Edexcel IGCSE Physics - Cosmology

how has the universe evolved over time?

it has expanded from an infinitely dense and extremely hot point; it is still expanding and cooling

what is the main theory for how the universe evolved?

big bang theory

what are the 2 main pieces of evidence that support the big bang theory?

• cosmic microwave background radiation

• red shift of galaxies

what happens if a wave source moves relative to an observer?

there is a change in the observed frequency and wavelength

what is the change in observed frequency and wavelength called?

the doppler effect

what colour of light has the lowest frequency?

red

what colour of light has the highest wavelength?

red

describe the doppler effect in terms of light

• if a light source is moving away from you, the waves behind will spread out and the observed wavelength will increase, decreasing the frequency meaning that the light is shifted to the red end of the spectrum

• the opposite will happen if a light source is moving towards you

how is the doppler effect of light seen in the universe (not galaxies)?

the light from distant stars is red-shifted - the light has a longer observed wavelength than we would expect stars to emit - only happens if the stars are moving away from earth

what is the doppler effect for galaxies generally called?

red shift of galaxies

what are absorption spectra?

• different elements absorb different frequencies/wavelengths of light

• when a light is passed through a sample of an element, dark lines appear on the spectrum where the wavelengths have been absorbed

what is the red-shift of galaxies?

• when we look at light from distant galaxies (compared to light from the sun/another galaxy), they have the same patterns of lines on their absorption spectra

• however, these patterns are at lower frequencies/higher wavelengths - they have been shifted towards the red end of the spectrum

why does red-shift of galaxies provide evidence for the big bang?

• more distant galaxies have a greater red shift than nearer galaxies - they have a bigger observed increase in wavelength

• this shows that more distant galaxies are moving away faster than nearer ones

• this suggests that the whole universe is expanding

• this is present wherever you look - galaxies are moving away from each other as well

which model is commonly used to demonstrate red shift of galaxies?

a balloon and pompoms

what equation is used to calculate red shift?

what is cosmic microwave background radiation?

low frequency microwave radiation that is detected in all directions and comes from all parts of the universe in all directions

why is cosmic microwave background radiation evidence for the big bang?

• it suggests that the universe expanded from a single point

• this radiation has also dropped in frequency, suggesting that the universe has cooled