Re: Illusion of C



Ben Finney wrote:

Lance Berg <emporer@xxxxxxxxxxx> writes:


Jefferson wrote:

If it takes 4.3 years for light to travel from star A to star B,
and you get in a ship and appear to live thru 4.3 years and arrive
at your destination, then it seems to you that you traveled at
light speed. If it feels like it took 2.15 years then you feel
like you traveled at twice the speed of light.

No. It feels like you covered half the distance.

How are those not synonymous?

If I have to travel five miles, and I walk it at one mile an hour, I
get there in five hours.


And your perception is that you travelled five miles.

Imagine I'm locked in a sealed box. The only way I "know" I traveled 5 miles is that when you let me out of the box at the end, I'm at a location which is five miles distant from my start. I might have traveled 10 miles in a huge arc, at 2 miles an hour. Or maybe you moved my destination to me, and the box just sat there. But to me, I start here, I end there, five miles. And my clock says 5 hours passed. Illusion is, I traveled 5 miles per hour.

If I walk it at two miles an hour, you -could- say that it feels
like I'm walking half as far


No, that would not describe your perception. Your perception is that
of covering the same distance faster.

Both seem the same to me, barring observation of nearby landmarks or air rushing past my head or something. Distance from start to finish, over time from start to finish.

Either way I get to my destination in half the time.


And either way, your perception of the distance (if you're actually
looking around you) doesn't change.

As you approach 'c', though, the *perceived distance* between objects
changes. The distance in the direction of travel visibly reduces.
Your apparent acceleration reduces the closer you get to 'c', but the
universe itself appears to compress in the direction of your travel.

Only while I'm actually travelling. Since I'm going to decellerate back to "stationary" (or in other words, to match speed with my destination) each time, when we get out of the ship, the universe isn't going to be looking compressed. I'm Here, Earth is "waaaay over there" 4.3 LY away. And when I return to Earth, Proxima Centuri is 4.3 LY away. Ipso facto, it looks like I traveled 8.6 LY. And since I only lived thru 6.45 years, it seems to me I traveled 8.6LY in 6.45 years... at the "speed of light" out, and at "twice the speed of light" back.

Since the people on earth are going to disagree with me about how long the trip took, I think it would be handy to know how much that disagreement is going to be.

Lance
.

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