Ran across this awesome time-lapse taken at Crater Lake, OR. During my time in grad school I only went there once, as it was a five-hour trek from Corvallis. The camping trips we took were generally closer to town.
Monthly Archives: December 2010
If Romeo Were a Physics Student
How does the light through yonder window break? Seriously, Juliet, tell me. I have a test tomorrow!
Uncertain Principles: How Does Light Travel Through Glass?
It’s important to note that when [the quantum] picture is valid the probability of being absorbed then re-emitted by any individual atom is pretty tiny– when the light frequency is close to a resonance in the material, you would need to do something very different. (But then, if the light was close to a resonant frequency of the material, it wouldn’t be a transparent material…) while the probability of absorption and re-emission is tiny for any individual atom, though, there are vast numbers of atoms in a typical solid, so the odds are that the photon will be absorbed and re-emitted at some point during the passage through the glass are very good. Thus, on average, the photon will be delayed relative to one that passes through an equal length of vacuum, and that gives us the slowing effect that we see for light moving through glass.
You'll Put Your Eye Out, Kid!
BA review: The Spyder III Arctic Blue laser from Wicked Lasers
But the blue lasers… I’ve heard about them. The brightness of a laser depends mostly on the power used*. A typical red laser might have a power of about 5 milliWatts (5 mW). My green one has a power of roughly 160 mW, which is a lot more than the red one. The blue one, though, has a power of 1250 milliWatts, nearly 8 times that of the green one!
So yeah, I wanted to try one out.
…
* Color is the next biggest factor, since our eyes are much more sensitive to green light than blue, or even red. Beam focus is another factor, and so on.
(edit: post seems to have disappeared. Erased from existence, using far less than 1.21 GW. Here is a copy of it from an aggregator site)
Thoughts:
More than a Watt of laser power in a handheld device? Damn dangerous. I agree, this is almost like having a gun in terms of safety & handling issues. The potential damage that could occur through stupidity and carelessness is significant. It comes with safety goggles, which not everyone will use, and even if Luke is wearing his blast shield while he waves his light-saber around, what about everyone else? I see trouble a’brewing.
The BA (sort of) underplays the significance of color. Color, or more specifically, wavelength, is in fact a huge factor in how bright a laser appears. In the early days of green lasers being available, they used some shady advertising tricks to exploit this by telling you the green laser was as bright as a red laser of a certain power, typically 5 mW. But in the fine print you found that the green laser had less than a milliWatt of actual output they were leveraging the fact that the sensitivity near 550 nm is more than five times the sensitivity out past 650 nm. So the BA has rigged the answer a little by using large difference in power. A green laser is going to look brighter than a red laser that has twice the power.
I suspect that one of the issues here is that the eye’s sensitivity is usually portrayed on a linear scale, like here (fig 154), which shows the photopic (light-adjusted) sensitivity ranging from 400 nm out to 700 nm, which is the usually-cited range. Notice that scotopic, or dark-adjusted vision really kills the sensitivity to the red, which is a killer in an optics lab using red lasers. Turning off the lights has a smaller effect in one’s ability to detect a spot because of the loss in sensitivity fighting the reduction in background.
But the effect isn’t best portrayed on a linear scale, because you can still detect photons beyond those boundaries, and the linear scale doesn’t give this impression. If you look at it on a log scale, you see that while the photopic vision has a shoulder near 700 nm, it doesn’t stay flat. You can see light out near 800 nm (we use a lot of 780 nm in the lab, for Rubidium, and you can see diffuse reflections from a few-mW source), but your eye is a million times less sensitive to it than to green light. Put another way, if you see even dim light in the near-infrared (NIR), it’s fairly powerful. I once saw a spot from a misaligned 852 nm laser (used for trapping Cesium), which was disconcerting, because it must have been really, really fracking powerful.
One might cut the BA some slack, because my examples aren’t laser pointers, and while he said lasers, he probably meant laser pointer and was thinking of only those wavelengths — color kind of restricting one to the 400nm-700 nm range — rather than what one might find in a lab. And they don’t make laser pointers in the IR, because what would be the point? Right? Well, not so fast. Green laser pointers are commonly made from pumped, frequency-doubled IR light, and this arrangement can let a lot of the IR through if there is no filter, and there may not be one. So you can get a blast of 808 nm light from the pump, and 1064 nm from the beam that doesn’t get doubled to 532 nm. While often the bright green light would trigger a blink to help save your eyes, it’s possible that it won’t, because light that has refracted or diffracted (phenomena which depend on wavelength) won’t line up anymore. You could potentially get an eyeful of IR, while the green spot doesn’t hit your eye. By the time you notice a problem, it will likely be because retinal damage has already been done.
So color is a big deal in how bright something appears. Let’s be careful out there.
NonOedipal Snakes On a NonOedipal Plane.
But here’s the thing: if someone asked me five minutes ago what tangled-up snakes demented checkerboards and crazy twisty surfaces have in common, what would you have answered?
This is why I love mathematics. The moment when you realize that something seemingly arbitrary and confusing is actually part of something. It’s better than the cleverest possible ending to any crime show or mystery novel, because that’s only the beginning.
There’s more wonderful doodling at her website, or on youtube. All full of math-y goodness, puns, denunciation of poor teaching, stop-action video and a remarkable lack of commas. (Does she ever inhale?)
Binary trees
Infinity elephants
Stars
You can show these to people, and it’s possible they won’t know they learned some math. Sneaky.
You Autocomplete Me
A map of the US, filled in the the Google “Autocomplete” feature.
Not Professionals. Do not Attempt, Anyway.
What’s crazier than jumping from the top of a building into a snowbank?
How about not jumping into a snowbank:
The Gospel According to Bruce
I had an epiphany while was watching the movie Jaws recently: it occurred to me that the movie is an allegory for some of the science vs ideology political battling we have going on, especially if one looks at the "debate" surrounding anthropogenic global warming. It sounds weird, I know. But the really strange part is that the parable of the shark predated the AGW debate by about three decades, and that alone should be able to convince one of its divine truth.
Larry Vaughn is, quite simply, a denialist. As the Mayor of Amity Island, he's responsible for its well-being, and to him, this means primarily the economic well-being. As long as the people on the island are making money from the tourists, his job is secure. A shark attack is bad for business, so it simply cannot be allowed to be true. So the first death becomes a boating accident; all it takes is a small change in the coroner's report. Hey, we’ll just change the wording of this study’s conclusions
The story of the first attack has gotten out, so when the locals catch a shark, it is assumed that it’s the shark. When he’s presented with the opportunity to obtain actual evidence by cutting open the shark, he declines. But at least now it’s acknowledged there is (or was) a shark. Well, there is warming. But it’s natural! No reason to spend money on it.
When Hooper gets a shark tooth from Ben Gardner’s boat, it’s not enough that he has seen this — he can’t actually show the mayor the tooth, so at that point, the evidence doesn’t exist as far as Vaughn is concerned. He gets people to go in the water and downplays the shark attack with a reporter. Warming stopped in 1998!
*Bruce was the name given to all of the mechanical sharks from the movie. I am not sure if any of them taught Hegelian philosophy.
Java Applet, You're the One
A rubber-ducky-free Liquid demo
Let Them Taste the Triple Gun
Navy test fires electromagnetic cannon
The story tells you it was a 33 MegaJoule shot, and it traveled (or would travel) 200 km. What it doesn’t say is how big the projectile is. The maximum range for a projectile is going to be v^2/g, in the limit of no air resistance (and also assuming a flat surface, but we’ll ignore that because that’s probably a small effect here). If we pop in the equation for kinetic energy and solve for the mass of the particle, we get m = 2E/dg. The amount of recoil energy given to the ship will be negligible; momentum is conserved and KE = p^2/2m, so the amount of energy scales with the mass ratio, which will be some number measured in kg compared to a kilo-metric-ton or so, which gives us a part in a million. So yeah, we can ignore that.
So 33 MJ gives us a mass of about 33 kg. But that’s assuming the energy of the pulse is the same as the energy of the projectile, i.e. the system is 100% efficient, and still ignores the pesky air resistance. This article mentions an earlier test, and puts the weight of the projectile at 7 pounds, or about 3.3 kg, meaning the system is at least 10% efficient.
The article also mentions the launch happening at five times the speed of sound, which is about 5*340 = 1700 m/s, which for a 3.3 kg projectile, is just under 5 MJ. All of those estimations seem to agree reasonably well. It also predicts the ideal maximum range of about 290 km, so we see just how much loss we have due to the air. Engadget says Mach 7, which is 10 MJ. Still ballpark; I wonder if one is launch speed and the other is impact speed, since the maximum range formula assumes a 45º launch, and in reality this isn’t the case.
The time it takes the shell to travel this path is at least four minutes. I’m guessing that the final version would not be “dumb;” you would attach a gps guidance system to it and have some better control of where it would land.
The Other Java Jive
Photographer Olivier Grunewald has recently made several trips into the sulfur mine in the crater of the Kawah Ijen volcano in East Java, Indonesia, bringing with him equipment to capture surreal images lit by moonlight, torches, and the blue flames of burning molten sulfur. Covered last year in the Big Picture (in daylight), the miners of the 2,600 meter tall (8,660ft) Kawah Ijen volcano trek up to the crater, then down to the shore of a 200-meter-deep crater lake of sulfuric acid, where they retrieve heavy chunks of pure sulfur to carry back to a weighing station. Mr. Grunewald has been kind enough to share with us the following other-worldly photos of these men as they do their hazardous work under the light of the moon.
Burning liquid sulfur. Wow.