Re: Is there an Upper limit for the EM waves in the Universe ?

Thank you Birol - excellant question, or make that questions. First "is 
their an upper limit for the EM spectrum"? That really puts the extreme 
in extremely high energy physics. First the energy of a photon, that is a 
quantum of the electromagnetic force, is proportional to the frequency 
(inversely proportional to the speed of light in a vacuum divided by 
wavelength). That proportionality constant is Plank's Constant. Here's 
the quantum quandry. We "know" of no upper limit to the energy of a 
photon. The upper end of the EM spectrum (higher frequency implies larger 
energy). But larger energy also means shorter wavelength. Quantum theory 
is summed up in the Standard Model (SM). The SM does an excellant job at 
explaining the quantum world. But it does not include one of the key 
forces of nature - gravity. Logically, it seems reasonable to me to 
assume a finite limit to top end of the EM spectrum. For starters, 
something must provide the energy to reach that level, and since mass and 
energy must be conserved, the maximum energy of a photon cannot exceed 
the total mass/energy of the universe. Also high energy photons can 
interact with the vacuum resulting in particle - antiparticle pairs. At 
some point the particles might reach sufficient mass so that their local 
energy density might self-gravitate into a micro-black hole (which should 
then explode in a burst of Hawking radiation, returning that energy to 
the universe). But we have no quantum theory of gravity. The closest is 
String theory (M-theory, which is a variant of superstring theory to be a 
bit more precise). But this theory is still in its infancy. But under 
string theory, one could envision a limit set by the fundamental unit of 
length, the Planck length since as energy increases, wavelength must 
decrease. Still this is poorly understood. The SM is giving some small 
evidence that it has some flaws. Plus it has the one glaring defect of 
only handling 3 of the 4 basic forces of nature.

Is there a border where Maxwell's equations might not apply? Maxwell's 
Equations are classical (not quantum mechanical) relativistic field 
equations for the EM field. But they have been extended to the quantum 
world as well, although the form looks a bit different. So the answer 
somewhat depends on what you mean "might not apply". In their purest 
sense, they would not apply if one was describing a quantum of the EM 
spectrum since James Maxwell had no notion of the quantum world when he 
penned these elegant equations in 1865. But given the quantum analog 
to his classical equations, they in fact hold for the EM spectrum. So I 
believe one would again have to reach a point where modern quantum 
mechanics would fail, as I described above.

Measurement limits? Good question! This depends on the inventiveness of 
the researcher in designing new experiments. In the field of extremely 
high energy research, the laboratory is increasingly becoming the 
universe. While we lack the technology to generate extremely energetic 
gamma rays here on earth, there are terrific factories for these particles 
in our universe. I believe the highest energy photons have been detected 
around 5000 GeV (5,000,000,000,000 electron volts). I suspect it can go 
higher by at least a couple orders of magnitude. 

As to your question about the Tesla Coils, I do not like to say "it 
absolutely won't work", but I seriously doubt it will work. Energy must 
be conserved. So it still must have the energy provided from some 
location. Sadly there is no free lunch.