The Big Bang Theory


How and why would anyone come up with the idea that an enormous explosion created the universe billions of years ago?

The competing idea that the universe has existed forever, while still somewhat unfathomable, is at least simpler and more understandable. So why would someone propose this fantastic counter-notion, and why do so many scientists believe it?

The reason is because the “Big Bang” theory answers a lot of questions about what we see happening in the universe today.

Before discussing the questions it answers, let’s clarify what the theory says, exactly.


According to the theory, the universe used to be extremely small, unbelievably hot, and incredibly dense. Everything that existed was condensed into a compact space. It was not just a spot IN the universe, it was the ENTIRE universe. Absolutely nothing, not even empty space, existed outside of this miniaturized cosmos.

Then, 13.7 billion years ago, something happened. Everything contained in that mini-universe began expanding outward extremely rapidly. The big bang theory doesn’t explain why, but the sudden, rapid expansion is similar to what we’d expect to happen from an enormous explosion, hence the name.

Within the first second after this event, energy in the form of photons began to break down into particles, and particles began combining to create protons. After a few minutes, the first simple atoms of helium formed. The universe was expanding immensely and cooling.

The energy from the event was still enormous, however, and by 300,000 years later the entire universe had cooled to the same temperature as our present-day Sun. It would take 500,000 years for things to calm down enough that protons and other particles could combine to form other types of atoms. It was not until 1,000,000 years later that the stars and galaxies began coalescing.


The first big mystery that led to the proposed theory was the observation that all the galaxies in the universe are moving away from each other at a uniform speed, and the ones farther away are moving away faster. The big bang provided a convenient rationale for why this would be happening. But that wasn’t proof.

The proof came after scientists concluded that if such a cosmic explosion had occurred, it would have created enormous amounts of radiation that should still be present throughout the universe. It wasn’t until 1964 that we had the technology to detect such radiation. And we did, confirming that part of the theory.


There are still many fundamental mysteries of the universe that have not been completely answered by the Big Bang theory, but none of those mysteries support the argument that it didn’t happen that way. We just don’t yet understand enough to explain them. New, exotic theories are being proposed to explain our latest observations, but those theories are still consistent with the Big Bang.