The Dinosaurs of Copenhagen: A Platonic Dialogue by MC Complete

(Note: if you don’t have some familiarity with quantum mechanics and the two most popular interpretations -- Copenhagen and Many Worlds -- you may have trouble following this post.  Have a look at my post, Decoherence and Flying Fish.)

Hugh: Very clever Niels.  But what about the dinosaurs?

Niels: The dinosaurs?

Hugh: You know what I mean.  If the only thing that’s real is scientific measurements, doesn’t that imply that the dinosaurs are not real?  No living, breathing dinosaur ever entered a laboratory.  And if dinosaurs are not real, then what are all those bones doing there?  And what about the Big Bang?

Niels: Good question, Hugh.  Did you ever read MC Complete’s blog post, Science does not make Predictions?

Hugh: Of course.  It was very clever, but it was written from a philosophical point of view that I can’t identify with.

Niels: What do you mean?

Hugh: Well, it was written from a skeptical point of view.  It was based on the philosophy of David Hume, who rejected matter, memory and induction. I’m a realist, so skeptical philosophy, while sometimes interesting, is not personally relevant to me.

Niels: I think you misunderstood MC Complete’s point.

Hugh: Really?  What was his point, then?

Niels: When Descartes said “I think therefore I am”, was he denying the existence of the outside world?

Hugh: Of course not.  Descartes was a realist.

Niels: Ultimately, Descartes was a realist, but he started from a very solipsistic foundation.  When he said “I think therefore I am”, was he affirming the existence of the outside world?

Hugh: No, not really.  His affirmation of realism was yet to come.

Niels: So at the point in his argument when he said “I think therefore I am”, he was agnostic on the existence of the outside world.  At that point, he neither affirmed it or denied it.

Hugh: OK.

Niels: So that was MC Complete’s point.  He posited a minimalist, conservative, lightweight ontology, one where memory exists, but it may not be a true record of anything, and one where matter may or may not exist, and induction may or may not be valid.

Hugh: OK.

Niels: And he showed that given the minimalist ontology, we still have math and science.  Science is a generalization over the apparent past.

Hugh: So you’re saying that the minimalist ontology of the “Predictions” post neither affirms nor denies realism.

Niels: Exactly.  MC Complete’s point was not to reject realism, but rather to show that science does not need realism.  It makes no commitment to realism and does not depend on it.

Hugh: And what about the dinosaurs?

Niels: Exactly.  What do you think MC Complete would say about the dinosaurs?

Hugh: Well, I suppose he’d be agnostic about the dinosaurs.  He’d say that dinosaur bones are a feature of the apparent past, but did actual dinosaurs exist?  Who knows.  Science doesn’t need real dinosaurs.

Niels: Exactly.  I can generalize over the apparent past by positing virtual dinosaurs, but the actual existence of dinosaurs is the domain of philosophy and metaphysics.

Hugh: And that’s your answer about the dinosaurs too?

Niels: Yes.  MC Complete thought he was very clever with his declaration that science is generalizations over the apparent past, but really he was just clarifying the Copenhagen approach to science.  In fact, Werner Heisenberg came very close to MC Complete’s “Predictions” post when he said: “Physics must confine itself to the description of the relationship between perceptions.”

Hugh: Very clever, Niels.  But there’s still one thing that I don’t understand.

Niels: And what would that be?

Hugh: You said that the Copenhagen philosophy of science is noncommittal towards more expansive ontologies.

Niels: Yes.

Hugh: So why do you reject the Many Worlds interpretation?

Niels: I don’t.

Hugh: Wait a minute.  In real life, you *did* reject it.

Niels: Yes, I did.  It’s too bad I never got to meet MC Complete.  I’m sure he’d have shown me that Copenhagen and Many Worlds are not mutually exclusive.  In fact, you and I have been talking past each other all these years.  Copenhagen is philosophy of science, and all other interpretations, such as Many Worlds, are metaphysics.  All I can say is this: before quantum mechanics, if you wanted to be a realist, all you had to do was adopt a few extra axioms, what I like to call the dogmas of common sense.  After quantum mechanics, if you want to be a realist, you have a lot of explaining to do.

Hugh: The Many Worlds interpretation does provide an explanation.

Niels: Indeed it does.  And maybe it’s correct.  Who knows?

Decoherence and Flying Fish

“I think I can safely say that nobody understands quantum mechanics.” -- Richard Feynman

We usually assume that at any given time, all objects have a definite location.  For example, last week I was in the US; this week I am in Israel.  But quantum mechanics postulates that microscopic particles can be in two (or more) places at once.  So if I was a microscopic particle, I could be 25% in the US and 75% percent in Israel, etc.

Now here comes the weird part.  When somebody looks at (or observes, or measures) the particle, the particle chooses one of these locations, at random.  So if I was a microscopic particle who was 10% in Tel Aviv and 90% in Jerusalem, and then you called my cell phone to see where I am, there would be a 10% chance that I would be in Tel Aviv and a %90 chance that I’d be in Jerusalem.

You might ask, what is the difference between saying that a given Libicki Boson is 10% in Tel Aviv and %90 in Jerusalem, and saying that we simply don’t know where it is, but we would bet 9 to 1 that it’s in Jerusalem?  It turns out that there is a big difference.  The particle’s “superposition”, as it is called, is responsible for what is known as the interference effect, which in turn is responsible for some of the wavelike properties of microscopic particles.  See http://en.wikipedia.org/wiki/Double_slit_experiment

In my arrogant opinion, one of the most important aspects of quantum mechanics that needs to be pinned down is what counts as an observation or a measurement.  Microscopic particles are in many places at once, but if we look, they appear in only one of these places.  This choice of position then affects the future motion of the particle.  So the critical question is: what counts as looking?

The branch of quantum mechanics that tries to pin this down is called “decoherence”.  I tried reading about decoherence and it went way over my head.  There was a lot of math.  After five minutes of absolute confusion, I gave up and watched a YouTube video:

http://www.youtube.com/watch?v=gAjzH0vWSIA

Flying fish!  How cool is that?