Is there true randomness in the universe?

Question

Is there true randomness in the universe?

In: 80

Answer 1

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.