Astronomers are used to things that change slowly, over millions or billions of years, so when something goes BANG in the sky, we tend to kind of lose it. It’s certainly partially just the novelty, but it’s also because events like this give us a chance – and a fleeting one at that – to watch some of the most energetic and revealing processes in the Universe as they happen.
They only mention building materials in the paper’s abstract, so this ignores C-14 decay, which is important because people are radioactive, too — any accounting of the radioactivity of a room should be compared with what you can’t avoid because it’s an internal dose.
This all seems clear enough. Rutherford is referring to Kelvin’s cooling argument. But this argument is invalid, because it assumes no new source of heat, and such a source exists, namely radioactivity. Or so says the popular myth. The truth is more complex, and more interesting.
[T]he technological applications of quantum physics are so ubiquitous that we often forget they’re quantum, saving that term for the odder and harder-to-understand aspects of the field.
However, it’s really important to remember that physicists and chemists do understand quantum mechanics pretty well.
Reporting this month in Physical Review Letters, Grzegorczyk and colleagues at the Swiss Federal Institute of Technology in Lausanne say that they’ve used lasers to arrange about 150 beads that are 3 microns in diameter to produce a flat, reflective surface. In the experiment, the beads are contained in a water-filled glass cell. A laser beam shines under the beads, causing them to align themselves into a flat surface. To show that the surface was indeed a mirror, the researchers used it to reflect an image of the number eight made by shining light through a transparent ruler. They also calculated that a reflective surface made by shaping a flock of tiny particles into a parabola could focus an image just as a telescope mirror does.
This sounds pretty cool. I can’t access the paper at the moment, but if the viewing wavelength is large enough, any roughness of the assembly won’t matter — it will “look” smooth to longer wavelengths.
If the atomic clock in the University of Colorado Boulder’s JILA laboratory had been started when the earth came into existence, its time would still be perfect down to the very second today. Likewise, if the clock were reset now and kept running, it would likely outlast life on Earth.
Aye, there’s the rub. …and kept running. But it doesn’t — it only runs for a few hours. Which means my standard disclaimer applies: this isn’t a clock, it’s a (kick-ass awesome) stopwatch.
So when Jun Ye says “You can expect more new breakthroughs in our clocks in the next five to ten years.” what he means is that they will continue to push for even more stable clocks — greater levels of precision and, if these are going to become primary or secondary frequency standards, greater accuracy. They are not going to to be pushing the envelope with respect to robustness of the technology unless it furthers the goal of better accuracy/precision — that’s not really their job. It’s my job. (Yeah, I’m starting work on an optical clock)
A confusing this is that they mention a competitor’s clock and claim it uses Cesium, but the linked article says it also uses Strontium. When it says it measures time in a “non-standard and still unaccepted way” I think they are referring to the fact that it’s an optical transition, and not at the ~9.192 GHz transition that defines the second. But non-standard and unaccepted? Not so much — the Rubidium fountains I have helped build, and Hydrogen masers that are in widespread use don’t/can’t rely on that transition, and these clocks are reported to the international Bureau of Weights and Measures.
Those stumbles aside, the applications mentioned at the end — precise sensors for gravity, for example (I think “quantity” in that bit is an autocorrect casualty and is supposed to be “quantum”), but not so much for timekeeping.
[T]hat [number] almost certainly overestimates the number of people working directly on a Theory of Everything. The fact is, the physicists whose work is genuinely in crisis as a result of recent developments (or, more accurately, the lack thereof) are a tiny minority of professional physicists. They’re vastly overrepresented in the media, in large part because wildly speculative stuff about multiple universes is sexy and provides lots of opportunities for stoner-friendly CGI, but if they all got sucked into a black hole tomorrow (thus settling the “firewall” debate for good and all), physics as a whole would continue on with barely a hiccup.
It’s not ATRAP! (It’s ASACUSA)
In a paper published today in Nature Communications, the ASACUSA collaboration reports the unambiguous detection of 80 antihydrogen atoms 2.7 metres downstream of their production, where the perturbing influence of the magnetic fields used initially to produce the antiatoms is small. This result is a significant step towards precise hyperfine spectroscopy of antihydrogen atoms.