Things faster than light ... (Is there a physicist in the house?)

[ponderingturtle]

Yes, I know. But I thought you were saying we'd infer a high velocity from the facts you mentioned (which were be from our POV here on Earth). Yes, if you observe the pulse sweeping across distant objects (and those objects don't necessarily have to be at our distance, that's just one example) you'd see the appearance of very high velocity.

Are we just miscommunicating or do you really think there is something wrong in posts 2 and 12?

It seems it was miscommunication. I thought you might have been partaking in the fallacy that fields like EM fields are objects and would rotate like a solid object with out the rate of propagation of the rotation being an issue.

 

[RecoveringYuppy]

No, fields aren't objects, but I am pointing out there are circumstances where they can give that appearance. But where the appearance breaks down is when you realize that some part of the "solid object" is moving faster than c. And the appearance is due to a coordinated change propagated through the field.

I probably have used phrasing such as "as the field sweeps", that sort of phrasing is pretty common. But I think I understand that fields aren't material objects.

 

[MRC_Hans]

The basic 'trick' is that what travels faster than light is an event. I think the easiest to understand example is a wavefront hitting an obstacle in an oblique angle. Imagine a beam of coherent light hitting a surface at, say, a 85 degree angle. The incident of each wave-top hitting will move sideways at a speed much faster than light. If something happens as the lightwave hits (e.g. it triggers secondary emission), then from certain observation positions, you will observe something that appears to happen faster than light.

Hans

 

[ponderingturtle]

No, fields aren't objects, but I am pointing out there are circumstances where they can give that appearance. But where the appearance breaks down is when you realize that some part of the "solid object" is moving faster than c. And the appearance is due to a coordinated change propagated through the field.

I probably have used phrasing such as "as the field sweeps", that sort of phrasing is pretty common. But I think I understand that fields aren't material objects.

You are getting into all kind of issues there. Defining what is material is an interesting point in itself, and you can certainly argue that feilds are material. But the idea stems from that they radiate out at infinite speed as many lay people do not understand that they have a rate of propagation.

 

[RecoveringYuppy]

Imagine a beam of coherent light hitting a surface at, say, a 85 degree angle. The incident of each wave-top hitting will move sideways at a speed much faster than light. If something happens as the lightwave hits (e.g. it triggers secondary emission), then from certain observation positions, you will observe something that appears to happen faster than light.

And the most extreme example is if the coherent light arrives at right angles. At that point the whole things comes on instantly possibly making it appear that the a phenomena spread across the incident object instantly.

You are getting into all kind of issues there. Defining what is material is an interesting point in itself, and you can certainly argue that feilds are material. But the idea stems from that they radiate out at infinite speed as many lay people do not understand that they have a rate of propagation.

Yes, those could be interesting issues. But for this conversation I think it would be most useful to consider them to be constructed of virtual particles.

 

[UGottaB]

One observation. Light emitting from a large circular pattern to a distant point in space would give the impression that it is traveling faster if the sequence of flashes is progressing toward an observer but slower when the sequence is moving away from the observer. True as long as the observer isn't at right angles to the circle which would provide a constant change.