Parallel light reflection for a one-way speed of light measurement setup

[hutchphd]

It will require two distinct measurements. It is up to you whether you want to call one of them callibration. The result will be a measurement of the round trip time.

 

[OWSOL]

When you say that the light will hit the two sides of your mirror at the same time, you are implying that two synchronized clocks would have the same reading when the light hits them there.

I have moved away from the mirror in post 22, replacing it by a mechanical means of stopping both clocks 'supposedly simultaneously'.

Now if the rotating shaft is not suited, then we could substitute for a linear motion, having the same step motor pushing a flat surface holding the two blades until they reach each clock's photo cells, stopping them.

This is just a thought experiment, implying that both blade's edges are at the same distance, thus entering the photo cells at the same time. You might say, "well, how can you make sure they are at the same time ?", that's just it, it's a thought experiment, so in that thought experiment they are...

I mean, can't we have some degree of accuracy about the edges being aligned the best they could be, and have some degree of accuracy as to how the flat surface moving towards the photo cells in a steady way ?

Anyway...

 

[Nugatory]

Now if the rotating shaft is not suited, then we could substitute for a linear motion, having the same step motor pushing a flat surface holding the two blades until they reach each clock's photo cells, stopping them.

You are assuming that these devices are built out of a perfectly rigid material, such that if one part of an object is displaced all other parts of the object will be be simultaneously displaced by the same amount - that's the definition of an ideal rigid body.
However, there is no such thing as an ideal rigid material; if there were we could send a faster than light signal simply by pushing on one end of a long rigid rod and expecting the other end to move as soon as we do. In practice when we displace one part of an object there is a time lag before the impulse propagates via the electromagnetic forces between the atoms to the rest of the object; that time lag will only be the same in both directions if the speed of light is the same in both directions. Thus we cannot use any mechanical device to stop the two spatially separated photocells "at the same time" - we've just found another way of assuming what we've set out to prove.

 

[OWSOL]

All I can say here is, please close this thread...

OWSOL

 

[OWSOL]

that time lag will only be the same in both directions if the speed of light is the same in both directions.

Ok, maybe not yet...

Nugatory, what do you mean by "in both directions", the flat surface is moving towards both clocks in only one direction.

Thank you

 

[FactChecker]

Ok, maybe not yet...

Nugatory, what do you mean by "in both directions", the flat surface is moving towards both clocks in only one direction.

Thank you

But it will travel along the length of the rod at some finite speed, so there will still be a problem. If your thought experiment assumes an instantaneous motion along the entire length of the rod, then you have assumed away the real-world facts that got us into SR in the first place. You will find that the physical rod (even ideal) has all the same types of problems that light had.

Example: the rod is assumed to rotate so that two windows, separated along its length, allow two light beams to pass through "simultaneously". Suppose you start with the rod not rotating. That is one way you can say that the windows are oriented the same initially. Then you start the rod rotating. Does the rotation start at the same time all along the rod rather than traveling down the rod over some time? The only way to tell is if you have "synchronized" clocks at both locations and measure when the rotation starts.

 

[Dale]

why does my proposal require clock synchronization ?

Because it discusses a one-way speed. One way speeds don’t exist without a synchronization convention.

Again, please read the reference I posted.

 

[OWSOL]

You will find that the physical rod (even ideal) has all the same problems that light had.

Ok,

What if numerous 'dry' measurements were made by starting and stopping the clocks via the mechanical way, giving the average difference between clocks 1 and 2.

Couldn't we then substract this difference from the test setup readings and get proper owsol speed ?

Would this be close enough to have an acceptable result ?

 

[Dale]

What if numerous 'dry' measurements …

The experimental details are irrelevant. As soon as you seek a one way speed you cannot avoid the need to define a simultaneity convention. Once you define that convention then you have fixed the one way speed of light

 

[phinds]

@OWSOL, I really have to admire your perseverance but not your unwillingness to listen to what you are being told (over and over).

 

[OWSOL]

Dear phinds,

yeah, I know...

I guess as I said in an earlier post, I am being naïve and expect things to be as easy to understand as what I perceive or see.

BTW, talking about sight, if light is anisotropic, how can we make anything of what we are looking at on an everyday basis ? I am here in my house and turn my head from left to right and see what I see everyday... how can anisotropy of light be so precise as to render a perfectly harmonized landscape ?

Just another thought...

 

[hutchphd]

Our neurons send signals that move at perhaps a hundred m/s. For any practical purpose light travels instantaneously. So that was just a dumb question (some of your others have not been).

 

[phinds]

I guess as I said in an earlier post, I am being naïve and expect things to be as easy to understand as what I perceive or see.

We are animals that evolved in what turns out to be a very narrow range of physical existence and our "logic" and "intuition" and "common sense" are all based within that narrow range. There are lots of things in cosmology (the very large) and quantum mechanics (the very small) that are totally counter-intuitive to what we think "natural" or "logical" or whatever and to assume otherwise often not only doesn't work, it is counter productive. Expecting it to be otherwise will not be helpful in your pursuit of STEM knowledge. Go with the evidence, not with your expectations.

 

[Dale]

I am here in my house and turn my head from left to right and see what I see everyday

What you actually see is a measurement. As with any other measurement it is unaffected by the choice of synchronization convention and therefore is unaffected by the one way speed of light. The expectation that it should be affected is incorrect.

 

[pervect]

The experimental details are irrelevant. As soon as you seek a one way speed you cannot avoid the need to define a simultaneity convention. Once you define that convention then you have fixed the one way speed of light

Another way of saying this - if one creates an experiment that measures one-way speeds, that experiment itself defines a notion of simultaneity.

Non-rigorously, hypothetical results representing an infinite speed of propagation would represent a surface of simultaneous events. Relativity itself can be said to impose a notion of "ultimate speed", so such hypothetical results can't be physically realized within the theory.

The thought experiment that shows that special relativity with it's constant speed of light does not have a singe, observer independent concept of simultaneity is known as "Einstein's train". There are a large number of other posts on the topic of the relativity of simultaniety.

To draw an analogy, it is known that in Euclidean geometry , it is impossible to square the circle using compass and straightedge. So claims to the contrary will be dismissed, because it's been proven impossible within the context of the theory.

The situation in special relativity is similar. Einstein's train shows that different inertial observers have different notions of simultaneity. Thus, an experiment that gives the same notion of simultaneity independent of any choice of inertial frame can't be based on special relativity.

My recommendation would be to study the notion of the "relativity of simultaneity", of which there has been a lot written, both here on the forums and in the literature. I would particularly suggest "Einstein's train" as one of the less abstract approaches, but there are many. I can dig up my usual reference to papers by Scherr that explores student resistance to correctly dealing with the relativity of simultaneity there is interest. Or just search for the author's name (Scherr) in posts by me in this forum.

 

[Vanadium 50]

There is no such thing as "the one-way speed of light". It is purely conventional. It is equivalent to solving one equation in two unknowns.