It is very clear that light travels ~186,000 miles per second. Once the light starts traveling away from the source, does the light's velocity change if the source changes position? No.

Checking... yeah, still true.

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If I throw a ball at 30 ft/sec, and while the ball is in flight I change my position, does that mean the ball's velocity changed? No, the ball's velocity is measured from the point I released it. It has nothing to do with my position after release.

MDT, I am genuinely curious; why do you think only you are correct while all the evidence and theory contradicts you?

Does the light's velocity change if the source changes velocity?

No.

You talk about "the" ball's velocity as if it were an absolute quantity. It is not. That's what everyone has been saying, this is what EXPERIMENTS say. You are the only one who doesn't get it.

Again, you are being sloppy about frames of reference. Fix that, and you'll have taken a big step toward figuring things out.

Do you not see how this answer is inconsistent with your assertions re: absolute velocity in post #148?

Whoa, hold on a minute.

There is a big difference in saying I accelerated the ball 30 ft/sec^2 from its original velocity, to saying the ball's velocity is 30 ft/sec.

If a ball is traveling in one direction at 1,000 ft/sec with me in my hand, and I accelerate the ball 30 ft/sec^2 in the opposite direction of travel,, that doesn't mean the ball changed direction of travel, it means I "decelerated" the ball's velocity. The ball's velocity is reduced, but still traveling in the same direction as before I accelerated the ball.

ie... If a ball is traveling along with a train at 100 MPH, and I toss it off the back of the train, the ball continues to travel in the same direction, just at a reduced rate. The velocity of the ball is in the same direction of travel as the train.

Balls and light behave very differently.

If you are on the train at 100mph and throw one ball forward at 5mph and one backwards at 5mph (both relative to you and the train). An observer on the embankment will see the balls moving at 105mph and 95mph.

Agreed?

If you are on the train at 100mph and send a flash of light forwards and one backwards you will see both beams of light fly away at c. An observer on the embankment will also see both beams of light travelling at c. (Not 100+c and 100-c)

Agreed?

If not, why not?

Are you saying the observer on the train is traveling 100 MPH? Does he know that he is traveling 100 MPH relative to the tracks? Does he also know the ball is traveling 100 MPH?

Does that matter?

If so, why?

Do you agree with the previous statments or not?

If not, why not?

Whoa indeed. Again, here is what you said originally, in full:

Note the conspicuous absence of any explicit reference to acceleration in the quote. You only talk about the ball's velocity being measured from the point of release. By your statement, that velocity is 30ft/sec. Don't shift things around after the fact. It makes you look...shifty.

The observer on the train accelerated the balls to 105 and 95 relative to the tracks whether he realizes it or not.

Do you agree with the two scenarios in #160 or not?

If not, why not?

I agree that the ball was accelerated to 105 MPH relative to the tracks, and 95 MPH relative to the tracks. The train was in motion at 100 MPH, relative to the tracks, whether he realized it or not.

Good. And do you agree with the second part?

If not, why not?

The light will travel at c away from the point it was released, but if the observer does not have a true zero velocity, the light will not be an equal distance from the observer after the light travels a specific duration of travel.

There is no "true" velocity. Your velocity is always in relation to some other object and since the universe has a near infinity of different objects that means you have an equal number of velocities. What we can say is that anything travelling away from you at c will always be 299,792,458m away from you in 1 second according to your watch no matter what direction you say you are travelling in and no matter what what direction that object travelling at c is going.

Like it has been said before no matter how fast you say you are going, compared to some other object, you can NEVER gain ground on something travelling at c. The "something" travelling at c will always move away from you at 299,792,458m/s. This has been tested. This has been tested over 150 years ago and since then our test have only got more accurate and you know what not a single test EVER has shown any light moving away from its emitter slower or faster then c even if the emitter is moving, because as it has been said over and over, everything is moving relative to other objects in the universe.

Light always travels at c. If I am traveling at .5c and shine a light, how far away is the light from me after 1 second?

I'm sorry but you were quite happy to talk about the balls' relative velocity to the train (+5 and -5 mph) and the track (105mph and 95mph) but now you are being all ambiguous and evasive again.

What is the velocity of the light relative to the source on the train?

What is the velocity of the light relative to the of the tracks?

If you are on the train at 100mph and send a flash of light forwards and one backwards you will see both beams of light fly away at c. An observer on the embankment will also see both beams of light travelling at c. (Not 100+c and 100-c)

Agreed?

If not, why not?

............me 1 sec (93,000 miles from point of release)
.................................light 1 sec (186,000 miles from point of release)

You are travelling at .5c relative to some other object that is not light. The light will always be 299,792,458m away regardless of the direction you say you are travelling in and regardless of the direction of you point the light. Welcome to SR, remember this HAS been tested MANY MANY MANY times. I'm sure there are a few university students here on these boards that can give you first hand accounts how they verified this while going to university. There are probably even a few people that proved this while in high school of even earlier for a science project and or fair.

The train is irrelevant to the speed of light. Light travels at c. What the train is doing during that same time is irrelevant to the speed of light.

The tracks are irrelevant to the speed of light. Light travels at c, regardless of what the tracks do during that time.

The speed of light is always c, so light will be 186,000 miles away from the point in space that it is released. The train, or tracks have nothing to do with the speed of light.

yes to an outside observer to you that you are travelling .5c relative to

to you
me 1 sec (0 miles from point from you)
.................................light 1 sec (186,000 miles from you)


this is what SR lets you figure out. What do other frames see.

Yes 1 person can make a measurement and say something is 1 mile long and another person can make the same measurement and say it is 2 miles long. This is allowed. This has been tested. Just because you are ignorant, and seemingly wilfully by your repeated statements that you are and your refusal to listen to the many explanations given to you and the many links provided showing the test that verify it, doesn't mean it is wrong. It only means that you are being wilfully ignorant and argumentative and proud of your wilful ignorance.

Exactly! It doesn't matter if the train is parked at the station, travelling down the tracks at 100mph or if the train was launched into space at .5c. The train will always see light move away from itself at 299,792,458m/s and it doesn't matter what direction. This is because space and time get contracted in the direction the train was accelerated in.

No one is disagreeing that it will be 299,792,458m from the point it was released 1s later, according to that point's clock and meter stick. What we are saying is that the train, that you say is moving, who has a clock that runs at a slower rate then the clock at the side of the track, who has a meter stick that is contracted to be smaller based on the formula

will also see it 299,792,458m away after 1 second of their clock and 1 of their meter stick.

See 2 different frames that measure 2 different things and everything is fine because SR provides the formulas to work out what the other will measure.


If SR was wrong then the formula above that is used to calculate your GPS position would have you in some random location around the world by now.

Is "whether he realizes it or not" significant to you? If so, why? I can't figure out why you mentioned it.

So close, and yet so far (relatively speaking).

After one second (and allowing for an approximation of c):

1. The speed of light is always c relative to the observer, so the light sent forwards will be 186,000 miles away from the source on the train.

2. The speed of light is always c relative to the observer, so the light sent backwards will be 186,000 miles away from the source on the train.

3. The speed of light is always c relative to the observer, so the light sent forwards will be 186,000 miles away from the observer on the embankment.

4. The speed of light is always c relative to the observer, so the light sent backwards will be 186,000 miles away from the observer on the embankment.

As MDT-1 seems oblivious to evidence and explanation, I am out of here. I am beginning to suspect [s]he is just having a laugh.

[just realized there are all sorts of assumptions that I have elided in there - I hope the principle is still clear]

OK. One last question. Why do you believe your view is right, in the face of all the evidence? Is it one or more of:

a) You have some evidence that contradicts what is currently known?
b) You have read about SR and interpret it this way?
c) It is based on something else you have read?
d) You just "know" you are right and everyone else (and the evidence) must somehow be wrong?
e) Other reason?

e

Velocity has a direction of travel, a distance traveled, and a time traveled.

If I have a velocity, it is my own velocity, not relative to another object. I can be the only object in space with nothing to compare to, and I can have a velocity. That velocity means I traveled a distance in a specific time interval, relative to nothing!

Furthermore, distance and time can not be measured in the now, they are measures of the past, of what already happened.