4 ms·
Even if you could measure altitude to centimeter precision, the clock speed would depend on gravity, not altitude, and the Earth is too lumpy (in terms of densi
by SiVal 12y ago
Even if you could measure altitude to centimeter precision, the clock speed would depend on gravity, not altitude, and the Earth is too lumpy (in terms of density) for that centimeter to tell you much when comparing two different locations. I also think (speculate) that with this degree of sensitivity, we will be able to measure some gravitational fluctuation due to the currents of molten iron swirling inside the Earth.
With all this uncertainty, all you could do, after getting two clocks to approximately the same altitude, would be to say that clock A is currently running a factor of X faster than clock B. What you wouldn't know is how much of the delta was due to altitude, how much due to unequal density underneath, and other such factors, compared to how much was due to the internal differences in the clocks themselves that you were trying to factor out by using multiple clocks.
- jofer 12y ago> we will be able to measure some gravitational fluctuation due to the currents of molten iron swirling inside the Earth. As a geologist, I really wish that were possible, but what you're describing is just far too small of an effect to be detectable from the surface. Gravitational acceleration follows an inverse square law. Any signal from flow in the outer core is completely swamped by the far larger (at the surface) changes from things like local hydrological conditions, ongoing human activity, etc. On the bright side, though, we can already measure changes in the acceleration of gravity incredibly precisely without directly using relativistic effects. Even from orbit, things like regional flooding and changes in the mass of ice sheets can be detected purely from changes in acceleration of gravity. Have a look at some of the work that came out of the GRACE mission (also see the ESA's GOCE satellite): http://www.jpl.nasa.gov/news/news.php?release=2004-224 http://www.jpl.nasa.gov/news/news.php?release=2004-224
- jacquesm 12y agoI think there is a huge difference between having a measurement of time be affected by gravity and detecting that such an effect influenced your measurement. After all that implies an even better standard to compare against and that's the whole problem here. So even if this difference is undetectable for geological purposes it could very well screw up really accurate time measurements. It all depends on whether or not those effects compound or cancel out, in the case of gravity they will likely only compound.
- HCIdivision17 12y agoThat is crazy. Like, I always knew that was technically possible, but we quickly shot the thought experiment down as silly in high school/college. I mean, feeling the changes in gravity to monitor the surface of a planet? That's patently absurd. I'm having a lot of fun being wrong today! EDIT: Aaaand that's from 2004. Which means I really wasn't paying attention while in college. Considering my roommate went to JPL to work on a sister project, I feel a bit of shame just learning about it now.