21.5 The expanding universe Key concepts: What is the big bang theory? How did the solar system form? What do astronomers predict about the future of the universe? Key terms: big bang, hubble’s law, cosmic background radiation, solar nebula, planetesimal, dark matter, dark energy

How the universe formed The universe exploded into what scientists call the Big Bang According to the theory, the universe formed in an instant, billions of years ago, in an enormous explosion. It eventually cooled and atoms and other stuff floated around until it formed planets and stars and other space junk

Moving Galaxies Edwin Hubble – American astronomer Discovered important stuff that helped the BB theory Discovered that all galaxies are moving away from us and from each other. There is a relationship between the distance to a galaxy and its speed. Hubble’s law states that: the farther away a galaxy is, the faster it is moving.

Cosmic stuffffff Cosmic background radiation – in 1965, two physicists accidentally discovered faint radiation on their radio telescope. It was coming from all directions. They concluded that it was cosmic background radiation (the leftover thermal energy from the big bang).

Age of the universe 13.7 billion years That’s older than yo’ mama

Formation of the solar system Solar Nebula – the large cloud of gas and dust that forms a solar system. Ours collapsed about 5 billion years ago to become our solar system. Planetesimals – small asteroid-like or comet-like bodies made of gas and dust. Building blocks of planets. They collide to form planets. Inner planets – temps were high, so water and other stuff vaporized. Gases escaped. Outer planets – much cooler, gravity increased so they took in H and He and became large.

Future of the universe The universe will likely expand forever. Maybe. No one really knows. So like, whatevs. Dark matter – matter that does not give off electromagnetic radiation. Its presence can be inferred by observing the effect of its gravity on visible objects. It’s probably 23% of the mass in the universe. Dark energy – mysterious force causing the universe’s expansion to accelerate.