4 ms·

> 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 we

by 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 ago
I 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 ago
That 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.

by jofer 12y ago

jacquesm 12y ago

I 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 ago

That 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.