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tonedef's avatar

Problems with Laplace's Demon?

Asked by tonedef (3935points) February 18th, 2009

Pierre LaPlace proposed a theoretical method of being able to know the entire past and future of the universe (linky). If you knew the position and velocity of every particle in the universe, then you would be able to calculate where each particle was headed, along with where each particle came from. In a macro sense, it’s the same idea behind simple temporal deduction: if you’re running at me at 5 miles an hour, and no forces have intervened, then I know exactly where you were an hour ago.\

This is a very old theory, however, and it works best in a simple Newtonian context. I’ve read that this method of calculation breaks down when you add entropy to the mix, as information is lost in thermodynamic interactions. But while chaotic, knowledge of every particle’s position and momentum would still let you figure out the past and future, right? It’d just be a lot more number crunching. Can the idea be debunked with thermodynamics alone?

Also, here’s a wikipedia quote that seemingly puts a nail in the whole idea: There has recently been proposed a limit on the computational power of the universe, i.e. the ability of Laplace’s Demon to process an infinite amount of information. The limit is based on the maximum entropy of the universe, the speed of light, and the minimum amount of time taken to move information across the Planck length, and the figure was shown to be about 10^120 bits.

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12 Answers

Grisson's avatar

That is the concept of infinite determinism. It works best in a Newtonian context because as soon as you put it into the universe of quantum mechanics it falls apart. You cannot know every particle’s position and momentum. (Heisenburg’s uncertainty principle). You can only know one of them precisely.

psyla's avatar

Schrodinger’s Cat would say that doing the math would alter the future. Simply calling the particles “waves” would change the future result as well. The top-secret military Phoenix Project time travel team could undo your math. If you made any number of simple daily life choices your end result would also be different, as your current conciousness would flow, according to Superstring Theory and Hindu/Wiccan beliefs, into an alternate dimension/reality. If your math was made to be faulty by any of the preceding factors, your future would also differ. If all current physics is incomplete due to science not understanding a force that affects your conclusion, such as Gravity, your calculation may also be incorrect.

psyla's avatar

The way to do it would be to create a superstring-based computer using quantum information flow that harnessed all 16 dimensions, but you could only calculate the past & future of one dimension at a time.

Foolaholic's avatar

Dresden Codak suggests simply exorcising the bastard.

Grisson's avatar

@Foolaholic Yes, even daemons need their exorcise.

psyla's avatar

How can I exorcise Mailer Daemons?

Grisson's avatar

@psyla I think the ritual involves the use of spam.

psyla's avatar

On the label on the back of each can is a different spam ritual. They also have the new gift set with 2 cans of spam, a dead bat, & 2 black candles.

Grisson's avatar

It goes well with eye of newt and toe of frog.

psyla's avatar

Mayo, on bread, with a side of monkey brains… delicious!

steelmarket's avatar

Drilling down past the Standard Model just seems to reveal more levels of complexity, some of which we may never even be able to detect. So, that particle count is probably meaningless.

In summary, we will probably never be able to completely model the future of (all the components of) even one slice of Spam. Which, by the way, needs to be fried to bring out all of the flavor!

Strauss's avatar

Don’t forget to add Time Wave Zero and Novelty Theory to the mix, and bake until 12/21/2012.

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