🚀 go-pugleaf

In article <BsBI3x.5F1@wpi.WPI.EDU> phillies@wpi.WPI.EDU (George D. Phillies)
writes:

>This is the third in a series of posts on teaching orthodox 
>special relativity.  The objective is to treat points at which students 
>become confused, usually through a failure to gain a complete, precise, 
>and correct understanding of various concepts.  As in previous posts, 

...

>I always begin this treatment by emphasizing to the students that there are
  two 
>sorts of teaching: installing blank facts on a vacuum, and installing true 
>facts where false facts already are in place.  The latter is a lot harder.  
>Unfortunately, that is what is now necessary, because most students reach 
>special relativity with wrong ideas about time.  The ideas are very
  deep-seated, 
>because they are built into the English language, rather than only having
  been 
>introduced in High School Physics.

...

>relativity.)  The flaw is symbolized by a single questions, heard by students 
>at least since pre-school: 
>
>"WHAT TIME IS IT?"
>
>The question is wrong.  By "wrong", I mean that by asking a schoolchild a 
>question you are implicitly teaching the child that the question has a well-
>defined answer.  The answer taught to every schoolchild implicitly teaches
  the 
>child a false picture of the world.  The answert taught to every school
  child, 

...

>There is a further issue (here Einstein appears to have confused matters, at 
>least for third parties, at least a trifle), involving speed of signal delays.
>Suppose one sees a stroke of lightning, and then listens for the thunder.  As 

...

>"Simultaneity" has nothing to do with speed-of-signal delays.  No matter 
>whether signals are sent as light in vacuo, sound waves in air, or
  hand-written 
>notes whisked down pneumatic tubes, it is always true that there is a delay 
>between the moment of departure of a signal, and the moment when the signal 
>arrives at its destination.  By careful construction of an experiment, one
  can 
>always determine what the speed-of-signal delay is, and correct for the delay.

...

>  It is not unusual for students to ask "will you actually see that effect if 
>  you look with a telescope", meaning "what happens if you examine the 
>  experiment in terms of a single observer".  Some of these students are
    acting 
>  on the belief that special relativity is purely a description of speed-of-
>  signal effects, underlying which is a universe in which Newtonian clocks
    and 
>  Newtonian simultaneity reigns.  Some of these students have the inverse 
>  error, namely that the underlying universe obeys special relativity, but
>  relativistic effects are masked by speed-of-light delays, so that a real 
>  observer will never actually see relativistic phenomena.  These students
    need 
>  their thoughts clarified, so that it is made clear that relativity is not 
>  caused or hidden by speed-of-light delays.  
                                                                         ^^^
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


THIS IS VERY MISLEADING.  THE FACT IS THAT THE EFFECTS OF SPECIAL RELATIVITY
(ESPECIALLY THE AMBIGUITY OF SIMULTANEITY FOR OBSERVERS MOVING AT DIFFERENT
VELOCITIES) ARE CAUSED IN A SIMPLE AND DIRECT WAY BY SPEED-OF-LIGHT DELAYS.

PHILLIES SEEMS TO BELIEVE THAT SPEED-OF-LIGHT DELAYS ARE UNIMPORTANT BECAUSE
YOU CAN ALWAYS JUST CORRECT FOR THEM.  THE PROBLEM WITH THIS IS THAT THE
ALGORITHM FOR CORRECTING FOR SPEED-OF-LIGHT DELAYS IS CRUCIALLY DEPENDENT ON
THE VELOCITY THAT YOU BELIEVE YOU ARE TRAVELING AT.  IF YOU ARE STANDING
STILL THEN YOU SHOULD FIGURE THAT YOUR RADAR PULSES HIT THEIR TARGETS EXACTLY
HALF-WAY IN TIME BETWEEN SENDING THEM AND RECEIVING THEM BACK, WHEREAS
IF YOU YOURSELF ARE MOVING THEN YOU HAVE TO FIGURE THE DIFFERENCE IN DURATION
BETWEEN THE FORWARD AND RETURN TRIPS.  AS A RESULT, THERE IS NO VALID
ALGORITHM FOR CORRECTING FOR SPEED-OF-LIGHT DELAYS WITHOUT KNOWING YOUR OWN
VELOCITY RELATIVE TO SOME MASTER INERTIAL FRAME, AND OBSERVERS MOVING AT
DIFFERENT VELOCITIES, EACH CONVINCED THAT THEY ARE THE ONE STANDING STILL,
ARE UNABLE TO AGREE ON THE MEANING OF SIMULTANEITY, EVEN AFTER THEY HAVE
TRIED TO CORRECT FOR SPEED-OF-LIGHT DELAYS.

THAT'S ALL THERE IS TO IT:  SPECIAL RELATIVITY IS THE STUDY OF THE DISTORTED
PERCEPTION THAT OCCURS WHEN A MOVING RADAR OBSERVER TRIES TO CORRECT FOR
SPEED-OF-LIGHT DELAYS, WORKING UNDER THE ERRONEOUS ASSUMPTION THAT THEY
THEMSELF ARE STANDING STILL.  GIVEN THIS HINT, ANY BRIGHT FIFTH-GRADER CAN
WORK OUT THE KINEMATICS OF SPECIAL RELATIVITY ALL BY THEMSELF.  (OF COURSE
OTHER ASPECTS OF SPECIAL RELATIVITY GOING BEYOND THE MERELY KINEMATIC, SUCH
AS "E=MC^2", ARE A LOT HARDER TO UNDERSTAND, BUT THAT'S ONLY BECAUSE THEY
DEAL WITH CONCEPTS, LIKE "ENERGY", WHICH ARE HARD TO UNDERSTAND EVEN IN A
NON-RELATIVISTIC SETTING.)

THE KINEMATICS OF SPECIAL RELATIVITY IS SIMPLE COMMON SENSE, A SIMPLE AND
INEVITABLE RESULT OF SPEED-OF-LIGHT DELAYS.  (ROBERT FIRTH AND DARYL
MCCULLOUGH HAVE EXPLAINED THIS RATHER CLEARLY MANY TIMES HERE ON SCI.PHYSICS,
I THOUGHT.)  IF YOU ARE TRYING TO LEARN SPECIAL RELATIVITY, PLEASE DON'T
ALLOW ANYONE TO CONVINCE YOU THAT IT IS NECESSARY TO CHECK YOUR COMMON SENSE
AT THE DOOR AND REPLACE IT WITH REVELATIONS SUPPLIED BY THEM.  SUCH WOULD-BE
ARBITERS OF ORTHODOXY MIGHT STAND A LITTLE "THOUGHT CLARIFICATION"
THEMSELVES.



-JAMES DOLAN