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The modern description of gravity, Albert Einstein’s general relativity, is one of the most successful and best-tested theories we have. The core of that theory is a set of principles that say basically “physics is physics, wherever you are and no matter how fast you’re moving”. In particular, an experiment performed under the influence of gravity alone should work exactly the same as if you’re performing the same experiment deep in space without any gravity at all.
That’s a tricky concept to verify, but scientists at the National Institute of Standards and Technology (NIST) in Colorado have provided the best test for it yet, using Earth itself as the laboratory. They performed precision experiments in atomic physics (one of NIST’s specialties) and compared those results to those obtained at labs around the world, with data taken over a period of 14 years. The result: general relativity’s predictions were upheld once again.
[Read the rest at Forbes…]
Cartoon showing X-ray laser probing of Rydberg states in argon atoms. [Credit: Adam Kirrander]
I really love how many experiments are beginning to probe to the limits of quantum measurement. I wrote about a pair of cool studies in December that revealed the quantum wavefunction — the mathematical structure governing the behavior of particles. Today, my latest article in Ars Technica examined a proposed experiment using X-ray lasers to study the dynamics of electrons
in argon (and other inert gases) in both space and time.
Rydberg atoms have the electrons in their outer layers excited until the electrons are only weakly bound to the nucleus, making the atoms physically very large. The increased size allows light to scatter off the outermost electrons without much interference from the nucleus or from the inner core of electrons. In other words, it’s a way to isolate the electron dynamics from other messy phenomena. Noble gases like argon are particularly useful for this, since they are largely non-reactive chemically and relatively easy to model theoretically. [Read more….]
Danish physicist Niels Bohr, whose model of atoms helped explain the spectrum of light emitted and absorbed by different elements, as illustrated by the spectrum emitted by the Sun. [Credits: AB Lagrelius & Westphal, via Wikipedia (Niels Bohr photo); N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF (solar spectrum); moi (composite)]
Many of us are familiar with the Bohr atom: a simple model with a nucleus and planet-like electrons orbiting in circular paths. It’s a useful picture, even though it’s not complete. Bohr proposed it in 1913, but it took about ten more years for physicists to work out why
it worked — and to refine it into the quantum-mechanical picture of atoms we have today. However, we’re still probing the structure of atoms, especially the really bizarre behaviors under extreme conditions. Bohr’s contributions are still relevant today
Despite a century of work, atomic physics is not a quiet field. Researchers continue to probe the structure of atoms, especially in their more extreme and exotic forms, to help understand the nature of electron interactions. They’ve created anti-atoms of antiprotons and positrons to see if they have the same spectra as their matter counterparts or even to see if they fall up instead of down in a gravitational field. Others have made huge atoms by exciting electrons nearly to the point where they break free, and some have made even more exotic “hollow atoms,” where the inner electrons of atoms are stripped out while the outer electrons are left in place. [Read more…]