Is there true randomness in the universe?

In: 80

Not at any scale useful to humans, though we can get close enough for many applications.

Let’s say you were rolling a fair die. There’s a 1 in 6 chance of any result before you roll. But once you do, the result is determined by how you move your hand, air currents in the room, the surface it is being rolled onto, and so on. If the starting conditions were copied exactly, the result would be the same every time. And if you had infinite knowledge of everything except the result of that roll, you would be able to predict it perfectly, so it is not truly random.

However, humans do not have the ability to control for all those factors, so for most people, the die roll functions as a random event.

At the subatomic level, we don’t know enough to determine if there is true randomness. It’s possible that, the moment of the Big Bang, everything in the history of the universe was fixed by physics we don’t yet understand.

Various quantum events appear to be truly, fundamentally unpredictable. For example, nuclear decay is random. You can make broad predictions about the half-life of a collection of atoms – you can say that within a given time, roughly half of the sample will have decayed. However, given any single atom you can’t predict when it will decay. You can say it will *probably* decay within a certain amount of time, based on its half-life, but that’s it. And there’s no guarantee that it will decay within that time.

This is *not* just a limitation of our math or our equipment. As another example, imagine you have an electron and you want to know where it is and how fast it’s going. In order to measure it, you have to *interact* with it, like by sending it through a magnetic field. You measure the change in the magnetic field, but the field also affects the electron.

So if you try to figure out where it is, its velocity changes so you have no idea how fast it’s going. If you try to measure how fast it’s going, you have no idea where it actually is.

Let’s say you try to be clever. You can take a heavy particle and split it into two electrons. Since energy and momentum are conserved, you know that if one electron is going at x speed, the other one must be going at y speed in the opposite direction. You could measure the position of one electron and the momentum of the other, and do math to work backwards and you’ll find the position and momentum of both!

What you find is that you still can’t. Both electrons seem to somehow “know” that the other was measured, and each is affected as if it were the one measured that way. They fly off in random directions so that you still can’t know both their position and momentum.

There are other quantum states, like spin, that are fundamentally unpredictable. No amount of clever techniques to measure spin will make it predictable. There is no technology (that we know of) that can get around this problem.

It *could be* that there are “hidden variables” influencing these quantum states that we don’t know exist and/or can’t be measured (maybe not *yet*, maybe not ever). So it could be that the universe is deterministic in a way that we don’t understand, but right now the consensus is that these quantum states really are random in a way that is fundamental to the universe.

The problem is: this question is meaningless unless you define what “true randomness” is. It’s one of those words everything thinks they know what it means but is actually quite difficult to articulate its specific properties.

Basically impossible for us to say with our current knowledge.

If I assume your define “True Randomness” as “the outcome is impossible to predict from starting position” then the thing is we just aren’t sure.

There are things we think are truly random (radioactive decay, quantum observation,, things like that) but all we can say for sure is that they behave as if they are random, which we can also say about casino dice. The difference is that we can describe the starting conditions and motions of dice and why they rolled what they did, but we can’t say for sure if there is an underlying system that can predict everything.

We don’t know.

At the quantum scale behavior does appear “probabilistic” – it follows a random chance distribution. You can measure the distribution but can’t predict a specific outcome.

But we don’t know if it’s truly random or if there’s an underlying “deterministic” mathematical rule that’s being followed and we simply haven’t discovered it yet.