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Q: Is quantum randomness ever large enough to be noticed?

The original question was: …true randomness on a quantum level has experimentally been shown to exist. My question is, does this quantum randomness ever/often/always bubble up to our readily observable world of Newtonian physics to create truly random everyday events?

Physicist: Hard to say.

Quick aside: The difference between quantum randomness, which is absolute, and classical randomness, which basically means “very hard to predict”, is covered a bit in this older post. In a nutshell, up until the science of quantum mechanics came along it was assumed that if you (somehow) knew everything about an object at one moment, you would be able to perfectly predict how it behaved the next. However, it turns out that even if you know absolutely everything about a radioactive atom, for example, it’s still impossible to accurately predict when it will decay. This is called “fundamental”, “irreducible”, or “quantum” randomness. Back to the point:

Large scale effects can be thought of in terms of lots of small-scale effects being averaged together which usually (and counter-intuitively) leads to much more predictable (classical) results. This is the same idea that shows up when you flip lots of coins: the total number of heads is very predictably about half. Generally speaking, any individual quantum event will be drowned out by the noise of all of the other quantum events around it, and the average is the only important thing.

Large scale events that rely on a small number of atoms and interactions are likely to have the same kind of randomness as “legit” quantum phenomena. For example, the meter on a Geiger counter is an example of quantum randomness on a large-scale.

Nuclear decay is a quantum mechanically random process. Normally, the effects of nuclear decay are washed out. For example, you’re hit, on average, by about one high energy particle per exposed square centimeter every second. Ever notice? But a Geiger counter detects every high energy particle that passes through its detector (the wand on the right) and notes the event by moving a needle (which is huge by quantum standards) and clicking. So, what Geiger counters and other sensitive detectors do is “exaggerate” tiny events and bring their effects into the macro-scale.

Normally, large-scale events are fairly well determined. Whether or not you go to lunch is probably not particularly random. If someone somehow got every possible piece of information about what everything in the nearby universe was doing, they’d be able to predict large-scale events, including your lunch schedule, with fair accuracy.

However, if you determine whether or not to go to lunch based entirely on the results of a Geiger counter reading, then your lunch outing is a genuine, fundamentally random event. This wouldn’t change the experience; you won’t see different versions of yourself walking around, and you won’t end up “spread thin” across different versions of the universe. A quantum random number generator is essentially the same as an ordinary random number generator.

That all said, there’s chaos inherent to most of the stuff that happens in the world (tiny errors becoming bigger errors, becoming bigger errors, …). However, there’s nothing particularly special about the original source of the errors being quantum mechanical. As far as prediction goes, randomness due to quantum mechanics and randomness due to a lack of perfect knowledge (which is pretty hard to avoid) are pretty much the same. This is a pretty subtle distinction.

You can expect that, after a lot of time, the randomness of quantum processes will lead to worlds that are wildly different from each other because of the butterfly effect. But that’s pretty unsatisfying. It would be more interesting to be able to point at a large thing in the world and say “that is dependent on just a couple of quantum events”.

The most dramatic example of exactly that is probably biological life. The earliest development of a creature is strongly influenced by the interactions of a relatively small number of chemical interactions. An atom in the wrong place in the flagella motor of a sperm can determine whether or not someone is born at all. More than that, the evolution of entire species can be changed by a single mistake in the replication of a strand of DNA (this is one mechanism for mutation).

On a more individual basis, it’s hard to say how much the process of thinking is affected by the actions of just a few atoms. The fact that you can lose a heck of a lot of brain cells without noticing implies that the activity of a handful of atoms probably isn’t too important when it comes to human behavior. That said; maybe?

By the way, it’s a little dangerous to tread this close to the intersection between quantum mechanics and living things and consciousness in casual conversation. To be clear, the important thing about life here is that it can change a lot based on the actions of just a few atoms. Change a few atoms in a rock, and you’ve still got a nearly identical rock. So the nature of the physical, gooey, grey matter is what’s important here, and not on the nature of consciousness itself.

In general, there probably aren’t too many day-to-day events that “turn on a quantum dime”. The only exceptions (I can think of) is in the effects of the earliest, single-celled, development stage of complex organisms, when the actions of just a couple of atoms consistently result in very large changes later on, and in the lab, where sensitive equipment can detect and report on the fundamentally random actions of individual particles.

The highly predictable dog picture is from here.

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