If Two Spaceships close at a speed of 1.4c ?

[JesseM]

This is terrible news for the Cosmological Red Shifters - but maybe GOOD news for Halton Arp...

Again it seems like you're trolling. If you don't explain your basis for the claim that the closing speed must be c (or find a single example of a reference which says this), or explain why you think this is in conflict with the idea of cosmological redshift, then I suspect this thread will soon be closed, this forum is supposed to be for substantive discussion rather than taunts and one-liners (also see the IMPORTANT! Read before posting thread, which points out that people aren't supposed to use this forum as a soapbox for arguing that mainstream conclusions in relativity are flawed).

 

[Lightheavyw8t]

The bottom line is the maths. If ships A and B are a distance L apart in the Earth frame when they turn their headlights on then they will see each other after a time t_{see} = L/(v+c) and they collide after a time t_{collide} = L/(2v). For any v<c, (v+c) will always be greater than (2v) so it will always be true that t_{see} &lt; t_{collide} and they will always see the other ship before the collision. Neither ship is "surprised".

Thank you for the math, it's really flattering. But no matter how you slice it, light is NOT going to go from A to B faster than c - unless you, too, wish to refute Einstein...

 

[yuiop]

The bottom line is the maths. If ships A and B are a distance L apart in the Earth frame when they turn their headlights on then they will see each other after a time t_{see} = L/(v+c) and they collide after a time t_{collide} = L/(2v). For any v<c, (v+c) will always be greater than (2v) so it will always be true that t_{see} &lt; t_{collide} and they will always see the other ship before the collision. Neither ship is "surprised".

Just for fun I thought I would add that if only one ship turns their headlights on, so that they are relying on the radar reflection to warn them of imminent collision, then the equation for the radar return time is 2Lc/(v+c)^2 and this is always less than the collision time L/(2v) so they will still always have a warning period before the collision even if they have to wait for a radar reflection.

 

[Dale]

Sigh - another Einstein refuter, apparently...

You would do well to check your attitude at the door. Janus and JesseM are well qualified and understand relativity very well. The fact is that you do not understand the terminology being used.

Specifically, a "closing speed" is not the velocity of either information or any object, so it is not limited to c. Here is a brief glossary:

velocity - the derivative of the coordinate position wrt time
speed - magnitude of the velocity
displacement - the difference in the coordinate positions of two objects
distance - the magnitude of the displacement
closing speed - the derivative of the displacement wrt time
relative velocity - the velocity of an object in a coordinate system where the reference object is stationary

From these definitions all of what the other posters have been trying to teach you follows.

 

[Doc Al]

Thank you for the math, it's really flattering. But no matter how you slice it, light is NOT going to go from A to B faster than c - unless you, too, wish to refute Einstein...

You've given us a good chuckle, but enough's enough. Thread closed.

 

[Janus]

Thank you for the math, it's really flattering. But no matter how you slice it, light is NOT going to go from A to B faster than c - unless you, too, wish to refute Einstein...

If anyone here is refuting Einstein, it is you.

The following quote is taken from his own book on Relativity:

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

Now in reality (considered with reference to the railway embankment) he is hastening towards the beam of light coming from B, whilst he is riding on ahead of the beam of light coming from A.

In his own words he is saying that the closing speed of light is not always c.

Before you accuse people of refuting Einstein, be sure you know what he actually says first.