"The light & heat which appear to have come from the sun have never left the sun"
Bzzzt...wrong.
E=MC2
The sun is gradually depleating in both energy and mass...simple physics tells us it must therefore be going somewhere?
In actual fact, the enregy is being expended by driving the frequency and photon transfer that is being emited, as electromagntic energy (light), creating both the waves that light "travels" on as well as the resultant heat which results from the destruction of mass in the genration thereof.
The fact is that light, which is really just a term for the specific type of electromagnetic energy (photons), that travels at a specific frequency range (waves), in reality is a combination of both a transfer of enrgy via a static host which supports waves and particles in motion. Light is entirely different to the waves we might see in the ocean, which in essence are a simpe energy transfer via a host medium (water in this case), from the source to the point where it is converted back to it's original form (light and heat)...or indeed, mass.
Uising your argument that nothing actually leaves the source, I suggest you tell that to the the 100's of thousands killed by the Tsunami waves that terminated on their beaches. What they "recieved" was the enregy that was transfered from the source and reconstructed on their beaches.
In a similar vien, light can be viewed as the energy that travels from the source, but in it's case, accompanied by a photon "package" that washes up on the shore of the first non-host material (for it's waves) that it encounters...where it is converted back to it's original form (both light and heat - ie, energy).
This particle-like behavior is not restricted to the visible-light portion of the electromagnetic radiation spectrum...infrared rays, radio waves, ultraviolet rays, X rays, gamma rays and indeed visible light all consist of photons, each of which contains a particular amount of energy that depends on the wavelength.
