Category Archives: Physics

Seeing Red. Or the Opposite.

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Why Do Doctors Wear Green Or Blue Scrubs?

Green could help physicians see better for two reasons. First, looking at blue or green can refresh a doctor’s vision of red things, including the bloody innards of a patient during surgery. The brain interprets colors relative to each other. If a surgeon stares at something that’s red and pink, he becomes desensitized to it. The red signal in the brain actually fades, which could make it harder to see the nuances of the human body. Looking at something green from time to time can keep someone’s eyes more sensitive to variations in red

I’ve noticed the opposite effect in the lab; when I work with lasers I wear laser safety glasses, which block the wavelength being used, and for quite a while this has been in the NIR. The glasses block everything above ~650 nm, so the glasses look bluish-green and deprives your eyes of any red light. After taking them off, everything has a pink hue to it.

It's ATRAP!

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Antiprotons Reflect a Magnetic Symmetry

Physicists have improved the measurement of the antiproton magnetic dipole moment, further narrowing how close to identical it is in magnitude (with opposite sign) to the proton value. I ran across a number of poor articles describing this experiment, all obviously cribbing from the same press release. One mentioned magnetic charge, another claimed that that the experiment determined the charge of an antiproton and seemed to confuse the Penning trap and the proton beam at the LHC. One put the emphasis on the act of trapping antiprotons, as if this had not been done before (it has).

This is a good one. There’s also a link to the free PRL.

[The ATRAP collaboration] look for a difference in the magnetic moments of the proton and antiproton. To enable this test, they precisely measure the magnetic moment of a single, trapped antiproton, achieving the most sensitive measurement to date of this quantity. They compare their result to the known value of the proton’s magnetic moment and find that the magnitudes are equal within experimental uncertainty, as predicted by the CPT theorem. Though there have been other tests of CPT with better precision overall, the work reported by ATRAP improves the limits on CPT violation in the difference of the proton and antiproton magnetic moments by nearly three orders of magnitude

Plancking is Still a Big Thing

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What The Entire Universe Is Made Of, Thanks to Planck!

[T]his picture is far more exquisite than any that came before. In the early 1990s, the COBE satellite gave us the first precision, all-sky map of the cosmic microwave background, down to a resolution of about 7 degrees. About a decade ago, WMAP managed to get that down to about half-a-degree resolution.

But Planck? Planck is so sensitive that the limits to what it can see aren’t set by instruments, but by the fundamental astrophysics of the Universe itself! In other words, it will be impossible to ever take better pictures of this stage of the Universe than Planck has already taken.

Planck being an ESA satellite mission to measure the cosmic microwave background differences down to a resolution of a few parts per million.

No Time for Photons

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Neil deGrasse Tyson explains the timelessness of photons

Caveat emptor: he’s doing a radio show, so there’s a necessary downconversion of the depth of the discussion. He does err when he implies that massive objects traveling at c is a technological/engineering barrier, and we just haven’t figured it out (like breaking the sound barrier), rather than a physics barrier that would demand that current theory be wrong or incomplete, with some new physics necessary to explain what’s going on.

In general the “photons don’t experience time” is a bit of a tiptoe in the mine field, because we can’t definitively say what things look like from a photon’s perspective — relativity doesn’t afford us a description of what things look like to a photon. The Lorentz transforms — what we use to see what things are like for massive objects — “blow up” when v=c, which means that the photon is not in an inertial frame, and all that physics we do is for objects in inertial frames. The reason I hesitate is that an equation diverging from some infinity showing up means that the equation has failed, so the fact that a term is tending toward infinity (or zero) as it fails isn’t a guarantee that infinity (or zero) is the right answer when the equation no longer applies.

The idea does paint a nice picture, though, and seems consistent with the QED path-integral idea that photons sample all paths and most of them destructively interfere, and what we see is the result, but I think it’s easy to take the idea too far and imply things that don’t have any experimental backing to assure us they are true.

Freaky Water

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You need to a flashplayer enabled browser to view this YouTube video

A fun stroboscopic effect. The water isn’t really spiraling, of course, the effect is because the frame rate and sound wave frequency are the same, so the locations here the sound displaces the water (or doesn’t) is the same whenever a frame is recorded. Or close to the same, when he goes 1 Hz in either direction. Same effect as wheels looking like they are revolving backwards in some movies. You’re sampling images at the difference frequency.

The Little Refrigerator That Could

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NIST Quantum Refrigerator Offers Extreme Cooling and Convenience

[T]he NIST refrigerator’s cooling elements, consisting of 48 tiny sandwiches of specific materials, chilled a plate of copper, 2.5 centimeters on a side and 3 millimeters thick, from 290 mK to 256 mK. The cooling process took about 18 hours.

One thing not mentioned: this almost certainly does not scale up. It works starting at ~300 mK, but the performance

The cooling power is the equivalent of a window-mounted air conditioner cooling a building the size of the Lincoln Memorial in Washington, D.C

doesn’t mean you are going to be able to build an air-conditioner-sized device and actually cool the Lincoln Memorial, unless you got it down to 300 mK first. (Then we’ll talk)