Astronomical observations have shown us that galaxies are moving away from our Milky Way galaxy at great speeds. This, along with the discovery of cosmic background radiation — leftover light from the beginning of the Universe — support the big bang theory and the expansion of the universe.
- Fast Fact: A Belgian priest and scientist named George Lemaitre first suggested the Big Bang theory in the 1920s.
The universe is expanding not because something is pushing it along, but because of inertia. Once an object is set in motion (in this case, the universe at the start of the Big Bang), it continues to "go" unless something happens to slow it down or stop it. Sir Isaac Newton described this in his First Law of Motion, which states, "an object in motion will stay in motion unless acted upon by another force". The expansion of the universe was set in motion over 13 billion years ago, and so far nothing has acted on it to slow it down or make it stop.
- Fast fact: Nothing existed — not space or time — until the moment of the Big Bang.
Will the universe expand forever? Possibly. It depends on whether the gravity of all the stars and matter in the universe is enough to put the breaks on.
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This answer was written by Susan Cannon
