Exploring the Evidence for Visible Light as EM Radiation

[bhobba]

Hi All

In discussing another issue it occurred to me the only experiential evidence I know that normal visible light is EM radiation is Faraday Rotation. I strongly suspect we have a lot more these days.

Amusing story. Fermi's wife had a degree in general science that did not cover Maxwell's Equations so he decided to teach it to her. He reached the end and showed they imply radiation at the speed of light, so light must be EM radiation. She disputed that, correctly claiming that proves diddly-squat - it's only suggestive and such a claim would need further investigation. At which point Fermi gave up . And that from a first class experimenter.

Thanks
Bill

 

[Ibix]

The free electron laser? You just wiggle a charge up and down and out comes radiation between microwave and x-ray, if Wikipedia is to be believed (I had no idea the frequency range was so great). Maxwell's equations tell you that's EM radiation and your eyes tell you it's light, and I think you'd be fairly deep into the realms of magic (edit: or at least, you'd be proposing unknown effects that are incredibly well correlated with known effects on no evidence I'm aware of) if you wanted to deny the connection.

 

[Vanadium 50]

I predict this thread will degenerate quickly into "what counts", with some people saying "what about X" and others saying "no, that doesn't count".

As an example, are we allowed to assume infrared light is the same phenomenon as visible light? Microwaves? Radio? For that matter, are we allowed to assume yellow light is the same phenomenon as green light?

I would also suggest we are asking to compare two theories:

1. Light is an example of electromagnetic radiation.
2. Light matches the properties of electromagnetic radiation in every respect we can test. However, it is actually from a completely separate and unknown process. Furthermore, the process of visible electromagnetic radiation doesn't exist.

I think Theory #2 is an uphill battle.

 

[A.T.]

He reached the end and showed they imply radiation at the speed of light, so light must be EM radiation. She disputed that, correctly claiming that proves diddly-squat - it's only suggestive

Obviously, experimental evidence cannot prove a theory, just support or contradict it.

 

[bhobba]

Obviously, experimental evidence cannot prove a theory, just support or contradict it.

Of course - I was simply asking what further evidence we have since Faraday did his famous experiment. What level of evidence would be enough to convince Fermi's wife, or if she was just poking a bit of fun at her famous husband, one of the few physicists that was both a first class theorist and experimentalist, one can never know.

Regarding experiment proving anything of course it never can - but it can be so overwhemling to doupt it would mean you have rocks in your head. To me what IBIX wrote I think would convince any reasonable student, so as far as I am concerned the question is answered.

But, Vanadium, is correct, this has the potential to degenerate into something of little value. I will leave it open for now, but it goes off the track it will be shut.

Thanks
Bill

 

[Vanadium 50]

By the way, you can make visible light from synchrotron radiation. Not healthy to look at, but can be seen with a camera. Does it count?

In other fields, my Theory #2 can be expressed as "The Odyssey was not written by Homer, but another blind poet of the same name."

 

[bhobba]

By the way, you can make visible light from synchrotron radiation. Not healthy to look at, but can be seen with a camera. Does it count?

Of course.

Thanks
Bill

 

[ZapperZ]

I'm a bit puzzled by this thread. What is so special about the visible spectrum that it requires such a "proof", while other parts of the EM spectrum don't? I mean, if the UV and shorter wavelengths are accepted to be EM wave, while IR and longer wavelengths are accepted to be EM wave, why shouldn't the small range in between them be that as well? It's not as if there is a discontinuous or exact boundary between them, i.e. there is no "phase transition" here.

Zz.

 

[Vanadium 50]

So there you go:

 

[bhobba]

What is so special about the visible spectrum that it requires such a "proof", while other parts of the EM spectrum don't? I mean, if the UV and shorter wavelengths are accepted to be EM wave, while IR and longer wavelengths are accepted to be EM wave, why shouldn't the small range in between them be that as well? It's not as if there is a discontinuous or exact boundary between them, i.e. there is no "phase transition" here.

Yes - evidence as well. But then we need the evidence the others are EM radiation. Like a lot of things it's an acculmation of evidence that makes doubting it very difficult.

Thanks
Bill

 

[ZapperZ]

Yes - evidence as well. But then we need the evidence the others are EM radiation. Like a lot of things it's an acculmation of evidence that makes doubting it very difficult.

Thanks
Bill

But that's different. If someone asks for evidence to support that EM radiation in general has oscillating E and B components, then I can understand and can set up appropriate experiments to show that. I only need to select a particular frequency, and presumably, the person will be satisfied if I can show on an oscilloscope the signal that my pick-up antenna sees from that EM radiation.

But to make it that specific that someone has issues ONLY with the visible range, that's a different psychosis entirely.

Zz.

 

[bhobba]

I only need to select a particular frequency, and presumably, the person will be satisfied if I can show on an oscilloscope the signal that my pick-up antenna sees from that EM radiation.

Yes - but how do you know all those things are EM radiation? I have zero doubt it's true. Ibix answered it to my satisfaction, other answers are extra evidence showing why this is well accepted. So maybe its time to close the thread. Would anyone be unhappy?

Thanks
Bill

 

[bhobba]

OK - let's shut it.

Thanks
Bill