2.14 Understanding our Universe – how did it all happen?

12 April 2023

How significant are you?

Key terms

• Red shift: light from stars that are travelling away from us comes from closer to the red end of the electromagnetic spectrum than light from the sun

• Big Bang theory: the theory that the Universe began as a single point

• Cosmic background radiation: electromagnetic energy that comes from all directions in space and is predicted to have come from the Big Bang

Our Universe (1)

• So far we have looked at our Solar System, but our Sun is not the only star in the region

• It is one of about 100 billion stars in our galaxy, which is called the Milky Way

• The Milky Way is a spinning spiral disc• On a clear, dark night without any pollution

or street lights, you can see it as a ‘milkyish’ light band

Our Universe (2)

• Our Solar System is on the edge of the Milky Way

• It takes about 220 million years for our Solar System to orbit the Milky Way, even though it is estimated to be travelling at 10 000 miles per hour

• This means that it has just completed one orbit since the first creatures appeared on Earth

Our Universe (3)• Our galaxy is the second largest in a group of

seventeen galaxies• The nearest galaxy to the Milky Way is called M31, the

Andromeda galaxy• Beyond this are other clusters of galaxies, with their

own stars and planets• These clusters form a shape which is like a

honeycomb• These clusters combine to form the Universe• There are an estimated 100 billion galaxies in the

Universe

What is the name of our galaxy? Name another…

Expansion of the Universe (1)

• Many astrophysicists believe that the Universe is expanding

• You can imagine this as bread with raisins, the raisins representing the galaxies moving away from each other

• Light coming from galaxies provides evidence for this expansion

Expansion of the Universe (2)

• Light forms a spectrum of wavelength and frequency

• The visible part of the spectrum starts with violet and ends with red

• The further you go towards red, the longer the wavelength

Expansion of the Universe (3)

• Astrophysicist have found that light coming from distant galaxies is shifted towards the red end of the spectrum

• The more distant the galaxy, the bigger the shift is

• This is called the red shift (or the Doppler Shift)

• This suggests that the galaxies are all moving away from each other – the Universe is expanding

The Big Bang theory• According to the Big Bang theory, the Universe

once existed as a single point 13.7 billion years ago

• This theory also suggests that radiation was emitted at this time and it should be still detectable

• This radiation is called cosmic background radiation and was detected in the 1960’s

• NASA confirmed this discovery in 1992, using its newly built satellite called COBE

What next for the Universe?

• Cosmologists believe that the Universe could follow one of the following paths:– Continue to expand forever– Expansion slows down but won’t quite stop– Expansion stops and the Universe collapses

to a single point (the Big Crunch)