Some Things About Science

Dot Physics: Some things about science

Aristotle and the other Greeks: They started with assumed truths like heavy things fall faster than lighter things. From that they deduced ideas about motion. The problem here is that if your “assumed truths” are wrong, you are in big trouble. They did not actually test their assumed truths. If they did, they wouldn’t be assumed.

This is a common bugbear of the crackpot, too, who starts with some flawed assumption about how nature behaves and ends up concluding that his perpetual motion machine will work.

Two For One

One of the things we’re investigating is pulsed laser systems, because they’re fun, but (especially for funding purposes) also because they are the basis of optical frequency combs (as I’ve mentioned). And things are pulsing along. One of the things that was noticed was that light from the pulsed system, running at 1560 nm, was showing up on a Silicon CCD camera. The Silicon response peaks at 900 nm and drops pretty sharply, petering out at 1100-1200 nm. There’s no way it should respond to a 1560 nm photon.

And it isn’t. It’s responding to pairs of 1560 nm photons. This is a pulsed system, so you have high peak power making it a lot easier to see nonlinear responses like two-photon transitions, because they scale as the square of the intensity. (more photons incident per unit time means a better chance to have two interacting at once, Having n photons means that if you look at any photon, the chance of another photon being around is n(n-1)) Two photons have enough energy for the interaction, since that’s the same as having a 780 nm photon, which is well above the “to be detected you must be this tall” energy cutoff

Here are two images. The square is a beamsplitter cube, and the white blob is the light. The top image is the pulsed laser, and the bottom one is a CW beam, both with around 10 mW average power.

twophoton-pulsed

twophoton-cw

The pulsed laser is saturating the heck out of the CCD, so the spot is really a lot brighter than from the CW beam, though we can’t say for sure based on this quick look. Even though the average power is about the same, though, the pulsed laser is repeating at about 10 MHz, and the pulses are less than a picosecond, so all of the light is being delivered in less than 10-5 of the time, so the peaks have powers measure in kW.

Worthless? Bah!

physics and physicists: “I’ll Never Use The Skills I Learned In Physics”

zapperz attacks this in a couple of ways, such as the idea that you (can) learn critical thinking skills

The “skills” that one learn out of a physics/science course goes BEYOND physics. It is a skill of thinking things through and systematically. It is the skill in knowing what KIND of evidence is required for something to be considered to be VALID. This is highly important no matter what you do. How do you know that something somebody utters on TV is valid? Most of the time, people are persuaded not based on valid evidence, but based on personality of the presenter and all the bells and whistles. Apply this to the world of politics, where phrases fly off into the air as if they are facts, or as if simply by saying it, it is true. The same can be said with regards to the battle between evolution and creationism. The inability of some members of the public to actually think through something THIS obvious clearly shows that the skill of analytical thinking isn’t there!

That and the other points are certainly important, but I’ll go a step or two lower and look at some actual physics applications. I don’t know precisely what is taught in Physics 140: How Things Work, but I’d guess a few basics involved would let you figure out that the truth about turning the heat down during the day if nobody’s home. “Conventional wisdom” says that it takes more energy to heat the house back up, but the actual physics confirms the conventional wisdom to be wrong. Or a simple analysis to verify that buying a long-life CFL will save you money over incandescent bulbs once you figure out actual energy use, despite the cost-per-bulb being higher. E = Pt is simple physics, but physics nonetheless.

A word of advice for Ms. McMillan: if someone asks you to invest in a device that creates energy, for which you will be able to charge money and make a profit, it may appear to be a sound investment from a financial perspective. But the physics you so casually dismiss guarantees that it is not.

(on a personal note, I’ve found that most of basic finance is pretty easy if you can do physics. Problems in financial literacy and science literacy do share a common problem: math literacy)