What medium does light move in?

[aiop]

Waves on water require water to move, sound waves require a medium of the like. My question is what do light waves move in. Empty space contains not much more then low density hydrogen, what medium could light possibly be moving in.

 

[Doc Al]

Light does not require a medium.

 

[jtbell]

One could say that the electromagnetic field that permeates the universe is the "medium" for light.

 

[litup]

Light does not require a medium.

Nope, doesn't need a medium or an astrologer:) Just a good storyteller like Einstein:)

 

[DarkBabylon]

Waves on water require water to move, sound waves require a medium of the like. My question is what do light waves move in. Empty space contains not much more then low density hydrogen, what medium could light possibly be moving in.

Classically? The electro-magnetic field.
Quantum mechanically? It is its own medium...okay, slight fib, still electro-magnetic field, but there is no requirement for anything but light for it to move. Essentially, free space is enough.

 

[pixel]

Empty space contains not much more then low density hydrogen, what medium could light possibly be moving in.

It was once thought that there was a medium, called the aether, that was required for light to propagate. The famous Michelson-Morley experiment failed to find evidence of this.
https://en.wikipedia.org/wiki/Luminiferous_aether

 

[Dale]

The famous Michelson-Morley experiment failed to find evidence of this.

As have all subsequent experiments with ever greater precision and a multitude of techniques.

 

[BillTre]

Could one say the medium through which light moves is space-time?

Without space-time, there would be nothing for the light to do movement-wise.
Also a warped space-time affects the movement of the light.

 

[DarkBabylon]

Could one say the medium through which light moves is space-time?

Without space-time, there would be nothing for the light to do movement-wise.
Also a warped space-time affects the movement of the light.

It would seem to me that space time is this fundamental layer on which all the rest of the fields exist. While true that light does get affected by space-time, but so is everything else regardless if charged, neutral, magnetic or relativistic. Anything that has energy gets affected by space-time.
In conclusion: The electro-magnetic field rests on top of space time, and that field gives rise to photons.

 

[Nugatory]

Could one say the medium through which light moves is space-time?

No. Although it makes sense to speak of moving in space (the position changes with time), it is not at all clear what could be meant by moving in space-time - what's changing with respect to what?

 

[BillTre]

Perhaps my understanding of medium is limited.
How is it defined?

 

[lychette]

One could say that the electromagnetic field that permeates the universe is the "medium" for light.

wasn't that called the aether 100 years ago?

 

[davenn]

Perhaps my understanding of medium is limited.
How is it defined?

as a substance for the/allows the wave to propagate ( supports the wave propagation)
eg a sound wave won't propagate without a medium/substance ( liquid, gas, solid etc)

Light and any other E/M will happily propagate where there is no medium eg a vacuum

 

[BillTre]

as a substance for the/allows the wave to propagate ( supports the wave propagation)

So why not space-time?
It allows light to propagate.

 

[davenn]

So why not space-time?
It allows light to propagate.

@Nugatory already answered that ... he is welcome to expand on his comment if it wasn't enough for you

 

[russ_watters]

So why not space-time?
It allows light to propagate.

How? What are it's properties that are harnessed for propagation of light? For example, air has mass/density, pressure and elasticity (compressibility) that enables sound propagation.

 

[lychette]

How? What are it's properties that are harnessed for propagation of light? For example, air has mass/density, pressure and elasticity (compressibility) that enables sound propagation.

It's properties are 'none'
Light travels at the speed of light...time stands still at the speed of light...there is no such thing as 'time' for light...there is for us
It follows that there is no such thing as 'distance' for light...light simply links things together.
No properties of any medium are required by light. !

 

[BillTre]

Thanks @russ_watters and @lychette.

So, sounds like you guys are saying the defining property of a medium, in this sense, is that the medium is involved in the movement of a wave itself (a propagated displacement), such as water or air waves move through a medium of water or air because the water or air molecules are actually moving (up and down or back and forth) instead of just something it moves through.

In which case it seems to me that space-time would be the medium for gravity waves but not light waves, but no one has said that (at least in a way that I understand).
Seems to be required for propagation, affects the propagation of light (as ether was claimed to do).

 

[Dale]

Could one say the medium through which light moves is space-time?

One of the key characteristics of a medium is that it has a rest frame. Spacetime does not. If you were to make such a statement then you could only do it by redefining the term "medium" to get rid of that key feature.

 

[lychette]

Thanks @russ_watters and @lychette.

So, sounds like you guys are saying the defining property of a medium, in this sense, is that the medium is involved in the movement of a wave itself (a propagated displacement), such as water or air waves move through a medium of water or air because the water or air molecules are actually moving (up and down or back and forth) instead of just something it moves through.

In which case it seems to me that space-time would be the medium for gravity waves but not light waves, but no one has said that (at least in a way that I understand).
Seems to be required for propagation, affects the propagation of light (as ether was claimed to do).

There is NO medium necessary for light...what else is there to add?...how do you go from this point?

 

[BillTre]

My questions were directed at getting a better understanding of how the word medium was defined in this context.
In the process, I have been exploring other

It seems to me that the term medium has 2 characteristics relevant to the situation (based on responses):
1) basis of a propagated wave, such as air or water waves, little bits that move in response to their neighbors.
2) having a rest frame of reference (had not thought of that before)

This is getting at a definition, which is what my initial post was about.

Sorry to upset you.

 

[lychette]

My questions were directed at getting a better understanding of how the word medium was defined in this context.
In the process, I have been exploring other

It seems to me that the term medium has 2 characteristics relevant to the situation (based on responses):
1) basis of a propagated wave, such as air or water waves, little bits that move in response to their neighbors.
2) having a rest frame of reference (had not thought of that before)

This is getting at a definition, which is what my initial post was about.

Sorry to upset you.

You should never worry about causing upset here!
What is slightly worrying is that a fundamental basis of modern physics can be doubted (that there is a 'medium' necessary for the transmission of light) doubting this means that all the conclusions based on this premise are also doubted. Anyone with these doubts should look at the evidence in modern physics and re-asses their doubts.

 

[Aaron Crowl]

wasn't that called the aether 100 years ago?

Aether theory had some specific properties. Namely it was thought of as some kind of substance that light waves could propagate through. The aether was supposed to permeate the universe and have an inertial reference frame. They even created a sophisticated experiment to detect the Earth's movement through the aether. It was the famous Michelson-Morley experiment. The results were negative.

It appeals to our common sense that light should have a "medium" to travel through. That's how waves on the ocean work. That's how sound waves in air work. However, the Michelson-Morley experiment showed us that this is simply an incorrect way to think about it.

 

[BillTre]

What is slightly worrying is that a fundamental basis of modern physics can be doubted (that there is a 'medium' necessary for the transmission of light) doubting this means that all the conclusions based on this premise are also doubted. Anyone with these doubts should look at the evidence in modern physics and re-asses their doubts.

Wanting to understand the meaning of the term medium does not imply doubting a the modern results.
It is also involved in understanding of the historical development of the field and understanding basic associated concepts.
When I have things I don't understand I ask a lot of questions.

 

[David Lewis]

...it is not at all clear what could be meant by moving in space-time - what's changing with respect to what?

You are moving from one point in time to another.

 

[jbriggs444]

You are moving from one point in time to another.

Or: "Your position in space time is a continuous, non-constant function of your experienced proper time", thus avoiding the term "move".

 

[Dale]

This thread has gone off track. Several posts have been deleted and the thread is closed.