Thread: Special Relativity misconceptions

Originally Posted by cmind

Well, I'm glad someone finally at least understands the concept...

Hey now. I understood from the beginning...

Why not measure speed that way?

Because it's confusing and obscures some stuff that's pretty fundamental to understanding relativity?

Suppose you're in a spaceship on a one-way trip to a star 100 light years away. Now, you can do the calculation for yourself if you know the math, but if we assume 1g acceleration in the ship frame with a turn-around at the halfway point and 1g deceleration, the entire trip takes just over 9 years in the ship frame, and just over 101 years in the Earth frame. The speed at the halfway point as measure on Earth is 0.9998c, and what about the speed on the ship? Well you could say that the ship is going at a speed of 0 in the ship frame, but much more useful would be to count the landmarks as they pass by. Using this pseudo-speed, the ship peaks at 52c.

As you've already pointed out, but as I feel the need to reemphasize, you're completely ignoring the fact that the observer on the spaceship measures the distance travelled shrinking. This is how that observer accounts for the fact that they've travelled 100 light years in 9 years.

Originally Posted by PhilosopherStoned

As you've already pointed out, but as I feel the need to reemphasize, you're completely ignoring the fact that the observer on the spaceship measures the distance travelled shrinking. This is how that observer accounts for the fact that they've travelled 100 light years in 9 years.

Yes, and? The point I'm trying to get across is that if you're willing to make it a one-way trip, you can indeed get places faster than 1 year per lightyear.

Originally Posted by cmind

Yes, and? The point I'm trying to get across is that if you're willing to make it a one-way trip, you can indeed get places faster than 1 year per lightyear.

Not your light-year.