PDA

View Full Version : Relativity question



Damburger
2004-Nov-26, 12:02 PM
From another thread:


Damburger wrote:
If you could run fast enough for lorentz contraction to make a 5 foot surfboard look 4 foot long, why would you need to take a bus? Eh?

To win 2 poiints on Mind Games, obviously
(and it wouldn't "look" 4 foot long, to the bus driver it would "be" 4 foot long)

Not sure if I understand that question. What is the difference between the board 'looking' only 4 foot long and it 'being' only 4 foot long if it is only so from the perspective of the driver?

Surely all he can know about the board is what he can measure about it, so is there an appreciable difference between lorentz contraction merely altering his measurements, and it altering the 'actual' length of the board in his perceptual universe

:confused:

AGN Fuel
2004-Nov-26, 02:33 PM
I think the distinction was simply being made that the reduction in length of the surfboard is not an optical illusion. In other words, if the bus driver (in the stationary frame of reference) were to actually measure the length of the board (in the moving frame), he would measure it at 4 feet, not the 5 that the person carrying the board would measure.

Evan
2004-Nov-26, 04:03 PM
Here is a thought. If the surfer turns the board sideways does it suddenly become narrower instead of shorter? What's happening to the atoms and structure from the stationary frame viewpoint? And, how does the Fitzgerald Contraction affect quantum mechanics?


Oddly enough, though Einstein published his famous relativity paper in 1905, and Fitzgerald proposed his contraction several years earlier, no one seems to have asked this question until the late '50s. Then Roger Penrose and James Terrell independently discovered that the object will not appear flattened

In other words, the board will not appear shorter to the bus driver.

Some answers (http://math.ucr.edu/home/baez/physics/Relativity/SR/penrose.html)