[time-nuts] gravity, space and time

Tom Van Baak tvb at LeapSecond.com
Fri Dec 12 22:39:07 EST 2014

> If I understood it well, we should occasionally encounter gravitational
> waves going through, well, the whole galaxy. As time and space are
> intertwined, those ripples may be measured somehow I guess.
> Isn't this that "we as time nuts community" can help the scientific
> world with? E.g. create some kind of grassroots effort where our very
> accurate clocks can detect this?

Hi Folkert,

Perhaps you are confusing accuracy with sensitivity. When you want to measure something you need a sensor. If you have a choice you pick the one that's most sensitive.

The very reason atomic clocks so accurate is that they are poor sensors. I mean, if you want to measure gravity, a plain quartz oscillator is much better. A pendulum clock is even better. Or just drop a rock off a building. You want something macroscopic, not something atomic. To measure those alleged space time ripples, you want something that measures motion, not something based on quantum mechanics.

Consider that LIGO, the coolest gravity experiment in the world, is essentially a mirror hanging by a thread. It's a macroscopic, mechanical experiment.

If you still don't believe me, here's a quick comparison of two gravity sensor technologies:

1) You can measure g to one digit of accuracy by dropping a coffee cup off a 4 foot table. The equation is d = gt²/2. If the cup takes 0.5 seconds to fall, then the result is g = 2d/t²= 9.7 m/s². Nice result; easy experiment.

2) To make a similar measurement of g using atomic clocks, you do something like http://leapsecond.com/great2005/tour/. The equation is df/f = t/T = gh/c². Here t (time dilation) was 22 ns, T (elapsed time) was 42 hours, h (altitude gain) was 1340 meters, c (speed of light) is 299792458 m/s, so the result is g = tc²/Th = 9.7 m/s². Nice result; hard experiment.

What's wonderful about the universe is that the two methods agree. But which method could easily be improved if you wanted many more digits of resolution, or wanted to measure short-term variations in g?


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