QUANTA

In the world of astronomy, the Puerto Rican Arecibo Observatory is a giant. For over 50 years, Arecibo has been the world’s largest single-aperture telescope. With a 305 m (1000 ft) diameter full dish, few others can come close in scale. However, by the end of this year, China will have completed construction on the Five hundred meter Aperture Spherical Telescope (FAST). With a 500 m (1640 ft) diameter, FAST will become the largest telescope in the world and offer the opportunity to look farther into the universe than ever before.

(Image: Arecibo Observatory, Puerto Rico)

But what exactly is it? FAST is a single-aperture radio telescope, which means it uses a single dish to reflect radio signals. Because there are many artificial, non-galacti...

Ultracold atoms and lasers seem to be opposites. Yet, “laser cooling” is one of the most common methods low-temperature physicists use to cool substances to within 1 degree of absolute zero.

Light amplification by stimulated emission of radiation (LASER) usually heats objects, and many industries employ lasers to cut - or rather, burn - through steel plates. The confusion with laser cooling is that most people mix up lasers’ ability to emit light of a specific frequency with lasers just being one color. Technically, laser cooling refers to a variety of techniques, but it most commonly refers to Doppler cooling, so named for its use of the Doppler Effect.

To understand how Doppler cooling works, let’s take a brief journey into quantum mecha...

For approximately 4.5 billion years, the moon has orbited the Earth, stabilizing the tilt of its axis. Without the presence of a moon, the tilt could vary by up to 10 degrees, causing climate change on a global scale. Fortunately, Earth does have a moon, and such concerns are largely irrelevant.

A much more plausible effect is the moon’s influence on the tides. The moon’s gravitational force pulls the water towards it, raising the water level on Earth’s surface. Since gravity becomes weaker with increased distance, the water directly below the moon is pulled more strongly than the water to the side. This makes the ocean bulge, causing the sublunar tide. By similar logic, the water on the opposite side of the Earth experiences the weakest...