Friday, July 8, 2011

Where our idea of causation goes wrong or playing dice with the universe

I am going to argue that quantum mechanics undermines our intuitive understanding of causality.

In almost every case where someone begins a debate about the existence or non-existence of something and they make an appeal to quantum mechanics to back up that claim, you should immediately start waving a red flag and telling them to hold up.

So, I'm not going to go into this without seriously backing up my claims.

I want to begin by saying that nothing I'm going to say here is controversial in physics. I'm not going for anything that isn't mainstream stuff. Please, follow my sources for further reading.

I'm not going to give an introduction to quantum physics here. If you really want to read a consumer-friendly book on the subject (and you should because it has implications for all kinds of things), you should start with How to Teach Physics to Your Dog by Chad Orzel. You should also be reading his blog, Uncertain Principles. It is one of the friendliest blogs on the internet dealing with this thorny subject. Another good blog on this topic over at Science Blogs is called Starts With A Bang. Both blogs cover cosmology and quantum physics.

I'm going to assume you at least have a decent grasp of the double-slit experiment, the Heisenberg Uncertainty Principle, the Copenhagen Interpretation and Schrodinger's Cat.

The implications of the double-slit experiment and the Heisenberg Uncertainty Principle is what led to the Copenhagen Interpretation. The reaction to Copenhagen is Schrodinger's Cat. If that is gobbledy-gook to you, stop now and go read the links...

Okay, back? Good.

Now, there are three possible implications for the findings of quantum physics (see below). How you side on these implications determines which of the various interpretations you prefer.

Here's what's probably surprising to my readers. I'm not going to advocate for any one interpretation. I would be stupid to do so. We don't know which interpretation is true. We don't know if we will ever know which interpretation is true. I am agnostic about which interpretation of quantum physics is correct. I have no preferences. I'm in the shut up and calculate camp until we have some way of testing which is correct.

That doesn't mean we can't rule out some interpretations. Additionally, the ones left over after we've ruled the others out have massive philosophical implications (especially for causality).

There are three broad approaches to answering the issue of indeterminacy in quantum mechanics (instrumentalist approaches are not actually attempts to answer the issue but to ignore it).

1. Indeterminacy is a feature of our universe and our classical idea of causality breaks down. Instead, nature is fundamentally probabilistic. (e.g. Copenhagen interpretation).
2. Our universe is determined, but the variables that determine it our hidden and travel faster than the speed of light. (i.e. Non-Local Hidden Variable Theories)
3. Our universe is determined, but the variables that determine it are hidden and do not travel faster than the speed of light. (i.e. Local Hidden Variable Theories)

Everybody who likes our current intuitions about causality want #3 to be true. It isn't.

Einstein was wrong when he said, "God does not play dice with the Universe."

So, what are the implications for #1 and #2 for our traditional view of causation?

Well, #1 says that it is simply incorrect. Probability, not determinism, is what it all boils down to. Once you get the outcome of the probabilities, things are determined afterwards (which is why we experience causality in everyday life).

Non-local hidden variable theories (#2), require faster-than-light travel. That means time travel, folks. Time travel breaks causality too.

So, that's the argument. Our intuitions about causality don't square with our empirical observations of quantum physics. People like Craig can argue that our understanding of causation is a "metaphysical principle" all they want, but if that principle doesn't square with empirical observation, that principle shouldn't be used as the justification for a premise in someone's argument for the existence of anything, especially the existence of anything having to do with the Big Bang.

Next, I'll deal with Craig's objections to this whole line of reasoning.


Edit: The Many Worlds Interpretation of QM does allow for locality and determinism, but it creates entirely new problems for Craig. He would never appeal to it. There is still a probability built into Many Worlds in that there is no way of knowing which universe you ended up with until after the fact. It also means that Jesus only died when Craig believes in this particular universe. There is up to an infinite number of other universes out there where this did not occur. See Craig on infinity to understand why he would balk at something like that.

It salvages causality to spite everything else Craig holds dear. Of course, it might very well be true. Only time and science will tell.

Edit again: The Many Worlds Interpretation isn't entire local. It sort of gets around the local vs. non-local issue by just circumventing it.

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