# On Einstein's explanation of the invariance of c

Discussion in 'Pseudoscience Archive' started by RJBeery, Dec 8, 2010.

1. ### Motor Daddy☼☼☼☼☼☼☼☼☼☼☼Valued Senior Member

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5,105
Maybe you can tell me how you measure the speed of light in the box to be c?

In exactly which direction did it take light exactly .5 seconds to travel from the source to the receiver??? The x direction? How about the y and z directions, at .65 seconds????

There is no place in the box that you can measure the speed of light to be c, period. As a matter of fact, the speed of light in the box depends on which direction you measure it, as I've showed with numbers, that you yourself agree with.

3. ### phytiRegistered Senior Member

Messages:
318
Here is a progressive method that keeps v < c.

d is distance from origin to each clock
v is speed of origin
t_r is time (ls) for light to reach each clock from the origin
v_r is a speed component
r ranges from 1 to 3

time for light to travel d is:

t_0 = d/c = d light seconds, with c=1

select random time t_1

v_1 = 1-(t_0)/(t_1)

To assure v<c

t_2<( t_0)/[1-sqrt(1-(v_1)^2)]

v_2 = 1-(t_0)/(t_2)

To assure v<c

t_3< (t_0)/[1-sqrt(1-(v_1)^2-(v_2)^2)]

v_3 = 1-(t_0)/(t_3)

v = sqrt[(v_1)^2+(v_2)^2+(v_3)^2]

5. ### Neddy BateValued Senior Member

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1,767
In the real universe, the time for light to travel from the center of your 1.0 lightsecond cube to the center of any face would be 0.5 seconds, even if the cube is moving at a constant speed, in a constant direction. That is because the speed of light would be 1.0c in all directions inside the cube, as long as the cube is not accelerating. I understand that this idea does not seem to make sense at first, but if you studied relativity long enough, you would eventually understand how it all fits together.

Instead, you have chosen to imagine a different universe where the speed of light is only 1.0c in the absolute reference frame. There is nothing wrong with that, but considering that real life experiments do not support the idea, there is no reason to assume that is how the real world operates.

I agree with your numbers because I am exploring your imagined universe where there is an absolute reference frame, and the speed of light is only 1.0c relative to that one frame. In such a universe, the speed of light inside the cube would depend the cube's motion through the absolute frame, just like you said.

Since you had said that you were able to determine the absolute velocity of the cube from inside the box, I tried to help you find an equation that would make it relatively easy for you to make that calculation. Unfortunately the equations we came up with are still rather tedious when the absolute velocity of the cube is not known.

7. ### phytiRegistered Senior Member

Messages:
318
There's a difference in the propagation speed being constant due to electromagnetic properties of space, and measuring methods contrived to serve a specific purpose.

"That light requires the same time to traverse the path AM as for the path BM is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity." Einstein 1961

8. ### AlexGLike nailing Jello to a treeValued Senior Member

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4,304
Einstein died in 1955.

9. ### rpennerFully WiredValued Senior Member

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4,833
Since you dated it to 1961, I really don't know what point you are trying to make.

Einstein wrote that as part of a fictional dialogue with the reader in a pop-science work. But it is not an example of a naked claim resting only on Einstein's scientific authority.

It dates to the 1920 English version of Relativity: The Special and General Theory and a full quote makes it clear that the speaker is other than Einstein's, even if Einstein agrees to work with that definition, aka
"Distant events are simultaneous if a particular flash of light emitted from the midpoint of the straight line connecting the events reached the place of the events at the time of the events." (My paraphrase)

The argument may be predicated on the assumption, but the physics is always to be judged against Nature. So your quibble is baseless, because it's part of a rationale, not a fiat claim that stands by itself.

http://www.bartleby.com/173/8.html

Indeed in the previous chapter, Einstein describes why the claim is physically reasonable.

http://www.bartleby.com/173/7.html

The next chapter then shows that definition of simultaneity leads to this new thought: "Events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa (relativity of simultaneity). Every reference-body (co-ordinate system) has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event." (Actual quote)

http://www.bartleby.com/173/9.html

The next chapters develop this theory mathematically.

Then in chapter 13, Einstein applies it to 19th century experiments, and it checks. In chapter 14, we have the summary of the previous chapters: "Experience has led to the conviction that, on the one hand, the principle of relativity holds true, and that on the other hand the velocity of transmission of light in vacuo has to be considered equal to a constant c. By uniting these two postulates we obtained the law of transformation for the rectangular co-ordinates x, y, z and the time t ... the Lorentz transformation.
The law of transmission of light, the acceptance of which is justified by our actual knowledge, played an important part in this process of thought. Once in possession of the Lorentz transformation, however, we can combine this with the principle of relativity, and sum up the theory thus:
... General laws of nature are co-variant with respect to Lorentz transformations. ... If a general law of nature were to be found which did not satisfy this condition, then at least one of the two fundamental assumptions of the theory would have been disproved."

http://www.bartleby.com/173/14.html

So the consistency of the speed of light is an assumption of the argument, but a mere hypothesis in the physical theory -- a theory which passes many stringent tests every day in our world 90 years since this appeared in print.

If you just included it to sort out Motor Daddy, good luck with that.