Monthly Archives: August 2013

Reminder: Lake Wobegon is Fictional

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Lake Wobegon, where all the women are strong, all the men are good looking, and all the children are above average

You are likely special and your friends probably not normal

What are the odds of being normal?

I think a better word here would be typical in the way that Bee is using it, but that really doesn’t change the thrust of the discussion. The really short version is that if the typical family has 2.3 children, then nobody is typical.

It’s interesting, I think, this mix of “I’m average” is some ways of thinking and “I’m above average” in others, and the Wikipedia article included in the link does (as I expected) discuss the Dunning-Kruger effect as part of overestimating our abilities. Though I expect that works in reverse, too: people thinking they are typical in some way when they aren’t, like that guy who ran for president last year (Mitch Rumbly?) who tried to portray himself as a regular guy and failing pretty miserably. (But that’s politics, so we don’t know how much of that is pretend)

However, this is something that I have thought about and never formed it into a blog post, but (as so often happens) now that I have a catalyst I will make a few comments. Or just ramble.

Not only do we think of ourselves as average or typical in many respects, I think we view experiences as being typical as well. Consider buying some widget or gizmo, as a first-time customer of ACME, and finding that it has some flaw. It doesn’t really matter if ACME has 99.99% positive quality control on their gizmos, and you were just unlucky enough to get that 10,000th unit off the line that’s faulty — there’s a decent chance you’ll just say that ACME sucks, thinking that this happens to everyone. Same thing for getting poor treatment at customer service. It doesn’t matter to you that you’re unlikely to be treated poorly if a second chance came up, because you won’t give the company that chance. (and I’m guessing there’s some neuroscience description of all this I know nothing about, because I’m a physicist and not a neuroscientist.)

The bottom line is we’re bad at assessing probability and risk for unusual events because see them as being more typical than they really are. It’s also something that many (or at least some) companies realize, so they work hard at not losing you with a first-time bad experience, or giving you a common experience that’s better than their competitors (like with customer service, or when visiting a restaurant, etc), and also fed by the news, which reports unusual events but not mundane ones.

It's Not Einstein Against the World

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New York Times Wants to Fight Einstein, Einstein Declines

Short, snarky version: Everyone should be shocked, SHOCKED! that general relativity doesn’t work where quantum theory is needed.

Matthew also rightly points out that framing a relativity experiment as a cult-of-personality exercise is a bad idea.

Newer theories supplant older ones conceptually, but every theory is provisional, constantly tested by experiments and observations. Einstein, important as he was in 20th-century physics, is not the ultimate authority even on his own theories, and refinements to his work should not be framed as proving him right or wrong.

Of MOTs and ZOTs

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I know I already linked to the beginning of Chad’s series on the Tools of the Cold-Atom Trade, but Tools of the Cold-Atom Trade: Magneto-Optical Traps is good stuff, MOTs are also the workhorse of research I’ve been doing for 20+ years, and I was short of time last night as a fire alarm in my apartment building (kitchen/cooking incident, minor damage but 7 trucks plus support vehicles showed up) performed an act of bloggus interruptus.

More Mirrors

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In the last post I explained that mirrors do not flip left and right, and the example (also used in the Feynman video) was seeing an image of yourself.

I thought of another example — written words. They look backwards in a mirror as well, but if a mirror doesn’t flip left and right, how can that be? As I demonstrate, it’s because we always rotate whatever the words are written on. If we don’t do the rotation, the words are unchanged.

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(I apparently started talking a second or two before the recording actually began, but this isn’t Hollywood, so I only did one take)

It may be a little tough to see the uninverted image in the mirror in the tiny youtube video, so here’s a still

Magic Mirror, On the Wall …

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A couple of things (beyond “neat video”):

He doesn’t answer the question about what would happen if you left the light on. You might think this is no big deal, because he correctly says that the light dies out quickly. If you were in a mirrored room such that the average photon trip was 3m (and somehow not interact with you at all), and the mirrors are 99.99% reflective, a photon would reflect 10^8 times a second (i.e. once every 10 nanoseconds), but only reflect 10,000 times on average, so you would expect the room to go dark in less than a millisecond. However, if you keep the light on, you get a build-up of photons for that time. To reach equilibrium, your production rate and loss rate have to be equal, and you only lose 0.01%, or 0.0001 of your photons. If you have just a 1 Watt source of visible light (which would emit around 10^18 photons a second), you need to have 10,000 times as many photons inside to have 1 Watt leaking out.
Put another way, your source is emitting 10^10 photons per bounce interval (10 nanoseconds) but only 10^6 photons leak out. In the next interval, another 10^10 photons are added and 1,000,010 photons leak out (0.0001 from each generation). And so on, with a decaying exponential buildup, until you have 10^14 photons hitting at each bounce, so that 10^10 can escape. That’s when you reach equilibrium.

So your little 1 Watt light gives you a power buildup and you are doing the equivalent of hugging 10 kW of space heaters. Actually the scenario is worse, because your body emits around 100 Watts, in the infrared, so if the mirrors reflected IR you would cook yourself to death. Fast.

The other issue I have is where he says that mirrors flip left and right and not top to bottom. The initial explanation is right — they flip perpendicular to the plane of the mirror, but then he claims that L-R is perpendicular while U-D is parallel, which is nonsense. It’s a plane, so they are both parallel. Mirrors flip front-to-back, i.e. perpendicular. The confusion is that the mental image we have is of someone walking around the mirror to the other side, and that’s not what is going on. It’s a confusion of inversion and rotation, which are two different ways of getting an image like that. There is no left-right flip! Your right hand is still on your right, it’s just that you expect it to be on your left, because of that were a person in the mirror (who has rotated on an axis to look like that), it would be their left hand.

Maybe you’ll like hearing Feynman explain it.

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Tell Them!

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The Utility Of Physics

Excellent points about the general question of why physics is important and should be funded.

Even in areas in which it is difficult to argue for the application and usefulness to the public, we can bring out the argument that it is difficult know the future applications of such knowledge. The history of physics is littered with many such examples, including quantum mechanics. The early development of quantum mechanics had almost no emphasis on the usefulness and application. If we only want to fund work that had such clear utility, then we would have missed out on the development of quantum mechanics.

This, in particular, given the recent (and incredibly myopic) push to limit research funding to areas with commercial or national security applications.

Playing Small Ball

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Why Do Small Science?

Chad breaks down the advantages and disadvantages of the user facility model, and why AMO physics is better off without it. I think he hit the high points, like the “economy of scale” advantage of having staff technicians to handle the equipment that isn’t part of your particular experiment, and disadvantages like

[I]f your small experiment that plans to use the particle beam from some accelerator or reactor breaks just before your scheduled beam time, well, try again in six months or a year, assuming they give you another block of time.

This was a constant fear when I was at TRIUMF, and something always broke just before we had beam time, requiring long hours to fix right before we went into “experiment running 24/7” mode, and had to surrender time on at least one occasion. We also tried to be ready to grab someone else’s beam time in case of problems, when the right target was in the beamline, and I have a vague recollection of doing that, as well.