March 15, 2018

Yesterday, March 14, famed British theoretical physicist Stephen Hawking died in Cambridge, England, at age 76. Hawking made some of the most important discoveries about gravity since Albert Einstein. Einstein, a German-born physicist, invented general relativity, the modern theory of gravity, in 1915. Hawking worked to increase our understanding of the earliest history of the universe. His work supported the theory that the universe began in a cosmic explosion called the big bang.

British theoretical physicist Stephen Hawking answers questions on a computer attached to his wheelchair during an interview in 2007. Hawking died on March 14, 2018. Credit: © John Raoux, AP Photo

Hawking is probably best known for his theories about objects called black holes. A black hole’s gravitational force is so strong that nothing—not even light—can escape it. Hawking used a field of physics called quantum mechanics to show that a black hole nevertheless gives off particles and radiation until it eventually disappears. These emissions became known as Hawking radiation. He also proposed that tiny, atom-sized primordial black holes were produced in the early moments after the big bang. In addition, Hawking worked to combine quantum mechanics and gravity into a single unified theory.

Three of Hawking’s books became international best sellers. They were A Brief History of Time: From the Big Bang to Black Holes (1988), The Universe in a Nutshell (2001), and The Grand Design (2010), which he co-wrote with American physicist Leonard Mlodinow. Following the success of A Brief History of Time, Hawking became a recognizable figure in popular culture, appearing in or lending his distinctive image and voice to various television shows. In 1991, American director Errol Morris made A Brief History of Time into an award-winning documentary film.

Hawking suffered from amyotrophic lateral sclerosis (ALS), an incurable disease of the nervous system. He could not speak or move more than a few hand and face muscles. Using a wheelchair and a computer voice simulator, however, he wrote and gave professional and public lectures around the world.

Hawking received numerous prestigious awards, including the Royal Society’s Copley Medal, the Gold Medal of the Royal Astronomical Society, and the American Presidential Medal of Freedom. He spoke on issues concerning science and society, such as genetic engineering, the colonization of space, and artificial intelligence.

Stephen William Hawking was born on Jan. 8, 1942, in Oxford, England. In 1966, he received a doctorate degree from Cambridge University. He afterward held a variety of research posts there. From 1979 to 2009, he held the prestigious position of Lucasian professor of mathematics at Cambridge, a chair once held by the English scientist and mathematician Sir Isaac Newton.

January 22, 2014

One of the filaments of matter that scientists think connects galaxies in a “cosmic web” has been imaged for first time. The images were captured by scientists from the University of California at Santa Cruz using the Keck telescope on the top of Mauna Kea in Hawaii. Many astronomers have long believed that the matter in the universe is not spread out evenly but is distributed in a weblike structure, or cosmic web. The filament imaged by the scientists was in a very large, bright, nebula that is about about 2 million light-years across. The scientists were able to see the filament because it was illuminated by a powerful black hole at the center of a galaxy located on the filament.

A filament in the cosmic web is illuminated by the light from a quaser in a computer simulation of one section of a nebula. (S. Cantalupo (UCSC); Joel Primack (UCSC); Anatoly Klypin (NMSU))

Computer simulations have shown how these filaments could form. However, finding direct evidence has not been so easy. The scientists were assisted by a type of super-massive black hole called a quasar. This type of black hole, like many huge black holes, sits the center of a galaxy. Unlike many other galaxy centers, however, a quasar shoots out two powerful jets of energy and matter. Like a flashlight, one of the jets lit up the filament leading up to the quasar, enabling the scientist to spot it and take an image.

The discovery has provided supporting evidence for the cosmic web theory. In addition, the finding is giving scientists much-needed clues about how the matter in the universe is distributed. Early information from the discovery suggests that there is much more matter in the filaments than many models have predicted. If correct, the evidence could force scientists to rethink the most widely accepted models of the structure of the universe.

Additional World Boook articles:

• Dark matter
• Interstellar medium
• The Formation of Galaxies and Other Structures

Three United States-born astronomers won the Nobel Prize in physics for their revolutionary discovery that the universe is expanding at an accelerating (increasingly faster) rate. The force driving this expansion is thought to be a mysterious antigravitational force known as dark energy. The prize winners were Saul Perlmutter of the University of California, Berkeley; Adam G. Riess of the Space Telescope Science Institute and Johns Hopkins University; and Brian P. Schmidt of the Australian National University. Schmidt is also a citizen of Australia.

The finding by the three astronomers expands on another revolutionary discovery about the universe made in 1929 by American astronomer Edwin Hubble. He had observed that the farther apart galaxies are from each other, the faster they are moving away from each other. From this, Hubble determined that the universe is expanding at a uniform rate. Later scientists found evidence that the expansion began 13.7 billion years ago with a cosmic explosion known as big bang. For many decades, astronomers believed that the expansion was slowing down because of the counter force of gravity on the universe.

Galaxies in the universe are speeding away from one another at a faster and faster rate. NASA/ESA/S. Beckwith (STScl) and the HUDF Team

Then in 1998, Perlmutter, Reiss, and Schmidt shocked the scientific community with their finding that galaxies are actually speeding away from each other at a faster and faster rate. Studies of the light from supernovae (exploding stars) indicate that this expansion began about 5 billion years ago. To account for the acceleration, scientists concluded that the universe was full of some kind of invisible energy, which was named dark energy. Later measurements confirmed that approximately 70 percent of the mass (amount of matter) of the universe consists of dark energy.

Additional World Book articles:

• Astronomy 2001 (Back in Time article)
• The Dark Side of the Universe (special report)