Category Archives: Physics

Expert Texpert

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Don’t you see the joker laughs at you?

Over at Physics and Physicists, a followup to an earlier post, to which I had added my two cents.

In an earlier post, I responded to a writer who called professional scientists the “most scientifically illiterate group in the US” and pointed out several fallacies of that statement. The problem here is that the level of expert knowledge that scientists consider themselves to have. We know what it means and how it feels to know something very well. This is why when we read other area of studies, we know we do not have the same level of expertise and would rather be inclined to refer to a true expert in such a field.

Once again I find myself agreeing, and wanting to add a little more than would comfortably fit in the comments.

What is it to be scientifically literate? We really have to define the term before deciding whether scientists are or are not. When stories surface about scientific illiteracy, it seems that they are pretty basic science questions that are being asked, not in-depth inquiries that require an advanced degree to answer. If we’re going to set the bar that high, then virtually everyone is scientifically illiterate, but that means that “literacy” is the wrong word. “Literacy” is being able to read at an nth grade level or college level (argue amongst yourselves, both of you, as to what that means), but it doesn’t require that you be a literature major, capable of dissecting the works of Hemingway in great detail. But there is a continuum of ability above the threshold of “literate” in terms of what you can get out of the material. Being literate means you can read “An Old Man and the Sea” and understand it. If you think you have to be able to discuss the imagery in it to be considered literate, you’re just making it up.

So scientific literacy has to be the ability to understand the basics of science in general, and some of the major tenets of various disciplines. i.e. how is science conducted, and what’s important about physics and stamp collecting biology, chemistry geology, etc. Do you possess some knowledge, and can you apply it?

I think it boils down to how good your bullshit detector is.
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But Why is it so Hot in the Okefenokee?

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Evaporative (Swamp) Coolers

I was discussing this with our resident mechanical systems guru just a few days ago — really hot, humid weather had some of the HVAC systems gasping, and if you can’t reject heat anymore, the system stops cooling (a basic bit of thermodynamics lost on some people). He was reminiscing about when he could use swamp coolers, in the southwest part of the US.

Evaporation works as a cooling mechanism, which is why we sweat when we get hot, because the molecules that go to the gas phase take more than their share of energy with them — somewhere around 2300 J/g, depending on the temperature. And the energy to change that one gram of water’s temperature by a single degree is 4.18 J, so if I have 100g of water and lose one gram to evaporation, the remaining water will cool by 5.5ºC! (Assuming, of course, no other heat transfer to warm it back up. But hey, we’re physicists. Our cows are spherical and inclined planes frictionless)

You can use this cool things off without ice — put the beverages in a canvas bag and hose it down and let evaporation do the work (the canvas holds on to the water, so it doesn’t just run off). It won’t make the beer frosty, but as long as the water can evaporate, it’ll cool it off some. (rule of thumb — if your cold beverage containers tend to “sweat,” then this probably isn’t going to work very well. But here’s another trick for you, from my navy days aboard the USS Disneyworld — to keep that pitcher cold, fill a tall glass or cup with ice and let it float in the pitcher. Cold but no dilution.)

What Mr. Slack Got Wrong

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What neo-creationists get right

[I]n the debate over evolution, I also think creationists’ doggedness has to do with the fact that they make a few worthy points. And as long as evolutionists like me reflexively react with ridicule and self-righteous rage, we may paradoxically be adding years to creationism’s lifespan.

I think that the creationists’ doggedness has far more to do with the fact that their ideology comes first, and they mangle science to conform to that worldview. When “facts” are presented that can be falsified by just looking around, sometimes ridicule is the only option left. But there was much more in the article that bothered me, and to a greater degree.

Mr. Slack goes on to make four points. On the first two, I say this —
Yes, science is incomplete — I don’t think any competent scientist is claiming that there isn’t more to be found. This is true of all fields of science, and the “designer of the gaps” is a false dilemma. The complexity of the cell being unknown to Darwin also falls short and points out the misdirected nature of many arguments against “Darwinism,” (much like arguments against Einstein and relativity) because the theory has advanced quite far since the original proposal. I’ll get to the misuse of “faith” a little later on.

On to the third point
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It's Not Gnu, But it's as Good as Gnu

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Plastics unite to make unexpected ‘metal’

Both TTF and TCNQ are electrical insulators. But Morpurgo’s team found that a 2-nanometre-thick strip along the interface between the two crystals conducts electricity as well as a metal.

So it’s “metal” in the sense that it’s plastic, but conducts very well along the interface. Apparently using “conductor” in the title would have broken some journalistic creed. Why go for accuracy when you can have imagery?

Neat result, though.

The Photon Push-Me Pull-You

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A few weeks ago, over at Built on facts, I threw Matt a bit of a knuckleball in the comments.

[C]onsider a solid bar of the same index [as water]. You send in the pulse of light (assume a really good AR coating so there’s no reflection). What happens to the speed of the bar?

This was sneaky because it is one of the unsolved issues in physics (I feel no remorse for doing this, and Matt realized that something was up) — the theory is complicated enough that it’s really easy to miss out on some of the subtleties and end up with an invalid answer. There are two schools of thought: Minkowski, who had taken the approach that the photon’s momentum in the medium should be nE/c, and Abraham, whose approach gave the momentum as E/nc. Clearly, the results are at odds, and this came to be known as the Minkowski-Abraham momentum controversy.

I found a number of articles on the topic, but perhaps the best one is a review article from Reviews of Modern Physics. Momentum of an electromagnetic wave in dielectric media by Pfeifer et. al, No. 4, October–December 2007 pp. 1197-1216. (link is to a pdf file) The article points out that this isn’t a simple problem, because a photon in a medium can’t be naively treated as just a photon — both solutions have merit, but must include the interactions with the medium, which are obviously different depending on the approach you take — in the end there can be only one you can only have one answer for the momentum of the system.
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