The radius expands at the rate of ~186,000 miles per second from the original point of emission and from the current position of the source. c being constant for any frame of reference...

Correct, at any given position in space, light is ~186,000 miles from that point in every direction one second later. I am talking about the velocity of the source, not the velocity of the expanding light sphere. The velocity of the source can be measured from the point in space the light sphere was initiated to the distance the source traveled away from that point one second later.

The problem is that certain experiments say that is not true with light. And we can’t just automatically use an illustration for sound and apply it to light.

I just wanted to point out that your illustration is not ATM. In fact, here it is the same NASA illustration on a Ned Wright webpage:

http://www.astro.ucla.edu/~wright/doppler.htm

The illustration works for sound, but not for light, since sound waves travel in the medium of the air. The “waves” of sound are air molecule waves. But it’s believed that light does not require a medium of any kind.

So my point is, that while your illustration itself is not ATM, you can’t automatically describe a situation with light and compare it directly to a situation with sound. The M-M experiment and other experiments say that what you describe in words is not correct, even though your type of illustration is used on mainstream websites.

So I don’t know the answer to this apparent conflict between these kinds of illustrations and actual experiments and observations here at the earth. Maybe someone else here can explain it.

The measure of distance and time is not debatable, it is how we do it. If light travels at ~186,000 miles per second, one second later it will be ~186,000 miles from the point in space it was emitted, regardless of what the source did during that time. If the sun emits light towards the earth, regardless of what the sun does, that light is going to hit us ~8 minutes later.

Well, actually, I think it is debatable. I’ve seen plenty of debates here and elsewhere about it.

Yeah. Everyone isn't up to speed just yet.

The point is, because c is constant (to every observer) the source will still be at the centre of the original light sphere even though the source has moved. Which makes measuring velocity relative to the light sphere tricky. By your definition, it would make the velocity zero.

Everything MDT-1 says is valid in a frame where the Sun appears to be moving, so no one can tell him he is wrong in any kind of absolute way. However, what he is saying is indeed wrong in a frame where the Sun is not moving, i.e., in the frame of the Sun. There's no point in trying to tell him he's wrong, because he refuses to enter the frame where he would be wrong. Ever listen to a broken record? That is where this thread is heading.

How would you identify that position in space where the light is emitted? What is it relative to? In other words, if a source were to emit light in all directions and the light spread out in a sphere according to an observer at that source, then another oberver that is moving relative to the source in Euclidean space would see the center of the sphere moving as well, along with the sphere itself, so that position where the light was emitted is moving according to the second observer also, right?

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Every statement MDT-1 is going to make will come from a single reference frame, and every question you ask him will be answered in that frame. He sees every other frame as "mistaken." There is no point in trying to convince him that he is making an error because there is nothing wrong with that perspective, it just isn't the way physics is done, because physics is built for physicists, and physicists can be in different frames from MDT-1. This is the sum total of everything coherent that will ever come out of this thread.

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MDT-1,

(bold added)

Using Mach's principle of relativity there is no truth to how fast either car is moving so you could choose either car as a rest frame. So the answer to your question is yes.

Relative to the surface of the Earth both cars are moving at 60 MPH. Relative to the position of the Sun the Earth is turning on its axis about once every 24 hours. On the surface at the equator, this is a speed of about 25,000 miles per hour. The Earth travels around the Sun once a year. The radius of this path is about 93 million miles and the diameter about 186 million miles. The circumference of this path is roughly 584 million miles, the distance that the Earth travels around the Sun in one year. That's about 66,700 miles per hour. The solar system revolves around the Milky Way. The Milky way orbits the center of the local group of galaxies. There is also relative motion within the local group such as the motion between Andromeda and the Milky Way. We are also supposed to be moving in the direction of the Great Attractor -- so how fast are the cars really moving. There is no ultimate answer since motion is a relative condition.

If one adheres to alternative theories concerning relative motion involving preferred reference frames, such as gravity-centered reference frames for instance, then everything's motion within the reference frame should be measured relative to the frame itself as determined by the theory, such as the surface of the Earth for instance.

In the frame of the road, yes. This is called separation speed and it is equal to the sum of the two speeds.

v_separation=v_1+v_2

For v_1=v_2=v

v_separation=2v

In the frame of either car, no. The speed calculated in the frame of either car is called relative speed and it is equal to:

v_rel=(v_1+v_2)/(1+v_1*v_2/c^2)

In your example v_1=v_2=v, so:

v_rel=2v/(1+v^2/c^2) so,

v_rel<2v

You are misunderstanding how light works. You will always see the light as moving at c relative to you. Other observers need not.

Not to call you out on this specifically, but it is really important to drop this "what the observer sees" language, because it is often untrue and often confusing.

Relativity theory is about what coordinates one should assign different events. Often, events are assigned coordinates that are simultaneous with other events even though both of these events can only be assigned by a given observer long after the events happen (for the reference frame co-moving with that observer).

Observers are free to use whatever reference frames they wish. Often observers use detecting devices that make measurements within their co-moving reference frame easier than in other frames, but this does not restrict them.

Bold mine.

MDT-1:
The bolded statements, and therefore your entire thought experiment, are meaningless. Why? Because you fail to establish a reference that these two cars velocities are being compared to.

Next time, please present a complete thought experiment so that you will learn where you are making your mistakes.

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He said “on a road”. Surely everyone knows what a "road" is. Surely everyone knows what “stopped on a road” and “moving on a road at 60 mph” means.

Sam5:

Of course he said "on a road", in fact he said He didn't say, as you incorrectly quote, moving on a road at 60 mph. Please note that I did not dream up quote out of thin air.

Just because they are on a road doesn't mean that they are traveling relative to a road.

He further confuses the issues by asking inane questions regarding velocities as referenced to ???

And, please, from now on, leave your sarcasm to yourself.

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A "road".

[QUOTE]
Bold mine.

You ASSUME!

And, assuming that you are correct, then why is MDT-1 asking the questions

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That made absolutely no sense at all

The light you emit at any given time is ALWAYS the same distance away from you at a given interval in your reference frame.

Do you think if you have 2 flash lights and that if you are travelling at .5c in a given direction and that if you 2 lasers, in opposite directions, one in the direction of travel and the other opposite to the direction of travel that after 10 seconds the light pulse facing in the direction of travel will be closer to you then the one that is pointed in the other direction?

You are ALWAYS at zero velocity relative to yourself.

technically we are all glowing...just in the IR. Still doesn't help MDT-1's misconceptions.

Ummm you need to read up on SR.

BZZZZT, wrong answer. Yes it does, as does EVERY other object.

Test.
Measure the round trip time for 2 beams of light in opposite directions. 2 mirrors are placed 1000m from the light source in opposite directions. One to the east and one to the west. Since the Earth is rotating in your model the light bounced off the east mirror should return to the origin faster then the west mirror since the Earth is spinning in that direction.

Actual result, the light returns at the same point in time. This experiment is like over 150 years old.

First don't use mph, it is inexact and just not needed.
IF you are moving then when you emit light the distance in front of you is length contracted, time is also contracted. Net result you'll always observe light's position from you at the same distance.

Let me expand on this further. First of all by saying you are moving you are introducing a 2nd frame. What that frame sees and what you see are 2 completely different things.

Let us do the thought experiment.

You are in a HUGE sphere.
This box is 599,584.916km across.
You are in the centre of this sphere and you turn flash a light and as you expect 2 seconds later you "see" the wall of the sphere.

Now what would happen if you where moving?

You are always moving relative to something. So that something will see the light hit different points of the wall at different times but this is ok. This is what SR tells us will happen. To the person in the centre of the ball with the light source the light will hit every part of the sphere at the same time.

Lets go back to my experiment on the Earth.
The Earth's circumference at the equator is 40,075km. Divide this by 86,400 and you get about 464m/s.
Now we put 2 light detectors 2km apart and put a light source 1/2 way between them. The mirrors are due east and west of the light.
we flash the light and measure the time it takes to detect the light. Even though the Earth is spinning 464m/s the time it takes to get to both of those mirrors to people on the Earth is the same. Someone orbiting the Sun above the Earth would measure the time it takes the light to get to the 2 detectors as different.

Welcome to SR MDT-1. Please learn about it before telling others they are wrong about it.

AstroRockHunter,

What is your question?

Are you asking if the car is traveling on the road? Yes, the car is traveling on the road. Please assume full traction between the car's tires and the road surface. Furthermore, assume the tires are all 26.5" in diameter and remain that diameter for the purpose of this exercise. Also assume the tires are rotating at 761.0591 revolutions per minute, and that the rear gear is a 3.42:1 ratio and the transmission is in 4th gear at a 1:1 ratio. The engines are turning 2602.82 RPM. Furthermore, the load on the crank is 50 lb-ft, which means the engine is producing 24.7 HP at 60 MPH at a part throttle. The torque has a specific direction of "twist" on the axles.

Let's walk through the force and accelerations, shall we?

Sorry to hear that.

No it is not. If you throw a rock in the water and the waves travel away from the rock in a circular fashion, if you then moved the rock towards one edge of the circle, would the rock be in the center of the expanding waves?

How can I travel .5 c and be at a zero velocity?

Correct, we are all emitting light, and that light travels at c, regardless if we change position or not. Light travels ~186,000 miles per second after emission, regardless if you turn off the source or change the position of the source after emission or not. The light doesn't change its direction of travel if the source changes position, either.

Does it say if I travel .5c I can consider myself as stationary?