Stretch the Intellect Saturday…

Physics and Cosmology
Physics is not my specialty but I do follow it on a popular level. So when the cosmologists started babbling about “dark matter” I kind of wondered “is “the aether” making a comeback”? Well….no.

Yes, there is a similarity: neither has been directly detected; its existence has been inferred by observed effects. However both have been examined…and “the aether” has been discarded because experiments designed to detect it have failed (e. g. Michelson-Morley experiment)…in fact have provided evidence to show that it did NOT exist.

Roughly speaking, “the aether” was conjectured to provide some medium for light-electromagnetic waves to propagate in; at the time these waves were thought to be like sound waves (disturbances of some sort). Modern physics (relativity theory and quantum mechanics) have shown that these waves are very different from sound waves, though there are similarities.

On the other hand, evidence continues to pour in for dark matter and dark energy, as Sean Carroll explains:

Dark matter, in particular, is nothing at all like the aether. It’s something that seems to behave exactly like an ordinary particle of matter, just one with no electric charge or strong interaction with known matter particles. Those aren’t hard to invent; particle physicists have approximately a billion different candidate ideas, and experiments are making great progress in trying to detect them directly. But the idea didn’t come along because theorists had all sorts of irresistible ideas; we were dragged kicking and screaming into accepting dark matter after decades of observations of galaxies and clusters convinced people that regular matter simply wasn’t enough. And once that idea is accepted, you can go out and make new predictions based on the dark matter model, and they keep coming true — for example in studies of gravitational lensing and the cosmic microwave background. If the aether had this much experimental support, it would have been enshrined in textbooks years ago.

Dark energy is conceptually closer to the aether idea — like the aether, it’s not a particle, it’s a smooth component that fills space. Unlike the aether, it does not have a “frame of rest” (as far as we can tell); the dark energy looks the same no matter how you move through it. (Not to mention that it has nothing to do with electromagnetic radiation — it’s dark!) And of course, it was forced on us by observations, especially the 1998 discovery that the universe is accelerating, which ended up winning the Nobel Prize in 2011. That discovery took theoretical physicists around the world by surprise — we knew it was possible in principle, but almost nobody actually believed it was true. But when the data speak, a smart scientist listens. Subsequent to that amazing finding, cosmologists have made other predictions based on the dark energy idea, which (as with dark matter) keep coming true: for the cosmic microwave background again, as well as for the distribution of large-scale structure in the universe.

Of course, there is a long way to go in developing this theory.

Physics and Philosophy
Here is yet another “play nice” plea to physicists (Jim Holt in the New York Times):

Why do physicists have to be so churlish toward philosophy? Philosophers, on the whole, have been much nicer about science. “Philosophy consists in stopping when the torch of science fails us,” Voltaire wrote back in the 18th century. And in the last few decades, philosophers have come to see their enterprise as continuous with that of science. It is noteworthy that the “moronic” philosopher who kicked up the recent shindy by dismissing the physicist’s book himself holds a Ph.D. in theoretical physics.

Physicists say they do not need any help from philosophers. But sometimes physicists are, whether they realize it or not, actually engaging in philosophy themselves.

Here is my take. Physics is hard. Only the smartest among us do original research in physics and these people spend years in training to able to start. In fact, it takes an intelligent person with great math/science aptitude years of focused effort to even become conversant on the questions.

Those who haven’t spent that much concentrated time (and frankly, who have a lower aptitude for this subject) really don’t know what they are talking about; they really aren’t qualified to give comments that are worth listening to.

Note: I am talking about the science itself and its interpretation; I am NOT talking about, say, the ethical issues that come up (e. g., the use of nuclear weapons, the production of weapons of mass destruction, experimentation on humans, animal research, etc.) On these issues, I am happy to listen to philosophers because in these areas THEY have put in the concentrated long term effort and they have displayed some aptitude for this sort of thinking.

Statistics and Data: what does one consider when one tries to make sense of data?

Here is a baby case: suppose you want “the average household income of a neighborhood”; what do you use?
Well, it depends on what question you are interested in. If you are interested in, say, how the typical person lives (spending habits, energy use, etc.) then median income might be what you want, especially if the standard deviation (minus an outlier or two) is small.

If you are talking about, say, the total money that is spent from that region, then perhaps the mean (average) is better.

One uses the data germane to the problem at hand.
Paul Krugman patiently explains this:

Just a quick note on a question that comes up in some comments: why do I sometimes look at percentage changes in unemployment, sometimes at changes in absolute levels? Isn’t that inconsistent?

The answer, of course, is no. When you do stuff with data, here is the universal rule: do what makes sense given the question you’re trying to answer. It’s like the issue of where the y-axis in a diagram starts — it depends on context. Starting at zero isn’t a universal rule, certainly not when changes of a few percent up or down are in fact crucially important for the policy discussion.

So on unemployment, one favorite story out there is that we have lots of unemployment, and must have lots of unemployment, because the pre-crisis structure of the economy was unsustainable: too many people were building houses in Nevada, too few doing other stuff in other places, so there has to be unemployment as workers move from the occupations/localities that were oversized to those that were undersized.

OK, so what would be the “signature” if this story were true? There would be lots of job losses among construction workers in Nevada, of course; but for the story to make sense there should be rising employment in those other sectors people are supposedly moving to.

But of course, that’s not at all what you see. Instead, you see job losses everywhere, with most of the total job loss taking place in sectors that were clearly not overinflated by the bubble. And that is the relevant comparison: if non-bubble sectors are losing rather than gaining jobs, and in fact account for most of the job losses, then this story is just wrong.

He concludes:

But as I said, the universal rule for using data is to think about the question you’re trying to answer. A foolish consistency here really is the hobgoblin of little minds.

The problem here is
1. All (or at least 99.99 percent, myself included) of those who comment on his blog are significantly below him in intellectual level and many are completely unaware of this and
2. The pundit class does not constitute our finest minds. And from what I can tell, our pundits are blissfully unaware of this as well (left and right, I am sorry to say). Just read what they have to say about ANY technical matter; they almost always get it wrong.


June 9, 2012 - Posted by | cosmology, economics, economy, media, physics, science, statistics

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