GCSE AQA Physics P1b 7.1-7.3 The Origins of the Universe


P1b 7.1 - The Expanding Universe

Red shift occurs due to light waves from distant stars or galaxies becoming stretched and therefore shifted to the red end of the light spectrum.

Blue shift is the opposite process- light rays become squashed and so shift to the blue end of the light spectrum.

The faster a galaxy is moving, the greater the shift.

Red and blue shift are examples of 'The Doppler Effect' (discovered by Christian Doppler, 1842), an instance in which the wavelengths and frequency are changed due to the motion of the source to or from the observer.

Edwin Hubble found that a) distant galaxies are moving away from us and b) the speed of recession of a galaxy is proportional to its distance from us.

Therefore, it is believed that the WHOLE UNIVERSE IS EXPANDING.

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P1b 7.2 The Big Bang

'The Big Bang Theory' states that:

  • The Universe is expanding due to it exploding suddenly from a singularity
  • Space, time, and matter were created in the Big Bang

Cosmic Microwave Background Radiation (CMBR) is evidence for the Big Bang. It consists of high-energy gamma radiation created just after the Big Bang, and has been travelling through space since then.

As the universe expanded, the wavelength of the gamma waves was stretched until it eventually became microwave radiation, which has been mapped using microwave detectors both on Earth and in space.

The future of the universe is not currently known. Some believe that it will continue to expand forever until all stars die out (The Big Yawn), whereas others believe that if the density of the universe is a certain amount, it will stop expanding and go into reverse (The Big Crunch).


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P1b 7.3 Looking into Space

Unexpected objects we can see in the night sky include: 'shooting stars', comets, and supernovae.

Telescopes are used to observe the night sky. Because they are larger than eyes, telescopes can take in more light, making stars seem brighter.

Telescopes with magnification also make night sky objects appear larger.

However, the Earth's atmosphere can make images of space fuzzy.

Radio telescopes are used to map sources of radio waves (e.g. distant galaxies). Radiowaves, visible light, and some UV radiation can reach the ground.

The bigger the radio telescope, the greater area and further distance it can map.

Satellites carry detectors of EM waves that can't penetrate Earth's atmosphere. These types of detectors have discovered: massive gamma radiation-emitting stars, planets beyond the solar system giving off infrared radiation, and blackholes that can destroy stars at the centre of galaxies.

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