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Original post by DBX How about thinking about it in a somewhat wacky, possibly irrelevent, but different way. Imagine you were developing a game. This game's logic has a fixed timestep. Let's say it runs at 100 ticks/second while playing (ignore rendering for now). So, you're playing along in the game and it's ticking over as usual. If you stop ticking, time stands still and nothing changes. Carry on ticking and you're back to normal. Now, in the game, the Dr Alpha character creates an android. The androids take over the world, but then someone programs one android to go back in time. How do you implement this? Of course, you'd have to assume all characters are AI driver, since human players exist outside the known universe. For going back in time, you'd just have a physics (and AI) system that can go backwards - so you can just flip the backwards bit and carry on ticking. I can see two ways this will now continue. 1) The world state is split into two different worlds. One going forwards, and one going backwards with the time travelling android. The humans in the first state are expecting the android to stop all this happening - but it never will as the game is relentlessly ticking forwards and nothing is going to suddenly change. While in the second world state, the android completes his task, and the world continues a different future. 2) The world follows the time travelling android backwards. During this time, the future humans who programmed the android no longer exist in their future state (because we only store the current world state). The android arrives at his destination, time goes forwards again and he stops Dr Alpha creating the original android. The world will now continue ticking on, but with the addition of an android, into an undefined future. any other options?

This actually refers to how reality might work. The universe only stores the its state and a vast amount of possible future states, which are choosen from according to the set of rules we call natural laws.

Going back in time would be possible, but moving forward into the same time would be impossible, because the state is lost.

My approach would additionally store the current state and restore it if Dr.Alpha comes back. My game universe would have a current state-stack that is used to restore its state if the player travels back.

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Original post by orionx103 If this were true, then an atheist saying, "God doesn't exist," wouldn't be completely true. It'd mean God would exist in certain universes, the Heliopolitan gods would exist in certain universes, the Greek gods would exist in certain universes, all gods would exist in certain universes, and so on.

The idea of parallel universes says that anything that can happen will happen in at least one of the infinite numbers of worlds. Notice the "can", as in what's possible under the laws of nature. So it would be entierly possible that a god wouldn't excist in anny universe since it might be against the laws of nature (it certainly sounds like it is too me).

EDIT: Something that's rather deppressing about the parallel univers theory is that if it's correct then no matter how hard we try there'll always be a infinite number of people suffering. Of course there would also be a infinite number of people not suffering, but that doesn't weight up those who do.

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Original post by Trinka Another intersting thought... when you have space (exists) you get a distance (doesn't exist), when you add the movement (exists) you get the speed/time (doesn't exist). :-D

Allow me to jump in here and hopefully help the discussion. It's sounds like you, Trinka, are using "time" to mean a measured duration, or a measured rate-of-passage. Whereas other people are simply using "time" to describe the general concept, without actually caring yet about amounts. When you describe "movement", to me you are simply describing the basic concept of "time", devoid of measurements and values. A series of states with a specific logical order in a single point of space. No measurement of how much "time" passes from one state to the next, or how quickly.

I'm guessing that to most of us, movement = change = time, or at least movement = change => time. It's just a definitions thing, as others have said. Sound about right?

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Original post by Spearhawk The idea of parallel universes says that anything that can happen will happen in at least one of the infinite numbers of worlds. Notice the "can", as in what's possible under the laws of nature.

o know this theory, but i dont think it can ever be true. eery human makes a desision every milisecond or so. do i dont i type this letter for example. all these descisions interact with each other. so, we would created so much paralells, that it would be impossible. and how should they be created? mass is limited, it HAS to come from soewhere.

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Original post by Spearhawk So it would be entierly possible that a god wouldn't excist in anny universe since it might be against the laws of nature (it certainly sounds like it is too me).

this is a question you schouldnt ask because of the religious people ;). but it can also be the same god in every universe trough the quantum theory... never mind that ;)

You can go back into the past and kill your grandfather. When you go back to your time, you are still there. No problem.

The biggest reason you can't understand why this is ok is that you still think time goes in one direction. Once you realize that time is just another spacial dimension it all becomes clearer.

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Original post by kaysik I had a phyics lecturer who was really into this stuff and he managed to explain it like this - there is never a first time! You can't have different versions of time (as in its impossible to change it) because there is never an original version. If you look at the Dr Alpha thing like this: He thinks up robots, one appears and he stops working on it, life goes on! Thats FINE! Because there was never a version of time where he did create the robots. Now some of you will state the obviouse that how could the robot exist to stop him, but your thinking about it wrong - you want cause and effect which don't have to exist. You can only every have 1 version of time and its played the same no matter what - just because cause and effect are broken means nothing. There will only every be one time stream and it'll always play out the same ... or so the theory goes :D

I am all for this idea, since I've already decided that it's rather clear [to me] that cause-and-effect is not an absolute rule of reality (due to the first cause problem).

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Original post by Agony Quote: Original post by Trinka Another intersting thought... when you have space (exists) you get a distance (doesn't exist), when you add the movement (exists) you get the speed/time (doesn't exist). :-D Allow me to jump in here and hopefully help the discussion. It's sounds like you, Trinka, are using "time" to mean a measured duration, or a measured rate-of-passage. Whereas other people are simply using "time" to describe the general concept, without actually caring yet about amounts. When you describe "movement", to me you are simply describing the basic concept of "time", devoid of measurements and values. A series of states with a specific logical order in a single point of space. No measurement of how much "time" passes from one state to the next, or how quickly. I'm guessing that to most of us, movement = change = time, or at least movement = change => time. It's just a definitions thing, as others have said. Sound about right?

yup ur get it. trinka and i am "discussing" that. thats why there is a full page about what time is. we cant find a solution cause we are both right. time an come in many forms. time is for me something that always is here, even if nothing happends, something is in that statefor some time. trinka however is also right that time is just a human thing to describe how long somthing is, and so, time has no real meaning. i guess where both right :D

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Original post by Anonymous Poster You can go back into the past and kill your grandfather. When you go back to your time, you are still there. No problem. The biggest reason you can't understand why this is ok is that you still think time goes in one direction. Once you realize that time is just another spacial dimension it all becomes clearer.

i wont agree with you. if you kill your grandfather, how can you ever exist to kill in the first place? and about the dimension thing.... it wont do. lenght and height are also dimensions. alter then and you alter all. just like with time

We are all time travelers. I'm doing it right now. I'll show you how:

Sit very still in your chair. Now count to five, slowly.

1... 2... 3... 4... 5...

You have now "Time Travelled" five seconds into the "future."

You have moved--at least in the sense of 4 of the dimensions--through space-time.

Remember: Just because you don't know how to do a thing doesn't mean it can't be done. People once thought the world was flat, the speed of SOUND couldn't be broken, witches floated, the Earth moved on the back of a turtle, and that god existed.

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What do you base this assumtion on? Current cosmological models can describe the universe very close to its beginning (about one Planck time ~ 10-43s).

I said "the universe in some form or other", which means I meant whatever the universe was before it was the universe (and due to stuff like conservation of energy and matter and the like, I assume it was at least something)

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Basic assumption: time 'started' when the universe first changed its state, e.g. came to existence.

But if time didn't exist before the universe first came into existance, what governed when or perhaps more accurately, why the universe did change state and become the universe.

It's like saying that a character from a movie can control the playing of the movie from inside the film (weird example I know, but still relevant). What happens when that character presses pause? The character now cannot move and therefore cannot press his finger down on the remote to "unpause" himself.

This is what I mean by time, it is not as we know it as (I think this has already been stated but I just wanted to show where I got my conclusion from). I am by no means as qualified to answer these questions as you appear to be, but I figure that the less I know about what's been established, the more abstractly and openly I can think.

Good point made that all theories assume something (which in itself is a theory which assumes that there won't be a theory which doesn't assume something in the future). ;)