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The great mystery at the heart of the Big Bang is to explain how an entire, fantastically enormous universe of space and energy can materiahse out of nothing. The secret lies in one of the strangest facts about our cosmos. The laws of physics demand the existence of something called "negative energy." To help you get…
Once the matter created by the Big Bang cooled sufficiently, the universe consisted of a vast cloud of hydrogen atom consisting of a single proton surrounded by a single electron—along with a smattering of slightly heavier elements, including helium (with two protons) and lithium (with three). The universe at that…
Hubble's observations suggested that there was a time, called the big bang, when the universe was infinitesimally small and infinitely dense. Under such conditions all the laws of science, and therefore all ability to predict the future, would break down. If there were events earlier than this time, then they could…
The next obvious feature of the universe in which we live is that it is old, very old. It took intelligent life about 3.5 billion years to develop on Earth. Hence, our existence requires a universe that accommodated our arrival by lasting billions of years. The current best estimate for the age of our universe is…
That the universe is expanding was news to Einstein. But the possibility that the galaxies are moving away from each other had been proposed a few years before Hubble's papers on theoretical grounds arising from Einstein's own equations. In 1922, Russian physicist and mathematician Alexander Friedmann investigated…