From: V Laxmanan (vlaxmanan@hotmail.com)
Date: Thu Aug 21 2003 - 04:20:01 PDT
Eratosthenes, Newton, and Asteroids Posted by V. Laxmanan, August 21, 2003 Following up on the recent postings (August 17 and 19, 2003), we again return to the question of the meaning of time. In the Eratosthenes Experiment, students measure the length of the shadow cast by a vertical stick, at “local” noon, on the day of the equinox. In other words, each student must use some kind of a clock. Hence, we must be clear about the meaning of time itself, and must also be clear about how time is measured. This, surprisingly, is not as simple as it sounds when it comes to the world of physics. As discussed here, Newton uses the rotational motion of the earth (relative to the fixed stars, he uses sidereal day) to compare the magnitude of the centrifugal forces acting on a body placed at the earth's equator and at the latitude of Paris. Newton's calculations are aimed at establishing support for his inverse square law for the force of gravity. This also means that in physics, we must use the sidereal day as the basis for the accurate measurement of time. Einstein, however, proposes tthat we use light as the basis for building a clock. However, he also uses the Newton's inverse square law for the force of gravity. This means that a clock such as the one envisioned by Einstein must be calibrated using the the measure of time emerging from the rotational motion of the earth (sidereal day). In this context, it is also of interest to note that in a recent article, published in 2001, Su has argued that puzzling results of the famous Michelson-Morley experiment can be understood if we allow for the corrections due to the earth's rotational motion. In Su's work, earth bound electromagnetic waves were used to determine the propagation delay times using a global positioning system (GPS). The GPS satellite re;eatedly broadcasts microwaves carrying a unique code. The propagation delay time from sateliite to receiver can be determined very accurately. The earth's orbital motion (annual journey around the earth, taken into account in the original Michelson-Morley experiment) is shown to have no effect on the propagation of electromagnetic waves. However, the earth's rotational motion is shown to have a significant effect. Su concludes by noting that this interpretation is fundamentally different from that based on (Einstein's) special relativity theory (of 1905). I can be reached at vlaxmanan@hotmail.com. Attachments: Newton3.doc _________________________________________________________________ <b>Get MSN 8</b> and help protect your children with advanced parental controls. http://join.msn.com/?page=features/parental