Is the EM field the medium for light waves

[S Beck]

EM waves can propagate through empty space, but there is also the EM field. Is this field really empty space or is there something that exists that the light wave disturbs, like some kind of fluid? In areas of space where values of the field is 0, is this like empty space or more like calm water? The field is sometimes said to be a mathematical tool to measure a force across space between remote particles and sometimes said to be a physical object that exists throughout all of the universe that gives the impression there is some kind of medium, like an ocean or a mattress, that gets disturbed by charges and light waves.

 

[jfizzix]

This is an interesting point where physics meets philosophy, and the two possibilities you mention (mathematical tool vs physical object) are both legitimate positions to take. I like to think of it as a physical object because it's easier for me to reason with, physically, but that's my bias.

That said, there is no fundamental medium that electromagnetic waves travel in, like sound waves travel through matter.
Once upon a time (1860s to 1880s), it was thought that light had to have a medium to "wave" in because all other known waves did and there was no reason to think of light as special. This hypothetical medium was given the name the luminiferous aether.

The reason we know that no such aether/medium exists is due to the Michelson-Morley experiment (circa 1887). which very carefully measured the speed of light at different angles while the Earth was zooming around the sun. If there was a medium, we would be able to see the speed of light change at different angles depending on how fast we were moving through the aether. However, the most careful observations showed that the speed of light remained constant no matter how fast we were moving or in what direction.

A little under 20 years later (1905), people figured out how physics can work in a world where the speed of light was an absolute constant, and the theory of (special) relativity was born.

 

[S Beck]

This is an interesting point where physics meets philosophy, and the two possibilities you mention (mathematical tool vs physical object) are both legitimate positions to take. I like to think of it as a physical object because it's easier for me to reason with, physically, but that's my bias.

That said, there is no fundamental medium that electromagnetic waves travel in, like sound waves travel through matter.
Once upon a time (1860s to 1880s), it was thought that light had to have a medium to "wave" in because all other known waves did and there was no reason to think of light as special. This hypothetical medium was given the name the luminiferous aether.

The reason we know that no such aether/medium exists is due to the Michelson-Morley experiment (circa 1887). which very carefully measured the speed of light at different angles while the Earth was zooming around the sun. If there was a medium, we would be able to see the speed of light change at different angles depending on how fast we were moving through the aether. However, the most careful observations showed that the speed of light remained constant no matter how fast we were moving or in what direction.

A little under 20 years later (1905), people figured out how physics can work in a world where the speed of light was an absolute constant, and the theory of (special) relativity was born.

Thanks for the informative and great response. Yes I agree that both viewpoints, though contradictory, have legitimate points supporting them.

"However, the most careful observations showed that the speed of light remained constant no matter how fast we were moving or in what direction."

Most matter particles in the SM are electromagnetic in nature. Charge and spin properties respond to the electromagnetic force. As light is also electromagnetic, what if that has anything to do with the speed of light being an absolute constant? I think the MM experiment accounted for this medium to be separate from the rest of the universe hence why they couldn't detect it, but maybe I am wrong. I am not up to snuff on special relativity, but here's a hypothetical scenario, say the speed of sound in a certain medium is a constant (sound travels different speeds in other mediums of different conditions), and we are just made of sound waves in the same medium. If all matter around us, including us, is actually just a disturbance of the same medium as sound travels in, could the speed of sound be an absolute constant to all us observers? Could time slow down as we travel towards and faster to the direction of that sound? I am no aether proponent but this has seriously been on my mind for the past week.

Or am I just talking nonsense? Kindest regards.

 

[Ibix]

Look up Fizeau's experiments, where he measured the speed of light in flowing water. Also look up stellar aberration experiments, which compare light speeds in vacuum. https://www.physicsforums.com/insights/speed-light-galilean-relativity/

It's not that people gave up on the idea of a medium for light waves. It's that so many different lines of research require contradictory properties of any such medium that the idea is implausible.

Another thing to be aware of is that the constant $c$ that appears in relativity does not need to have anything to do with the speed at which electromagnetic radiation propagates. It's possible to start from just the principle of relativity and show that there are only two possibilities consistent with that - one with an infinite invariant speed (Galilean relativity) and one with a finite invariant speed (Einsteinian relativity). Experiment shows we're not in a universe of the first type.

Furthermore, it's possible to construct a modified version of electromagnetism in which the speed of light is not $c$, corresponding to a photon of non-zero mass. This has wide-ranging consequences which have never been detected, leading to an upper bound on the mass of the photon of about 10^-50kg, I believe.

Those two paragraphs should tell you that your speculation about sound is baseless. You don't need light speed to derive relativity, and you can construct relativistic electromagnetic theories where light doesn't travel at $c$. Furthermore, although atoms are held together by electromagnetic forces these are not electromagnetic waves. And the particles themselves are not excitations of the electromagnetic field, but rather of the electron field and the various quark fields (according to my limited understanding of quantum field theory).

 

[jfizzix]

The Physics of light waves is different than sound waves in one critical fashion. The speed of sound is defined relative to the medium it's in being stationary. The speed of light on the other hand appears the same from all sources whether you are moving toward/away from them, or they are moving toward/away from you.

For example, if you are moving at near the speed of sound compared to a stationary source emitting sound waves, you would see those waves as concentric circles with the source as the common center. On the other hand, if the source is moving, and you are stationary, the source sound waves are no longer concentric circles. The center of each circle is different depending on where that sound wave was emitted.

With sound waves, you can tell whether you or the source is moving relative to the medium it's in because they look different. With light waves, these situations look exactly the same.

I used to think that the space/time effects of relativity were artifacts of our measurement devices being electromagnetic in nature. However, this time dilation effect is seen in sources whose change is not electromagnetic in nature (e.g., radioactive decay). If a nucleus is radioactive with some decay rate, that decay rate will be much slower if the nuclei are moving near the speed of light.

Thanks for the informative and great response. Yes I agree that both viewpoints, though contradictory, have legitimate points supporting them.

"However, the most careful observations showed that the speed of light remained constant no matter how fast we were moving or in what direction."

Most matter particles in the SM are electromagnetic in nature. Charge and spin properties respond to the electromagnetic force. As light is also electromagnetic, what if that has anything to do with the speed of light being an absolute constant? I think the MM experiment accounted for this medium to be separate from the rest of the universe hence why they couldn't detect it, but maybe I am wrong. I am not up to snuff on special relativity, but here's a hypothetical scenario, say the speed of sound in a certain medium is a constant (sound travels different speeds in other mediums of different conditions), and we are just made of sound waves in the same medium. If all matter around us, including us, is actually just a disturbance of the same medium as sound travels in, could the speed of sound be an absolute constant to all us observers? Could time slow down as we travel towards and faster to the direction of that sound? I am no aether proponent but this has seriously been on my mind for the past week.

Or am I just talking nonsense? Kindest regards.