Module 8 – From the universe to the atom Notes

Resource Description

Module 8 – From the universe to the atom Notes by R.C

Origins of the Elements
Inquiry question: What evidence is there for the origins of the elements?

● Investigate the processes that led to the transformation of radiation into matter that followed the ‘Big Bang’
Big Bang ≈ 14 billion years ago
An incomprehensible amount of energy was released during the big bang. This universe was pure radiation. Too hot for any matter to exist, however, as it expanded it cooled, and radiation ‘condensed’ to form matter. E = mc → huge amounts of energy required 2 to form small amounts of matter.
As matter appeared, the universe cooled more, which produced more matter… and so on. This period of rapid expansion is known as inflation. BUT as radiation was turning into matter, it was also turning into antimatter (opposite).

Example:
Matter
Electron = negative
Both have the same mass and behave the same way

Antimatter
Positron = positive
Both have the same mass and behave the same way

When matter and antimatter collide we get mutual annihilation and energy is released.
e − + e + → γ
Electron + Positron → gamma radiation
This occurred extensively in the early universe but eventually we ended up with more matter than antimatter.

The first particles were the fundamental particles → the leptons, neutrons and quarks – and zero mass particles like gluons and photons. As the temperature fell further quarks started combining to form the hadrons, such as protons and neutrons, initially as isolated particles.

This explains the huge amounts of hydrogen in the universe.

● Investigate the evidence that led to the discovery of the expansion of the Universe by Hubble

Albert Einstein
Einstein’s theory of relativity which included a set of equations, stated many things including that the Universe is expanding. Einstein firmly believed that the Universe was constant and introduced a ‘cosmological’ constant into his equations to force them to give him the result he wanted – that the Universe was static

Aleksandr Friedmann
Friedmann set about solving Einstein’s equations without the constant. He found that they predicted either an expanding or contracting Universe, and so put forward two possible models:
1. In his closed Universe, time and space have a beginning and an end. They both began with a ‘big bang’ and will end when gravity stops the expansion of the Universe and pulls all the matter in it back together.
2. In his open Universe, the Universe began with the Big Bang and will continue to expand. Time and space have no end.

Edwin Hubble
In the early 1900s, the Andromeda nebula was thought to be part of the Milky Way galaxy (as all stars were thought to be). In 1924, while examining this nebula Hubble discovered a pulsating star – a variable whose brightness varied in a regular pattern (the spectra appeared shifted toward the ‘red’ end). He calculated its distance from Earth and found it to be 800 000 light years – much farther than the most distant star known to be in the Milky Way. He showed that Andromeda was a separate galaxy and went on to discover over 20 more galaxies. This was the first evidence scientists had that the Milky Way was a small part of a much larger Universe. In 1927 Hubble applied the idea of the Doppler shift to his newly discovered galaxies. Nearly all galaxies were moving away from us, no matter in which direction he looked. Hubble then went further to show that the further away galaxies are, the faster they are moving away.

● Analyse and apply Einstein’s description of the equivalence of energy and mass and relate this to the nuclear reactions that occur in stars

The work leading up to and including Einstein’s special theory of relativity also led to the concept that mass and energy are equivalent. We could consider mass as a solid form of energy, referred to as the rest energy of that mass, given by rest energy = m c0 2 Rest energy is not directly observable or useful as energy. We observe rest energy as pure energy only when the conversion is made, and this only occurs on earth when nuclear reactions take place. During nuclear reactions some of the mass of the reacting nuclides is converted into pure energy. This is the source of our nuclear energy.