# Questions about the Speed of Light, Time, etc.

• B
• John Mcrain
In summary, the speed of light in a vacuum is a constant, as stated by Einstein's theory of relativity. Time is what a clock measures and is not an illusion. The ratio of distance and time is known as speed, and in order to keep the speed of light constant, both distance and time must change in concert due to the relativity of simultaneity. This is explained by the Lorentz transforms, and it shows that even though distance and time may not be absolute, the speed of light remains absolute.
John Mcrain said:
I know that light beam has diagonal trajectory, but I cant see it from this position/case..
This is a bit like a batter saying that he cannot measure distance when watching an approaching baseball with one eye closed. Then complaining when the ball hits him in the face. "Hey Ump, that ball could not have been moving because I could not see it moving!"

Say that the train is moving at 0.6 c and the light clock is 4 feet in height. If the light pulse has a 5 foot diagonal trajectory, it will take 5 nanoseconds to follow that trajectory, not 4. Even if we look from in front rather than from the side. The train and light pulse will have moved 3 feet forward in this time.

vanhees71 and Ibix
Ibix said:
So you have no concept of depth? How do you not walk into walls in your every day life?
No problem, in everyday-life only Newtonian spacetime is correct, and there are no such troubles as time dilation, length contraction, and all this...

vanhees71 said:
No problem, in everyday-life only Newtonian spacetime is correct, and there are no such troubles as time dilation, length contraction, and all this...
Yeah, but either @John Mcrain's visual function works different from every other person's on the planet and he's unable to conceive of perspective, or he's not thinking about what he's saying.

phinds and vanhees71
Ibix said:
... he's not thinking about what he's saying.
Forum decorum prohits a response

vanhees71 and berkeman
phinds said:
Forum decorum
I like that. Poetic, even.

vanhees71