As nearly everybody with a blog has already noted, the annual "World Question Center" question has been posted, with answers from the usual huge range of thinkers. This year's question:
When thinking changes your mind, that's philosophy.
When God changes your mind, that's faith.
When facts change your mind, that's science.WHAT HAVE YOU CHANGED YOUR MIND ABOUT? WHY?
Science is based on evidence. What happens when the data change? How have scientific findings or arguments changed your mind?
I'd love to say something deep and thoughtful about the answers, but honestly, it's just too much. My eyes start to glaze over just reading the selected highlights posted at Biocurious and Cosmic Variance. I can't imagine attempting to wade through the whole thing to pick out the highlights.
I will do the obligatory thing of highlighting a couple of responses that I jumped out at me, though:
I used to pride myself on the fact that I could explain almost anything to anyone, on a simple enough level, using analogies. No matter how abstract an idea in physics may be, there always seems to be some way in which we can get at least some part of the idea across. If colleagues shrugged and said, oh, well, that idea is too complicated or too abstract to be explained in simple terms, I thought they were either lazy or not very skilled in thinking creatively around a problem. I could not imagine a form of knowledge that could not be communicated in some limited but valid approximation or other.
However, I've changed my mind, in what was for me a rather unexpected way.
Surprisingly, the reason is not "It's pointless to explain things with analogies, because every time you do, some literal-minded jackass on the Internet will pop up to complain that the correspondence isn't absolutely perfect in every detail." Instead, he's rediscovered the idea of lies-to-children. Which is a more general case of the same thing, I suppose.
The other answer to really jump out at me was Carlo Rovelli on quantum mechanics:
I have slowly came to realize that in its most common textbook version, quantum mechanics makes sense as a theory of a small portion of the universe, a "system", only under the assumption that something else in the universe fails to obey quantum mechanics. Hence it becomes self contradictory, in its usual version, if we take it as a general description of all physical systems of the universe. Or, at least, there is still something key to understand, with respect to it.
The reason why this caught my eye ought to be obvious.
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I have run across this particular meme in a couple of places on blogs. I also ran across it in a different situation last week. I was discussing the concept of science and what a theory was with a right wing catholic man I work with. He stated, "That's why I know evolution is wrong. You keep changing what you know."
I used an analogy to answer him. Sometimes they can be real useful. It went like this (not the exact words, my memory is going (course I have two teenagers, so no wonder)):
Darwin (and other natural philosphers at the time) came up with a theory to explain what they see in nature. Since then, as new methods and new discoveries have been developed and described, the details have been fleshed out. Another way to look at is, Darwin said (in effect) the way to get from Scranton, PA to Hagerstown, MD, is to go south. Each new generation of scientists (and amateur naturalists) adds to the directions: one discovered I-81; one developed the idea of a speed limit; one discovered exit ramps; one discovered Lackawanna Ave.; one discovered Jefferson Ave.; one discovered the Hazel Highlands; one discovered Harrisburg; one discovered the Cumberland Valley; one took a wrong turn onto U.S. Route 30; one changed the idea of a speed limit to 55mph. Each discovery or idea did not necessarily invalidate what came before, they added details. Some details were wrong, were found to be wrong, and were disposed of through peer review. We are now at the point in evolutionary study where the milemarkers are in place, and scientists are trying to find out what happens every foot of the way between Scranton and Hagerstown. Some parts we will never know. But Darwin pointed us in the right direction.
His response? "Yeah, but you still have to take it all on faith. There is no proof."
Why do I try?
Analogies can work in severely selected circumstances. I did not change my coworker's mind. No surprise.
Sorry for the long post. Occupational hazard.
Hut's example of a phenomenon that cannot be analogized is:
Why isn't Schrödinger's cat a valid analogy for explaining the inability to determine the exact state of a given object?
And being a non-physicist, is the idea of a Hidden Variable Theory dead and buried, or no? Have you blogged about this before?
I've changed my mind. The 3 point play was good for basketball.
As far as lies to children, physics is an onion. I TELL my students that we model things, check it, develop better models, etc. We start them off with simpler models in classes (no friction, yada yada). Then I tell them the short answer is that we lie to them less each year as we get further into the onion. And I also tell them we don't know all about the onion yet, so they can catch up to us if they like.
Rovelli is wrong I think, unless he considers Thermodynamics inconsistent. QM as in say Griffiths applies to closed systems only. The collapse measurement is an approximation that ignores details of the measurement process. But QM tells us that we must then use QM for the measurement system to avoid approximations. This is best dealt with by saying that in QM real systems (ie open ones) have density matrices, which may in some special cases factorize into the outer product of two vectors. This doesn't seem inconsistent, just that often it is CONVENIENT to approximate things! In classical/thermo one should usually use probability distributions too, but we approximate.
There is no one distribution of velocities, just one thats very likely for lots of particles. And how do the 10^23 atoms know they are all at 300K when they don't interact? Hmmmm.
Open systems are messy!
Derek - there is no classical analogy for Bell's theorem. Correlations like "if I find a right shoe the other one must be a left" happen, no action at a distance at all. Quantum weirdness for one particle can be summed up by making QM look as much like statistical classical physics, but the weirdness manifests as a negative value for the joint probability for position and momentum. No classical analog.
Two particle quantum weirdness manifests itself via bizarre properties of joint probability distributions for two properties of both particles. One form is Bell's inequalities. Again no classical analog.
For two particles with more than two states each, or for more than 2 particles, you are looking at a distribution of at least two properties for N particles, or 2N dimensional distributions. What is classical and what is not can be hard to sort out this way! Hence the confusion/debate on how to measure/characterize this thing called entanglement for systems with more than two particles with two states. There is no longer just one test....it gets hard.
If you look at 1, 2, or N particles, and you restrict yourself to measurements of ONE variable and NEVER look at the other, then you can often (always???) find a classical model that gives at least qualitative agreement.
I'll be curious to see what the dog has to say about this Chad!!!
It's amusing that someone says "Quantum mechanics as in Griffiths" because there's also a book by Griffiths called 'Consistent Quantum Theory' which explains how to replace the Copenhagen interpretation with something that doesn't invoke neuroscience black boxes or external, classical systems.
And Carlo Rovelli's a bit behind, since Landau says exactly the same thing in section one of volume three of the Course of Theoretical Physics. Thankfully, it's not true, but Gell-Mann et al hadn't yet figured out how to exorcise the problems of the Copenhagen interpretation at that time.
Personally, I think the two particle "weirdness" in quantum mechanics shows up because everyone insists on doing the analysis with tuples of states instead of bags (multisets if you prefer) of states. We're all used to thinking about sets and tuples, and so we want everything to be these, even when the natural expression is a bag.