Category Archives: Physics

Skinner!

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Chalmers scientists create light from vacuum

“The result was that photons appeared in pairs from the vacuum, which we were able to measure in the form of microwave radiation,” says Per Delsing. “We were also able to establish that the radiation had precisely the same properties that quantum theory says it should have when photons appear in pairs in this way.”

What happens during the experiment is that the “mirror” transfers some of its kinetic energy to virtual photons, which helps them to materialise.

I would like to take this opportunity to caution anyone against taking this result and recasting it as some hocus-pocus, or a magical way to tap the vacuum as an energy source, but it’s already happened. An article in Forbes is the kind of thing that opens up that door.

After rotating the SQUID at those high speeds, the team were able to detect several real photons that were essentially created from nothing.

No, not essentially. The interesting detail here from QM (and specifically quantum electrodynamics) is that the vacuum isn’t “nothing” and Forbes just completely ignores that to create an abracadabra moment.

And Physics He Might Have Disliked

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Microwave Math That Einstein Would Have Loved

Measuring the speed of light with a microwave is a pretty standard DIY experiment, though I prefer using chocolate chips, given the premise that one should eat the experiment if it’s about food. (Then again, the article suggests Velveeta. Put that on your spam and wonderbread sandwich and it’s still food-free). Sure, Einstein might have liked that.

My nit is with this

To get the most out of your microwave, it helps to understand that it cooks with light waves, much like a grill does, except that the light waves are almost five inches (12.2 centimeters) from peak to peak—a good bit longer in wavelength than the infrared rays that coals put out.

A grill is not really that much like a microwave. A microwave uses (non-thermal) radiation to cook food. A grill uses convection, conduction and radiation. If it just used radiation, you could put a transparent* vacuum system in between the food and the coals and still cook the food, but that wouldn’t give you the expected result. The air is hot, as is the grill itself — you get a pattern burned into your hamburger patty or hot dog from where it lies on the hot grill. Conduction and convection. All three modes of heat transfer play a role.

What is said about the wavelength isn’t wrong, but it does tend to reinforce the mistaken conception that infrared radiation is synonymous with heat. The blackbody radiation that would be emitted wouldn’t have a specific wavelength, since it would be a continuum, and it would include wavelengths longer and possibly shorter than IR, if the source were hot enough. The microwaves, of course, are not heat in a physic sense — in thermodynamic terms that would be considered work, since they do not come from a thermal source; it’s not coming from a temperature difference. An infrared laser could be used to cook, but that wouldn’t be heat either.

I really have no idea if Albert would have liked or disliked such an example, but I suspect glossing over details that give the wrong implication might have bothered him.

*Certainly not one made of pyrex

Olivia Newton-John Physics

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Guest Post: David Wallace on the Physicality of the Quantum State

In quantum mechanics, we routinely talk about so-called “superposition states” – both at the microscopic level (“the state of the electron is a superposition of spin-up and spin-down”) and, at least in foundations of physics, at the macroscopic level (“the state of Schrodinger’s cat is a superposition of alive and dead”). Rather a large fraction of the “problem of measurement” is the problem of making sense of these superposition states, and there are basically two views. On the first (“state as physical”), the state of a physical system tells us what that system is actually, physically, like, and from that point of view, Schrodinger’s cat is seriously weird. What does it even mean to say that the cat is both alive and dead? And, if cats can be alive and dead at the same time, how come when we look at them we only see definitely-alive cats or definitely-dead cats?

It Takes All Kinds

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How much radiation are you exposed to on a plane?

“If you use a classical dosimeter, it is measuring photons and electrons, but those account for less than 40% of the total dose aboard aircraft,” he says. “The difference comes from the fact that you have other particles like neutrons, and those represent most of what you receive in a dose aboard an airplane. They can’t be detected with classical dosimeter. You need very specific technology for that.”

Expensive, specialized dosimeters pick up the particles that are most common at flight altitudes. Normal, old dosimeters don’t. To McManis, that difference makes a lot of sense.

“I was using a personal alarm dosimeter that relies on ionizations to work, and neutrons don’t ionize things,” she says.

That last statement is a tad misleading. Neutrons are considered ionizing radiation. They just don’t register in dosimeters that rely on direct ionization through electrostatic interaction — neutrons are uncharged. Which means they penetrate and give a whole-body dose.

Neutrons can immediately ionize some things, like hydrogen — if you slam a high energy neutron into a proton (or other light nucleus), it will leave the electron behind, and both will be energetic and do damage to nearby molecules in the cell. Thermal neutrons typically do damage through absorption into a nucleus and causing it to become radioactive (neutron activation). The subsequent decay gives off ionizing radiation.

One Down, Several to Go

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Neutrino experiment affirms faster-than-light claim

One set of concerns centered on the relatively long timescale – 10.5 microseconds, or 10.5 millionths of a second – of the proton pulses produced at CERN that result in the neutrino pulses OPERA detects. OPERA did not know whether individual neutrinos received at Gran Sasso corresponded to protons early or late in the proton pulse, creating uncertainty around their detection of them. In October OPERA therefore asked CERN to generate shorter proton pulses lasting just 3 nanoseconds. They have now recorded 20 events in the new data run and say that they have reached a similar level of statistical significance to the first time around, with the neutrinos again reaching Gran Sasso 60 nanoseconds faster than a light beam would do.

However,

But concerns about the experiment’s use of the Global Positioning System to synchronize clocks at each end of the neutrino beam are unlikely to be as easily allayed, The use of GPS is novel in the field of high energy and particle physics and the same system was used for both the original experiment and the new run.

I must point out that GPS common-view is not a novel technique outside of high energy and particle physics.

See Me, Feel Me

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Seeing sound

The technique builds on a piece of technology developed for the study of mechanical vibration; the laser vibrometer, and relies on a phenomenon called the acousto-optic effect. This describes the slight change in the speed of light in air when it passes through an acoustic field, causing a phase shift in the light that can be detected using the vibrometer.

The construction of the walls of that studio is baffling.

There is No Pink Spoon

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The physics of pink – why it isn’t in the rainbow

We see pink when our eyes register a mixture of red and blue light. However, there’s no wavelength corresponding to pink, because the spectrum of light (or electromagnetic radiation) is more like a long line stretching from really low energy radio waves which carry our favourite TV shows, to microwave, infrared, red …your favourite rainbow acronym… violet… ultraviolet, x-rays etc. There’s no red-pink-violet, only red-orange-yellow-green-cyan-blue-violet.

Hate the Sin, Love the Sinter

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

In this video, researchers at the University of Texas, Austin, guide viewers through the process of laser sintering. This technique, a type of 3-D printing, produces solid objects from polymer and metal powders.