From year to year, the moon never seems to change. Craters and other formations appear to be permanent now, but the moon didn’t always look like this. Thanks to NASA’s Lunar Reconnaissance Orbiter, we now have a better look at some of the moon’s history.
Category Archives: Physics
Is It Hot in Here, or is it Just the Army?
US military unveils non-lethal heat ray weapon
On-demand hot-flashes. The menopausotron unveiled!
The technology has attracted safety concerns possibly because the beam is often confused with the microwaves commonly used by consumers to rapidly heat food.
“There are a lot of misperceptions out there,” lamented Taffola, saying the Pentagon was keen to make clear what the weapon is, and what it is not.
The frequency of the blast makes all the difference for actual injury as opposed to extreme discomfort, stressed Stephanie Miller, who measured the system’s radio frequency bioeffects at the Air Force Research Laboratory.
The system ray is 95 gigahertz, a frequency “absorbed very superficially,” said Miller.
The beam only goes 1/64th of an inch (0.4 millimeter), which “gives a lot more safety.”
In other words, the heating is all at the surface, not in the interior, so it cooks your skin, not your internal organs. It’s not a direct quote, but one might get the impression that the message is “it’s not microwave, it’s radio-frequency” and playing on the notion that radios are harmless. But AM and FM radio bands are at around 1 MHz and 100 MHz, respectively. However, ~ 1 GHz from microwave ovens is microwave, so 95 GHz is well into the microwave band of the spectrum.
You Can't Get There From Here
Q. If I find myself in a free-falling elevator, is there any position that might increase my chance of survival? (Climbing on top of other people is not an acceptable answer.)
A. The best option would be to lie on your back on the floor as flat as possible, said Eliot H. Frank, a research engineer at the Center for Biomedical Engineering at the Massachusetts Institute of Technology.
Yes, that makes sense, but how does one get to the floor and lie flat, while in free-fall?
Here Now the Neutrinews
Neutrinos not faster than photons — the lab results have come back and they were juicing, so they’ve been stripped of their title. Sean Carroll has included a graph of the results, in Superluminal Neutrinos are so 2011, which shows that the new ICARUS results are statistically well-separated from the OPERA data.
A few other summaries-
Neutrinos not faster than light
This Time, ICARUS Really DOES Refute OPERA
This is the way it works in science all the time. A first experiment makes a claim that they see a striking and surprising effect. A second experiment tries to verify the effect and instead shows no sign of it. It’s commonplace.
Watson, Come Here. Neutrino.
First Digital Message Sent Using Neutrinos
MINERvA is one of world’s most sensitive neutrino detectors and yet, out of 10^13 neutrinos in each pulse, it detects only about 0.8 of them on average.
Nevertheless, that’s enough to send a message. The FermiLab team used a simple on-off protocol to represent the 0s and 1s of digital code and transmitted the word “neutrino”.
Not particularly practical, though the story notes there are potential applications, such as submarine communication. You would use neutrinos to reach regions inaccessible with EM radiation — you need a situation where you are leveraging the one advantage you have: penetrability.
Pulling Entangled Photons Out of a Hat
… or perhaps not.
Entanglement Is Not That Magic
That said, though, it’s fairly common to hear claims of the form “when two particles are entangled, anything you do to one of them changes the state of the other.” This is not strictly true, though, and it’s worth going through in detail, if only so I have something to point to the next time somebody starts using that line. This will necessarily involve some math, but I’ll try to keep it as simple as I can.
Still Better Than Shipwreck Cove on the Island of Shipwreck
A Random Walk through Oddly Named Physics Things
In spite (or perhaps because) of the overwhelming boringness of much technical jargon, scientists are drawn to whimsical or poetic names more than you might suspect. Here are some of my favorites.
…
In a 1969 paper entitled “Mixmaster Universe,” physicist Charles Misner set out his idea for a solution to the paradox. Although it sounds like a 1980′s proto-hip-hop group, the theory actually gets its name from a kitchen appliance, the Sunbeam Mixmaster.The idea was that the early universe went through a phase of so-called chaotic evolution, which did for the cosmos what the Mixmaster does for cake batter, mixing its contents until they were smooth and even.
National Thermometer
I saw parts of National Treasure again recently; I’ve pointed out before that Riley should have used an IR laser to set of the heat sensor in the plan to steal the Declaration. One of the other things about that sequence that has nagged was how fast the thermometer shot up when he zapped it. I can buy that the sensor would trip, since there is a lot less thermal mass, but what about a glass thermometer? The issue is how much thermal mass there is — temperature will respond quickly if there is a small combination of specific heat capacity and mass. I decided to look into this and do a quick experiment.
I grabbed a thermocouple, which I thought would respond fairly quickly: you have a small bead of your dissimilar metals, with a volume of a few mm^3, and since the density of the materials is going to be a little less than 10 mg/mm^3, we’re talking about a few milligrams of material that has a specific heat capacity of around a Joule/gram-Kelvin, so a several Milliwatt laser should be able to raise the temperature in short order. It’s going to depend on how much of the light that hits gets absorbed vs reflected. I have a ~20mW green laser that also emits an unknown amount of IR (the 532 nm is frequency-doubled 1064 nm light, derived from an 808 nm pump, which imperfectly filtered. This can be a safety issue, as explained in this NIST pdf tech note). If we can get 10 mW onto a target with a heat capacity of 10 mJ/K and absorbing 10% of the light, that’s a Kelvin every 10 seconds, or a degree Fahrenheit every 5 seconds.
The response was impressive. In about 30 seconds the indicated temperature jumped almost 7ºF (I used ºF since that’s the scale on the thermometer), which is not as fast as it might have been, but the beam is larger than the target and is well in the ballpark of my prediction and more than enough for what was happening in the movie with a sensor that may have even less thermal mass.
The alcohol thermometer is much more massive. Even though you want to heat up the alcohol, the surrounding glass in contact with it has to heat up as well, so now we’re talking grams of material, so the heating may be slowed by a factor of 100-1000. I shined the laser on the bulb for a full minute and only saw a rise of between 0.5 and 1 ºF. However, confounding this is that the alcohol in my thermometer was without coloring, as opposed to the red I recall in the movie (it was a fairly old device, so maybe it was red at one time, but red dyes have a way of breaking down). Having dye in the alcohol would make it heat up faster. I’m not convinced that it would have risen as far or as fast as was in the movie, but it’s not entirely implausible either.
You Keep Using That Word…
Ultra-efficient LED puts out more power than is pumped in
The LED produces 69 picowatts of light using 30 picowatts of power, giving it an efficiency of 230 percent. That means it operates above “unity efficiency” — putting it into a category normally occupied by perpetual motion machines.
As the article goes on to explain, the LED doesn’t actually violate conservation of energy, because the LED is tapping into the thermal energy present, as manifested in lattice vibrations i.e. there is a conversion of phonons to photons occurring, which means that the LED is acting as a heat engine (a term that’s not mentioned until the last paragraph). However, efficiency isn’t typically used in this context because it’s misleading; what you discuss is the coefficient of performance: how much energy do you move around vs how much energy you put in, because for a given energy input, you can deliver/remove many times that energy to/from your target. This is what heat pumps do and why they are used.
The neat thing here is that the rejected heat from the LED is light, which is pretty neat. At such low powers (tens of picoWatts) this is not yet a usable light source, so there is a question of whether it can scale, and as mentioned, there is the possibility of using this as a cooling component for small-scale devices.
Plumbing the Plums, and Beyond
1901 — the year the nuclear atom was “invented”!
[The] planetary model is an important one historically, and was accurate enough in its time (and still today) to forgive its faults. It arose naturally in the early 1900s, in a period of great confusion and uncertainty about atomic structure. With tantalizing and rather bewildering experimental hints, scientists speculated wildly about the nature of the atom. The strongest contender was the “plum pudding” model of J.J. Thomson, in which atoms were visualized to be a “pudding” of positively-charged fluid within which were embedded negatively-charged electron “plums”. In Thomson’s original paper, these plums were arranged equidistantly around a circle within the pudding and orbiting within it