[stryker]

That's precisely why Einstein's theory of relativity was so groundbreaking. It stipulates that the speed of light must be the same relative to every frame.

Let's say you're moving nearly as fast as the speed of light. Are you flying side by side with light particles? No, because if they were, you would measure their speed as being close to zero relative to you. The theory says you will STILL measure the beams of light as flying away from you at the speed of light relative to you.

Imagine how the universe must conform to make that the case! The universe essentially makes your time tick slower in order for light to still travel that much faster relative to you.

This phenomenon has been confirmed (along with basically every other prediction that Einstein has made). There are some subatomic particles that we know has a half-life of X seconds. However, when they're traveling quickly, they actually end up living orders of magnitude longer because of time dilation.

In every day life, if you throw a ball at 70 mph on top of a car that's going 30 mph, the ball moves at 100 mph. You can't do the same math once you start reaching the speed of light.

[fennecfoxen]

More pedantically, the math you've been trained to do to find a velocity 's' as the sum of two velocities 'v' and 'u' in the same direction is s = v + u.

The real formula is s = (v+u)/(1+(vu/c^2)).

For small values of v and u, vu/c^2 is approximately 0, leaving you with the standard (Galilean) formula, but only as an approximation.

See Wikipedia for a discussion and formulae for vector addition: http://en.wikipedia.org/wiki/Velocity-addition_formula

[mcguire]

"The theory says you will STILL measure the beams of light as flying away from you at the speed of light relative to you."

It's not really "the theory"; in this case, the actual experiment[1] predated the math.

[1] http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experi...

[bane]

"Let's say you're moving nearly as fast as the speed of light. Are you flying side by side with light particles? No, because if they were, you would measure their speed as being close to zero relative to you. The theory says you will STILL measure the beams of light as flying away from you at the speed of light relative to you."

Something you said just clicked. I think I may now clearly "grok" relativity for the first time.

It reminded me of the http://en.wikipedia.org/wiki/Mahalanobis_distance

which calculates different distances given a vector field w/r to a Euclidian space.

It's not the same thing, but when thinking about what Mahalanobis distances measure, I used a helpful mental model of the measure forcing the vector field apart, enforcing a kind of constant distance between the vectors and then measuring that delta. It seems like a similar concept is at play here, only what we're measuring is different.

I'm aimlessly musing here, but I feel a kind of grokiness I haven't felt before after your post.

[malexw]

You explained in 8 sentences something that I have been struggling to understand for years. Amazing, thank you!