Twenty years of physics: Astrophysics

MAY 01, 1968

Lodewyk Woltjer

RADIO SOURCES had just been discovered twenty years ago, but their nature was unknown. The 21‐cm hyperfinestructure line of hydrogen had been predicted but was not yet observed. Theories of stellar and galactic evolution were primitive: The origin of the elements was a mystery, and the nature of cosmic rays was obscure.

This article is only available in PDF format

More about the authors

Lodewyk Woltjer, Columbia University.

Physics Today is looking for a Senior Editor. Apply Now.

Related content

Features

Article

Oppenheimer reflects on his early career

Interviews now available to the public bring the famed physicist’s lesser-known early years to life.

May 06, 2026 11:38 AM

Features

Article

Building graduate programs that support mental well-being

Graduate students in physics and astronomy struggle with mental health. Support from peers and advisers is critical; so is institutional change.

April 13, 2026 11:17 AM

Features

Article

The paradoxical phenomenon of quantum scarring

Inside certain quantum systems, where randomness was thought to lurk, researchers—after a 40-year journey—have found order and unique wave patterns that stubbornly survive.

April 02, 2026 12:26 PM

Features

Article

Black holes aren’t black

A half century after the discovery of Hawking radiation, we are still dealing with the quantum puzzle it exposed.

March 26, 2026 12:23 PM

This Content Appeared In