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The Question

(Submitted November 08, 1997)

What is the big bang theory? What do you believe?

The Answer

The big bang theory is the theory that the universe started from a single point, and has been expanding ever since.

This has been well-established by observations, such as the apparent movement of galaxies away from us, and the cosmic microwave background radiation believed to be the leftover light from the big bang.

The evidence for a big bang having taken place about 15 to 20 billion years ago is overwhelming, so I naturally believe that it is the case.

However, if your real question is "why did the big bang happen in the first place?" then that ceases to be an astronomical question, but a religious one.

Some astronomers, who are religious, argue that the big bang theory confirms the existence of God and the basic elements of the creation story as told in the Bible. First came light, then the heavens, then the Earth ...

However, many other scientists do not. Scientists, like people in most any profession, have a vast diversity of religious beliefs. Some of us attend houses of worship, others do not. Some of us consider ourselves very religious, others consider ourselves staunch atheists. Just because we study astronomy does not mean we have any more agreement as to the ``why'' questions than anyone else.

On the other hand, it is safe to say that as scientists we can agree on an approach to learning about nature and the universe. This approach is one of using observations to test theories. And when a theory has been tested as much as the big bang theory, with each test reconfirming its validity, then we believe that it likely true -- at least more true than those theories which have failed the observational tests.

Good luck on your quest for the truth.

Jonathan Keohane
for Ask an Astrophysicist

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