G-whizzes disagree over gravity
[T]he relentless honing of G may have hit a stumbling block. Two recent experiments are in striking disagreement with earlier findings, and the overall uncertainty in the value of the constant may be set to increase.
Category Archives: Physics
Eddy's Back
Fun stuff. The nonmagnetic but conductive materials will see a changing magnetic field, or will “break” field lines, as the jargon goes, which induces eddy currents to flow and produce a field (that’s Faraday’s Law), with the induced field opposing the change (Lenz’s Law). This gives a braking effect, as you can see. Interesting that the nickel is largely unaffected by this; the composition is 75% copper and 25% nickel, while for the quarter, it is 91.67% and 8.33%.
I’ve linked to eddy current effects before, but still wanted to do my own video. I tried to narrate it while filming, but keeping everything in the frame and talking (while my hands were occupied with the demo) was too tough. I did a couple of disastrous takes and then had a fit and stormed off to my trailer, vowing to never work with myself again. I finally calmed myself down and did the silent shot, then waited impatiently for me to do the post-production.
Strange Things Done 'neath the Midnight Sun
The strange case of solar flares and radioactive elements
As the researchers pored through published data on specific isotopes, they found disagreement in the measured decay rates – odd for supposed physical constants.
Checking data collected at Brookhaven National Laboratory on Long Island and the Federal Physical and Technical Institute in Germany, they came across something even more surprising: long-term observation of the decay rate of silicon-32 and radium-226 seemed to show a small seasonal variation. The decay rate was ever so slightly faster in winter than in summer.
Was this fluctuation real, or was it merely a glitch in the equipment used to measure the decay, induced by the change of seasons, with the accompanying changes in temperature and humidity?
“Everyone thought it must be due to experimental mistakes, because we’re all brought up to believe that decay rates are constant,” Sturrock said.
The Pièzo de Résistance
“The piezoelectric effect has never been manipulated at this scale before, so the range of possible applications is very exciting,” explained Pooja Tyagi, a PhD researcher in Professor Patanjali Kambhampati’s laboratory. “For example, the vibrations of a material can be analyzed to calculate the pressure of the solvent they are in. With further development and research, maybe we could measure blood pressure non-invasively by injecting the dots, shining a laser on them, and analyzing their vibration to determine the pressure.”
(The title was the pun I forgot to use in my thesis defense talk, in describing our homemade diode laser systems)
Nobody Can Do the Triple Lindy
Bee has a short post on the triple-slit interference experiment: Testing the foundations of quantum mechanics. Contrary to the prediction of the writers at Nature, she does not appear to be “flummoxed” by QM.
If you know one thing about quantum mechanics, it’s Born’s rule: The probability of a measurement is the square of the amplitudes of the wave-functions. It is the central axiom of quantum mechanics and what makes it quantum. If you have a superposition of states, the amplitudes are sums of these states. Taking the square to obtain the probability means you will not only get the square of each single amplitude – which would be the classical result – but you will get mixed terms. These mixed terms are what is responsible for the interference in the famous double-slit experiment and yield the well-known spectrum with multiple maxima rather than one reproducing the two slits, as you’d get were the particles classical.
Serious Water Rocketry
Entanglement Done Right
I finally found post about quantum entanglement that does a great job of explaining entanglement, in the context of an attempt to entangle macroscopic objects: Spooky Mirror Tricks. As far as I have seen, it contains none of the “wall of shame statements” I ranted about recently. Quite the opposite.
[Entanglement] allows two particles to form a quantum object even when they are far apart.
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[I]f one measures, on one particle, the quantum property through which that particle is entangled with other particles, the same property will promptly be determined for each of the particles involved.
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[E]ntangled quantum particles behave similarly: there seems to be a strange connection between them. However, even this image is misleading, as there are no physical forces in play. In addition, only certain properties are ever entangled. For light quanta, for instance, this can be what is known as polarization, which can be imagined as a small pointer.If two entangled photons are prepared in a certain way, then the polarizations of both photons must point in exactly the same direction.Now, although the two photons must obey this strict “principle of conservation,” the quantum world does not dictate the direction in which the polarizations must point in relation to their surroundings. This is a further quirk of the entangled quantum world: as long as a property isn’t measured, it isn’t fixed for the object being observed. Only when someone measures the polarization of one of the two photons does he give it a direction relative to its surroundings. The polarization of the other photon must then immediately point in the same direction, no matter how far away it is.
Voilà! It can be done! Hear ye, hear ye. Let the journalism world know that you can explain entanglement properly, without mentioning Star Trek at all.
The Tipping Point
There’s a neat effect just after the 2:00 point of this video: the pilot does a barrel-roll, and the beverage in his cup does not spill. Then, he pours iced tea into his cup while doing the maneuver. The beverage in the cup remains pretty much parallel to the support the whole time.
The physics here is the same as with a swinging bucket; one must realize that the plane isn’t simply rotating along its axis — it’s following a circular path, and there is always lift (i.e. a force) going from the bottom of the plane to the top. I recreated this (to an extent) with a clear container and some Romulan Ale (I only use it for medicinal purposes). The first frame is where I was holding the bottle, so it’s at rest. The liquid is clearly at an angle to the container, and is parallel with the floor.
And the second is while the bottle is a freely swinging pendulum, and you can see the liquid is now level with the bottom of the container.
Blah, blah, blah. Oh, balls. I was working on this a while ago and now find that Rhett has a post up about it, though not following the same path I was going to take. Pouring tea in a plane – upside down, where he’s worked out all of the physics, with diagrams and pictures with circles and arrows and a paragraph under each one explaining what it is. So I’ve abandoned my v/2 (half-fast) explanation in favor of a link to his.
Turning, Turning, Turning Through the Years
Physicists say cosmic rays affect the length of day
I’d like to add a warning to this (along the lines of the Journalism Warning Labels by Tom Scott): Article title implies much more certainty than the article; the article is more restrained than the title would indicate, and the paper (at least the abstract) even more so. Changing the angular momentum of the earth would affect the moment of inertia, but the correlation here is with the sunspot cycle — the connection to cosmic rays is more tenuous.
The abstract actually says
We conclude that variations in mean zonal winds are modulated by the solar activity cycle through variations in irradiance, solar wind or cosmic ray intensity.
I’ll have to consult my local experts on earth rotation and get their opinion on this.
One Ringy-Dingy
The Virtuosi: Ringing A Bridge
When you strike a bell, it rings at a given frequency. This frequency is called the resonant frequency and is the natural frequency at which the bell likes to ring. Just about anything that can shake, rattle, or oscillate will have a resonant frequency. Things like quartz crystals, wine glasses, and suspension bridges all have a resonant frequency. The quartz crystals oscillate at frequencies high enough for accurate timekeeping in watches, the wine glasses at audible frequencies to make boring dinners more interesting, and bridges at low enough frequencies that you can feel it when you walk. It is the resonant frequency of bridges that we decided to measure.