changing the past not possible through time travel?

[Begrudge]

Was just sitting here reading about people argue about time travel being possible, and this occured in my mind, if you go back and change something about the past you wont even know you did it since that event would of never happened, and then you wouldn't have had to go back in time to change that event, so you would of never went back in time to change that event, which means it would still happen, which means you can't change the past with time travel. Sounds legit?

[An-Tuirseach]

What you're describing is the Grandfather Paradox. Like, if you went back in time and killed your own grandfather, you'd cease to exist, but then you wouldn't be able to go back in time and kill your own grandfather, so he isn't killed by you.

What the poster above me is talking about is the theory that there are an infinite amount of parallel dimensions that you would travel to in the events of "time traveling" when in reality you'd be traveling to a dimension in that time period and altering that dimension's developing history, making that particular event different from your own dimension's. There are a bunch more time travel theories, but it's all really a moot point as time travel is currently impossible as far as we know.

[Endus]

The Grandfather Paradox isn't really a paradox.

There are two possibilities, if you can travel back in time; either you can change things, or you can't. Simple, yes?

If you can't change things, then you can't kill your grandfather. You going back in time changes nothing, because you've always gone back in time. No paradox, anyway.

If you can change things, then causality is already borked and doesn't really work the way we think so, to begin with. And that's why the Grandfather Paradox isn't a paradox; it's predicated, fundamentally, on causality. That your grandfather begat your father, who begat you. Cause and effect, leading to cause, and effect. But if causality doesn't work that way, you can have causes that precede their effects, or causes without effects, and effects without causes. If you go back and kill your grandfather, you become an effect without a cause. You'll live out the rest of your life, however it plays out, from that point forward. The lack of a "you" that will go back is irrelevant. If you're going to throw causality out the window, you can't then start saying "but what about the causal connections?!"

[breadisfunny]

Was just sitting here reading about people argue about time travel being possible, and this occured in my mind, if you go back and change something about the past you wont even know you did it since that event would of never happened, and then you wouldn't have had to go back in time to change that event, so you would of never went back in time to change that event, which means it would still happen, which means you can't change the past with time travel. Sounds legit?

who says the event i want to change is to make it so it didnt happen?

[ophion1990]

Was just sitting here reading about people argue about time travel being possible, and this occured in my mind, if you go back and change something about the past you wont even know you did it since that event would of never happened, and then you wouldn't have had to go back in time to change that event, so you would of never went back in time to change that event, which means it would still happen, which means you can't change the past with time travel. Sounds legit?

Pretty sure this was part of the plot for some crappy movie. But aside from that. there's no way to know since timetravel doesn't exist.

[breadisfunny]

Pretty sure this was part of the plot for some crappy movie. But aside from that. there's no way to know since timetravel doesn't exist.

there's a lot of movies with time travel in them. exactly what proof do you have it doesnt exist?

[belfpala]

If you can change things, then causality is already borked and doesn't really work the way we think so, to begin with.

Whew. I just got back from 2002 where I stopped myself from inventing a time machine. It was a close call, but I stopped myself.

I mean, obviously there aren't time machines now. That's because I stopped them from being invented.

Edit: /sarcasm tag.

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there's a lot of movies with time travel in them. exactly what proof do you have it doesnt exist?

A version of the Fermi Paradox? In short, where are the time travelers?

[Aitch]

Everything I know about time travel, I learner from Star Trek: Voyager. I suggest you do the same.

[Endus]

A version of the Fermi Paradox? In short, where are the time travelers?

That's the biggest issue with the idea.

If time travel is possible, then you have to figure out why nobody from the billions of years in the future has ever come back. And not just good people; some future anti-semite stealing a time machine and going back to give Hitler phase cannons and forcefields never happened. Either there's something much, much stronger than us stopping us mucking with the time stream, or it isn't possible, or time travelers would have been a known fact of life for thousands of years. Important events would have been packed with billions of future people wanting to observe it.

[Soeroah]

Whew. I just got back from 2002 where I stopped myself from inventing a time machine. It was a close call, but I stopped myself.

I mean, obviously there aren't time machines now. That's because I stopped them from being invented.

Edit: /sarcasm tag.

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A version of the Fermi Paradox? In short, where are the time travelers?

Perhaps using future tech to hide themselves, since they are smarter in the future?

No one knows if time travel is possible or how the universe resolves paradoxes, it's all basically fiction for now.

[breadisfunny]

That's the biggest issue with the idea.

If time travel is possible, then you have to figure out why nobody from the billions of years in the future has ever come back. And not just good people; some future anti-semite stealing a time machine and going back to give Hitler phase cannons and forcefields never happened. Either there's something much, much stronger than us stopping us mucking with the time stream, or it isn't possible, or time travelers would have been a known fact of life for thousands of years. Important events would have been packed with billions of future people wanting to observe it.

but wouldnt that lead to the present day people wondering what all these extra people are doing here and thus change history just by the fact that there are that many extra people there? also if it was possible and people knew about it wouldnt that make them extra suspicious of attempts to do just that? for example some strange person approaches a leader and tries to convince to do something odd wouldnt that raise suspicion if they know time travel exists and that there may be people attempting to influence it?

[Herazim]

If you went back to change the past, nothing in the future would change for this world line.

Why? Because if time travel was possible, someone already changed what was going to be changed. So nothing changed at all, as far as we're concerned.

So yeah, kinda.

There's no actual proof of this, as time travel doesn't currently exist that we know of.

There's a theory that you can only time travel to the point when the first time travel machine was made. Which means that its impossible for us to actually go back in our current history, only people 1000 years from now will be able to come back to the point when we will invent a time traveling machine if ever. Why ? I have no idea, it would of made sense if we could of only time travel to the point of the first travel which would of made a rip in time and space and it could of been traceable with another time machine. But the dilemma here is if we were to invent a time machine tomorrow it wouldn't be operable with this theory because there is no other time machine to connect to the first one...

[Endus]

Perhaps using future tech to hide themselves, since they are smarter in the future?

If time travel's possible, then at some point, some jackass is going to get a time machine. Because there's billions of years ahead of us, and many more billions of jackasses. And he's gonna take it for a joyride, or use it to deliberately screw up history, or some such thing. We don't even need some evil future regime, just one single jackass in all of mankind's potential future. One future neo-Nazi who thinks Hitler should have some phase cannons. One future chucklehead who wonders what would happen if Rome never collapsed. Etc.

Either it's not possible, or there's something WAY bigger than us that's preventing us mucking with things (and it's impossible to get around), or all of history would be rife with time travelers screwing with things.

[ComputerNerd]

Perhaps using future tech to hide themselves, since they are smarter in the future?

No one knows if time travel is possible or how the universe resolves paradoxes, it's all basically fiction for now.

But all it would take is one not interested in hiding themselves.
Afterall there would be the rest of time for that to happen.

[Kurioxan]

What the poster above me is talking about is the theory that there are an infinite amount of parallel dimensions that you would travel to in the events of "time traveling" when in reality you'd be traveling to a dimension in that time period and altering that dimension's developing history, making that particular event different from your own dimension's. There are a bunch more time travel theories, but it's all really a moot point as time travel is currently impossible as far as we know.

Always found multiple time lines to be "bad writing", kind of a lazy excuse for a time travel plot... a bit akin to modern version of "because magic"
Either way, even if this were to be true, in a sense its not really time travel as you cannot change your time line, only travel to another version of reality, more akin to dimensional travel than time travel.

[Deleted]

To OP : You can't time-travel to begin with like people tend to think as shown in movies etc. The only possible sorta time-travel option is to slowdown time around you while time for everything else is as fast as normal. You can lag behind so to speak. To realize this you need vast amounts of energy to push your speed near lightspeed, because the faster you go the slower time will go by. But as you go so fast you can't change anything because all other things will still go slow, you can't realy interact with it other then torpedo in something...

So say you would have traveld near lightspeed for 10 years in normal time, for you it would seem like a month (just picking a number here) and you have returend home.
You would see that your 2 year younger brother is now 8 years older then you. Same goes for you brother, he sees you're much younger then him now.
For you it would seem like he comes from the future and for him it seems like you have been stuck in time.

If you would have crashed into your home tho as oposed to landed softly near it, the crash still appears in real time for the both of you, that "real time" being 1 month for you and 10 years for your brother.

So you can change things in the past, but it will be the past for some-one for whom time went faster then your time, but for the both of you things still happen in "real time". They say time is in the eye of the beholder for a reason

[breadisfunny]

If time travel's possible, then at some point, some jackass is going to get a time machine. Because there's billions of years ahead of us, and many more billions of jackasses. And he's gonna take it for a joyride, or use it to deliberately screw up history, or some such thing. We don't even need some evil future regime, just one single jackass in all of mankind's potential future. One future neo-Nazi who thinks Hitler should have some phase cannons. One future chucklehead who wonders what would happen if Rome never collapsed. Etc.

Either it's not possible, or there's something WAY bigger than us that's preventing us mucking with things (and it's impossible to get around), or all of history would be rife with time travelers screwing with things.

what bad would come of rome never collapsing? there really isn't anything neccesarily preventing them from doing the same major technological advances. by the time rome collapsed they had already accepted christianity. im sure given enough time they would have stopped using slave labor for everything.

[Endus]

but wouldnt that lead to the present day people wondering what all these extra people are doing here and thus change history just by the fact that there are that many extra people there? also if it was possible and people knew about it wouldnt that make them extra suspicious of attempts to do just that? for example some strange person approaches a leader and tries to convince to do something odd wouldnt that raise suspicion if they know time travel exists and that there may be people attempting to influence it?

It doesn't really make any sense that the creation of time travel in 4,000 years (or whatever) will suddenly mean changes will happen to the here-and-now. That's a strange perception bias. If time travel's possible, it's because time is a dimension, like space. If you're falling, you're traveling through space. You don't have any real capacity to change your speed or direction; you're falling. If you can suddenly move yourself upwards, though, to a higher point, you're still falling. You didn't change the fall at all. Just your height.

Again, people are making this assumption that things won't change until we hit that future, when the entire point is that the discovery being in the future doesn't matter; time travel will have always existed, because you can travel through time.

[Kurioxan]

If time travel's possible, then at some point, some jackass is going to get a time machine. Because there's billions of years ahead of us, and many more billions of jackasses. And he's gonna take it for a joyride, or use it to deliberately screw up history, or some such thing. We don't even need some evil future regime, just one single jackass in all of mankind's potential future. One future neo-Nazi who thinks Hitler should have some phase cannons. One future chucklehead who wonders what would happen if Rome never collapsed. Etc.

Either it's not possible, or there's something WAY bigger than us that's preventing us mucking with things (and it's impossible to get around), or all of history would be rife with time travelers screwing with things.

Indeed, considering the very nature of time travel, it would have happened already. This leaves the idea of dimensional travel to be more acceptable, assuming such a thing even exists in the first place. Either way, it means its not possible to change your original time line

[Mormolyce]

Fortunately, time travel is impossible.

Or at least, it is possible, but only in the forwards direction. At a rate of 1 second per second.