Tuesday, October 6, 2015

Getting physical

News about physics being a popular topic on SF and Nonsense, herewith a few interesting (but not especially publicized) tidbits ...

White light thru yonder prism breaks
Old-fashioned light bulbs emit a broad spectrum of colors. LEDs? They're red or green or (and this was difficult) blue. If you wanted white light -- white, of course, being a blend of colors -- you needed to mix the emissions from separate red, green, and blue LEDs. But maybe not for long. See (from IEEE Spectrum), "The First White Laser."

The heart of the new device is a sheet only nanometers thick made of a semiconducting alloy of zinc, cadmium, sulfur, and selenium. The sheet is divided into different segments. When excited with a pulse of light, the segments rich in cadmium and selenium gave off red light; those rich in cadmium and sulfur emitted green light; and those rich in zinc and sulfur glowed blue.

Elmers has nothing on "Big G"
New topic. Physicists speak, seemingly glibly, about universal constants. You might ask: how can anyone know that, say, the gravitational constant (referred to as "Big G"), is, in fact, constant across all of space and time? It ain't easy! But the great thing about (most) science is the notion that theories must be testable and findings repeatable.

We can't repeat the birth of the universe, but we can peer far across the cosmos. And when we do? From Astronomy magazine, see that "Gravitational constant appears universally constant, pulsar study suggests." (Think of pulsars as very distant, very powerful, astronomical metronomes. This particular pulsar co-orbits with a white-dwarf star. If G changed with time, the properties of that co-orbit would change, with effects, in turn, on the observed rate of pulsing.) That pulsar study shows a constant value for G. The binary star involved is >3000 light-years distant, so (a) the radiation being studied was >3000 years on its way to us, and hence (b) G was constant >3000 years ago as well as (when measured in our home Solar System) recently.

Waves: a matter of gravity
Speaking of testing and retesting, an unconfirmed prediction of Einstein's acclaimed theory of General Relativity -- a century old this year -- is that cataclysmic astronomical events, like colliding black holes, produce discernible gravitational waves. As such waves propagate (says the theory), the very fabric of space-time must compress and stretch. See (from Mashable), "Ripples in space-time created by colliding black holes go undetected after 11-year study." It's starting to get interesting / puzzling / worrisome that efforts to detect gravitational waves continue to fail.

You may remember the big announcement last year that gravitational waves had been detected. That report has been discredited. (From Nature, "Gravitational waves discovery now officially dead: Combined data from South Pole experiment BICEP2 and Planck probe point to Galactic dust as confounding signal.")  If the newly operational Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) doesn't soon find evidence of such waves ... that will really be worrisome with respect to our understanding of the universe.

And on a much smaller scale, consider (from Ars Technica) that "Experiment confirms that quantum mechanics scoffs at our local reality: The last loopholes for determinism squeezed out in latest work."

Tearing out his hair?
That is to say: quantum entanglement -- the property of QM that Einstein derided as "Spooky action at a distance" -- seems more and more, no matter the affront it poses to our intuition, a true part of physical reality.

What else is super-interesting? Superconductors! Suppose that, to stay free of electrical resistance, a material didn't need to be kept in the deep freeze. How many applications might there be? How much more energy could be used rather than dissipated as waste heat in long power lines?

Perhaps in my lifetime I'll find out. See (from Physicsworld.com), "Hydrogen sulphide is warmest ever superconductor at 203 K." That is, by superconducting standards, balmy: -97 degrees Fahrenheit. Parts of Antarctica are occasionally that cold. Alas, to superconduct at that temperature, the hydrogen sulphide must be under extreme pressure: ~1.5 million atmospheres. That's a condition we don't see anywhere on Earth (and I'm okay with that).

Graphene: stick-and-ball model
And there's more superconducting news. It appears that a sheet of graphene with suitable doping offers no electrical resistance -- it superconducts -- at room temperature. (See, from IEEE Spectrum, "Graphene 'Decorated' With Lithium Becomes a Superconductor.")

A 2-D (one-atom-thick) sheet of material is never going to carry a lot of power, but there are other prospective uses:

The researchers who demonstrated last year the role phonons played in the superconductivity of graphite and calcium, Patrick Kirchmann and Shuolong Yang of the SLAC National Accelerator Laboratory, believe this latest work could usher in the fabrication of nanoscale superconducting quantum interference devices and single-electron superconductor quantum dots.

I can't speak for anyone else, but that's enough exciting news to keep my mind spinning ...


Keith Kenny said...

Reality can seem very unreal if one requires it to conform to what is within arms reach. Speculation about these concepts can move the reality boundary further out. For example, entangled particles are always co-located in another dimension, no matter how far apart they are in this one. Time and gravity seem to have only one vector—time goes forward, gravity pulls down—but they only half manifest in this dimension. In another they might operate both ways, i.e., enabling a SF author to time travel or defy gravity. But then the mysterious dark energy might be the long speculated anti-gravity, i.e., the Cavorite of steampunk stories.

Edward M. Lerner said...

Hi Keith,

Without disagreeing with your speculations, all are (to my knowledge) beyond any experiment ever performed. Moreover, extra dimensions, a la string theory, and the nature of dark energy, merely a label for our ignorance, remain beyond the domain of any proposed experiment. The joke is that economics is a great science, because economists successfully predicted 9 of the last 5 recessions; likewise, not every physics theory pans out when experiment catches up to it.

That said ... as these speculations cannot be disproven, they're all fair game for SF. Have at it ;-)

- Ed