# Affecting Light Velocity

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Imagine an airplane that will start at point A and travel to point B and return to point A. Also that a wind is traveling in the direction of A to B. Say the plane travels 100mph the whole way, and the wind is traveling at 50mph. On the first segment of its trip it will travel at 150mph (wind speed added to initial velocity), and on the way back it will travel 50mph (wind speed subtracted from initial velocity). So the speed of the wind will be inconsequential because it's speed will be increased and decreased by the same speed of the wind. Therefore it does not matter if there is wind or not the plane will always return to it's starting point in the same amount of time. Now imagine the same experimental situation although the airplane is replaced by light, and at point B is a mirror which will reflect it back to its starting point. So, if the same circumstances hold (as proven by the airplane) we should not be able to recognize if the light was effected or not by the wind. Thus, how can we be sure that light can not be effected by an external force?

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The michelson morley experiment was designed to test this very notion. They expected it to show that there was a change in the velocity of light, but it proved conclusively that there was not.

http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

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Imagine an airplane that will start at point A and travel to point B and return to point A. Also that a wind is traveling in the direction of A to B. Say the plane travels 100mph the whole way, and the wind is traveling at 50mph. On the first segment of its trip it will travel at 150mph (wind speed added to initial velocity), and on the way back it will travel 50mph (wind speed subtracted from initial velocity). So the speed of the wind will be inconsequential because it's speed will be increased and decreased by the same speed of the wind. Therefore it does not matter if there is wind or not the plane will always return to it's starting point in the same amount of time. Now imagine the same experimental situation although the airplane is replaced by light, and at point B is a mirror which will reflect it back to its starting point. So, if the same circumstances hold (as proven by the airplane) we should not be able to recognize if the light was effected or not by the wind. Thus, how can we be sure that light can not be effected by an external force?

Check your math. Or, to be more precise, actually DO the math.

Let's say the trip is 100 miles each way. 100 mph = 1 hour each way = 2 hours.

100 miles at 150 mph = .667 hours

100 miles at 50 mph = 2 hours

total = 2.667 hours

Conclusion: the wind speed matters, and you can see if it's there.

(Which was the whole point of the M-M experiment, as Klaynos has already pointed out.)

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Oh yes, ok the michelson morely experiment did have simalarities although it was actuall to objects in motion traveling in a vertical and horizontal direction.

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@ physman - there is hardly any difference between what you are trying to prove and what the MM experiment tried to prove. The only difference is that you have replaced ether with wind. Anyways, it does not hold for light. The speed of light is a constant in physics. Just like the e/m ratio, G constant or Planck's constant. If you measured the ratio of the charge of electron to its mass in Andromeda, it would not change. Same for light.

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Thanks Gokul, I know of these constant ratios, but what I was most wondering about was, if this could be the reason that we cant see the change in light velocity.

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By change in light "velocity", in english this means "a vector", if I do not make a mistake, but it seems that with the lorentz transform, only the "speed" is invariant, "the norm of the velocity" ??

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By change in light "velocity", in english this means "a vector", if I do not make a mistake, but it seems that with the lorentz transform, only the "speed" is invariant, "the norm of the velocity" ??

A good example of why mathematics is required in physics.

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Light follows a geodesic, so to change the direction (in a vacuum) requires you bend the coordinate system, i.e. what general relativity discusses.

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Yes light woud have to bend as it has been proven to do so by experiments with eclipses and different positions of a single star. Although I was trying to specify the use of a mirror.

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Let us remain in the constant speed regimes (special), then, the speed addition can be summarized as this :

Addition of v (red), with several orthogonal speeds (determined by the green graduations)

Galilean(classical) :

Lorentzian(spec. rel.) : $c\oplus_r v=c$

If we however want that the velocity becomes an "vectorial absorbing" element : $\vec{c}\oplus^\perp_r \vec{v}=\vec{c}$, the speed addition would looks like something like this :

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Addendum : forgotten was the fact that in dimension 2, the relativistic speed addition is not commutative (i.e. $\vec{c}_y\oplus_r\vec{v}_x=\vec{c}_y,\forall v<c$, but $\vec{v}_x\oplus_r\vec{c}_y=\vec{c}_{\theta}$, theta is defined as in the graph)

hence, 1+2 does not equal 2+1, which is quite bizarre. (depends if you consider the train before the person walking in, or reverse order)

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