# Inverting the laws of physics [closed]

Are there any good theories on inverting the law of physics?

To make physics work the opposite way of what it does.

Ok, I'll try to explain better. I was taking a smoke break and started thinking about time travel, and somehow I concluded that to travel in time itself is impossible.

But then I thought that, what if we instead of travel in time, could reverse all processes in the world, or in an area for example. To make all particles do all what they have already done, but in reversed order.

i.ex. A candlelight produces heat and light emitting from the flame, the candle itself melts and turns into vapor.

If we reverse that, all the heat, vapor and light would be absorbed by its origin point and reassemble the candle the way it was.

Damn this is hard to explain. And there are so many holes in what I'm thinking here.

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## closed as unclear what you're asking by Emilio Pisanty, Chris White, BebopButUnsteady, Waffle's Crazy Peanut, DanAug 26 '13 at 21:05

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$\vec{F}=m\vec{a}\to \vec{a}=\vec{F}/m$, done? –  Kyle Kanos Aug 23 '13 at 13:43
Oh, well, for me it was obvious what it meant, didn't know it needed explanation. –  Mathias Madsen Stav Aug 23 '13 at 13:52
@KyleKanos I don't even know what that means. –  Mathias Madsen Stav Aug 23 '13 at 13:58
Pick a specific law, say newtonian gravity: $F=GMm/r^2$. what does it mean to 'reverse' this? Move the $r^2$ up top? make it repulsive? There are many possible things you could call "Reversals" for any given law, and it's unlikely that there's one intuitive idea of reversal that would apply for all of them. Did you have something specific in mind? –  Robert Mastragostino Aug 23 '13 at 14:03
Are you talking about the reversibility of processes in physics? If so you should clarify the question and the title a bit. –  Dilaton Aug 23 '13 at 15:50

I suppose that what you are thinking about is the principle of causality.

We have two events: a cause and an effect, where the second event is a consequence of the first. That is how we perceive all events around us and what we intuitively accept as true.

In physics, however, we sometimes obtain two different solutions: first with the cause before the effect, second with the effect before the cause (such solutions come, for example, when deriving potentials dependent on time in electromagnetics). You could say that the second one reverse the arrow of time. Indeed, there is no reason other than the principle of causality to discard this solution (when time flow backwards), but this is what is usually done.

Interestingly, lack of that principle would suggest that we don't have free will and the universe is deterministic.

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Thats it man! You know of any good books on this subject? Well, what is free will anyways? You should check out "Thinking fast and slow" by Daniel Kahneman. –  Mathias Madsen Stav Aug 23 '13 at 15:03
Hey QD, Please don't add user signatures under your posts, when you have your own user ID below all your posts ;-) –  Waffle's Crazy Peanut Aug 23 '13 at 15:24
Mathias, unfortunately, I don't recall any. On the subject of free will, however, Sam Harris had some interesting ideas (check out his lecture about his book "Free Will" on youtube). Crazy Buddy, well, it makes sense. ^^ –  QuantumDrzewo Aug 23 '13 at 16:32

Now that your question is a little more clear I believe that the answer is no.

What you say cannot be done spontaneously (entropy variation should be >0).

You can reverse some things in some systems, but not everything.

I don't know if this what you mean but maybe this can help: http://en.wikipedia.org/wiki/Spontaneous_process http://en.wikipedia.org/wiki/Entropy

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