Macroscale laws from Nanoscale randomness
The question was:
If everything obeys the rules of Cause and Effect is it not true that everything happens for a reason?
"Cause and Effect" is not a law. To the contrary, many quantum effects do not follow 'cause and effect' and are fundamentally unpredictable. If you irradiate an atom and stuff some extra neutrons into it - it will eventually decay back down to it's original state by emitting a neutron. When will that happen? Well, we don't know, we cannot know - it's truly, utterly random. Where is the "cause" of that neutron being emitted? There isn't one.
If this is true it would seem that nothing can be random and everything is predictable.
To the contrary, at its heart absolutely everything is completely random and unpredictable. The only thing that makes the universe seem stable and follow nice cause-and-effect rules is the effect of statistics. We don't know when one irradiated atom will decay - but we know with great precision how a kilogram of atoms will decay. We can't know the exact position of an electron - but we can deduce the position of a planet orbiting a star a hundred light years away by measuring the tiny wobble it induces in that star. The universe on the large scale obeys rules - but at the small scale, it's truly random. But the large scale effects are pure statistics. It is perfectly possible (although exceedingly unlikely) for a grand piano to appear out of nowhere in your living room right now. It's only statistics that enables us to say that this "Won't ever happen".
Look at it like this, if you flip a coin, you have no idea whether it'll come up heads or tails. If you flip 100 coins, you can be pretty sure that between 40 and 60 heads will show up - but predicting that you'll get 50% heads is a bit 'iffy'. If you flip a million coins, you can be quite sure that between 499,000 and 501,000 heads will show up - so a 50% prediction is a fairly accurate 'law'. If you flipped as many coins as there are atoms in a grand piano, your prediction of 50% heads would be precise to within one part in a billion billion billion (probably much better than that actually). In effect, you have a cast iron "law" of nature that says "when you flip coins you absolutely always get exactly 50% heads" - but that's not even close to being true for four coins - and it's POSSIBLE to flip a million coins and for them all to come up heads...it's just so unlikely that on a large scale, it's not going to happen. That's how our "large scale" laws operate. They are so accurately true that we can rely on them - even though at their heart, they are relying on completely random events.
Before we get carried away though - the critical 'take away' point here is that while these macroscopic laws are "only" statistical, the magnifying effect of the sheer quantity of particles on the certainty of the result makes the resulting law quite utterly cast-iron. You cannot and must not take from my explanation the idea that the macroscopic laws are broken routinely because of this statistical stuff. On human scales - they absolutely are not. The probability of anything measurably different from what we expect actually happening is so astronomically small that this makes it impossible for any practical measure whatever. So "certainty" is still present at our scales. But when we deliberately make the small scale visible on the large scale, weird stuff can happen. Listen to the individual clicks of a Geiger counter picking up background radiation - each click is the result of the decay of a single atom producing a single neutron. Guess what? It's utterly random - you can clearly hear that - there is fundamentally no way to predict when the next click will happen.
