From a paper published at the Cornell University Library (published in Phys. Rev D):
There are very few direct experimental tests of the inverse square law of gravity at distances comparable to the scale of the Solar System and beyond. Here we describe a possible space mission optimized to test the inverse square law at a scale of up to 100 AU. This experiment would extend our understanding of gravity to the largest scale that can be reached with a direct probe using known technology. This would provide a powerful test of long-distance modifications of gravity including many theories motivated by dark matter or dark energy.
(Nb: the paper is published in Phys. Rev D, I link to the arxiv article. The form of publication is common where one publishes in arxiv before sending to a journal in order to provide open access to an article published in a subscriber only journal.)
(Score: 1, Interesting) by Anonymous Coward on Wednesday December 02 2015, @12:58AM
It is designed to look for a Yukawa-type correction to 1/r^2, which is an exponentially decaying term with distance. This isn't my bailiwick, but why specifically that form?
It is assuming a minimal effect from the Kuiper belt, and suggests a trajectory such as polar would do that, but we don't know jack about the Kuiper belt and its mass distribution; we only know about the things we can see.
It would be unlikely that this mission would go forward by itself. That would be a pretty big budget hit for the gravity guys. A mission like this would have science requirements creep. If you're sending a probe outside the heliosphere in about 7 years, you're going to want to have plasma probes, particle detectors, etc. on it. How does having all this stuff (and the resulting drag) on the spacecraft change the expected results?
(Score: 2) by Post-Nihilist on Wednesday December 02 2015, @01:39AM
I fail to see the troll, in the above post, it feels like gibberish but so does the paper. The abstract quite accessible but the paper quickly become impenetrable to someone outside the field of space probe desing.
Be like us, be different, be a nihilist!!!
(Score: 2) by Post-Nihilist on Wednesday December 02 2015, @01:47AM
After further reading, would replace space probe desing with deep knowledge of cosmology.
Be like us, be different, be a nihilist!!!
(Score: 0) by Anonymous Coward on Wednesday December 02 2015, @10:17AM
What is a desing anyway?
(Score: 1, Interesting) by Anonymous Coward on Wednesday December 02 2015, @01:41AM
They mention Yukawa because it is the form that 1/r^2 forces take when their carriers have mass. In other words, if you can show that gravity takes a Yukawa form, it proves that the graviton has mass. The funny thing is that if gravity has a Yukawa form that can be detected bu such a probe, it might be able to explain dark energy (not going to try to run the numbers, myself), but it makes the dark matter problem worse. Likewise, if you modify gravity to eliminate the need for dark matter, the dark energy problem becomes worse.
Back to Yukawa - the form the potential takes in a Yukawa type theory, up to factors of hbar and c, is exp(-mass * r)/r. For the technically inclined, yes, that is a modified spherical Bessel function of the second kind.
The people who study background radiations would love to put a camera or two (or photometers, at least) on a mission like this because it would be well outside of the solar system's dust cloud that is thought to be the dominant cause of disagreement between the direct vs indirect measures of background radiation in the optical to mid-IR.
(Score: 0) by Anonymous Coward on Wednesday December 02 2015, @03:47AM
Thanks for the reply (I guess a Yukawa fanboi must have been the one to mark it "Troll" :) ). So I see how this makes for a nice test of graviton mass, but what if gravity is 1/r^(2+epsilon) or some sort of polynomial expression?
I'll have to dig into the paper a bit. It isn't very often those theory guys write a paper that talks about real measurements, which is something I can wrap my head around, so as an experimentalist I feel compelled to turn the tables on them and put their feet to the fire for a change. :)
You'd just have to put particle detectors and magnetometers on it. To measure the interstellar environment would be awesome.
(Score: 1, Informative) by Anonymous Coward on Wednesday December 02 2015, @08:34AM
No. It's designed to look for various types of deviation. You have to look at more than the beginning of the article.
From section IV.B.:
In section IV.C. they also explicitly mention Modified Newtonian Mechanics (MOND).