Time travel? Changing events?
 

I'm a big fan of shows like Doctor Who and such, and the time travels in things similiar to it always gets me thinking - can we actually find a way to travel in time, and if so, can we change events?

I believe it was Einstein who theorised time travel in itself was indeed possible (general relativity?) given correct conditions (e.g Wormhole, Faster-Than-Light travel), but what do you guys think?

Also, if one could time travel at will, do you think we will actually be able to change events?

Personally, I believe that changing events, and therefore time travel in itself is impossible...sort of.

Think about it, you want to change the past so your grandafather is rich, will will in turn make you rich, however - in the new timeline, you would have incentive to time travel and make your grandfather rich, and therefore, you would not travel back in time to do so, which means no change would occur!

I think it's more likely that if we did change events, a parallel universe would be the product of such a thing.

Thoughts?

Re: Time travel? Changing events?
 

If it was/is possible, I don't think you'd be able to go back and change events concerning yourself, or time travel itself. Of course, then there's the whole multiverse stuff(You stop an event from happening, and when you go back you find the future that you had changed, but the universe you came from stays unchanged). Or at least that's what I think it is. Do correct me if I'm wrong.

Re: Time travel? Changing events?
 

We're travelling through time as we write. It's just that it's only one way, and the speed is fixed.

Why? Just because it's easier for you to get your head round it? :lol:

Re: Time travel? Changing events?
 

Well idk how far this is gona go, but I believe that its possible for time travel to work, its just a question of what damage that can be done by it. And then depending if we still have money when the they around to building such a thing, the cost....

Re: Time travel? Changing events?
 

If time travel is possible (and that is a big if) I also suspect a branching universe would result. The paradoxes that result from linear time just seem to much. I.E. you go back in time to change something, so because it was changed you no longer have a reason to go back in time to change it, so you don't go back in time, but now you want to go back in time to change it. Lather, rinse, repeat.

Multiple timelines is the easiest way to solve that paradox. My main thing against time travel is that if it is possible it has already happened, since the future would have to coexist with the present and past, and so everything that can happen would have already happened. As a result someone would have already traveled back in time and we'd like see the results already.

I can, however, see the plausibility in recreating the past. After all time is just a measurement of change, so if you rearrange all of the molecules in an area to represent what that area would have looked like 5000 years ago you would have effectively traveled back in time, at least locally.

Re: Time travel? Changing events?
 

So technically there would have to be an extra two dimensions for this to fit. Because for every single, infinitesimally small period of time, there would be an infinite number of different possibilities that could result. And then because some of those branches are interconnected, there would have to be a method of skipping directly from one to another, which gives us the second extra dimension. So...6 dimensions. Fun. I doubt these are the ones envisaged by the string theorists, though...probably just figments of my imagination. =p

Re: Time travel? Changing events?
 

Would you want to? Think about it.

Everything in the world is as it is today because of everything else that has happened in history. From the significant events (D-day invasion, invention of lightbulb) to the very small (me typing this), you dont wanna go fucking with the past.

If someone killed your great grandparents, you have no idea what ramifications that would have to the world today. Most likely, not too much, but you could go back in time and alter the course of humanity with a few simple steps.

You traveled the speed of light for 6 months and then came back to earth everyone would have aged multiple years.

Again, you wouldnt want to.


Exactly. Just thinking about time travel and trying to understand it will give you a headache.

Re: Time travel? Changing events?
 

It depends how you measure this. If the six months is by stationary standards, then obviously it will have been 6 months. However, if the six months is by speed of light standards, then it will be infinitely long.

Re: Time travel? Changing events?
 

This makes no sense as an explanation.

6 months in seconds counted by an atomic clock on board your spaceship is what I assume he meant, and then yes if you were actaully travelling at the speed of light (and not just "near to" it) an infinite amount of time would've passed.

It isn't.

Tbh, travelling backwards in time is a relative impossiblity; and in the simplest of terms is actually impossible, peopel get overly conerned with the notion of wormholes etc. and if you ask a physicist this isn't actually time travel, it's something different.

Re: Time travel? Changing events?
 

How do we know time travel is impossible? Or relatively impossible?

Re: Time travel? Changing events?
 

Unless you travel at relativistic speeds every other day, then it's close enough to not make a difference for most people. And I mean most as in 99.9999% of the Earth's population.

Re: Time travel? Changing events?
 

We don't. We have to have faith. That's why there's a little known and discredited area of physics known as temporal physics. It's the physics of time travel.

And heck no you do not want to change the past, because once you do, you can't change it back no matter how hard you try. Even being in that point in time changes that moment in time. So, in order to not change the past, you do not go back in time.

About paradoxes: Non-linear time is the answer.

This is my conjecture on time (I call it the Initial Timeline Conjecture).

From zero time (big bang or creation via current theory), one timeline is created that moves at a certain speed (think time dilation). I'd believe it to be the speed of light, but we'd have to create a unit of time-speed to truly measure how fast time is moving.

Anyway, this first timeline is the initial timeline. This timeline has no future; it only has a past. Everyone lives in the present, and all events within space-time contribute to the next "orientation" of everything in space-time at the very next instant. In other words, there is no destiny or fate because the "future" (which really doesn't exist here) is being created by the consequences of the events of the present.

Now, what if a time travel event occurred? Skipping the conjecture on how it would happen, the moment that person arrives in a chosen point in time, a new timeline is created because every event's space-time coordinates are now different. In other words, things have changed. The original timeline goes on, but a new timeline is now created which starts at the exact moment the person arrived back in time. This timeline has a destiny because events will almost match those of the initial timeline, but it won't have a future. Thus, forward time travel is totally impossible. The effect of "destiny" on the new timeline depends on the amount of new events that occurs in the new timeline. The time traveler who created this new timeline will only propagate through the new timeline at the speed of time and not faster.

I created (thought up) this conjecture to solve the familiar "Grandmother Paradox." This is the one where someone goes back in times and kills their parents or grandparents before they were born, preventing them from existing. The confusion then begins.

Well, actually, this is what happens: you don't stop existing when you kill your parents/grandparents/whatever because you're from another timeline in which you did come into existence. When you create the new timeline, you'll only prevent yourself from existing in the new timeline at the same event coordinates as in the old timeline. That's it.

I've since thought of some variations based on temporal theories like Stephen Hawkings "Crono-Protection Conjecture" where if you attempt to change the past, events will occur that will stop you. To me, that's a new timeline that's trying to create events such that it matches the initial timeline. Unfortunately, it can never return to its original state because it has a new event in its past.

Re: Time travel? Changing events?
 

So you if you went back in time to yesterday, and lived the day on thru to today, would you HAVE to go back to yesterday?

But then again....why would you want to go back in time? For some horrible moments to undo I can understand, but you are messing with the universe, dont think you want to do that. Like..to stop your parents from dieing in a car crash or something, I could understand, but....isnt life about going forward?

Now if there was a way to go back in time just as a ghost observer and you couldnt interact with anything, that would be cool. I'd go back in time, and watch the D-Day landings, and then come back a week later, having seen the entire first week of the D-day campaign.

Re: Time travel? Changing events?
 

Well time's just the concept we tack on to explain rate of change, right? However you measure it, with the vibration of a particle, or the expanding of a spring, you're measuring the change in that object and then appealing to this concept to explain time. If someone asks you what time is you point to something changing and go, 'Look: time!' I mean it runs faster or slower in some areas but it's still rate of change. Like acceleration. What I'm getting at is when you go from 80 miles an hour to 0 you've accelerated. And when you go from 0 to 80 in reverse you've accelerated again. It doesn't really seem possible for time to go backwards any more than acceleration can go backwards.

Can you run events in reverse? That's a different question. That just seems to be a matter of reversing the vectors of all the particles concerned with those specific events until you get to the point where you want to start going forwards again. Once you acknowledge that it's not time you're reversing, any more than acceleration reverses when you put the car into reverse, then most of the contradictions involved in time travel seem to fade away. Physically impossible, perhaps, but it doesn't seem to involve a logical contradiction.

Re: Time travel? Changing events?
 

The theory of time travel has been around for a while, and many people have stated their opinions on what the outcome would be. Would anything actually change? Would another Universe be created? Would we ultimately kill ourselves in the process?

Someone has already said here, that if we went back in time and altered something, which would have a consequence on our birth, then we wouldn't have been born, therefore, we'd not be able to go back in time in the first place.

It is possible, that time is fixed, and anyone who attempts to travel through it, ultimately seizes to exist. Think of it as hitting a brick wall; if you decided one day to travel from 2010, back to 1910, you may get there, only because you don't exist there, simply don't arrive at your destination. The minute you attempt to go back in time, your molecules and such burn up.

Then you're got the directions. Would you go back in time, or forward in time? Essentially, you can't go forward in time, because it doesn't exist yet. How would you go somewhere that doesn't exist? Equally, if you were to manage time travel to the past, you'd be stuck in the same situation. In the past, the future (your present) wouldn't exist, so how would you get back there?

It may be possible that once you go 'back in time' you're stuck there, though would you, or would you not alter the future? Even if you did, you'd not know, because there would be no way of getting 'back' to your present.

Anyone confused yet?

Also, if time travel is possible... Nobody has come back to 2009 from 3009 yet have they? I personally believe that time travel isn't possible, and I'd very much hope it isn't. I can only imagine the damage that could be caused by it. The only thing I will say, is that it may (in the future) be possible to 'view' the past.

We know, that if we look into space, we see other planets etc as they were, not as they are. Therefore, if we developed the technology to move to other planets, we may be able to view Earth in its past; heck, we may even be able to develop something that allows us to view things in realtime, such as you'd go to a location on the planet, hit a button on said device, program a time, date etc, and then you'd see (maybe through some special goggles) the past.

All speculation, but something worth discussing I think.

Re: Time travel? Changing events?
 

IIRC the present theory is that if you went back and say killed your grandfather you would at that point cause the timeline to split and create a alternate timeline where the two possibilities create two realities and for every difference you just created a split off from the original timeline.

Re: Time travel? Changing events?
 

Not possible. We see space in it's past state because of the limited speed of light and electromagnetic waves (or photons) which carry all of the information about a point in space. To know what's there now, we'd have to instantly go there.

If you leave Earth at the speed of light, and then looked back on it, you would see the Earth in a point in the past history relative to the current time on Earth, but you could not see past when you left. The only way to see the past beyond that is to find and catch the photons carrying that information, all of which are radiating away from their origin at the speed of light. Good luck catching every single photon you need (there are an infinite number that originated from that spot). This applies to looking at the past history of other planets as well.

It could be possible, but it would be a large task. We'd first have to break the speed of light to even start on it.

Re: Time travel? Changing events?
 

Actually Newton's first law means we could reconstruct the past, given enough information and processing power. Since every action has an equal and opposite reaction you can take the position of every particle in the universe, it's velocity and direction, and work backwards to find out where they were at any given time. Essentially everything that has happened is the only way things could have happened, because there is no variation in the reaction. It is always equal and opposite, one way or another. Basically the universe is the reaction to the action of the big bang, and can only have happened one way.

Re: Time travel? Changing events?
 

Only if we intended to take the same route to get to the interception point as the photon. =p Although I agree it would make it a lot easier.

Re: Time travel? Changing events?
 

Afterburner, please read about the Heisenberg Uncertainty Principle.

Also, even if it were possible to specify this sort of thing, to build a computer that could encode all that data you would effectively have a computer the size of the universe; well actually to deal with processing the data, larger than the universe.

Re: Time travel? Changing events?
 

I don't mean we'd ever be able to do it, I just pointing out that there is only one way for events to unfold, which makes them inherently predictable, if you could get past the uncertainty principle (and you don't have to tell me you can't.)

Though that reminds me of a funny joke we'd always make about one of our robotics mentors. We joked he followed Heisenberg's uncertainty principle because we never knew both where he was and what he was doing at the same time.

Re: Time travel? Changing events?
 

But we built a Heisenberg Compensator. :D

Re: Time travel? Changing events?
 

Go back in time and spray a can of raid on the first microbes.

See wtf happens...

Re: Time travel? Changing events?
 

Well actually this is untrue as well; and is well demonstrated within Quantum Field Theory.

Re: Time travel? Changing events?
 

We don't all have time to study advanced physics so could you explain as simply as possible?

Re: Time travel? Changing events?
 

Ok basically there is a degree of randomness to all events. The idea that things behave "linearly" or predictably is actually untrue.

In fact you don't need to go as advaned as QFT, so I'm sorry I did.

The simplest example is what is known as the "three body problem".
Basically if you have a "2 body" problem (i.e. an interaction between 2 discrete bodies) the result can be calculated exactly.
However, for 3 bodies and beyond one has to use a perturbative approach and you are left with a "remaining degree of freedom" whereby some of the outcomes of the interaction are not well defined and could take a range of values. So here we see an actual "uncertainty" inherent even in Newtonian physics.

Sorry for the short and useless post earlier.

Re: Time travel? Changing events?
 

Just because we can't predict it doesn't mean it's random. If I see a light dancing about my wall apparently at random I'm not going to just assume it's random because I can't come up with a formula that explains it, I'm going to make damn sure there's not some little shit with a flashlight lurking outside my window.

Re: Time travel? Changing events?
 

Thanks for actually going to read about 3 body problems rather than just completely disagreeing with me for no reason what-so-ever.

Nice. Also your anology missed the point entirely.

A remaining degree of freedom DEFINES variation/randomness in both local and global systems.

Re: Time travel? Changing events?
 

How many times has that actually happened?

Re: Time travel? Changing events?
 

And what if the light is still there and there is no little shit with a flashlight.

Re: Time travel? Changing events?
 

Unexplained variation is just a variation that hasn't been explained yet. Even if in principle it may be impossible to explain it if you have an incomplete set of the relevant variables when you start a calculation you're going to get a remaining degree of freedom. Randomness on the other hand is something that is uncaused. To claim something's random makes a claim that in principle is untestable short of omniscience.

In any case if you want to make u-variation and randomess synonomous definitions then these new definitions don't work in the context you were using them against Afterburner's argument. There wasn't only one way things could unfold because there's unexplained variation. It's not a very solid claim.

Considering my window is high in the air? Not many.

Draw the curtains and see if it goes away, check that there's not someone hidding under the bed with a flashlight. Do any of the myriad things to test for actual logical solutions to the problem before you start saying it's random. And if after all that you find that it still doesn't go away, then you write a general explanation for its behaviour and file it under unexplained variations, not, 'randomness.'

Re: Time travel? Changing events?
 

Ok unforunately you don't seem to understand how degrees of freedom work mathematically.
No it's not.
No actually, even if you know everything you would still not be able to predict the variation, that's sort of the point.

I'm not trying to suggest you can't approximate these variations - hence my use of the word perturbative - simply that since it is impossible to be entirely specific about the outcomes of 3+body events and even infinitessimal changes expanded over time can be extremely important to the outcome of an event (see thought experiments similar to the "electron at the end of the universe") we are left in a position where it is impossible to construct entirely consistent histories (futures/pasts) for any 3+ body system.

I'm trying very much to keep this in the area of "no need for maths"; as I don't think it's fair to venture down that route.

Re: Time travel? Changing events?
 

I don't understand. Why do you have to calculate the movement of 3 bodies like that instead of being able to model a set of differential equations on the force applied by each body varying with distance?

Re: Time travel? Changing events?
 

If time travel would've worked we would have known by now. People could time travel to our place and learn us all about it. Basically that's enough to convince me. You try to convince me that this is not okay.

Re: Time travel? Changing events?
 

To be fair this argument assumes all points in time coexist. We could be inhabiting the "initial" time line. If the future doesn't exist yet, than no one could have come back in time. Or we could be in a time line where some kind of temporal prime directive is in place, and is being enforced effectivly in the future. Or it could simply be that since time is simply a measurement of change that only the present exists at all, and the "past" and "future" are just alternate configurations of the particle sin the universe.

Re: Time travel? Changing events?
 

Re: Time travel? Changing events?
 

Unless time is branching, and the changes create a new timeline. That eliminates all paradoxes. You kill your grandfather and the you that would have been born in that timeline no longer will be, but you still exist because your grandfather is still alive in your original timeline.

And I don't see why we wouldn't perceive changes if they occured in the here and now. Let's say a time traveling robot tries to kill you to prevent you form becoming the leader of a human resistance in the future. You bloody well know the timeline is being changed because that change is shooting at you right now.

Re: Time travel? Changing events?
 

Actually time is branching if we are to believe what the cosmos suggests compared against the science of the day. Paradox might be temporarily extinguished for you for one specific micro-moment during your travel back in time, but not the infinite outcome entirely. If you went back and killed your grandfather, then yes you would cease to exist in that time line you just left, altering the outcome of whatever your family line impacted on that existence and no one outside of yourself, would perceive the change. However, what you didn’t realize is that by doing so you instantaneously created a new existence, in which you do live and so does your grandfather. In this instance you have created a quasality loop for yourself, and the only "change" you've created is the one for yourself. A trap so to speak, so yeah, you would perceive the change (or so we can assume), but no matter what you do to alter events you’ll continue to merge* into each new universe like a ripple spreading out from a pond never to achieve your goal of killing your grandfather, until such time you come upon one where your grandfather, or family line for that matter never existed…and I have no idea how to go about explaining that one. At any rate, the loop in itself is a paradox, other than your perception…so then, yes you would be immune, but not your counterparts in each universe you affected. It begs the question about people who claim to be from the future or other realities; are they being truthful in their plea that they are from where they claim or are they nut jobs? We as a society can discount their claim or believe them. Anyway, the events that unfold from your action have no bearing on the existence of those who continue on after your change; unless you come forward, but then you face contempt from those you interact with without solid tangible evidence to persuade your audience.

Quote:

And I don't see why we wouldn't perceive changes if they occured in the here and now. Let's say a time traveling robot tries to kill you to prevent you form becoming the leader of a human resistance in the future. You bloody well know the timeline is being changed because that change is shooting at you right now.

That would be perceived because it is a present tense situation. Lets use your example and step back 50 years to examine; any change in say our reality today would not exist for those of us that exist in a parallel universe from that occurrence. What you suggest is nothing new. Parallel Universes is something that was predicted back in the 1900’s. Hitler in our Universe never happened in another and so on and so forth. The theory suggests even now as you and I converse there are infinite possibilities being created some of which take on a parallel existence every second time marches forward. Again, paradox prohibits our awareness of infinite strings branching out from times movement in one direction or another. Now there are some mystics and soothsayers who believe that déjà vu shared by one person or several about a similar existence is our ability to perceive these alternate realities, other cultures (like my mom’s people) believe dreams are windows into our alternate selves. Kinda like looking at a mirror of our self into infinity. Who’s to say? But if we could perceive paradox, it would be highly disruptive, and to be frank human development couldn’t fathom living in a reality where we perceive ourselves in infinite possibilities – the then, the now and the tomorrow. Perhaps one day, but until then we’ll have to contend with God having the only ability to be in many places at once, or so we have come to believe.

*Current contemporary science believes that if one was to alter time one way or another that our string would vibrate into unison with the one we’ve created or merged with, essentially overlapping our counterpart in that existence, eliminating the prospect of meeting yourself in the new timeline and avoiding paradox - other than self realization that we have shifted out of our original existence.

Re: Time travel? Changing events?
 

To be honest, none of that made sense to me. Let's say you go back in time to kill your grandfather, here is how I perceive it would happen.

You would travel back in time, and at the instant you arrived a new timeline would branch off from yours at that point. If you now kill your grandfather he will be dead in the new timeline, but not the old one. So the you that traveled through time is still alive because the grandfather that gave birth to your father is still alive in your timeline. However in the timeline you just arrived in you are never born. The you from the first timeline is still there though because the grandfather you just killed isn't actually yours, it's parallel you's.

Now of course no one would know that history has changed in the new timeline, because it HASN"T. Nothing changed, you just made a new timeline. The old one is unchanged, and the new one has yet to be, so it can't possibly be changed. That doesn't necessarily mean the new timelnie isn't aware of the fact that it is a new timeline. If you told people and they believed you, for whatever reason, they would know. But still nothing changed, just new stuff was created.

Edit: However, the more I think about it the more a second option makes sense to me. There is no time "line" there is only the present configuration of the universe. IF you alter that configuration to resemble the past you will have apparently traveled backwards in time. Of course, you'd have to make sure the particles that made up you would remain intact in the reconfiguration process. From that point on you would just be running through the actions of the universe again, except with whatever changes your only particles might cause.

Of course, as we already went over, that sort of reconfiguration seems to be impossible. Or at least impossible for humans to artificially induce. I suppose some kind of cosmic force we haven't discovered yet could somehow induce it, though I'd doubt that.

Re: Time travel? Changing events?
 

Re: Time travel? Changing events?
 

The simplest explanation is the number of "variables" in the outcome is 1 more than the number of independant equations you are able to set up from the initial system. So no matter how you solve it you are always left with a 1 variable which is unknown. (This explanation, I am aware, doesn't explain the "randomness" I was talking about earlier).

Whereas for 2 bodies we have the same number of final variables as initial equations, as such are able to solve exactly.

I would love to see where you got that from. Being rather "avidly" interested in contemporary science I have yet to come across anything that even comes close to being as specific as you are being about how time-travel would work.

Re: Time travel? Changing events?
 

Cosmic String Theory, physicist J. Richard Gott is a good place to start. I've read many of his papers on the subject, very interesting stuff.:cool:

Re: Time travel? Changing events?
 

Hmmm all I can find is discussions and solutions regarding closed time-like curves (phys rev d 1991), and some development of the chronology projection conjecture for misner spaces. Maybe a link to a paper would help?

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Re: Time travel? Changing events?
 

Really? I think I'm pretty okay at maths, but seeing as I'm taking a biology-related degree I haven't done any in a while. But could you show me the equations please? I would be interested to see them for two and three body systems.

And if we have one more variable than equations, doesn't that mean that you have an infinite range of possible values rather than just a small uncertainty about the location of the bodies?

Re: Time travel? Changing events?
 

Time Travel isn't a topic I've ever been terribly interested in, but there are some very interesting perspectives in here.

As Nemmerle said (as Nemmerle always gets right :)), "time" is merely a label that helps our limited imaginations rationalize physical existence. Just like gravity, matter, etc. They are abstract categorizations, albeit practical and useful ones, we use to define our immediate experiences. Much of the time it is these self-imposed cognitive limitations that inhibit our understanding of the universe, and certainly our imaginings of what is merely mind-boggling versus what is physically possible or not.

That is where I leave you! As much as I am interested in all sorts of physics - as physics is the basis of all the physical, natural sciences - getting into the realm of niche theoretical physics is dangerously close to pseudo-sciencing I think. Not to mention I know nothing about most specialized fields of physics anyway. Interesting stuff nonetheless. :cool:

Re: Time travel? Changing events?
 

No parrallell universes space was proven to be flat.

Time travel in the sence of going back years in time will NEVER HAPPEN.
You will never go back and prevent WW2, EVER.

Re: Time travel? Changing events?
 

This thread is hilarious. You're all arguing about different laws of time travel that were explained to you in TV shows. There's nothing concrete to found any theory on. I fail to see how any of this could matter at all anyway. Regardless of how time-travel would work or if it's possible clearly affects us in no perceivable way.

Re: Time travel? Changing events?
 

Actually Astrophysicist Neil Degrasse Tyson had some comments on this subject. Humans on this planet could only go back to when the first time machine is built. We cant go back before that because the machine to do so does not exist here.

We would have to connect to a alien time machine built centuries ago to be able to go back to when their machine was built, assuming any Aliens even built time machines.

Re: Time travel? Changing events?
 

Neil Degrasse Tyson (& you??) envision a time machine as something that doesn't travel with you through time?? He (& you??) imagine 2 devices stationary in time?? I'm not sure why (especially since the entire idea is founded on nothing) but this idea seems a lot more plausible to me.

But like I said: Doesn't matter, no perceivable way, nothing more than theories, etc.