Causality

Causality is the study of cause and effect, and how things influence one other. This has to hold true with the classical laws of physics, and there are three basic principles:


 * Things have causes and don't happen of their own accord. If an apple falls from a tree, it’s because gravity has taken effect to break it loose from its branch, or some other force had broken the branch or knocked the apple off.


 * Effects follow causes in a predictable, linear manner. This falls into a series of events that forms a sequential causality line. Breaking this sequence would cause a causality violation and this has potential serious consequences for the integrity of dimensional structures.


 * Effects grow from little causes. A snowball would collect more snow as it rolls down an incline, gathering momentum. The laws of thermodynamics provide the rules about what causes can precipitate what effects, and the direction for causality in a flow of time.

Science presents a number of challenges to this classical and philosophical view of causality. Einstein’s special and general theories of relativity abandon the causality line and time is warped by the presence of large masses or when travelling at high speed, and passes at different rates for different observers.

Chaos theory is one potential study of the series of interactions of particles and events in a complex system. For example, a single trade on the stock market (the cause) could lead to a complex series of effects - seen to the untrained eye as chaos - but in reality, can be predicted by complex mathematical models.

Uncertainty is hard-baked into the quantum world and it violates the conventional view of cause and effect. One consequence is that pairs of virtual particles can pop up at random from an empty vacuum, as long as they disappear again quickly enough not to violate the uncertainty principle. As long as they exist, these particles can have effect without cause.

Time travel would create causality violations and paradoxes and this is resolved with breakthroughs in physics. Travel to another instance within a multiverse is possible, and if a time paradox event is attempted, you would be thrown into another instance to prevent a causality violation. The effect is that time would decay along this causality line or boundary and all associated matter (including the cause) would follow this decaying timeline.

Michio Kaku has an opinion on the grandfather paradox: ''The river of time forks into two rivers when you enter a time machine—in other words, the timeline splits. This means that you have killed someone else’s grandfather who looks just like your own grandfather but exists in another timeline in an alternate universe. So the multiverse resolves all time paradoxes.''