time travelling fun

[Jack Jack]

If you could bring back items with you in time, I would probably travel in the past, more precisely during probably Tiberius's reign. Then, I would use some weapons that I brought with me, take over the Roman Empire and crown myself Emperor. I would also meet with Jesus for I could. The End.

Bad idea. You can't stay in the past for extended period of time : the food of the past is rotten, you would get the flu and die. Unless you prepare your body by eating historically accurate food and water before you leave. Full of bacteriae and shit and piss. Good luck with that =D

It also a bad idea to go to the future : with the ever increasing potency of diseases, you are sure to get something benign from the locals that can kill you.

And also, you could arrive in a wall of concrete! Or inside a volcano, or in the radioactive ruins of the latest tchernobil. And don't go off anywhere near the coast just in case you end up in the ocean. Basically, the future is a blind leap.

Of course, all this is assuming you don't end up in deep space because the sun moves! That means the whole solar system is light-years away from where it was a century ago.

 

[cookie]

hey thanks for quoting cracked.com word-for-word

The feasibility of time travel is a topic worthy of its own thread.

 

[cantab]

Bad idea. You can't stay in the past for extended period of time : the food of the past is rotten, you would get the flu and die. Unless you prepare your body by eating historically accurate food and water before you leave. Full of bacteriae and shit and piss. Good luck with that =D

Proof please. An analagous situation is quite possible today - a westerner travelling to a third world country and eating the food there. And people in the past weren't stupid - in fact they probably knew a lot more than most of us do about whether food is safe to eat.

It also a bad idea to go to the future : with the ever increasing potency of diseases, you are sure to get something benign from the locals that can kill you.

Again, proof please. Diseases are becoming drug resistant, but that doesn't mean they're any more or less dangerous to a person who doesn't take the resisted drugs. You could still be in danger from an unfamiliar disease, like happened to Native Americans when European's arrived, but that's a consequence of your immune system not the disease.

And also, you could arrive in a wall of concrete! Or inside a volcano, or in the radioactive ruins of the latest tchernobil. And don't go off anywhere near the coast just in case you end up in the ocean. Basically, the future is a blind leap.

So send a robot first. Or you might have a time machine that's like a portal or wormhole that you can simple look through. (To be honest if you open it into a volcano/sun's core/chernobyl/etc, you're probably screwed if you approach it in the present!).

Another point - if you can build a time machine, I've a suspicion conservation of energy no longer holds, so you can build a perpetual motion machine - or conversely, build an energy-sucker.

 

[Polis4rule]

By the laws of physics, you can't technically time travel. You can use time-dilation, of course, to essentially travel forward in time. However, those effects are quite permanent.

 

[cantab]

Which laws of physics? General relativity has numerous solutions that permit travel backwards in time.

 

[vonFiedler]

If the world was made so that time travel is possible, there's no force that's gonna stop you from fucking with the time stream if you go back in time, anymore than that force would stop hurricanes (a byproduct of the way the environment works). Once you're back in time however, there are no time paradoxes preventing you from traveling back in time because you're already back there and matter cannot be created from nothing or turned into nothing. The fact that you can prevent your own birth and still exist shows that either we don't have the lab data to understand how time travel functions or time travel as we generally define it is impossible.

Another thing about time travel is that by going back in time, anything that was truly random would happen differently without your interference. But, we should debate about whether true random really exists another time.

I'd go to the past or future with the sole intention of getting rich to fuel my ambitions in the present. I'm leaning on past though, because I can do my research before traveling.

 

[Sprocket]

I would travel to the year 2300 to witness a recording of the Day of Lavos, and then travel back and forward in time until ultimately ending up in the year 1999, defeating Lavos, but in doing so create a time paradox.

Oh wait, that's Chrono Trigger.

But it does teach us, going into the far future to learn about the near future does open up the possibility of creating a paradox: If you go into the future to learn about an apocalypse, but then you somehow prevent the apocalypse, your future self would never learn about the apocalypse, thus you'd never go back to stop the apocalypse, thus your future self would then learn about the apocalypse...

Consequently going into the past to prevent a historical event would then result in you not going into the past to prevent an event, thus allowing the historical event to occur, thus driving you to...

That is assuming historical events are, in fact, able to be changed.

 

[vonFiedler]

You can't "cause" a paradox. We call them paradoxes because they can't happen.

 

[Brain]

The feasibility of unrestricted "time travel" is somewhat dependent on semantics. Appearance of time travel is certainly conceivable - just erase the current universe, replace it by whatever it was 20 years ago, reinsert the time machine and its contents, and it sure would appear like you have time traveled to 20 years ago. So in the end, you have to tell "true" time travel apart from methods that merely "appear" like time travel.

It is worth noting that the very notion of "change" entails a time progression. If one was to "change" the past, this entails that there would be a "past before the change" and a "past after the change". Say you go back in time and kill your grandfather. Clearly, since you went back in time, the present was such that you existed in the present. And since you killed your grandfather, the present is now such that you do not exist in the present. Since these are two different states, it should be obvious that they cannot occupy the same point on a timeline. "Changing X from A to B" means that X was A at time 1 and X was B at time 2. "Changing the timeline" is not an exception - it means that the timeline was A at time 1 and B at time 2 (perhaps in a second dimension of time - picture a horizontal timeline moving upwards). In this example, the present where you don't exist has to be ordered after the past where you kill your grandfather, and this past has to be ordered after the present you traveled from. If you insist that both presents have to be put at the same place, well, that's where you get paradoxes, but that's to be expected when you're trying to do things that make absolutely no sense.

In a nutshell, timelines are immutable by definition, because any and all changes (again, by definition) induce adding states to a timeline, that is, the state before and the state after (e.g. the "past before" and the "past after"). When you change the past, any changes you enact necessarily translate into new states on the timeline at the only place they can fit (the very end). It's not really a physical thing at all, it's purely semantic. Timelines don't actually exist, and presumably, neither does the past, nor the future (if the past existed, you would have to imagine that somewhere, somehow, there is a tangible version of the past that you could move into). If feasible, time travel would most probably involve remaking the past, or restoring it from a "backup", and in any case, in the absolute, you'd have a timeline where all events unfold until the present, then time travel happens, and events unfold from a past state with the time traveler in it. In my view, this is still proper time travel (it's not like you could tell the difference), but feel free to disagree.

 

[MrIndigo]

If the world was made so that time travel is possible, there's no force that's gonna stop you from fucking with the time stream if you go back in time, anymore than that force would stop hurricanes (a byproduct of the way the environment works). Once you're back in time however, there are no time paradoxes preventing you from traveling back in time because you're already back there and matter cannot be created from nothing or turned into nothing. The fact that you can prevent your own birth and still exist shows that either we don't have the lab data to understand how time travel functions or time travel as we generally define it is impossible.

Another thing about time travel is that by going back in time, anything that was truly random would happen differently without your interference. But, we should debate about whether true random really exists another time.

I'd go to the past or future with the sole intention of getting rich to fuel my ambitions in the present. I'm leaning on past though, because I can do my research before traveling.

You are correct that there is no "force" that prevents you from doing things.

It's exactly the same as the freedom you have right now to pick your nose.

The reason you cannot change time with time travel is that anything you did in the past would already have happened by the time you depart in your original time. What prevents you from changing the past is the same thing that prevents you from having not picked your nose after you chose to pick it.

The same thing applies to the future, but in a slightly different way. Assuming you can travel to the future, anything you see there MUST come to pass because of your actions when you return to the present. Essentially, once you arrive in the future, you are in exactly the same position as the first case, because returning to your time would be equivalent to a person from the future you are in travelling back, and they are bound by the same causal outcome.

On the other hand, if you did change events so that the future you visited didn't happen, then it wasn't really a future, it was simply a parallel present. The moment you allow multiple possible timelines, then the notion of time travel actually disappears because you are not actually moving forward or backward in time, just jumping between parallel universes. And then in each universe, the same rules apply and the "changes" you make were simply always going to happen anyway.

 

[vonFiedler]

But you're in the past. If you stab George Washington in the face, you've changed history. There's no self correcting effect that prevents that.

 

[Aura Guardian]

Obviously you failed to kill him, and that incident just never showed up in recorded history. Also, he recovered without a noticable/mentioned scar. Thus, you wouldn't have changed history. Of course, there is that "replace reality with a new reality" thing mentioned (Brain's mentioning of erasing the universe and replacing it). That would cause problems with time travel to be a non-issue. In that case, I'd like to give some technology to the ancients, maybe, and get humanity millenia more advanced faster.

 

[vonFiedler]

No, I stabbed him in the face five times and then I cut his head off and pissed down his neck. I took pictures, flew over the world and dropped mass pamphlets showing that I killed George Washington everywhere. I would repeat this process every 25 years until current day. But I guess didn't change history because that's not how the Booster Gold comics work.

 

[Aura Guardian]

Well, then we get into remaking the universe or creating alternate realities. Anything goes.

EDIT: Assuming you're allowed to go back to before the time machine was created, that is. And making similar assumptions.

EDIT 2: also assuming that in the alternate realities your older self's existence is independent of your ancestors' existenses. Because you exist because of another reality, which you cannot change anymore.

EDIT 3: I never meant to imply fading into nothing if you kill an ancestor of yours.

 

[vonFiedler]

If I kill my ancestor I do not fade into nothing because matter cannot become nothing.

 

[Brain]

You know, if time travel was possible, it would have to actually be done somehow - through a sort of procedure, which would of course very much depend on how the universe actually works regarding "time". So I think the question is not as much whether time travel is possible or not, but rather whether there exists a logically possible procedure which qualifies as time travel. Here's a bunch of possibilities:

1) Replace the present universe with a past universe, place time machine.

2) Start a new timeline with a past universe, move time machine there.

3) Assume that the universe is a giant 4D hypercube, one dimension of which is time. A machine, at every "tick" of its own clock, modifies each slice along the time dimension to correspond to a function of the previous. All time travel does is pop in a copy of the time machine in a previous slice. The effect would be a wave rippling through the hypercube from the insertion point to the time the time machine was activated. The length of the ripple would likely be the time difference. In this system, time travel would essentially "break" the structure of spacetime in such a way that... it ceases to act as a timeline. For instance, you very well might jump from the present to an unrelated ripple where Hitler was already killed. Also, jumping back to the present after having changed the past would reveal no changes, because the ripple has to get there first (it could work if the machine waits). In fact, this system would quickly become a chaotic mess. Note that the clock of the universe-running machine I spoke of keeps running forwards.

4) Same thing, except that the machine keeps an index corresponding to the present slice, and only updates the successor of that slice. Time travel would simply encode a signal for the machine to read, and as it reads it, it copies the time machine in a previous slice, and decrements its index accordingly. As with 3), this system would put spacetime out of sync, but it wouldn't be as chaotic. Note that "going backwards in time" is equated to decrementing the index.

In all cases, the time travel procedure itself works forwards in the universe-machine's time. There's no way around this. 3) and 4) are interesting in that they modify a reification of the timeline - the trick is that in doing so they put past and present out of sync. All of these implementations appear like time travel. Personally, I'd make the leap that they are time travel. Feel free to disagree.

If I kill my ancestor I do not fade into nothing because matter cannot become nothing.

This is what we posit to be a physical law, not a metaphysical necessity. If you're going to speak of the possibility of time travel, you can't ignore the possibility that there exists mechanisms that can outright erase matter. Heck, it is perfectly possible that there exist ways to consistently and majorly break every single law of physics, but that they are so contrived that we have never found them.

This being said, the idea that enacting a paradox makes you fade into nothing is indeed pretty stupid, since you can't enact a paradox to begin with.

 

[vonFiedler]

This is what we posit to be a physical law, not a metaphysical necessity. If you're going to speak of the possibility of time travel, you can't ignore the possibility that there exists mechanisms that can outright erase matter. Heck, it is perfectly possible that there exist ways to consistently and majorly break every single law of physics, but that they are so contrived that we have never found them.

This being said, the idea that enacting a paradox makes you fade into nothing is indeed pretty stupid, since you can't enact a paradox to begin with.

All true, but until we know how to break the laws of physics I don't buy the fade into nothing plot device either.

 

[Jack Jack]

The most fundamental thing about time travel is that the past is still the past and the future still the future.

So you aldready changed the past. If Washington is still alive, then you must have failed to kill him.

As an aside, as I have provided the link to cracked, I consider to have cited my sources. Althought maybe improperly.

 

[ginganinja]

Just wanted to define a Time Paradox (which is techniqually impossiable)

I believe that the whole I go back in time and kill my grandfather thus causing me to not exist is utter bs.

Instead I believe that anything I did when time traveling, the reprcussions of, are already being felt in the Future

 

[MrIndigo]

No, I stabbed him in the face five times and then I cut his head off and pissed down his neck. I took pictures, flew over the world and dropped mass pamphlets showing that I killed George Washington everywhere. I would repeat this process every 25 years until current day. But I guess didn't change history because that's not how the Booster Gold comics work.

The point is that if you had done that, it would already have happened by the time you started your time travelling journey. Since it hasn't, then it must mean that whatever your attempt in the past, you failed to do what you said you would.

That's why the 'fade into nothingness' plot device is stupid, but also irrelevant.

@Brain: I think time travel would have to permit an instantaneous breach of the Second Law of Thermodynamics at least, which doesn't seem entirely unreasonable since it's a statistical law anyway, not a physical restriction. The reason is that if you were to take any object back in time, leave it somewhere that so that your future self can find it and travel backwards in time, etc., the object contains within it some entropy. By taking the object back in time and depositing it in an earlier part of the universe, you spontaneously increase the net entropy of the universe, which is fine, but you DECREASE the net entropy of the universe at the point in time you left.

A possible mechanism for time travel that would not break this law is for your arrival in the past to displace an equal amount of energy/mass/entropy and put it in the point of time you were when you left.


Also, in regards to timetravel being possible; we are yet to find a violation in High Energy Particle Physics for the Charge-Parity-Time reversal operation (C, T, P, and CP all have detected violations). That means that a positron moving forwards in space and forwards in time is mathematically equivalent to an electron moving backwards in space and backwards in time. It means that you can construct a reorganised Feynmann diagram for the following collision:
- Electron moving forwards in space and time, positron moving forwards in space and time, collide to produce two gamma rays moving forward and backward in space (photons are identical under the time reversal operation).

The variant you can create is to have the electron moving forwards in space and time, interacting with a gamma ray, and then moving backwards in space and time.

If this event can happen, then it also opens up the possibility that every electron and positron in the universe are actually the same unit, moving backwards and forwards in time countless billions of times. It also becomes possible that the Big Bang was started by a particle from later in the universe moving backwards in time and hitting the origin point, thus disrupting the singularity and causing the event that went on the create the particle that moved backwards in time.

 

[Fatecrashers]

I was always under the impression if you were to change the past (eg kill your grandfather) a new parallel timeline would be formed that contained different outcomes (eg you not existing in the future) to the present timeline. Every time you time travel you would effectively add the branch to the infinite branches of time that currently exists.

 

[Brain]

@Brain: I think time travel would have to permit an instantaneous breach of the Second Law of Thermodynamics at least, which doesn't seem entirely unreasonable since it's a statistical law anyway, not a physical restriction. The reason is that if you were to take any object back in time, leave it somewhere that so that your future self can find it and travel backwards in time, etc., the object contains within it some entropy. By taking the object back in time and depositing it in an earlier part of the universe, you spontaneously increase the net entropy of the universe, which is fine, but you DECREASE the net entropy of the universe at the point in time you left.

A possible mechanism for time travel that would not break this law is for your arrival in the past to displace an equal amount of energy/mass/entropy and put it in the point of time you were when you left.

To be honest, time travel as it is usually portrayed would probably break every single law of physics and never think twice about it. I mean, what kind of laws would be such that at some instant there's thin air and the next there's a time machine with a guy in it? Certainly not any laws we've ever observed. Whatever mechanism that would produce conventional time travel would be exceptional and would override pretty much every other rule.

Also, in regards to timetravel being possible; we are yet to find a violation in High Energy Particle Physics for the Charge-Parity-Time reversal operation (C, T, P, and CP all have detected violations). That means that a positron moving forwards in space and forwards in time is mathematically equivalent to an electron moving backwards in space and backwards in time. It means that you can construct a reorganised Feynmann diagram for the following collision:
- Electron moving forwards in space and time, positron moving forwards in space and time, collide to produce two gamma rays moving forward and backward in space (photons are identical under the time reversal operation).

The variant you can create is to have the electron moving forwards in space and time, interacting with a gamma ray, and then moving backwards in space and time.

If this event can happen, then it also opens up the possibility that every electron and positron in the universe are actually the same unit, moving backwards and forwards in time countless billions of times. It also becomes possible that the Big Bang was started by a particle from later in the universe moving backwards in time and hitting the origin point, thus disrupting the singularity and causing the event that went on the create the particle that moved backwards in time.

If you imagine an electron moving forwards, interacting with a gamma ray, and then moving backwards in space (or the alternate interpretation with a positron), you still see three steps ordered in a forwardly fashion. The electron moved forwards, *then* it interacted with a gamma ray, *then* it moved backwards. It's like hitting undo while editing a document: the document might move backwards in time... but you don't. The point is, if you have to actually perform these three steps, no matter how you cut it, even if you have a single unit jittering about forwards and backwards in time, the sequence of these movements is a timeline running forwards, like a sequence of edits and undos. When you move, there is a before moving and an after moving. It really doesn't matter at all whether you move "forwards in time" or "backwards in time", if you keep a history of everything you do, you're still appending to it. You're still moving your history forwards.

Similarly, saying that an electron goes back in time to disrupt the singularity directly implies that at some abstract time-point there was a singularity, and **then** it was disrupted. No matter how you put it, this phenomenon is forwards bound, you have a before and an after associated to a singular point in time. And when the singularity explodes, no matter how you put it... this is still forwards-bound. I guess that what I'm trying to say here is that it's impossible to move backwards in all dimensions of time. To move backwards in a dimension of time implies that you are moving forwards in another, that is, you're moving forwards in the history of your motion. In other words, whatever mechanism is moving your electron forwards and backwards keeps on ticking forwards. If there is only one dimension of time, then electrons either all move forwards in time along with everything else, or they all move backwards in time along with everything else, they can't actually do both (though they could appear to do so).

Note that if your hypothesis is true, causality doesn't really need to stay valid within the time we perceive - spacetime becomes a dynamic entity evolving through another timeline.

 

[vonFiedler]

The point is that if you had done that, it would already have happened by the time you started your time travelling journey. Since it hasn't, then it must mean that whatever your attempt in the past, you failed to do what you said you would.

I haven't failed, I haven't done it yet. I'd have to know that George was the first president of the US for it to even be a relevant example. "I'm gonna stab that nobody that was once mysteriously stabbed" just seems pointless. Once I stab George Washington, you won't remember this conversation but I will. I might not even have been born anymore, but I'll still physically exist and I'll still remember a time when George Washington was the first president. Maybe it's presumptuous to assume that the laws of physics work with time travel, but I don't see anyone performing any experiments on the matter so throwing the laws to the wind is just bad science fiction.

 

[Wichu]

Let's all go to Brain's future dystopia!

Anyway, as an observer only, I'd choose the future. I've always had more of an interest in what could happen than what has already happened; I'd want to see all the new technology that will have been developed.

If I could interact with others, I'd like to go to the past and meet my past self, giving myself information and inspiration from the future :)

 

[Jack Jack]

I was always under the impression if you were to change the past (eg kill your grandfather) a new parallel timeline would be formed that contained different outcomes (eg you not existing in the future) to the present timeline. Every time you time travel you would effectively add the branch to the infinite branches of time that currently exists.

If that is the case, then time travel is pointless. It might as well be travelling in space in a universe that uncannily ressemble ours appart from being in a different point in history.

To be honest, time travel as it is usually portrayed would probably break every single law of physics and never think twice about it. I mean, what kind of laws would be such that at some instant there's thin air and the next there's a time machine with a guy in it? Certainly not any laws we've ever observed. Whatever mechanism that would produce conventional time travel would be exceptional and would override pretty much every other rule.



If you imagine an electron moving forwards, interacting with a gamma ray, and then moving backwards in space (or the alternate interpretation with a positron), you still see three steps ordered in a forwardly fashion. The electron moved forwards, *then* it interacted with a gamma ray, *then* it moved backwards. It's like hitting undo while editing a document: the document might move backwards in time... but you don't. The point is, if you have to actually perform these three steps, no matter how you cut it, even if you have a single unit jittering about forwards and backwards in time, the sequence of these movements is a timeline running forwards, like a sequence of edits and undos. When you move, there is a before moving and an after moving. It really doesn't matter at all whether you move "forwards in time" or "backwards in time", if you keep a history of everything you do, you're still appending to it. You're still moving your history forwards.

Similarly, saying that an electron goes back in time to disrupt the singularity directly implies that at some abstract time-point there was a singularity, and **then** it was disrupted. No matter how you put it, this phenomenon is forwards bound, you have a before and an after associated to a singular point in time. And when the singularity explodes, no matter how you put it... this is still forwards-bound. I guess that what I'm trying to say here is that it's impossible to move backwards in all dimensions of time. To move backwards in a dimension of time implies that you are moving forwards in another, that is, you're moving forwards in the history of your motion. In other words, whatever mechanism is moving your electron forwards and backwards keeps on ticking forwards. If there is only one dimension of time, then electrons either all move forwards in time along with everything else, or they all move backwards in time along with everything else, they can't actually do both (though they could appear to do so).

Note that if your hypothesis is true, causality doesn't really need to stay valid within the time we perceive - spacetime becomes a dynamic entity evolving through another timeline.

The whole point of time travel is to change the age of the entire Universe, except for yourself.

Time is relative, it may move forward for you, but it can, at the same time, go backward for all other particles and waves in the Universe.