MULT10011 Lecture Notes - Lecture 28: Big Bang, Photon, Cosmic Ray
15 Jun 2018
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L.E.U – Lecture 28
Forming elements
What is light?
• Can sometimes be considered to be a wave, and sometimes a particle
• Made of discrete entities – photons
o Photons have characteristics which are both wave- and particle-like
o Each photon has a wavelength and an energy
Building elements – fission/fusion
• Reactions that change elements are nuclear reactions
• Nuclear reactions only take place at very high density, pressure and temperature
• Where can you find these conditions?
o In the very early universe, a few seconds to minutes are the big bang
o In stars (ongoing)
Early universe
• Was a hot soup of photos ad atter
• At each point in time, as the universe expanded and cooled down, there was a
characteristic temperature for the photons and matter
o Corresponded to an energy for the photon
• Accordig to Eisteis theory of special relativity, ass ~ eergy → E = mc2
o Means a photon of sufficient energy could form a proton (for e.g.)
o All electrons, protons and neutrons formed in this way in early universe
o Then combined to form hydrogen, helium and a bit of the more massive ones
• As the universe expanded, it became too cold and rarefied for nuclear reactions to
take place
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