# B Superconductivity for light beams?

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1. Jun 2, 2017

### Tspirit

As is well known, superconductivity is described as a property of zero-resistance for electrical current, however, I want to know, is there any material with superconductivity for light beams, in which the light beams can propagate with no losses?

2. Jun 3, 2017

### davenn

do you understand what an electric current is and how it propagates in a conductor ?

do you understand what light is and how it propagates ?

when you answer those and understand the difference, you will discover a flaw in your idea/thought

Dave

3. Jun 3, 2017

### Ranvir

I think, it can be re-framed as "Do we know about any substance through which light can travel through without any attenuation?"
To which a good enough answer would be optical fiber. The point is light, being light, can die down as it progresses through a media, where as the current we think of as a flow of charge doesn't "die down" in a typical closed circuit. However, resistor can be treated as a dissipating agent just as easily as the opacity of a material for light.

Last edited: Jun 3, 2017
4. Jun 3, 2017

### davenn

please keep your derogatory comments to yourself !!

I am trying to see what understanding the OP has on the topic without giving direct answers
We here at PF try to get people to think for themselves, it aides in the learning process

5. Jun 3, 2017

### Ranvir

Point taken, that makes sense, the more I think about it.

6. Jun 3, 2017

### davenn

the problem is, we have no idea what the OP is thinking. So we need to get them to tell us their understanding and also to
more specifically define what they are wanting to know , which at the moment, from their opening post, is a little vague

Lets see how they respond

Dave

7. Jun 3, 2017

### Tspirit

Thank Dave and Ranvir for kind replies. Ranvir tells what I want to know. I am searching for a kind of material that won't introduce losses when the light propagates in, whatever the principle is. I have considered the optical fiber, but the losses will increase with the distance increasing. Thought of superconductivity, I asked the question. So, is there any solution, even in theory?

8. Jun 3, 2017

### davenn

nothing that I am aware of .... all mediums that will support the transmission of light will have losses

again I ask, since you didn't answer my questions ...

do you understand what light is and how it is different to an electric current ?

Dave

9. Jun 4, 2017

### Tspirit

As I know, light is essentially a kind of electro-magnetic wave, it can propagates in vacuum with a speed of $c$. It propagates in a medium with a speed of $c/n$, ""n"" is the refractive index of medium.
While electric current is a field formed by the moving of electrons, it also propagates with $c$, the difference to light is that it need a medium to propagate in. The moving of electrons will stopped or blocked by something called resistance and the corresponding current will decrease. At a very low temperature, some materials can have a property of zero resistance, which is called superconductivity.

10. Jun 4, 2017

### davenn

this bit needs revised a bit

The electric field exists regardless of it the electron ( charge carrier) is moving or not.
That is, a single motionless charged particle electron/proton already has an electric field around it

http://www.physicsclassroom.com/class/circuits/Lesson-1/Electric-Field-and-the-Movement-of-Charge

electrons don't move at the speed of light they actually move at a slow speed in a conductor ~ 1mm / sec give or take a bit depending of a few variables --- google electron drift

The electric field propagates at less than the speed of light in anything other than a vacuum, how much less depends on the conductor, insulation type etc
The electric filed will also happily propagate in a vacuum ... It does not need a medium. Same for the magnetic field

what I am aiming towards with these Q's and comments to you is that there is a very different process between the movement/propagation of an electric charge ... CONDUCTION and the movement/propagation of light ( an electromagnetic field) .... RADIATION
Light doesn't conduct ( well I have never seen it written anywhere that it does), therefore talking about superconductivity for light is meaningless

Dave

Last edited: Jun 4, 2017
11. Jun 5, 2017

### ZapperZ

Staff Emeritus
The words you use are at fault here.

What you want is a "lossless medium" for light propagation (presumably over a range of frequencies). You should use that phrase rather than invoking "superconductivity", because "superconductivity" involves a number of consequences and effects, NOT just "zero resistance".

Zz.

12. Jun 5, 2017

### f95toli

But only or DC; the losses in a superconductors increase as you increase the frequency. In fact, at frequencies above a few hundred GHz (which is taking you close to the far infrared; i.e. "light") the losses in superconductors can exceed those of normal metals at the same temperature.

13. Jun 5, 2017

### Staff: Mentor

This is not true. Optical fiber may be low loss, but most certainly is not zero loss. Just look at the need for optical repeaters in fiberoptic trans-Atlantic communication cables on the ocean floor...

https://en.wikipedia.org/wiki/Submarine_communications_cable

14. Jun 5, 2017

### Tspirit

Thank you for your detail interpretation. However, I am still a little confused. Both electrical current and light radiation, are propagating with the help of motion of electro-magnetic field and their speeds are both near the light speed. So in the concept of "field", what's the essential difference between them? Are they interpreted by classical Maxwell electro-magnetic equation?

15. Jun 5, 2017

### davenn

but the electric current ISNT moving at the speed of light !
did you do as I suggested and google electron drift ?

16. Jun 6, 2017

### Tspirit

Yes, I have followed your suggestion and I know that the velocity of electron drift is very slow. But the foundation of electrical field is very fast (nearly the speed of light), in other words, the transmission speed of information carried by electrical field is very fast. See https://en.wikipedia.org/wiki/Speed_of_electricity. So my point is why the electrical field of electrical current can't be seen as the light current, since they are both electromagnetic field in nature?

17. Jun 6, 2017

### Ranvir

Thanks, I will follow up on this

18. Jun 6, 2017

### davenn

because conductivity ( superconductivity) deals with current, the movement of charge carriers, NOT electric or EM fields
there is no such thing as "light current"

19. Jun 6, 2017

### Tspirit

Thank you for your kind help. I seem to get the point: superconductivity is a behavior of charge carriers and happens when the resistance of their moving is zero. The propagation of light don't need the help of the moving of something, so there is no corresponding resistance and thus superconductivity.

20. Jun 6, 2017

### rumborak

I'm a bit surprised to not see the obvious answer here: the most lossless medium for current and radiation is ... space.

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