Can effect precede cause? Does an action require a cause that comes before that action?
Above the subatomic level, no. Quantum objects may be a different story–read up on the double slit experiment if you’re interested.
Why would it not happen above the subatomic level? Wouldn’t it just be less probable.
Doesn’t General Relativity show, or perhaps even require, that effect precede cause at all times? This is due to the fact that the speed of light is a constant and a maximum; any reference frame in which effect precedes cause would require a speed faster than light.
Of course, nobody has yet completely reconciled relativity with quantum mechanics.
Ask Maxwell’s Demon.
This is pretty much why “nothing can travel faster than c”. It’s built into SR.
I think there’s no easy answer to this question.
I don’t undersand GR well at the nuts-and-bolts level, but qualitiatively, it’s possible to theoretically construct space-time metrics with closed temporal loops which can be traversed without locally exceeding c. So, as far as we know, it’s theoretically possible to travel backwards in time. Hence, causality violations are not obviously forbidden by GR.
I guess at this point the jury is still out. Some conjecture there must be something we don’t know yet that will provide a sound way to fix the theory and forbid causality violations.
In classical special relativity, and also in quantum field theories (SR+QM), information cannot be transmitted outside of the forward light cone, which is invariant under proper Lorentz transformations. Which is a highfalutin way of saying that cause precedes effect for all observers; everyone will agree on which of the two events happened first. (This is not true for all pairs of events, only for pairs of events with timelike separation, such that information and influence could have passed from one to the other.)
In general relativity, though, the jury is still out. Locally things look the same as in SR; but globally a universe might in principle have nontrivial topology, allowing for the presence of “closed timelike curves.” These would really mess with the idea of an ordering of events, and could allow one to send a message “back in time” (i.e., to the inside of your backwards light cone). A lot of relativists think that these are probably forbidden for one reason or another, but this hasn’t yet been proved, and may require a full theory of quantum gravity for the proof.
Excuse me for being esoteric and obtuse, but If it occurs at a quantum level wouldn’t it logically be “set inclusive” and applicable to everything composed of and belonging to the Quanta all along the microscopic/macroscopic spectrum telescopically? As above, so below… and vice versa?
Or, what Loopydude said.
Here it starts to matter what you mean by “cause” and “effect.” Information cannot be transmitted faster than the speed of light, at either the quantum level or the macroscopic level (this is what my earlier posts were referring to), but in quantum mechanics various more tenuous influences (the “collapse of the wavefunction”) can propagate faster than light; for example, in “quantum eraser” experiments (already discussed in GQ). I suspect this is what ultrafilter is referring to.
No. Quantum objects are fundamentally unlike classical objects.
It’s been suggested that quantum wave reduction is actually like running a time-paradox backwards: you start with a superposition of two alternate states (e.g., you went back in time and killed your grandfather, or you didn’t) and one or other alternative is tossed out. What finally occurs is an interference of all possible futures that could effect the past.
There’s reason to suspect that negative energy (which briefly appears at quantum scales) is actually reversed timeflow: all proposed schemes for faster-than-light travel, such as wormholes or warp drives, seem to require negative energy, and FTL travel brings up the whole time travel issue.
If I had been answering this before you posted, I would have to give a resounding “Yes!”
But since I am answering after your original post, my answer has to be in the negative.
The answer to your next question is “no” too.
This is actually a much more difficult question than it might seem at first. Although many people have referenced relativity, it has little relevance to this issue. If pure Newtonian mechanics were correct rather than relativity, and light propagated at a fixed rate in some absolute reference frame, it would be no more possible for effect to precede cause than it is in our universe. Relativity assumes the equivalence of reference frames, so requires that if causality can be violated in one frame it can be violated in any. Without such an assumption, the speed at which information can be propagated is irrelevant to causality.
Defining cause and effect in a universal fashion is actually quite difficult. Consider a simple deterministic system such as billiard balls bouncing around on a pool table: an ideal one, frictionless, with no pockets. Given the state of this system at any time, it is possible in principle to calculate what its state will be at any future time. However, it is also possible to predict what the state was at any past time. One would have no way to determine wether a video of balls moving on such a table were being run forward or in reverse. It wouldn’t seem reasonable to say that the past state causes the future state in such a system any more than that the future state causes the past.
Actual macroscopic systems don’t seem to behave this why, but exactly why this is true is a question about which there is little scientific agreement.
(Yes, I know it’s generally assumed to relate to the second law of thermodynamics. The deeper question is why such a law appears to hold.)
Just for a change of pace, I’m going to give a non-physics example. In Salt Lake City and its surroundings, there are now a number of arenas. Construction of these arenas was probably started in 2000 or 2001. What was the cause for them being built? The Winter Olympics, of course… Which occured in 2002. The effect is the arenas, the cause is the Olympics, and the arenas preceded the Olympics.
Ah yes, but that supposition is governed by conscious human purpose and our perception of time- cause A --> effect B. Logically, you could also say that those olympic buildings were built (Effect A) to fulfill the conditions of a random prior cause X beyond human purpose, knowledge, or perception.
cause X <-- effect (A) cause --> effect B
Funny, but not exactly accurate. The cause, as I see it, was the decision to hold the winter olympics in SLC, which happened, what, in '94 or thereabouts? That decision caused construction to start, and caused the athletes to show up on time, and the tourists, and the judges, and thus caused the actual olympic festivities themselves.
Asimov, Isaac: The Endochronic Properties of Resublimated Thiotimoline, Astounding Science Fiction, 1948