# Measuring speed of light with enhanced detectors

1. Aug 15, 2013

### Darko M

Only but few may disagree that the inverse squared law affects speed. For example, not only lengths of far away vehicles shorten, (with increase in distances from obsevation) the moving vehicles generally seem to have "slowed" down; the direction either from right to left or vise versa.
Please has anybody tried measuring speed of light, having inco-operated say, a telescope in to the measuring apparatus?

2. Aug 15, 2013

### ghwellsjr

I must be one of the few because I disagree that the inverse squared law has any effect on speed. Maybe I'm misunderstanding what you are referencing but I don't see how the two are related in any way.

Oh, that's what you are talking about. But this has nothing to do with anything actually slowing down or actually being shortened. Did you think that this is what relativity is about?

Yes, a telescope is often incorporated into a measuring apparatus designed to determine the speed of light, but what has that got to do with your previous statements?

3. Aug 15, 2013

### HallsofIvy

Staff Emeritus
I really don't understand what you are saying. I can't say I am one of the "few" that disagree that "the inverse squared law affects speed" because I don't know what you mean! There are a large number of "inverse square laws" (gravity, light intensity, etc.). Which one are you referring to? Distant vehicles seem to have slowed down? That is certainly not my experience? And I don't know what you mean by "incorporating a telescope into the measuring apparatus". EVERY experiment measuring the speed of light that I know of uses a telescope because of the large distances required to reasonably measure a time span for the motion at the speed of light. But, as far as I know, no experiment has shown that the speed of light varies with distance from the earth.

(I'm wondering if you are thinking that a telescope "sees" light many light years away? We can see what is many light years away but the light we are seeing is light in the telescope.)

Again, I need to type faster!!

4. Aug 15, 2013

### Staff: Mentor

I think the OP is confusing linear and angular speed.

5. Aug 16, 2013

### Darko M

Big thanks to you all, folks. Well I never knew telescopes were used. I was then only thinking that a very powerful telescope may vary the result of measuring the speed of light.
But as regards distant objects say buses, mine own eyes have always confirmed this observation to me.
It is like this: Assume you stand facing a road that "stretches" away horizontally from left to/through right. And then there is a considerable perpendicular distance of separation (of you) from this road. Now from what I have always observed, long buses seemed to have become shorter than usual; and their observed speeds seemed decreased compared to their actual speeds. That's it. I have always noticed this phenomenon. Maybe my lenses just have their own way of creating this mirage of a sort; I probably may have to see an optician(?) soon.

6. Aug 16, 2013

### ghwellsjr

Again, my question: Did you think that this is what relativity is about?

7. Aug 16, 2013

### Staff: Mentor

None of this is relevant for relativity. Relativistic effects are what remain after accounting for all optical effects.

8. Aug 16, 2013

### Darko M

Certainly not.

9. Aug 16, 2013

### Darko M

Parden my ignorance, but have you ever experienced an observation of a sort?

10. Aug 16, 2013

### ghwellsjr

Then why are you asking it on the relativity forum?

11. Aug 16, 2013

### Staff: Mentor

Right, so what you are talking about is the optical effects of angular distance measurement, aka "perspective": http://en.wikipedia.org/wiki/Perspective_(visual [Broken])

Last edited by a moderator: May 6, 2017
12. Aug 16, 2013

### Staff: Mentor

Of course.

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