# Time Travel and Energy

1. Apr 23, 2003

### Moogle

Lets say that I travelled back in time and then travelled back to the present but I left an object in the past. Since the universe always contains the same amount of energy/matter, what would happen to the universes energy to explain the sudden change (bringing the said object from one time to another)? What would the universes energy be between the objects original time and the time it was brought to? Im pretty sure that all the energy would stay the same in the end but Im not sure (time travel is confusing).

2. Apr 23, 2003

### drag

Greetings !

Welcome to PF Moogle !
Very ! It is also impossible according
to current physics which makes such "what if"
questions a bit difficult to answer.

Live long and prosper.

3. Apr 23, 2003

### RuroumiKenshin

Could the future exist already? Then, your idea, moogle, could make sense if the object from the future would be left in the past. The law of thermodynamics will not be flawed, in that case(if the the future already exists).

4. Apr 24, 2003

### Zefram

If time travel to the past is possible then the way I see it, the future must "already" exist. If tomorrow a 40 year-old MajinVegeta visited you, this older MV could tell you all kinds of things about the future. From your point of view, older MV is from the future but from older MV's point of view, you are simply part of the past.

In other words, if 'older you' visits you then 'older you' must be coming from somewhere (somewhen). That somewhere must be the future. So the future would have to exist. This older you would have already done everything you're going to do up until the time you're 40 (college, career, whatever) so in a sense that's already "written." You'd just be retracing the elder you's footsteps. But then again, you are the elder you (i.e. you'd have to make the visit to young MV when you're 40) so it kind of balances out. See what I'm saying?

5. Apr 24, 2003

### RuroumiKenshin

if the old MV told me the future, then history would be changed. that's when the multiple history theory comes in.

6. Apr 25, 2003

### wimms

Maybe it would be fruitful to ponder for a moment about what Time actually is? It is not just another coordinate, its unique. Used as coordinate in motion equations, but that doesn't tell much about its nature.

Another good term to ponder about is "exist". What does it take to actually exist? I'd suggest approach similar to this:
That which is common to all things, is fundamental. What is common to absolutely all things? Form. Any even remotely imaginable thing must have some sort of form. Without a form, there is no thing. What is one form to another form? How do you perceive other form? By observing it through interaction. Thats the only means to realise existence of other form. In fact, form and interaction are congruent, like two sides of coin. They can't exist independantly. One form is what it appears to another form to be, observed via interaction. Thus, to exist requires to have some sort of form, and to have form requires interaction. And any interaction requires change.
Particle that never ever interacts with anything simply does not exist.

Now, coming back to Time, it is measure of change. Any kind of interaction requires existence of concept of time, change. Speaking of timetravel, it is now obvious that several requirements must meet: future and past must exist simultaneously, and they must be able to interact. Particle must be able to interact with its own past and future version. Simple causality rules would not allow to interact with form whose form depends on outcome of that same interaction. Such interaction cannot be defined. Therefore I tend to think that future and past can not interact, and thus can not exist relative to each other. There is no past, no future, only everchanging now.

7. Apr 25, 2003

### Zefram

Not necessarily. If old MV told you the future, that just means when old MV was your age an older version came and told old MV the future. Since you and old MV are one and the same. Once time travel comes into the picture you have two options: either the past is as flexible as the future, or the future is as inflexible as the past. Take your pick.

8. Apr 25, 2003

### dav2008

hmm...well first of all, when you say "Lets say that i travelled back in time.." all bets are off...

But if you consider time to be a 4th dimention and that energy is always conserved in these 4 dimentions(in other words ure allowed to move energy freely through time or something.).yea..now im confused...

"There is no past, no future, only everchanging now."
Yes, I would have to agree with that..i think that makes the most sense

9. Apr 26, 2003

### RuroumiKenshin

So history repeats itself? But what if the young MV actually chooses not to go back in time again..... Multiple histories again.....
This all implies that the future and the past would already exist.

10. Apr 26, 2003

### RuroumiKenshin

Time is the increasing of entropy. Time coordinates tell you where (or rather when) something existed; that is, at what point of the increasing of entropy it existed.

what do you mean by change?
Technically, our consciousness of time is based on the fact that our straitial neurons keep track of the interval between every electrical charge that permeates through a specific part (of which the name escapes me) of the straitum. Otherwise, time is the increase of entropy.

I don't see your point. You said a particle should interact with its future and past self, then you insist the past, future cannot exist. Of course, this creates a paradox. not only your seemingly contradictory statements, but if the particle meets its antiparticle, they'll collide and annihilate each other. So how then is the particle going to interact with itself, if it is no longer existent as mass?
What casualty rules do you speak of?

11. Apr 26, 2003

### Zefram

That's exactly what I was trying to imply with the above.

12. Apr 26, 2003

### RuroumiKenshin

And I agree. Multiple History theory permits this. On scienceforums.com, I was informed that universes are actually created! is this possible?

13. Apr 26, 2003

### Bunting

maybe the future is not a plane, but a sphere with time as a y-axis, space as an x-axis and a d-axis! There fore all the consists is the same, you are simply moving energy around the sphere ;)

14. Apr 26, 2003

### RuroumiKenshin

Multiple History theory could actually be seen as a series of planes on the surface of a sphere. Where, the future probabilities are perpendicular to the present. What's d supposed to be?

15. Apr 27, 2003

### wimms

Eh, would you please define which of 4 definitions of entropy you imply? Entropy is paradoxical in itself. You may call me heretic, but I don't buy equating entropy as complex concept with something as fundamental as time. They are incompatible. I love this defintion of entropy: Measure of amount of energy NOT available to do work. Measure of something nonexistent. lovely. But what is definition of energy? Capacity of doing work. Now, entropy is even more cute: Measure of amount of capacity of doing work NOT available to do work... And now lets increase _that_..

You are using coordinates as time, ignoring completely that to even remotely differentiate two states, or exercise entropy, you need preexistence of time.
But we may be talking past each other. You use time in context of _measure_, I'm talking about time as fundamental to existence. You see, term "existed" already includes concept of time. Concept of Energy, Work, Force, all they use concept of time for definition. Without existence, you can't measure anything. And you actually can't measure time, you can only measure relative amounts of changes.
Thats about something else. And imo starts from wrong place. Definition of term "exist" isn't even touched. If it were, it would be apparent that question of existence is meaningless. Concept is not.

I say that to exist is to interact. Entity that has no capacity to interact with anything, does not exist. Particle that will never interact with our universe, will never ever be detected. In principle.
I can't care less about our conciousness. I'm talking about fundamental logical principle. Look, two things that cannot be distinguished by any means in principle, are not two things, they are one and same thing. To distinguish two things, you need at least 1 whatever small measure of difference, be it position, size, time, energy or whatever. It requires, that to move from one thing to another needs change in that minimal amount of form. *Change*. When one form stays the same, for it there is no concept of time. Concept of time requires change. Amount of change is relative and depends on immediate environment. Same is with flow of time. There is no such thing as universal time, not even in principle, let alone GR.

Not casualty, _causality_, cause and effect. You don't read carefully. I showed that particle can't interact with its future, and from that it follows that future can not exist. Past becomes into now, and now becomes into future. But they don't exist relative to each other in same sense as you and me exist relative to each other. Future and past relate to each other more in a way as box being moved from one place to another. It was there, now its here. Can this box here interact with itself being there? This makes no sense.

You can't timetravel just because there is nowhere to travel. Best timetravel you can have is sleep. You stop interacting and let universe change more than you do, and you feel travel to future. But if you interact and change more than universe does, you don't travel into past. There is no way back. The only way would be to stop whole universe and force it turn back. But then you'll only get where you've already been, with no capacity to even know that turnback occured..

16. Apr 27, 2003

### RuroumiKenshin

Why do you believe this?

17. Apr 28, 2003

### wimms

er, believe, what?

18. Apr 28, 2003

### joonior

Existance is relative, isn't it? If you observe it, it exists... but if someone else doesn't observe it, it doesn't, right? I don't know...

19. May 4, 2003

### The_oMeGa

My eplanation for this would be:

Say you go into the past. The molecules that you are made of have been used to make up 1000's and maybe millions of different organisms. So if you went into the past, all of the organisms of that time period that used your molecules would then dissapear from them and make up your body. so you could eat a lot of dead epithelial cells from your worst enemy and go back to a time that without those exact cells he would die, and his skin would dissapear.
LOL

20. May 4, 2003

### RuroumiKenshin

You're joking, right? That doesn't make sense.