Re: [Phys-l] (no subject)

[Moses Fayngold <moshfarlan@yahoo.com>]

Marc "Zeke" Kossover wrote on Wednesday, February 23, 2011 10:38 AM:

> An unstoppable object is impossible by definition in a universe with an
> unmovable object and vice versa.
> That is, the definitions of the two objects are mutually exclusive.


   I would make even a stronger statement, that even each object taken 
separately is impossible at least physically if not logically.
   No amount of mass can make an object unmovable. It is not necessary to act on 
it with an infinite force to bring it to motion. Just jump into a passing train 
and say "good by" to the object - it will start moving in the new frame. And the 
train will be as good a place to observe or describe anything, the object 
included, as the original platform. This is not even Einstein's relativity, this 
is the Galilean relativity. If we accept this, we discard the possibility of 
unmovable objects. 
The same with unstoppable object. Such objects are impossible in Galilean 
relativity since we can stop any object by jumping into a train moving with the 
same velocity. In special relativity there can be only one such object - the one 
moving with the invariant speed, e.g. light in vacuum. But when it enters a 
transparent medium it slows down, which makes it stoppable. We just jump into a 
spaceship passing by with the same velocity as that of light in the medium.
  Such a spaceship (admittedly unavailable today) would be as good a Lab as the 
initial one, and may be even better to study a stationary optical wave packet in 
a moving medium. That would be a really exotic (but possible!) experiment.   
If we accept this, we discard the possibility of unstoppable objects.
  Thus, either object taken separately is inconsistent with physics as we know 
it today.
Their combination is even more so.

Moses Fayngold
NJIT        



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