The response they gave was warranted. The post by Stafford was a complete display of ignorance with respect to how time is used in relativity. At the same time he mads a ridiculous comment that 'high school students' wouldn't make the mistake Einstein made. Skip the first part of this example because it is just the derivation for a time travel equation I'm going to use to make a point.

If you put the derivative of the effective potential term (from the equation of motion) into quadratic form (to find critical values) you get

r*^2 - L*^2r + 3L*^2 = 0

Where

r* = r/M, and L* = L/mM

Divide through by L*^2 and manipulate to get

r*^2/L*^2 = r* - 3 [saving this for a later substitution]

Setting dr = 0 in the Schwarzchild metric and substituting dphi = (L*/r*^2)dTau the metric becomes

dTau^2 = (1 - 2/r*)dt^2 - (L*^2/r*^2)dTau^2

To find the ratio dTau^2/dt^2 divide through by the bookkeeper time dt^2 and simplify to

(dTau/dt)^2 = (1 - 2/r*) / (1 + L*^2/r*^2)

Now substitute 1/ (r*-3) for L*^2/r*^2 and simplify to

dTau/dt = (1 - 3M/r)^1/2

This is a time travel equation. What is the ratio dTau/dt when r is a very large number? It is ~ 1. In other words dTau ~ dt when r is very large. What if I take my rocket ship and free fall to r = 3.000001 M and maintain a knife edge orbit for
172,800 seconds (2 days) measured with my wristwatch and I call this dTau. Then I
use this time travel equation to predict how much time was measured on a wristwatch back on Earth, while I was in orbit at r = 3.000001M, and I call this dt.
It turns out that the prediction would be ~ 9.48 years had elapsed on the Earth
wristwatch while 2 days had elapsed on the rocket ship wristwatch. The important thing to note is what dTau and dt represent. Both measure wristwatch time in a specific frame of reference. Go back and read Staffords post and then figure out why Anderson and Preby said it was a crock of Language Removed that doesn't have anything to do
with physics. Saying Einstein made a mistake by not choosing dTau to measure time
in relativity is just ignorant.

• ridiculous comments do not augment science writing - occupant - May 14, 2002 - 15:48 UTC
  • They are much easier... - bruce - May 15, 2002 - 14:23 UTC
    • sly, clever - something - May 15, 2002 - 15:38 UTC
      • I agree with.. - bruce - May 16, 2002 - 03:31 UTC
        • So a metaphor is not ridiculous even if far from exact? - occupant - May 16, 2002 - 05:51 UTC
          • I agree with Patrick and Bilge... - bruce - May 16, 2002 - 20:29 UTC
            • thanks, you took the easier questions and left the others to - occupant - May 16, 2002 - 21:30 UTC
              • Not sure what you are getting at... - bruce - May 16, 2002 - 23:48 UTC
                • nibbling around at the topics - occupant - May 17, 2002 - 04:14 UTC
                  • Tell me what you think wrt universal time... - bruce - May 17, 2002 - 04:49 UTC
                    • Universal may be like relative time but context frame bigger - spazcon - May 17, 2002 - 19:11 UTC
                    • Were you going to reply this year? - carefuluniverse - June 6, 2002 - 16:21 UTC
            • I agree with myself - occupant - May 16, 2002 - 23:44 UTC