299,792,458 m/s - The Speed Of Light

Fact of the day: 299,792,458 metres per second - the speed of light in a vacuum.

The photon is the most abundant particle in the universe.
The photon is the particle that carries the electromagnetic force, or light.

The speed of light defines all metric units of distance, as light travels a metre in 1/299,792,458th of a second. All wireless telecommunications systems communicate using electromagnetism. Electromagnetism powers all sources of electricity for the power grid. Electromagnetism allows us to see.

We rely on this force so heavily, but we don't actually 100% know what it is. In some situations it behaves like a particle (e.g. the photoelectric effect), and in some it behaves like a wave (e.g. the double slit experiment). This effect of wave/particle also effects all matter, but is not noticeable at very large scales (except with electromagnetism). This is called the wave particle duality.
Until light is observed, it is considered as both. When it is measured, it either adopts the particle or wave form. When it does this, we say that the wave function has collapsed.

The reason that light is able to travel so quickly, even set the universal speed limit (explained by special relativity) is because in a wave of light there are two parts, the electric wave, and the magnetic wave. These both reinforce each other.

The type of science that studies how light interacts with other particles is called Quantum Electrodynamics, or QED. This area was greatly pioneered by Richard Feynman, who developed Feynman diagrams.


In this Feynman diagram (above) an electron (e-) and a positron (e+) annihilate, producing a photon (the blue line) which then decays into a quark (q) and an antiquark (q). The antiquark then radiates a gluon (g).

Electromagnetic waves have different energy levels. The higher the energy level, the shorter the wavelength or frequency. Here are the different parts of the electromagnetic spectrum from lowest energy to the highest:

• Radio Waves - Used by most telecommunications networks, hence the radio channels. Radio waves       can range in size from over 100Km long at (3 kHz) to 1m (at 300 MHz).

• Microwaves - Used by some telecommunications networks, and the microwave kitchen appliance to   heat the water molecules in food. Microwaves have 1m (at 300 MHz) wavelengths to 1mm (at 300 GHz).

• Infrared Radiation - This is basically heat. You feel the warmth of the sun because of the infrared radiation it produces. The size of the waves can range from 1mm (at 300 GHz) to 700nm (at 430 THz).

• Visible Light - This is a very small window of the electromagnetic spectrum that our eyes have become sensitive to. The lowest energy visible light is the red colour, and the highest is the violet colour. All of the ranges of colour of visible light create white light. The size of these waves ranges from 700nm (at 430 THz) to 390nm (at 770 THz).

• Ultraviolet Radiation - This type of light is part of the visible spectrum, but only a fraction of it is. Ultraviolet radiation can be used to purify water as it harms bacteria, because it is a very high energy light. The wavelengths range from 400nm (at 750 THz) to 10nm (at 30 PHz).

• X-Ray Radiation - This high energy light is used for medical purposes to identify broken bones, as it is opaque to bone. This light is considered to be dangerous if not controlled, as it is very high energy light. The size of the wavelengths range from 10nm (at 30 PHz) to 0.1nm (at 30 EHz).

• Gamma Radiation - This radiation is produced by the radioactive decay of atomic nuclei. This is radiation with the highest energy observed. All forms of this radiation are highly dangerous. The wavelengths are very small, below 10pm (at 10 EHz) and are smaller than the diameter of atoms.


(above) Visible light being bent by a prism

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