A small primer on optical attributes of Light.
( — largely edited, 18-19 January 2014, originally from; Wednesday, March 27, 2013 at 3:58 pm UTC + 05:30 )
If you ever seem, to be caught up between: they say light always moves at the same speed-c, they keep on harping, why then, its energy so different; we have light of various energy and frequencies. One that are harmful, like x-ray or ultraviolet and one that are quite soft on us all. The answer is there are two kinds of speed, when it comes to vector emissions like light, one speed is on the plane of polarization, giving us the energy or frequency or intensity of light waves, and the other, the speed perpendicular to that plane, that is; the speed at which energy of light is transmitted across the galaxy, its this latter speed, which is slated to be known as speed-of-light (instead of, speed of light’s energy transmission vs speed that determines the energy value of light transmission) and always a constant known as c, whose value is unchanged, as long as a single quantum of light is considered and in vacuum.
Note that vector emission means there are 3 dimensions, in which this wave is created or propagated, light wave, its a plane + a perpendicular dimension to that plane. The plane is called plane of polarization which always contains two fields, Electric and Magnetic field, and the perpendicular dimension is the direction in which the energy of the light wave is propagated, therefore, gives the light-wave-speed; which are again of two definition, the physical or actual speed known as group velocity, and the virtual, conceptual speed of each wave train, known as phase velocity. This definition of phase and group velocity are always to occur; for any kind of waves and not just light wave. So, the light-wave-group-velocity (for a single quantum-of-light, called photon) is always c = 2.99 x 10 (8) meters/second, in vacuum.
Note also that, its this 3 dimensional or vector nature of emission of light wave, which is the reason why, when the wave is quantized, to form quantum-of-light, photons, the photon is called as a vector particle, or in other words it has spin 1. A scalar particle would be a quantum of a wave or field of wave (or wave-of-field) whose spin would be 0, and only 1 dimension would be associated with the particle’s emission. Light, therefore, has 3 directions, in which its wave-function needs to be described, but for such spin 0 particles, the wave-function is uni-dimensional. Also there would be what are called tensor particles, because the wave functions are to be defined up the notch, in more than 3 vector dimensions.
Now remember that all particles have been defined only in two ways, called Bosons and Fermions. The Bosons are what are spin 0, spin 1, spin 2, spin 3 …. (integral spin) particles. The Fermions are what are spin 1/2, spin 3/2, spin 5/2, spin 7/2 (half integral spin) particles, in principle. Thus the light-wave-quantum; photon is a Boson. Its for such a reason Higgs Particle is called a Boson, the type of particle, when they occur in a large statistical sample, called an ensemble of particles, obey a certain rule of distribution, which was established by Bose, S.N. and Einstein, Albert, known as a Bose-Einstein Statistics. Therefore any particle with spin 0, spin 1, spin 2, spin 3 …. (integral spin) would be called a Boson as per the rule of distribution established by Bose and Einstein, and its not a particle physics discovery, its a discovery of Quantum Mechanics.
(its a discovery of Quantum Mechanics; new or modern mechanics rather, of the 1930s, by which Particle Physics was not even in its metamorphosis, what would be the spin of a penta-quark? Find that and argue why no one cries foul when a penta quark discovery is made.)
Light is wave; an undulation of magnetic field B, H and electric field E, D. These fields are two types of fields, in classical view, therefore forming a plane, often called a plane of polarization, as mentioned above. Then light is the fact, that, while these two fields are rotating, in the plane; the energy is transmitted along the perpendicular to the plane. Hence on sun’s surface the electric fields and magnetic fields are “rotating” but the sun’s light energy reaches us, because the ripples of disturbances, these two fields create, in the space adjacent to them, gradually reaches us, in 8 minutes this disturbance reaches from sun’s surface to us earthlings.
I did a off-the-top calculation, from 8 minutes, how far a light train would move, at 2.99 x 10 (8) meters/second and I see that its 143.52 million kms. Then, we are on earth, 143.52 million kms (or 1435.2 lakh kms) away from Sun’s surface from where a light train was assumed to set on for earth. Note that if we change the time of flight of light train, or speed of train of light, the distance would change.
We often forget that; there are 2 kinds of speeds. The linear speed and the angular speed. The angular speed is not defined, by distance, but angle which is why its a properness (in the proper-frame?) and same as, the frequency or rotation in a PLANE, that does not move. eg the sun’s surface, does not move; when light is exuberant.
Light comes out perpendicular, to that unmoving surface. A reason why we say Light has a plane of polarization and light moves perpendicular to that plane. But the surface has the angles (of these fields), which keep on rotating, to give us angular deflections. The rate, at which these angle move, is the frequency of light, where as, the rate at which the distance is covered, perpendicular to the surface, surface that does not move, is the speed or speed of light.
Which is why due to intensity, we see the sun, to be; a circular flame. — Because frequency is so high, that, the angles are rotating really fast and we see a circle on the face of the sun. That is light is coming from all angular patches on any circle on Sun’s surface, rather than just a thin line, as it seems to be the case with a star, with a star, the light from other angles has died out, in a small interval of time. The stars, that are too far away, they twinkle, because these rotation on its face are slow. The frequency of light is small because; the energy or intensity is low. So you see twinkles. But light is still moving at the same speed towards us.
It takes 4.5 years from some stars, while taking 8 minutes from sun, both at the same speed. But with sun, the face of the sun, or angles on face of sun are rotating really fast. That rotation gives us the energy and momentum but the speed at which they all move, is still c.
It seems its the same article as this one.