5. What is the universe made of?
All the world is made of atoms
Atoms are made of protons neutrons and electrons
Muons and Taus
Protons neutrons and mesons are made of quarks
Forces and their boson particles
Gravity, gravitons and black holes
electricity and magnetism, photons
strong nuclear, gluons
weak nuclear, W and Z bosons
5. What is the Universe made of?
The universe of science is made of particles and forces.
The atomic theory and the discovery of atoms. Ricahrd Feynman said that if he knew all scientific knowledge was about to be lost and he could pass just one sentence on it would be “ all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.”
In the 1800’s Chemists used the hypothesis of atoms to explain all chemical reactions. However atoms were so small they could not be detected, so in the view of Ernst Mach and other scientists they remained hypothetical particles as far as experimental physics was concerned. In 1905 Einstein showed how Brownian motion could be used to measure the size of atoms. Perrin did the measurement and received the Nobel prize. Atoms became particles.
Ernst Rutherford discovered the atomic nucleus in 1911. This led to the discovery of protons neutrons and electrons.
Protons and neutrons are both referred to as nucleons, they were found to be made of 3 quarks each in the mid 1960s. The quarks had three properties, which were named color charge. Since a group of all three different color charges experienced no direct nuclear force. The color charges are named red, green and blue. But Have nothing to do with color of light. Quarks also have a property named flavor, there are 6 flavors and the flavors are sensed by the weak nuclear force.
Electrons are leptons and have no substructure down to 10^-20 m. They are called leptons. There are two other leptons, the muon and the tau.
Associated with each of the leptons there is a neutrino. A particle with low mass, no charge, no color charge. A neutrino can go through a light-year of lead.
Antimatter: Every particle has an antiparticle with opposite charges, when a particle collides with its antiparticle they both annihilate and turn into energy.
A force is a push or a pull.
The forces of nature include:
Gravity which up to now has always been seen to be attractive, and which is proportional to one property of objects, their mass. Mass also is related to inertia, the resistance of a body to acceleration when a force is applied, and this explains why under gravity alone all objects fall at the same acceleration. Galileo discovered this in the 1600s replacing the ideas of Aristotle that more massive objects fell with more acceleration. Newton in the Principia made numerical the law of universal gravitation. The gravity force between to point masses is proportional to the mass of each and inversely proportional to the distance between the masses. He also invented calculus which allowed the force between non-point masses to be predicted using integral calculus.
(An experiment is being conducted at CERN to determine if antimatter is attracted or repelled by gravity.)
In the 1800s chemists had the law of conservation of mass in chemical reactions. Physicists had the law of conservation of energy.
Einstein discovered that mass and energy are related E = mc^2
Electrostatic force can be attractive or repulsive. It acts on a property called electric charge. Benjamin Franklin in the 1700’s found that there were two types of electric charge, he named them plus and minus, because when they combined in equal quantities their electric effects cancel.(at large distances) .
Magnetism acts between properties f some materials called north and south poles. The ancient Greeks knew about magnetic forces. The Chinese discovered the compass about 1000 AD. In the 1600’s William Gilbert discovered that compasses worked because the earth was a magnet. In the 1800’s magnetism was found to be caused by the motion of electric charges. In 1905 Einstein showed that magnetism was just electricity viewed in a moving frame of reference. This was the first example of unifying two forces under one mathematical description, and so electricity and magnetism became electromagnetism. (Einstein spent the rest of hiis career trying to unite electromagnetic and gravitational forces, he was not able to do this. But modern string theory might achieve this.
Strong Nuclear Force
In the early 1900s scientists discovered the atomic nucleus, made of protons and neutrons. Protons repelled electrically but were held together by the stronger attractive nuclear force. Neutrons also attracted other neutrons as well as protons to make up the atomic nucleus.
The quarks which make up protons and neutrons attract each other via the strong nuclear force. A force that grows stronger as the distance between the particles increases. The strong nuclear force is carried by a particle known as a gluon. The strong nuclear force carries over from one proton or neutron to neighboring nucleons. Thus binding together nuclei.
The weak nuclear force is weaker than the strong nuclear force and even weaker than the electromagnetic force. It is stronger than gravity. The weak nuclear force is carried by vector bosons, named the W and the Z. It causes radioactive decay as a neutron decays into a proton and an electron.
In relativity the electric force becomes the magnetic force by simply moving from one frame of reference to another. Thus relativity showed how electricity and magnetism were actually related under one force law, electromagnetism. This was the first unification of forces.
In the early 1970s the weak nuclear force and the electromagnetic force were shown to be describable in the same theory, and so were unified into the electro-weak force.
Today scientists are trying to unify all the forces of nture using string theory.
Scientific Explorations with Paul Doherty
18 October 2011