Some weeks ago I had contacted Professor Edwin F. Taylor at the M.I.T
regarding the discussions here about the GPS project "Project A"
in his book "Exploring Black Holes: Introduction to General Relativity".
He sent me the following info.

(I'm sorry being late in forwarding this to the newsgroup,
the reason is I hadn't checked this particular mailbox
of mine for some weeks now... :-) Sorry

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# From: Edwin Taylor eftaylor @ MIT.EDU
# To: "adem" adem @ topkale.net
# Subject: Fw: Taylor/Wheeler GPS time dilation calculation (ProjectA)
# Date: Mon, 13 Aug 2007 04:41:00 -0400
# Message-Id: ]
# In-Reply-To: 01d401c7dd5f$d3e80ba0$fe00a8c0@mx
# References: 00e701c7dd3a$86a8ce80$fe00a8c0@mx
# ]
# 01d401c7dd5f$d3e80ba0$fe00a8c0@mx

Dear Adem:

Thank you for the technical help. I have read through the interchange.
You may post the following from me if you wish.

**************
"Adem" has given me a heads-up about the conversation
in this group concerning the GPS project in our book
Exploring Black Holes (EBH), portions of which are posted
for download at eftaylor.com. Here are responses to the
three comments about the project that I can decode from the interchange:

1. In order not to clutter up equations with c,
we let v =(v/c)_conv where the subscript "conv" means
"conventional units." This is explained in Chapter 1 on the website.

2. In order not to clutter up equations with G,
we express the mass of a center of attraction as
M=(GM/c^2)_conv. This is in Chapter 2 on the website.

3. Equations (9) and (10) of the GPS project are for Newtonian mechanics,
and are used to give an APPROXIMATE value for the speed of
a satellite in orbit. It would be a mistake to substitute v^2
from these equations back into the GR equation (3).

If there are more than these three, please let me know at eftaylor.mit.edu

I especially appreciate seeing item 3. Those equations should
have the label (Newton) on them, and the use of these
nonrelativitic equations more carefully explained. Thank you.

John Archibald Wheeler is no longer active in physics.
Edmund Bertschinger of MIT and I are writing a second edition
of Exploring Black Holes. If you go to the website eftaylor.com
as revised in the past few days, you will see an invitation to
review new material for the second edition.

I am worried about the second edition in the following respect:
Drafts of the first edition were used in many classes. Moreover,
the students were required to hand in weekly "Reading Memos"
describing the difficulties they had with that week's reading.
These were immensely helpful in revision, draft after draft.

I have temporarily posted a published account of these reading memos
with the file name OnlyStudentKnows.pdf on the dropsite
http://www.eftaylor.com/pladropsite/

In contrast, only some of the new material for the second edition
was used in one class at MIT, and most of the new material will
not be used by us in a class at all. Any help you can give us with
comments and criticisms will be appreciated.

Sincerely, Edwin Taylor


Hello Mr. Taylor,

the discussion is in standard Usenet newsgroups (sci.physics, sci.physics.relativity).
If you don't have access to Usenet directly then you can use
the following link in your web browser:
http://groups.google.com/group/sci.p...b281addde7d50e

If the above link doesn't work due to its long length then try this shorter link please:
http://groups.google.com/group/sci.p...dde7d50e?hl=en
and then click on the "discussion" link on the top of the page
to see also the other postings under this thread.

The errors are described in the postings there. It seems some of
the given equations in the projectA-part of the book are erronous.

Regards
Adem

--
Edwin F. Taylor
eftaylor @ mit.edu
http://www.eftaylor.com/

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