10th April 2011 Dark Matter

Concerning the total energy and mass in the universe, about 73% is dark energy.  Of the remaining 27%,  about 4% is normal matter - all of periodic table, gas, dust, the planets and stars. Most of it is hydrogen.  The rest, that is 23%, is dark matter.  It's called dark as it doesn't emit or absorb electromagnetic radiation. It doesn't shine nor cast a shadow.  It is called matter because it has mass.  The only way we know it's about is because it interacts through gravity.

The first observation was made by Fritz Zwicky. He was looking at the speed of rotation of orbits.  Planets close to the sun feel a strong pull of gravity so Mercury is zipping around but Neptune doesn't feel such a pull.  You'd expect there to be a maximum speed and then to slow down but it reaches a maximum level and stays there so there must be more mass than we can see.  It causes distortions which can be detected by Hubble and mapped.  This shows galaxies embedded in dark matter.

There are alternative theories to explain the apparent gravity problems which do not require the existence of dark matter.

http://www.sixtysymbols.com/videos/darkmatter.htm
http://www.youtube.com/watch?v=iDRqfX4L2tI&

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.