The atomic clock is the most precise timekeeping instrument ever invented. In fact, the second is officially defined as 9,192,631,770 vibrations of the radiation emitted by cesium-133 atoms in a specific arrangement. The International time Bureau in Paris uses the readings of atomic clocks to determine the official time.

The same thing happens with light, with greater frequencies corresponding to different colors rather than higher pitches. The spectrum of light consists of red, orange, yellow, green, blue, indigo, and violet, with violet having the highest frequency (and thus, highest energy), and red having the lowest. Of course, since light travels extremely fast, you would not notice the color change if you were looking at a police car. You might, however, if you were looking at stars.

As stars move away from Earth, the frequency of their light decreases, shifting the light towards the red end of the spectrum. This is called "red shift." As a star moves towards Earth, its light is shifted towards the blue end of the spectrum. This is called "blue shift." In general, "red shift" and "blue shift" describe any decrease or increase of frequency and energy. Very strong gravity can also cause radiation to be red shifted. This is because it uses up energy for the radiation to escape the gravitational field, and since the velocity cannot change, the energy must be given up through decreased frequency.

However, because sound waves travel through air, the extent of the doppler shift depends on whever the source of sound is moving towards the listener or the listener is moving towards the source of the sound. If light moved through an ether, then it would also depend on whether the listener or the source of sound was moving. But in Einstein's relativistic universe, it cannot make a difference which is moving. Both frames of reference are equally valid. All that matters is the relative speeds of the two objects.

His first major study concerned the Saturn's rings, showing that they could only remain stable if they consisted of fine solid particles. Maxwell next considered molecules of gases in rapid motion, formulating the Maxwell-Boltzmann kinetic theory of gases in 1866. His theory showed that only the movement of molecules produced heat. He treated the flow of heat statistically, with high-temperature molecules having a high tendency to move towards low-temperature molecules.

Maxwell's most important scientific achievement was his expansion of Michael Faraday's theories of electricity and magnetic lines of force. Maxwell's simple, elegant equations described the behavior and interrelatedness of electric and magnetic fields, showing that an oscillating electric charge produces an electromagnetic field. Scientists regard Maxwell's equations as one of the greatest achievements in 19th century physics.

After calculating the speed of an electromagnetic field and comparing it to the speed of light, he concluded that light an electromagnetic phenomenon, with visible light comprising only a small part of the electromagnetic spectrum.

Maxwell used the luminous ether to explain that electromagnetic radiation did not involve action at a distance, proposing that the ether carried electromagnetic waves and magnetic lines of force were disturbances of the ether. Albert Einstein's Special Theory of Relativity showed that the ether was unnecessary, but Maxwell's equations did not depend on the ether and are still valid.

This burning of increasingly heavy elements continues until silicon is converted into iron. The creation of elements heavier than hydrogen requires an input of energy, and only occurs in the high-energy reactions that happen in the supernovae of very massive stars.

General Relativity predicts that the wavelength of radiation passing through a gravitational field will be shifted towards redder regions of the spectrum. It is more difficult for a photon to escape a gravitational field than to travel in empty space, but unlike people, photons cannot lose energy by slowing down. As it struggles out of a gravitational field, a photon loses energy by decreasing its frequency, and thus reddening in color. Experiments have measured red shift in the

Accelerational red shift is similar to gravitational red shift (as they should be, since relativity stated the equality of the two). When an object accelerates away from you, the wavelengths get stretched longer and longer, making the radiation redder.