The Newly-Revealed Curves Of Gravity
Scientists and engineers have for the first time directly measured the curvature of gravity which could eventually produce a diverse and interesting assortment of scientific benefits.
Gravity is one of the fundamental forces of nature yet it is quite distinct from all the other forces permeating the universe. Probing its secrets could yield insights and technological wonders unmatched by any other aspect of nature (just don’t expect an anti-gravity device to be one of them).
Measuring gravity’s properties has become increasingly precise over the years. We can now measure the change in gravity’s strength over tiny distance; as little as just a few feet. Still however, there’s much we don’t know about this enigmatic force.
These accurate measurements have have been accomplished in the past using an amazing device called an atom interferometer. You may be familiar with its cousin, the laser interferometer, which can be used to detect ultra-minute changes in distance. It achieves this by splitting a laser beam and then recombining it down-stream. This recombination can create interference fringes; patterns of light and dark caused by the wave nature of light. Once the beams split, if there are any subtle disturbances along one beam path and not the other (like a magnetic field or tiny movement of the reflecting mirror), then the interference fringes (caused by the waves recombining) can reveal very fine details about those disturbances. For example, if one beam takes a slightly longer path than the other, even amounting to just 1/4 the wavelength of light, then the fringes can reveal that minute distance difference.
Atom interferometers can reveal similar information except they use atoms instead of light. Since atomic frequencies are much higher than light frequencies, the measurements that can be made can be 10,000 times finer than what could be gleaned from laser light. But atoms aren’t like light you may say. Well Quantum Mechanics would disagree with you. It tells us that matter has a wave-like nature just like light does. Atoms can be induced into revealing their wave nature (as long as you don’t try to measure them while they do it) by creating interference fringes when the separated waves recombine just like light does.
In the past, as I mentioned above, this technology has been used to determine the strength of gravity between a couple of closely separated points. In these latest experiments, they did the same for 3 plumes of ultra-cold atoms, each at a slightly different altitude. This determines what’s called the gravitational gradient between the points. They then measured the change in this gradient created by large masses which were included in the experimental setup. This produced for the first time insight into a new property of the gravitational field called gravity’s curvature.
These kinds of refinements in our understanding of gravity and the technology we create to look under gravity’s hood are not just laboratory and theoretical curiosities. They could have very interesting real-world and scientific applications.
For example, using these techniques we could create exquisitely detailed gravity and density maps of the earth which would then use changes in gravitational curvature to find geologic or archeological structures (even oil) buried under the ground.
This could also allow highly precise tests of the wonderful and wacky worlds of quantum mechanics and general relativity. Who knows what that might uncover.
The other big hope for atom interferometry and gravitational curvature is a more precise measurement for the strength of gravity, also called simply “G” or “Big G”. We are awash in gravity 24/7. You’d think we’d have this fundamental constant nailed down by now. We do not. This is primarily because it is far far weaker than the other forces of nature (strong, weak, electromagnetic) making it exceedingly hard to measure accurately. How weak is it? Well compared to the Weak nuclear force for example, gravity is about 600,000,000,000,000,000,000,000 times weaker.
Don’t feel so bad about your name, Weak force. At least you’re not really the weakest.
Image Credit: Phys. Rev. Lett. 114, 013001