Red Shift and CMB Radiation

Red Shift suggests the universe is expanding:

Most galaxies seem to be moving away from each other → Evidence for this:

• Different elements absorb different frequencies(or wavelengths) of light

• Each element produces a specific pattern of dark lines at the frequencies that it absorbs in the visible part of the EM spectrum.

• When we look at light from distant galaxies we see the same patterns but at slightly lower frequencies than they should be.

• There’s an observed increase in the wavelength of light coming from the galaxies + the patterns have been shifted towards the Red end of the spectrum.

• Measurements of the red-shift suggest that all the distant galaxies are moving away from us very quickly

• More distant galaxies have greater red-shifts than nearer ones - they show a bigger observed increase in wavelength

• More distant galaxies are moving away fasted thsn nearer ones → provides evidence that the whole universe is expanding

There’s microwave radiation from all directions:

• Scientists have detected low frequency electromagnetic radiation coming from all parts of the universe → same temperature everywhere (10³² °C) → wavelength depends on temperature →CMBR

• Radiation is mainly in the microwave part of EM spectrum - it’s known as cosmic microwave background radiation

• According to the Big Bang theory model, the CMB radiation is the leftover energy of initial explosion

CMB is strong evidence for the Big Bang

• Red Shift can be explained by both the Steady State and Big Bang theories → in both models, objects are moving away from the observer as the universe expands

• However, CMB only supports the Big Bang model as it shows the universe had a beginning

Doppler Effect → supports Red Shift theory

Apparent change in wavelength of a wave due to the relative motion between a source and observer

How does the doppler effect work?

• If object is moving away from object → wave stretched → sound is lower pitched + light appears more red

• If object is moving towards object → wave squashed → sound is higher pitched + light appears more blue

Why can’t change in colour be seen on Earth?

Because no wave compares to the speed of light (3 × 10⁸ m/s)

Hubble's Graph is evidence for the univers starting 13.7 billion years ago

• Speed = distance/ time

• Hubble's constant → 70km/s/Mpc