Robittybob1

@Janus - That is rather difficult to understand but I'll have a go at it. The bit that really confused me was this: .Is that physically possible when you have set the center clock to fire at 0.00 sec? That sounds like a malfunction if it fires on two occasions.

I'll correct the errors first: "spacecraft A is moving at 0.9c to the right spacecraft B is moving 0.9c to the left. Neither craft is moving faster than 0.9c but if Observer in craft A measures the speed of craft B. (via doppler shift) he will get a Doppler shift of 1.8c. If craft A is going the same direction as craft B and the same speed he will measure a speed of 0 m/s via doppler shift. The light does not advance twice as fast. LIGHT ALWAYS MOVES AT C>>>>> You can however get different doppler red/blue shifts." That seems nearly right but in these relative motion situations one observer is at rest and the other will be in motion. I'm not sure how Doppler and relativity relate to each other. Do we add the two motions before you do the doppler calculations IDK.

In #43 Strange says "But, yes the maximum separation speed is 2c - but it is important to note that no one, in any frame of reference, sees anything moving at more than c." I accept this but if we look at the original example the craft is going at 0.5c not nearly 1c, so the separation will be 0.5c + 1c (for the light and the craft are going in opposite directions). Just as in the video when the light is going in the same direction as the ship the light advances twice as fast as the ship so it appears to have only gone half as far in front of the ship compared to the stationary ship. They then say time dilation accounts for some of the change, so there is more time to go the same distance but it didn't account for all the difference, and the implication is that length contraction accounts for the rest. This next bit is not in the video: If they fired their lasers to the rear can you use length contraction and time dilation to account for the even greater apparent distance traveled by the light? The arguments used in one direction seem inadequate in the opposite direction. There isn't "time contraction behind you" or "length dilation behind you" is there? When the direction of travel is opposite to the light travel it seems like you need the opposite of time dilation and length contraction to account for the rate that the light wavefront separates from the source. The EO has no problem accounting for the change, it is only those onboard the moving ship that need time dilation and length contraction explanations hence allowing c to be invariant. yet the ones onboard aren't aware of either of these two effects so they can't use them in their arguments. I tend to think the arguments in the video are wrong, for speed of light measurements are always based on the two-way speed of light. You can only sense the light when it comes back to you. Like it has to be reflected back and you measure the time interval for light to travel the distance and back. https://en.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatus is this a start? Mordred - I think you might have pasted your reply into the wrong thread http://www.scienceforums.net/topic/93472-gravitational-lens-and-gravitational-waves-question/page-3#entry909902 I can't see a connection to the topic sorry. If one was use the physics of the situation of the ball thrower throwing the ball and running toward the wall, then there might be a connection. But I don't see that. So throwing the ball is a separate event to the running toward the wall or away from the wall.

Remember we agreed that in the forward direction the craft moved at half the speed of light, but light shown to the rear would separate from the craft at 0.5c plus c. To the front they say it is because of time dilation and length contraction they can account for this apparent slower moving wave front (0.5c) but how do they account for the same at the rear? Can you see where the video is in error?

Would thoughts of time dilation and length contraction confound the experiment? I am wondering how they would explain the light from the forward direction going less distance per sec than to the rear directions as determined and defined by the EO? That's how they could try that, you have one source of light and split the beam of light into forward traveling and rearward light beams. Bounce them off the front and back walls and time their return.

OK but how does the inertial frame measure the speed of light (in the situation where it is moving forward yet firing the laser to the rear? As I see it the inertial frame (IFoR) is not aware it is moving so it doesn't have the concept of forward and backward, but they are noted by the external observer (EO) . Is the experiment to measure the speed of light done within the craft or exterior to it? I'm thinking it would have to be done in the craft, inside the IFoR.

Was I just trying to get out of having to express my psyche? I'm not even sure if I know myself that well. On the other threads I think they would find me complicated, yet I think of myself as being fairly basic, yet with the ambition to improve. I'll be back but I've got to feed the calves before it gets too hot.

I'm sitting here worried I might throw the wrong switch!

It reminded me of the switchboard for the different sexes. http://www.blog.joelx.com/wp-content/uploads/2008/02/man-woman-control-panel.gif

Well it could be a thought experiment or it could be an actual situation. If you on the ground use parameters that were recorded on the inertial frame you would need to think how you get to know these facts. It might seem basic but does it hold true when the inertial frame is going forward but fires the laser to the rear? Does the light waveform separate from the craft at over 1c? Is the maximum value of that separation 2c? I.e craft going forward at near c and fires a laser to the rear at c

If one of your inputs in your calculations is the speed of a missile from the perspective of the inertial observer, then I suppose that information has to be communicated. It might seem obvious but I wanted to check the relationship of the craft's speed compared to the speed of light at the full range of speeds. It would seem intuitive that the speed expressed in fraction of c relates to how fast the light front moves compared to the craft by simple subtraction. For instance if the inertial frame is not moving from my perspective (external observer) the laser light wave is moving at speed c away from it. So at all speeds, the speed of light minus the inertial frame velocity from the perspective (external observer) equals how fast the light front moves ahead of the inertial frame from the perspective (external observer). Do you agree with that bolded statement? Edit: I removed the word "stationary" ahead of the term "external observer" for all motion is relative.

Yes sounds right. So the craft is 0.5c slower than the light front. Yes that is what I was getting at in #7. For I was trying to see if these problems can be worked out without having to communicate with the other craft.

Sorry about that. In #7 I was varying Strange's statement and I deliberately gave the wrong answer (erroneous conclusion) , but immediately asked if it was right. I was hoping by doing that it would stimulate a degree of discussion, which it has, but not along the lines I was hoping for.

Fair enough, but I'd also say I tended to be attracted to heavier women too. It was something I noticed but I kept it to myself, in fact this is the first time I have admitted it publicly.

in #7 I said "Will it look like the light rocket moves ahead of the mothership at 0.5 c?" That is not from the perspective of the mothership but the perspective of the external observer. Yes I know that, but how fast will the laser wavefront move compared to the mothership from the perspective of the external observer?

Yes but if it fires a laser type weapon how fast is the light front moving as seen by the external observer? So is it obvious to the external observer that the craft is going at half the speed of the light front? That is what 0.5c must mean surely?

That 0.5c was 0.5c ahead of the mothership which already doing 0.5c. So the light rocket is definitely going at c in all frames (I'm sure I made that clear). A light rocket could be like laser gun. Yes that is clear, and I agree. But in my case when the mothership fires the light rocket, how fast relative to the mothership do I see the light front moving? The mothership is doing 0.5c and the light is doing c, so it seems that I would see the craft going half the speed of the light front. Surely?

We read about that, where people some people still see themselves as overweight and then they actually become anorexic. I'm not saying that is the case, but in your case as you say it is an insecurity because of the past. Have you tried saying affirmations? It was a craze many years ago.

What does that mean exactly? Fat personality - plenty of it, tons of it, more than enough to go around? Tells us some more.

In your example who is measuring the speeds? Are they being measured by two different people? Are you sure the rocket can't go at c, it is made of light after all in my case. If the rocket is made from light it will travel at c (the speed of light) and if the mothership is doing 0.5 c the light front of the rocket must be 0.5 c ahead of the rocket. All my measurements are from the friendly position, for I don't trust the aliens. On board the mothership the aliens think their light rocket is traveling at the speed of light, from their perspective the position I am at is passing them at 1/2 the speed of light. Their conventional rocket that does 1/2 the speed of light is moving at half the speed of the light rocket. From my perspective the conventional rocket is traveling 0.8 c as you say (I'll take your word on that).

I've been a bit amused lately where they add speeds recorded by different people. Imaging if the other craft is an alien and they don't speak our language, so we can't communicate with them, how do you describe what is happening then? "For example, if you are travelling past the Earth at 0.5c and you fire a rocket ahead of you at 0.5c then, from my perspective on Earth, I will see the rocket moving at 0.8c (rather than at c). becomes: For example, if you see an alien mothership travelling past the Earth at 0.5c and it fires a rocket ahead at 0.5c then, from my perspective on Earth, I will see the rocket moving at 0.8c (rather than at c)." Is that still true? I think the velocity of the rocket will be c therefore the rocket must be made from photons. Will it look like the light rocket moves ahead of the mothership at 0.5 c?

There is a little more to it. They are saying during the ringdown phase there could be a net motion of the merging BHs the center of mass could start shifting in space and on merger the CoM drifting off. Now I'm only taking their word for that as I can't quite picture that happening ATM.

"diminishing returns in increasing speed for each increment of energy increase" and "The speed increase is incrementally even smaller". Hit the nail on the head there. So can we explain it all just with mass and velocity?

Attraction to heavier women? Answer: They have more matter so they generate a lot more gravity.

It was one I was reading last night. http://w.astro.berkeley.edu/~gmarcy/astro160/papers/binary_black_hole_mergers.pdf