Illustration of the expansion of the Universe. The Cosmos began 13.7 billion years ago (left). Immediately it began expanding and cooling (stage 1). Its expansion slowed about 10 billion years ago (stage 2). We are now at stage 4. The expansion shows no signs of stopping and is in fact accelerating. The orange arrows indicate the force of gravity, which slows but does not stop the expansion.
MARK GARLICK/SCIENCE PHOTO LIBRA/Getty Images/Science Photo Libra