In the following website:

light movie

There is a little movie of EM waves progressing through time along the z-axis at the bottom. I was just wondering: is it true that there are points in time and space where the amplitudes of both the electric and magnetic oscillations are zero (as can be seen in the movie)? Does this mean that in that instant of time and space, an instrument would not pick up that there was an EM wave passing through???

I will answer to your question by a question: throw a stone in the upward vertical direction, it will rise and finally fall (all this with an acceleration of g). When the stone is in its maximal height, it has a zero velocity. If you use a velocity measurement device to measure the velocity at this point, at the precise time where the stone gets to that point, will it measure a zero velocity?

I think that (in the wave model) you can't detect EM radiation at any instant of time and space - you need a time component to detect the change of magnetic and electrical field strengths.

Think about a detector in constant electric and magnetic fields.

Fluctuations in Electric & Magnetic field strengths get cancelled out, almost, at 'dark' strips in an interference pattern.

No, but how about if u were measuring its deviation from a reference height (that at which u threw the stone)?

That is the question I have asked.

But surely u agree that at any instant of time there will be wave amplitudes! Are u saying that these cannot be measured though?

If you measure the electric field at the instant of time and at the space (I understand that you mean position) where and when the electric field is zero, you will measure zero electric field.

However if you leave the measuring device at the same position and measure at different times the electric fiel,' you will not measure a zero field, but what you will get is an oscillating electric field. If you move your measuring device in the z direction, you will measure an oscillating field but at a different rate (this is the Doppler effect). If you move slowly enough, this Doppler effect is the classical one, if you begin to move fast enough, it will be the relativistic one. To still measure a zero electric field your measuring device must move at the speed of the electromagnetic wave which is c, this cannot be done.

NB. In all I said, I was refering only to the electric field, the same happens to the magnetic field, since in EM waves, if you know the electric wave, by Maxwell's equation you automatically get the magnetic wave which is in phase with the electric wave.

Yes that is ok. That is what I thought. Just wanted to run it by some people here.