1st April 2011 Big Bang Theory

 Yesterday's Starts with a Bang is about the Big Bang Theory. It ties together the stuff I've been reading about the alpha beta gamma paper, red shift and blue shift and some theories about the universe.  These are some possible explanations for the observed red shift.

• light gets tired, and simply loses energy over time,
• the Universe oscillates, contracting and expanding over time, and we are simply close to an expanding portion of it,
• physical constants, such as the speed of light, or the gravitational constant, have changed over time,
• the Universe grows steadily and evenly, and creates new matter as it expands, 
• the Universe is rotating rapidly, and that the galaxies that are moving away from us more quickly also have large -- unobservable -- translational motions
• the Universe was expanding, and that the expansion rate was faster in the past! As the Universe moves forwards in time, it cools, expands, and slows down.

The latter leads to the following prediction:

• In the beginning it was so hot the neutrons, protons and electrons couldn't stick together.
• It cooled some and the protons and neutrons got together to form deuterium, helium-3 and helium-4. 

When the cosmic microwave background was discovered, it could be explained as the left-over glow from the Big Bang, supporting this idea.

26nd March 2011 - Alpha Beta Gamma Paper & Neutrinos

Alpha Beta Gamma  Paper (1948) -  In the first 3 minutes after the Big Bang,  protons and neutrons  bumped into each other they stuck together. There were about 7 protons to each neutron.  When 1 neutron and 1 proton stuck together they formed the nucleus of a Deuterium atom. It was too hot for the electrons to stick to make it an atom. If two of these Deuterium atoms stuck together, they formed an alpha particle, the nucleus of a Helium-4 atom.

By 17 minutes, all of the neutrons had bound themselves into Helium nucleii.

Not much happened until about 350k years when the electrons had cooled enough to join the nucleii to form Helium atoms.  Alpher came up with the idea that 75% of the universe is made of hydrogen, and 25% of Helium, by weight.   This is correct for interstellar space. It is supporting evidence for the Big Bang Theory.

The other, heavier elements are made in the centre of stars.


Neutrinos   - They have very little mass, if any, no electrical charge and they pass through pretty much everything.  It's been calculated that it would take 4 light years of lead to stop them! They are abundant. They are produced in the sun in fusion.  It starts with four Hydrogen nucleii which are basically protons. They want to form a Helium so two protons get converted to two neutrons.  When this happens, a positron and a neutrino are emitted. The neutrino shoots out of the sun and heads towards us.

Neutrinos are good candidates for dark matter.

There are  50 x 10^12 neutrinos passing through our bodies every second.

There are three types of neutrinos, electron, muon and tau These types are called flavours.  Neutrinos can change flavour which means they must have mass.

They were originally detected deep underground in carbon tetrachloride.  Sometimes they bump into a chlorine atom and transmute that chlorine atom into an argon atom.  You've then got to find that argon atom.  Talk about a needle in a haystack!

Nowadays, heavy water is used and the neutrinos are detected as light.  The reason it's deep underground is because cosmic rays will also produce the light reaction.