Our ancient ancestors very astutely noted that the World is composed of earth, water, wind and fire. They were describing three states of physical matter: solid, liquid and gas, and the electromagnetic force, which is the source of light, fire, electricity and magnetism. In 1879 Sir William Crookes presented us with a fourth state of matter which is a field of charged ions and free electrons. Plasma is the very stuff that stars are made of and is the most abundant form of matter in the World. Used as a medium for containing unstable and highly charged particles, it's recognized by most for the striking Borealis effects created when Solar winds pass around the Earth's magnetic field.
In 1927 Georges Lemaitre, a Belgian priest and astronomer, was the first to propose that the World came into existence from a single primordial atom with a "big bang" and has been expanding ever since. In 1929 Edwin Hubble proved that the Universe is expanding and successfully calculated the rate of that expansion. Using Hubble's Constant, we now know that the World has been in existence for 13.7 billion years, 96% of its content is composed of nothing but Space, and current math and science will take us back to within about 10 seconds after the The Event. To understand conditions prior to that moment in Time requires us to consider laws based on uncertainty, which suggest that, during that incredibly brief inflationary period, the four fundamental forces of nature: the Electromagnetic, the Weak and Strong Nuclear Forces, and gravity, were unified.
The Cosmic Background Radiation we detect is coming at us from all directions, not from any one point or position in space; so imagine our universe as an expanding bubble upon which all of its matter is positioned at various points on its surface. Get Adobe Flash player
We currently have a fairly accurate understanding of what's transpired since that moment. We know, for instance, that all of the known matter in the universe only makes up about 4% of its mass, and that not only has the universe always been expanding, but its rate of expansion has accelerated substantially over the last 4 billion years or so. These conditions strongly imply the existence of other form(s) of unknown matter.
Get Adobe Flash player Stars orbiting the center of a galaxy should obey Kepler's Laws of Orbital Motion, which state that the farther an object is from a gravitational mass, the slower its orbital speed should be. However, in the 1970s astronomer Vera Rubin discovered that the outer arms of galaxies are rotating at about the same speed as stars closer to the center.

This observation was strong evidence for an unseen mass of dark matter which would contribute the additional gravity necessary for preventing galaxies from flying apart.
In Isaac Newton's time naturalists assumed that space was composed of an "aether" through which light, sound and gravity propagated as waves. In 1887 an experiment conducted by Michelson and Morley allegedly proved the nonexistence of this medium and his results were later confirmed by Albert Einstein with his theory of relativity. However, in 2012 we confirmed the existence of the Higgs Boson, which provides mass to otherwise mass-less particles like photons, and explains how light is affected by gravity. This "dark matter" is said to occupy about 22% of all space and provides a force that has kept the universe expanding at a smooth and steady rate. The remaining 74% of the mass is believed to be in the form of an, as yet, undetected form of matter called Dark Energy, which is simultaneously pushing everything apart.

Might these two exotic forms of matter together constitute that aether?
The Standard Model of Particle Physics incorporates 2 types of fundemental particles: Fermions and Bosons. Quarks and Leptons make up the Fermions, which is what all Matter is composed of. Solid, liquid or gas; animal, mineral, vegetable or plasma, from galaxies and stars to bacteria and viruses. Bosons are the "Force Carriers which produce light, heat, electricity and magnetism. These particles are unbelievably small: If the orbital radius of an atom was the size of a football field, the nucleus would be the size of a grain of salt placed at the center of the 50 yard line, with its attending electrons the size of dust motes orbiting it from the stadium parking lot! The newly discovered Higgs Boson adds mass to massless particles and is thought to be a key component of Dark Matter, which makes up 23% of the universe's known mass. Only 4% is attributed to people and stars and the remaining 73% icurrently believed to be Dark Energy.
Electrons surrounding the nucleus of an atom take any number of orbital planes through angular momentum by which we only assume to be eliptical paths. Since we can't determine a particle's position and its momentum simultaneously, we have no proof that electrons actually "orbit" their nuclei. With the exception of plasma, hydrogen is the most abundant form of matter in the universe. Containing just one electron, Niels Bohr showed us that that electron is restricted to 4 orbital shells that are clearly quantized. The electron moves to a higher orbit when absorbing energy and drops to a lower orbit when emitting energy.
Click anywhere on the hydrogen atom below:
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Professor Bohr successfully calculated the size of the atom and because of his pioneering work we now know not only why electrons don't spiral into their nuclei, but that energy and angular monentum are quantized in all atoms. It should be noted, however, that this has never been absolutely confirmed for atoms containing more than 1 electron.

Helium is the second simplest form of true matter there is, containing just 2 Electrons, 2 Protons and 2 Neutrons. Protons are comprised of 2 Up Quarks and 1 Down Quark, while 1 Up Quark and 2 Down Quarks make a Neutron. Click on the nucleus of the helium atom:
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Photons are Elementary partices of the Boson family, which are spin-1 Force Carrier particles. In the case of light this means that its spin axis is parallel to its direction of travel, an effect most commonly observed in polarized glass. As an Elementary particle, Photons cannot decay on their own. Instead they transfer and absorb energy when interacting with other particles. They are known to be electrically neutral and of the rare class of particles considered to be identical to their Supersymetric (anti) particle, the antiphoton.

Photon absorption and emission is the primary method by which atoms interact with each other, and photons are theorized to also act as "messenger" particles.
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James Clerk Maxwell pioneered the electromagnetic theory of light.

The Interference pattern Photons make on a detection screen demonstrate the wave-like property of light, while at the same time are recorded as randomly scattered hits of a particle-like nature.

Albert Einstein's photoelectric effect clearly demonstrates that photons have particle-like interactions with other electrons and other elementary particles, and while they can be treated and manipulated as particles, they also express attributes such as frequency, wavelength, amplitude and other properties associated with wave mechanics.
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