Mike Albrow

As the expanding universe cooled after the Big Bang, protons and electrons found each other and made hydrogen atoms, with a little helium and lithium. Illustration: CERN

The existence of hydrogen in our universe was touch-and-go. During the Big Bang, it depended on a minuscule mass difference between two subatomic particles called quarks.

March 8 was the International Women’s Day, and Feb. 11 was the International Day of Women and Girls in Science. This article highlights the messages women working on the Auger Observatory have for girls.

Robot world

There is a world populated only by robots, roaming around or stuck in place. The hills and valleys are devoid of vegetation and not unlike some earthly desert scene. The sun is in a cloudless sky, but it is small, the light is dim; the sky is pale bluish grey. It is as cold as Antarctica in summer. The atmosphere is much too thin to breathe, and anyway it is mostly carbon dioxide. Sometimes dust storms are whipped up by fast winds. Can you guess what it is?

Five billion years ago what was to become the sun was a vast cloud of very thin gas, mostly hydrogen and helium from the Big Bang. There were also heavier elements like carbon, oxygen, iron, gold and all the others; they came from stars that collapsed and then exploded, flinging those atoms across space. That rarefied cloud was bigger than what became our solar system and was surrounded by a more perfect vacuum. Slowly it contracted under its own gravity.

For all antiquity nobody knew what stars were. When Copernicus realized that the sun, not Earth, is the center of the universe, the stars were placed on a far distant giant sphere. Some thought they might be holes through which shone the light of heaven. Copernicus, who was nineteen when Columbus first sailed across the Atlantic, started the Scientific Revolution, followed by Galileo and Newton, and the Age of Discovery began.

Can you picture something nine million miles across and yet is invisible? No, and neither can I or anyone else. It is a supermassive black hole at the center of our Milky Way galaxy, some 27,000 light-years away. The sun is eight light-minutes away, and the next nearest star about four light-years away. We are in an outer suburb of the galaxy. In contrast, there are dozens of stars within one light-year of that supermassive black hole, orbiting around it at speeds up to 8,000 kilometers persecond!