Swans on Tea

I should probably just let all of this crap about the Conservapedia’s odius maltreatment of science, in the abuse of relativity go; in case you missed the addendum, drkyskull has an extensive debunking up at his new digs (he gets most of them, with one exception being the “clocks on the geoid” issue I tackled)

But I just can’t.

And it’s not because Schlafly’s blathering about the tenuous connection to moral relativism, when his argument for scientific relativism (his version of science being just as good as the “liberal” science) melts my irony meter. No, it was a footnote on that page that got my attention:

Contrary to the claims of Relativists, the GPS system has never been based on Relativity. The Time Service Department, U.S. Navy, observed that “the Global Positioning System (GPS) does not include the rigorous transformations between coordinate systems that Einstein’s general theory of relativity would seem to require” in part because “the effects of relativity, where they are different from the effects predicted by classical mechanics and electromagnetic theory, are too small to matter – less than one centimeter, for users on or near the earth.”

Time Service Department, U.S. Navy? Hey, that sorta sounds familiar!

(At one point I ran across a statement to the effect that this “GPS has never been based on Relativity” was endorsed by The Time Service Department, but I can’t find it now. No hits to Conservapedia show up in Google, so I assume they don’t crawl the site, but that means no cached pages). Time Service being the department at the US Naval Observatory, since that’s where the link to the paper leads; I’m not aware of there being some other Time Service department within the navy. If there is we’ll go clean their clock.

The paper in question (PDF) is by Henry F. Fliegel and Raymond S. DiEsposti of the Aerospace Corporation, and was presented at a Precise Time and Time Interval (PTTI) Conference; all that’s going on here is a web site hosting some conference proceedings. So in general, to say that Time Service “observed” this is way too strong of a statement. And I’ll go a step further. I’m not an official spokesman, so nothing I say has any kind of official weight or sanction, but I’ll step up just as close to the line as I can and say that I can’t see any circumstances where the Time Service Department would claim that relativity is not part of GPS, because it’s blatantly untrue! I’ll decipher the chicanery that’s going on here.

The statement is paraphrased from the abstract, and that’s apparently as far as anybody involved with this claptrap bothered to read. What is actually written is this

The Operational Control System (OCS) of the Global Positioning System (GPS) does not include the rigorous transformations between coordinate systems that Einstein’s general theory of relativity would seem to require

See what he did there? He omitted the first clause of the abstract, and made it sound like GPS doesn’t incorporate relativity. But what the paper is really saying is that the OCS doesn’t incorporate relativity. Why? Because it’s incorporated in the satellites! If you read the paper, or any of the many, many, many descriptions of GPS, you’ll see that the kinematic and gravitational time dilation effects are compensated for.

[E]ach GPS space vehicle (SV) clock is offset from its nominal rate by about -4.45×10^-10 (= -38 microseconds per day) to allow for the relativistic offsets between the differences between the SV and the ground. Of this -38 microseconds per day, about -45 are due to the gravitational potential difference between the SV at its mean distance and the earth’s surface, and +7 to the mean SV speed, which is about 3.87 km/sec.

This intellectual dishonesty is, unfortunately, par for the course for this strain of crackpot.