So I was watching sound of thunder today (warning, it was horrible, watch at own risk) and now I'm wondering if you could devise an experiment, or algorithm, that could calculate how fast change ripples into the future. Is it instant? (i.e. kill butterfly a billion years ago and kapoot, universe disappears?) or does it take some time to get to the present? Do all the changes happen at once? Or do they come in waves (this is what happened in the movie)? And if they do come in waves, again, how long does it take?

Do you guys know of any research into this kind of stuff?

Define 'change'.

very fast - I jump into the swimming pool 1 second in the past and I'm completely wet in the present.

do you have specific question?

anyway, i watched the trailer to the sound of thunder, the review says bad thing about it so that i didn't bother.

You're assuming that the past and present both exist at once, and that it's possible to change one, having that change propagate to the other.

Before you can measure the speed of this propagation, you'd first have to prove your assumption is correct...

For an interesting thought experiment in the vein of how meaningless the question (potentially) is, allow me to refer you to Brian Greene's The Fabric Of The Cosmos in which he stipulates that, while apparently relative, time is a one-way arrow permeating a physical space which is temporally symmetric. Eg - if you were to reverse the direction of time's arrow and thereby all physics regarding particle interactions and thereby creating conditions under which it would be perfectly valid to have the "cosmic film" "run backwards" without violating of the laws of physics, you could not tell apart the reality we're experiencing and the "reverse" reality.

This seemingly simple tidbit implies more than it seems to: it implies determinism.

While something that cannot be proven, the question of when does something affect something else is moot: by generally accepted theoretical physics it either "has already happened" (string theory) or the results are indeterminate even in individual cases (quantum physics).

If you want quantification, then I suppose the "ripples" that you mention can only be quantified by reducing their speed to the speed of light in spacetime.

Or we're all wrong and ice cream is evil.

szecs: change.

FableFox: Yes, I do: "Do you guys know of any research into this kind of stuff?" Stuff meaning propagation of change from past to present in a world where time travel is possible. I don't know what to search for to find material.

Hodgeman: Why do I have to prove anything? It's hypothetical...

I know the word, thanks.

Interesting. So in spacetime, if an event happened at position a, and we are currently at position b, then |a-b| * c (?) for a ripple to reach the present? (with a and b being vectors (x,y,z,t) and c being the speed of light) But then can you use c in a space that has time as an axis?

And so you're saying that you can't go back in time so there's no point in asking the question? or that you can but if you do go back in time, change something, and come back, then you won't remember having gone back in time so it's already happened. Or are you just saying that everyone who's gone back in time has already done so and it's all part of the natural order... in which case if i were to be part of this natural order, go back in time, change something, would i not know what i've changed and would the change not affect my present?

Also, you think maybe you forgot about general relativity? which permits a number of ways to time travel...

Change occurs at a rate of one second per second.

Quote: Original post by IFooBar
Hodgeman: Why do I have to prove anything? It's hypothetical...

For argument's sake:

Quote: So I was thinking about monkeys that poo out ice-cream (warning, it was horrible, imagine at own risk) and now I'm wondering if you could devise an experiment, or algorithm, that could calculate what flavour it would be. Is it chocolate? (i.e. monkey-excreted ice-cream tastes like chocolate?) or does it take on a different flavour? Is the flavour constant? Or do they come in waves (vanilla on tuesday)? And if they do come in waves, again, how long does it take to change?

Do you guys know of any research into this kind of stuff?

Now, for there to be research on the flavour of monkey-excreted ice-cream, first monkey-excreted ice-cream would have to exist.

Seeing the original premise is fiction, it can only be answered with more fiction.

In order for research into the amount of time taken for past-changes to propagate into the present to exist, the concept would first have to make sense in physics, and it doesn't.
i.e. "kill butterfly a billion years ago" is nonsense. So, "how fast is nonsense" is equivalent to my "what flavour is nonsense" question.

[Edited by - Hodgman on October 24, 2010 6:21:32 AM]

I personally think that some actions can be isolated enough and so unroutine that they will have no further effect. For instance, I imagine all the actions as rocks being tossed into a pond: sometimes there are more ripples, sometimes ripples cancel each other, and sometimes there are no ripples. I guess it really depends on the scale you're using for comparison.