Three scientists walk into a cafe.
Table For Three
7 days later
Question for the community ... If two spacecraft leave Earth at the same time and are both travelling at 0.5 c but in opposite directions, can a light signal from one craft reach the other?
PapayaMandrill
I think the answer is yes, a light signal from one will reach the other. The real question is what are their velocities with respect to each other from each of their respective frames?
PM
4 days later
The signal from the ship will come out with a frequency of 1/2 and a speed of C. The signal will overtake the second ship. The frequency of the signal will again be halved.
Gary Simpson
I think not. If I knew why you need this information, I would answer more definitely.
Thank you for the reply. I think you are correct. At least this is the interpretation from SR. But we have never actually done such an experiment and may never be able to do such an experiment. So, how can we know with complete certainty?
Best Regards,
PM
Thank you for the reply. I do not need this information. It is simply a mental exercise. Prior to Einstein, your answer would be the answer that I believe everyone would give. But if you believe Einstein's postulate that the measured velocity of light is constant in all inertial reference frames, then the Newtonian addition of velocities is no longer valid.
My personal opinion is that the geometry that most of us conceive is not the geometry of the universe. Whether or not that implies space-time geometry, I do not know.
Best Regards,
PM
In my theory there is a simple explanation of Einstein's postulate. I proceed from my own considerations.
2 months later
- Edited
i have he suspicion / that there is not such thing that people call to be angle @[deleted] is this also your guess ?
IN - i have a friend that is pregnant she doesn't know physics and its busy with homework tasks , i would like to invite her at the next coffee
AE - I know who you speak about , it is a l little slow to walk saw you both last week in the mall,
IN - Yes, we were having an argument she was stepping behind annoyed, she has talent i 've asked her to count the corners of a cube mentally , with not much previous experience she figured out pretty fast less than a second
LE- By the way, the angles inside a cube can be verticefied, lets meet at the timelesscafee there we have more room
AE - E raised to aye theta equal the so called sum of cosine and sine of theta, is a nice equation , where is this place?
JM - Across the street with the kindergarten, IN have you made progress with that problem
IN - No i've reached a dead end
meanwhile , true story , the bug has exited the laptop,s hiding place , i've killed it in three steps, swept (broomed) off the table, he landed on his back hurt , and picked it with a piece of dried consruction yellow ducktape , in the waste plasticbag
Dear PapayaMandrill,
thanks for the very entertaining lunch talk! Since there is no free lunch, I am wondering who paid the bill in the end... 
Jokes aside, that was quite a nice idea, I wonder whether you also thought about more about our current cosmological standard model, because, it is based on Einstein's theory of gravity, yet, the Friedmann solutions still have one preferred reference frame, called the fundamental observers that more or less breaks Einstein's desire for full relativity in the sense of equality for all reference frames. (The fundamental frame is the one from which observers see the universe around them as homogeneous and isotropic in spacetime and on the matter-energy sector.) In that sense, I wonder, does Newton win the argument in the end by being able to keep a fundamental overall reference frame? And what would the three physicists have answered to LE with his idea introducing complex numbers about whether they appreciate or question a mathematical elegant formalism even if an immediate physical realisation of all variables is hard to find? (as you might have guessed, these are the two points I struggle with)
Bests,
BeigeBandicoot.