Home Discussion Forum What determines the speed of ratiation.. light .. sound .. etc?

What determines the speed of ratiation.. light .. sound .. etc?

We know that light (photons) has a specific velocity, so does sound waves, and other forms of radiation like X Rays,, gamma rays, etc,, What do you think decides these velocities? .. All of the above are some form of radiation or transmission of energy in some form or another, so at the quantum level (as far as I know) they are not composed of particles that vary significantly in mass..
This being the case, what factor decides that light should have the higher velocity than others?… if this is known, is it possible to engineer a form of radiation that exceeds the speed of light?


  1. My physics teacher told me once that the speed of light, which is the speed limit for all EM-radiation is determined by the permeability of free space…
    that is, that speed is the speed that the electric/magnetic fields can collapse and reform (i.e. wave crests / throughs)…and as they collapse and reform, they travel in all directions (from the radiating source) at the speed we know as 3 x 10^8 m/sec
    And so, this is the theoritical limit for how fast something can propogate through space (vacuum)
    Sound on the other hand is NOT EM radiation. It is simply air pressure (longitudal) waves. Speed depends on temperature, humidity, and air pressure, etc.
    EM radiation does not travel the same speed in something that is not a vacuum. The speed traveling through earth’s atmosphere is *slightly* slower than possible in space.

  2. Kasturi is correct, except that it’s both the permeability -and- the permitivity of free space that determine how quickly fields can form and collapse.

  3. The speed of waves is determined by the type of wave and the properties of the medium supporting the wave. For electromagnetic waves (which include heat, light, radio, x-ray and gamma rays), these properties are the electrical permittivity and permeability of the medium, because those waves are the interaction of electric and magnetic fields.
    Sound waves are pressure waves in a medium, so different properties (mainly density) are involved.
    In some cases, more than one kind of wave can travel through a medium, and they will have different velocities. This is the case for seismic waves; earthquakes produce a compression wave and a transverse wave. The compression wave travels faster, but the transverse wave causes the damage. At a distance from the center of the quake, the compression wave will arrive first, and it can be detected. This can be used to give a few second warning of the earthquake coming.
    To give a definitive answer, the mathematic equation of the wave must be derived (it’s called the wave equation). The solution of that equation will give the wave velocity.


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