davey2222

This thread has brought up an enigma for me. If photons are easily "visualisable" for very short wavelength rays like gamma and x-rays as packets of EM energy, how about radio waves whose wavelengths stretch for kilometers? How does it *fit* into a photon?

If the field involved is conservative then the answer is yes.

Actually radio waves (should mean its wavelengths) are large because its frequency is low and that makes its wavelength large (i.e. their product (frequency x wavelength) gives the speed of propagation of the radio wave)

That is why there is this thing called the wave-particle duality for the photon. Your question is easily answered when you consider the wave aspect of the photon and ignore the particle-uncertainty principle. The Heisenberg Uncertainty Principle is only significant at very small measurements and radio waves are not small.

The distance of action of gamma rays and radio waves are the same in a vacuum. It is easier to focus "short" waves such as gamma and micro waves compared to longer radio waves which just wraps around corners and bends. The physics concept is refraction. Try putting into your pool physical blocks of matter and continue to make waves of different wavelengths and observe how these waves move past the blocks. It is the same thing for the photons. Concerning the wave crests, I think you are measuring the distance between wave crests to determine the wavelength of the waves, you are not measuring the position of the photons (which would call the Heisenberg uncertainty principle into operation) so why does the wave want to collapse? Moving your giant sheet won't help the rest of the population, which is not moving relative to the nuclear detonation. The receding giant sheet may get a dose of radio waves but the stationary population will get their gamma rays. In my opinion there may be some confusion on your part concerning the energy of a photon in relation to its wavelength (or frequency). I call to your attention the photoelectric effect, where the intensity (i.e. amount of photons) of the light source does not affect the ejected electrons, only the wavelength (i.e. the energy of each photon emitted) of the light source does. In classical wave mechanics, the amplitude of the wave correlates to the energy of the wave. unfortunately I do not know how to offer a solution to the last part of you post, but you sure have an interesting question there tho. I was thinking of a solution from the Poynting Vector but.....

The answer to the change in frequency is the Doppler Shift. An example is the pitch of an approaching vehicle which has a higher frequency than when it is moving away from you. I am sure you can find illustrations showing this as this is an elementary physics problem. If you think in terms of waves instead of photons you can reduce the amount questions you have.

I think it is a logical fallacy to compare energy expenditure (i.e. work) between the two methods of observation. Try think about the 'problem' when it is applied to extra solar objects and you will quickly come to realise its logical fallacy. It is like comparing apples to oranges. But kudos to those who attempted to solve the problem directly. The more correct term, in my opinion, is efficiency. Using a telescope is more efficient compared to blasting off from planet Earth and going 'there' or anywhere in the universe for that matter. QED

I think if you move the bar magnet back and forth you are making changes in the magnetic field at an arbitrary fixed point. According to theory EM waves are created.

The shape we see today of our galaxy is what it was 200,000 of years ago. But then again it might not be in that particular shape to begin with because light speed was not and is not instantaneous.

Yes, but only if light travels in a medium. Yes, only in vacuum. No if you consider a medium.

Darn...physical limitations. How about if we use a flywheel made of diffraction grating? I suppose the result will be a broad spectrum of EM waves produced in the vacuum between the rotating flywheel.

Sorry, I meant electrostatic scalar potential not vector potential.

If we can have a big enough flywheel with mm slits cut into it and spun fast enough... Can magnets be used to wiggle electrons flow in synchroton in the optical frequency rate? I have thought about this. It seems that one doesn't need electric or magnetic field to generate EM waves, at least when it comes to heat. Is it accurate to state that EM wave is simply energy in its purest form?

I think there is this fundamental thing called the electric vector potential where the electric field can be derived from it in the presence of a charge. And if you view it from a moving reference frame then the electric field 'looks' like a magnetic field.

Since we can't do it electrically maybe we can do it mechanically. I have an idea. Let us direct two electron guns at each other in a line of sight. Place in front of each gun a circular disk with slots cut into it to enable the electron beam to pass thru the slots as it rotates. The other disk is positioned such that when it allows its electron beam to pass thru, the other disk blocks its own electron beam, and vice versa. What we have now is an AC system. If we can have a large enough disks with many slots and make them rotate such that the resultant back and forth electron beams are in the THz range, it just might work. Crude I think. Now place the whole setup in a vacuum. I predict the vacuum space between them would start to give off visible light as the setup is run. Any critique?

lemur and alpha2cen, A superconductor is defined as something that has zero resistance to the flow of current. Whether it loses energy or emits EM waves is not part of the definition. So it seems that up to the current technology wise we cannot directly show that light is EM wave, or to produce light using purely electric-magneto method. Seems that light can only be produced with 'classical' means like burning (i.e. sun, flame, light bulb) and atomic excitation (i.e. LED, laser, fluorescent tubes).

An imperfect conductor would resist that current and generate the corresponding amount of heat. To get this issue out of the way let us use a superconductor so that Ohmic heating would not occur. Now we are left with a zero resistance conductor carrying an AC producing an alternating magnetic field and producing radiating radio waves.

Lemur, We are discussing how to prove that light is an EM wave. We can generate x-rays from deceleration of fast electrons but this doesn't tie in with electromagnetism in that sense. We can get optical light from LED but this is just excited electrons losing their excitation and emitting photons in the process, hence still doesn't tie in with EM. Since we know a current produces a circulating magnetic field around it, according to Maxwell's, an AC current produces EM waves. If we can have current frequency in the optical range then the produced EM waves should be in the optical range and could be seen with the naked eye. As was pointed out by others, producing THz is a challenge. We don't even have such an oscillator to begin with. At such a high frequency the skin effect comes into play, causing surface heating, but this is not the issue. And then the inductive reactance becomes significant at this frequency and this can stop AC from flowing. Perhaps there is an indirect way of doing this?

What you are assuming is the Ohmic heating which gives of heat radiation and visible light. That can occur with direct current as well. Frequency of AC current is unrelated to its voltage and current magnitudes. What I was proposing was to jack up the frequency of an AC supply into the optical range. According to Maxwell's equations the EM waves produced should be in the visible spectrum also which we can then see with our naked eyes. This was supposed to prove that EM waves were made up of a magnetic field component. However there is a problem in regard to the skin effect at such optical frequency. This can cause heating and make the conductor glow. Separating the light produced from heating and Maxwell's is another problem. I suppose covering the conductor with an opaque layer can block out the glow due to heating.

Interesting. But how does it tie magnetic field component and EM wave together as a proof that EM waves are made up of a magnetic field component?

We know that alternating current in a conductor produces electromagnetic waves whose frequency is the frequency of the alternating current in the conductor. What if we can produce alternating current with a frequency in the optical region, will the conductor glow by giving off light? Can this be used to show that optical light is composed of magnetic field component? Has anyone done this before?

Have a look at the Faraday effect. http://en.wikipedia.org/wiki/Faraday_effect Is this considered as a proof?

An example of such interaction is the Faraday Effect.

If someone went back in time then would the future where he's from cease to exist? No future authority would be able to send 'time cop' to drag him back to the future.

Since the total amount of energy in the Universe is a constant at any one time, then time travel would violate this law? So maybe it is this conservation of energy law which prohibits time travel?