MYP Physics The Big Bang Theory Notes

What Evidence Suggests That The Universe Had A Beginning And Has Been Expanding Over Time?

1. Before modern astronomical observations, scientists held a very different view of the universe.
2. Early scientists believed the universe was static, meaning it did not change in size.
3. Galaxies were thought to be fixed in position, with no overall motion relative to each other.
4. This idea seemed reasonable because early telescopes could not detect galaxy motion.

Observing Light From Distant Galaxies

1. Modern telescopes allow scientists to study light from faraway galaxies.
2. Light from galaxies can be spread into a spectrum.
3. Scientists noticed that spectral lines from distant galaxies were shifted toward the red end of the spectrum.
4. This shift is called red shift.
5. Red shift shows that galaxies are moving away from the observer.

How Does Doppler Effect Play A Role In Galaxy Motion?

1. The red shift of galaxies can be explained using the Doppler effect.
2. The Doppler effect occurs when a wave source moves relative to an observer.
3. When a wave source moves away, the waves are stretched.
4. This increases wavelength and decreases frequency.
5. For light, stretching the wavelength shifts it toward red.

Hubble's Law Shows The Universe Is Expanding

1. Hubble identified a clear pattern in galaxy motion.
2. The further away a galaxy is, the faster it is moving away.
3. This relationship is known as Hubble’s law.
4. It shows that expansion is occurring everywhere in the universe, not from a central point.

What Does Expansion Mean?

1. If the universe is expanding now, it must have been smaller in the past.
2. Going back in time, all matter and energy were much closer together.
3. This leads to the idea that the universe began from a very hot, dense state.

The Big Bang Model