When this article came out a few months ago I was surprised it got so much press. If I'd had any idea it would get so much attention (and merit a paper in Nature) I would have pushed for us to do it :) The authors did a great job doing the experiment and addressing the possible systematics--doing torsion balance experiments the right way is difficult--but there doesn't seem to be anything too new here.
He called it “weighing the world”, because it allowed him to calculate the mass of the earth.
I felt a tiny bit sad he didn't go 5 minutes longer and estimate F and G with a little math from the video frames. He'd already demonstrated the noise amplitude nicely.
“The motion of the rod was only about 0.16 inches (4.1 mm)”
At first sight, I find that surprisingly large. Thinking of it, he used heavy objects (300kg in total), it isn’t hard to twist a wire, and falling down even a meter hurts, so perhaps it isn’t that surprising.
Light actually exerts a force (even like tweezers) so it's not a good choice for this kind of measurement.
They must have done an amazing job of removing any electrostatic or magnetic effects since those so quickly dominate at these dimensions. The gold ball isn't so bad to discharge, but typically glass fibers are used, which can build up charges. My expectation is that they used radically different frequencies on the two ball supports and very high oscillator Q (they're pendulums in a vacuum) to separate them mechanically since they have to be in the same chamber.
People have tried placing "screening materials" between the masses to reduce electro-magnetic coupling, but those tended to cause their own non-gravitational effects.
I reckon you might as well use neutrino's, they're easier to detect and easier to produce.
Remember how big and complicated LIGO and VIRGO are and that's to detect the loudest signals of that nature in the universe (at a very narrow frequency range)
I'm not sure why we'd want to even if we could, though I guess "hey look at this, I can push a black hole into another one" would likely be regarded as a rather meaningful kind of message on its own to anyone with the technology to hear it.
If you can do that, a lot of other civs are going to give you a wide berth. And some of the rest may consider you a problem.
I wanted to know what masses they were using ~90 mg, and that had the answer. It was surprising to me it wasn't in the article.
This was the most infuriating part of the article. How hard is it to use SI units in a popular science magazine?
If the BMV effect is observed it would falsify Penrose's conjecture that something unusual and nonlinear happens around the Planck mass (conversely the experiment could also begin to probe and measure that regime and find Penrose was on to something).
Of course I understand it's beyond any reasonable measurement capability --masses should be infinitesimal and the system be isolated from any other interactions, the question is about if it's theoretically possible. Like, "it's impossible because masses should be below the Planck mass"
A domain review paper https://iopscience.iop.org/article/10.1088/1367-2630/14/5/05...
"Abstract. This paper describes gravity experiments, where the outcome
depends upon both the gravitational acceleration g and the Planck constant h¯ .
We focus on the work performed with an elementary particle, the neutron"
The best model that explains all of the data is the Einstein Field Equations. The most useful way to interpret the model is to think of space and time geometrically (albeit a very weird kind of geometry in which one of the dimensions has the bizarre property that a straight line is the longest distance between two points). If you view it that way, the geometry acts as if it has intrinsic curvature: otherwise straight lines (like beams of light) don't go straight.
So... it doesn't get to directly measure curvature. It's not even clear if it's meaningful to "really" measure curvature. Push on the whole notion of "measure" hard enough and it turns out that it's not nearly as clear as we think it is. Everything is "theory laden": a measurement is always a matter of interpretation, even the most straightforward ones.