Re: What's wrong with this?

From: George Murphy <>
Date: Wed Jun 23 2004 - 19:07:55 EDT

----- Original Message -----
From: "Innovatia" <>
To: "ASA Listserver" <>
Sent: Wednesday, June 23, 2004 2:53 PM
Subject: Fw: What's wrong with this?

> I'm a little late in commenting on a dying thread, but I can't resist
> pointing out that the gravity gradient causes what NASA and aerospace
> engineers call "microgravity" across the height dimension of objects in
> fall. So one never attains to a pure weightlessness even in orbit.

True, which is why I used the qualification "locally." By proper choice of
coordinates one can get rid of gravitational "force" along a worldline
(i.e., at a spatial point over the course of time). But you can't get rid
of the _difference_ of forces at two nearby point - the "tidal stresses."
In general relativity these are related to components of space-time
curvature. This is why you die when you fall into a black hole: Even
though you're in free fall, eventually the tidal stresses pull you apart.

Received on Wed Jun 23 19:24:34 2004

This archive was generated by hypermail 2.1.8 : Wed Jun 23 2004 - 19:24:36 EDT