The Doppler shift of sound or light waves from a moving source is familiar to physicists and non-physicists alike. Now, researchers in China and Australia have seen the more exotic inverse Doppler ...

Scientists have demonstrated for the first time how 'twisted' sound waves from a rotating source can produce negative frequencies—akin to turning back time. A team of international researchers, ...

Conventional optical Doppler techniques suffer from fundamental limitations: linear Doppler cannot sense transverse motion; rotational Doppler fails to distinguish clockwise from counterclockwise ...

When an ambulance passes with its siren blaring, you hear the pitch of the siren change: as it approaches, the siren’s pitch sounds higher than when it is moving away from you. This change is a common ...

Twist and shift: Incident beams with opposite orbital angular momentum (green spiral) reflect from a spinning surface: some of the light in the reflected beam has been red-shifted after reflection and ...

The pitch of a blaring car horn rises as the vehicle approaches and falls as it moves away. That’s the Doppler effect, and it also occurs for electromagnetic radiation, enabling police to catch ...

As great as echolocation is, things can get rather messy once it’s not just you chirping away, but also hundreds of your ...

Researchers have observed the inverse Doppler effect at optical frequencies, using a technique that combines a moving negative-index photonic crystal and heterodyne interferometry. In 1843, Christian ...

At the time of its construction in the 1950s, the Dwingeloo Radio Observatory was the largest rotatable telescope in the world with a dish diameter of 25 meters. It was quickly overtaken in the ...