How many cameras are you wearing? (Chandler, to Monica)
candid camera, over at Cocktail Party Physics.
Richmond’s main hypothesis, however, was that the effect stems from the fact that the camera only has one “eye” (i.e., the lens), whereas human beings have two eyes, roughly 7 to 8 centimeters apart. The camera, it seems, lacks depth perception. The result is a kind of “flattening” effect that can make objects seem wider in photographs.
Particle and wave descriptions of light, duking it out in the early 19th century. What a drag: Arago’s Experiment (1810) over at Skulls in the Stars.
Before 1800, most scientists were proponents of the so-called corpuscular theory of light propagation. In this view, which was championed and solidified by Isaac Newton in his 1704 book Opticks, held that light consisted of a stream of particles. Newton explicitly argued against the wave theory of light and (seemingly) refuted arguments by early wave theory proponents such as Christiaan Huygens. Newton’s arguments, and his personal gravitas, left his particle theory mostly unchallenged until the early 1800s.
The other day Matt over at Built on Facts had an interesting post, “Pushing Things in Space.” And while it’s rocket science, it’s not really rocket science. It’s Newton’s Third Law in action (and reaction), which is first-semester physics.
There is a lovely scene where the titular robot [Wall-E] uses a fire extinguisher to propel himself through the vacuum of space. There’s no sense in critiquing the physics of a gentle animated film, but it gives us an opportunity to talk about the principal challenge of moving about in space – there’s nothing to push against. On earth you push against the ground with your feet while walking, or with your tires when driving. If you’re in an airplane, the propellers or jet engines pull in still air in front of the plane and push it out the back at high speed. Boats do the same thing with water. It’s just Newton’s laws in action.
Down in the comments, CCPhysicist, aka Dr. Pion, has the real content I want to dissect.
Your remark, “the principal challenge of moving about in space – there’s nothing to push against”, is false. The statement “If you want to push against something, you’ll have to bring it with you” is closer, but still conveys a false concept common in students.
Pushing on the ground does not make you move. It is the ground pushing on you that changes your motion.
I don’t think the statement is false. I think it’s easily misconstrued and is often found to be confusing from the perspective of a beginning student or a reporter. It reminds me of that famous quote that appeared in the New York Times years ago, critiquing Robert Goddard
That Professor Goddard with his ‘chair’ in Clark College and the countenancing of the Smithsonian Institution does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react–to say that would be absurd. Of course, he only seems to lack the knowledge ladled out daily in high schools.
This Einstein guy, that is.
In unique stellar laboratory, Einstein’s theory passes strict, new test
Precession of binary neutron stars.
Studies of other pulsars in binary systems had indicated that such wobbling occurred, but could not produce precise measurements of the amount of wobbling.
“Measuring the amount of wobbling is what tests the details of Einstein’s theory and gives a benchmark that any alternative gravitational theories must meet,” said Scott Ransom of the National Radio Astronomy Observatory.
The eclipses allowed the astronomers to pin down the geometry of the double-pulsar system and track changes in the orientation of the spin axis of one of them. As one pulsar’s spin axis slowly moved, the pattern of signal blockages as the other passed behind it also changed. The signal from the pulsar in back is absorbed by the ionized gas in the other’s magnetosphere.
Hope everyone has (or had) a happy aphelion. Don’t worry, the sun will start getting closer again.
The Quantum Pontiff on Occupational Arrows of Time
Time goes up, damnit, and that’s all there is to it. Or so say the physicists writing on their blackboards.
Oh I hear you. Yes there are physicists for which time doesn’t always go up, but which can also go up but also in a circle. Yes, Virginia, general relativity allows those crazy solutions (nevermind that they might not be stable.) But those are really loopy physicists who believe in closed-time-like curves. I mean, that sect of the physicists is always going on and on and on about killing their grandfather. Sheesh they’re enough to make Oedipus jealous (and why is that they kill grandfathers all the time and not their fathers?)
I think the kerfuffle is about grandfathers and their pair o’ ducks, but you get the idea.
Roundest objects in the world created
[A]n international group of engineers and craftsmen has . . . built a pair of nearly perfect spheres that are thought to be the roundest objects in the world.
The unusual balls, discussed last week at the SPIE Astronomical Telescopes and Instrumentation conference in France, were created as an answer to the “kilogram problem”.
High purity Si-28, and they hope to count the number of atoms to define the kilogram. With no danger to the pergium miners on Janus VI.
But even if all of the Avogadro Project’s research teams arrive at the same number of silicon atoms in each sphere, it’s far from clear that the International Committee for Weights and Measures will take up their definition.
[…]
These million-dollar spheres may be the roundest in the world, but will they be round enough?
One of the issues with international standards is that individual standards labs each want to be able to realize the standard. It’s not only a matter of having the absolute best measurement. If you make it too technologically advanced or involved, so it’s only within the grasp of a few labs, it’s not likely to be adopted.
My, what bright, glowing optical fibers you have.
One of my online compatriots recently explained a quick and easy way to do some IR photography. I felt compelled to try, and it was pretty easy. Cheap webcams are the most direct way to do this for a few reasons:
— they’re cheap. If you mess it up, you’re only out a few simoleans.
— they have manual focus. Modifying an autofocus camera requires you replace the IR filter with a glass plate, because removing it changes the optical path length. It’s a much trickier operation.
— it’s usually a fast modification
Just remove the lens — some of them simply unscrew — and check to see if the filter is mounted on the back. (If not, you’ll have to take the assembly apart. No biggie, though, it’s likely just one or two screws. You’ll need a jeweler’s screwdriver, probably phillips-head). Pop the filter off with a small screwdriver or equivalent; the filter may not survive in one piece, so don’t go into this expecting it to survive. Reassemble. You’re done. If the filter isn’t there, it’ll be covering the CCD/CMOS chip, but my extensive data (three points) says that it’s mounted on the back of the lens.
Plug it in to your computer and start taking pictures.
Expectations: This isn’t thermal imaging, so don’t expect bodies to show up glowing. Silicon, the element of choice, has a pretty sharp cutoff starting at about 950 nm, so what you’ll see in the near-IR. Something would have to be about 3000 K to be peaked at that wavelength and thermal images of body temperature targets peak between 9 and 10 microns. Also, the images will be small, since cheap webcams generally run only about a megapixel.
I just happen to have access to several infrared lasers (852 nm and 780 nm, the images use the latter), to give extreme examples of what you can see. This first picture is a laser table with the room lights off. You can see scattered light from several optical components, as well as light emanating from two optical fibers — not all of the light gets coupled into the fibers, and you’re seeing some of what leaks out (some probably in the wrong mode, since these are single-mode fibers, and the bending probably contributes)
In this second photo, there are two images of the same scene, taken with the room lights on. On the left, some shutters are shut, and on the right they are open, and you can see two fibers lit up. Also note the cylinder to the left — that’s a vapor cell with rubidium gas in it, set up for spectroscopy for servo-locking the laser. The laser is on resonance, so you can see the fluorescence as the beam passes through it.
As you can see, there’s quite a lot of scattered light, so normally this is encased in opaque plexiglass. None of the bright features shown are visible with the naked eye.
I remember reading about this last January, and now I see via Bee at Backreaction that it’s in the news again.
Floating banana’s appeal for funding slips
Despite getting about $105,000 from Quebec and federal art-funding agencies, Canadian artist Cesar Saez’s flying-banana project appears to be meeting turbulence. According to his project’s webpage, the Geostationary Banana Over Texas has failed to get enough grassroots funding to ensure its planned launch date in August.
[…]
People can think it’s a hoax,” Mr. Arpin added, “but artists have been doing a lot of interesting things that a lot of people haven’t been able to follow. He [Mr. Saez] is pushing the boundaries and letting people think outside the box – or the fruit basket.”
Maybe some people thought it was a hoax because you can’t get a helium balloon high enough to be in a geostationary orbit, and a geostationary orbit can’t exist over Texas. Geostationary is a scientific/technical term. It has a specific meaning. If you just make crap up, some people won’t take you seriously.
The project’s Web-based fundraising drive says it needs $1.5-million.
Oooh. My badger project needs $1.5 million. I can’t describe how badly it needs it. Pony up, people. Or at least start buying some t-shirts.
Researchers tug at molecules with optical tweezers
MIT researchers have developed a novel technique to measure the strength of the bonds between two protein molecules important in cell machinery: Gently tugging them apart with light beams.
They don’t really go into what’s novel about this. The optical tweezers technique has been around for a while.