in time) you wouldn't be creating a paradox or even an alternate time line (as they already existed) you would simply be jumping from one dimension to another. However, the chance of ever returning to your dimension at the exact time you left would be, well, IMPOSSIBLE or at least highly unlikely and even if you did manage to jump back you would never really know that it was in fact the Dimension you came from as there would likely be tens of thousands of IDENTICAL dimensions to yours that are only milliseconds apart in time.