Was the universe always here?

Or did it have a beginning?

If so, how did it start?

From ancient times, philosophers and theologians have debated these questions.

But it wasn't until the 20th century that a series of stunning scientific discoveries

finally enabled us to get some answers.

The story begins in 1912 when American astronomer Vesto Slyther observed that light coming

from distant nebulae, clouds of dust and gas in outer space, appeared redder than expected.

Why was this important?

Here's where your high school science pays off.

Remember learning about the Doppler effect?

The frequency of sound, light or other waves changes as the source and observer move toward

or away from each other.

To demonstrate this, your science teacher likely played a recording of a train whistle.

The pitch of the whistle lowers, that is the sound wave stretches out as the train receipts

into the distance.

What the same thing happens with light.

If a distant star or galaxy is moving away from us, the light coming from that object

will also stretch out.

Since in the spectrum of visible light, red light corresponds to the longest wavelengths,

physicists say light that has been stretched out has been redshifted.

This evidence of redshift suggested the nebulae were moving away from us.

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