Built on Facts

Failing at Gravity

A while back I mentioned I was starting the project of reading Neal Stephenson’s rather lengthy Baroque Cycle. I’m most of the way done with the second book, so we’re coming round to the 2000-page mark. It’s a brilliant work thus far, though it’s very difficult to summarize. The plot is rather, well, baroque. If I had to cram it into one sentence I think it might be “The world undergoes a phase transition from medieval to modern via the development of science and finance.”

The series is heavily populated by actual historical people. Among these are the transcendentally brilliant Isaac Newton and a somewhat less capable and today less-well known scientist named Nicolas Fatio de Duillier. Newton developed the theory of gravitation and Fatio tried to explain its mechanism of action. This is a sticky thing to do, because it’s not actually necessary for a theory to have a mechanism of action. Some do – the classic ideal gas law PV = nRT is a consequence of the fundamental properties of gas molecules bouncing around, for instance – but other properties of particles and fields just seem to be fundamental. There might be mechanisms, and mechanisms for those mechanisms, but in some cases the chain of regress does seem to terminate with a fundamental principle that is simply built into the laws of the universe. To this day, gravity as described by Newton (and refined by Einstein) is one of those things.

But Fatio gave it his best shot. He proposed that the universe was suffused with a gas of tiny and nearly undetectable particles randomly moving around in all directions just like the molecules of a gas.* A planet sitting in space has these particles crashing into it from all directions, but since the particles are moving in all directions there’s no net force from any side.

But if you have two planets, then some of the particles crashing into Planet A will never make it to Planet B. Therefore Planet B has a deficit of particles hitting it from the side facing Planet A, and it feels a net force in that direction from the rest of the particles hitting it from the other side. Same thing for the other planet. Here’s Wikipedia’s visualization:

i-5ccee919fae08093853b93721b1263f4-150px-Pushing2.png

The farther apart the planets are, the less of the particles are blocked. In fact, if you assume some of the particles are absorbed or substantially slowed by the planet they hit, you can argue that the net loss of particles due to a planet is constant. Distribute this imbalance over an imaginary large sphere of radius r surrounding the planet and you’ll see that the net-flux-per-area scales as 1/r^2, just like the force law in Newton’s gravity. So maybe Fatio’s theory does provide an actual mechanism for gravity without just a priori accepting the inverse square law.

But there’s problems, too. There ought to be “air resistance” from the particles as the planets move through space. Then there’s the fact that the force is proportional to surface area hit by the particles, not to the mass. This can be remedied by assuming a tiny interaction cross-section due to the particles, but if this is true they must be moving very fast indeed to produce the required force – many times the speed of light. And in that case the heating due to the “air resistance” of the particles would be impossibly high. Furthermore, if the particle shadows of two planets overlapped, the sun’s gravity on the farther planet should be shielded. No such effect has been observed.

For these and other reasons Fatio’s theory had to be rejected as unworkable. Still, like many wrong theories it wasn’t a total loss. Some of the theoretical and mathematical tools used to explore the consequences of this type of gravity ended up being useful in the kinetic theory of gases and the theory of the behavior of dust in plasmas and interstellar space. We can’t all be Newton, but I like to think Fatio would have at least been pleased his idea found some new life in those other forms.

*Not an unreasonable guesss; we know that this is pretty much the actual story for neutrinos and probably the story for dark matter. However, neither would work to produce the effect postulated by Fatio.

Comments

  1. #1 Matt
    February 10, 2010

    Sounds very similar to the Casimir effect.

  2. #2 JM
    February 10, 2010

    I’ve seen at least one crank reproduce this with “spin-0″ gravitions.

    But how about an entropic force ala Verlinde (very much in the news lately). Wouldn’t that produce a similar effect?

  3. #3 Uncle Al
    February 10, 2010

    Fatio’s theory is easily tested. Make a torsion balance (in a vacuum tube, etc) with a centrally-suspended light stiff bar. Its one end is a tungsten bob a meter above an American southwest flat desert floor. The bar’s other end is another tungsten bob (slightly lighter to balance) suspended from 20 meters of stiff carbon fiber hanging below ground level.

    Sunrise, moonrise, sunset, moonset. There will obviously be periods when the two bobs are differentially shielded from the “particle wind” by at least 11 miles’ thickness of dirt and rock (density ~3 g/cm^3) vs. atmosphere. Long-arm interferometer for torsion rotation readout.

  4. #4 karlo pinar
    February 11, 2010

    “Fatio gave it his best shot. He proposed that the universe was suffused with a gas of tiny and nearly undetectable particles randomly moving around in all directions just like the molecules of a gas.* A planet sitting in space has these particles crashing into it from all directions, but since the particles are moving in all directions there’s no net force from any side.” an interesting conclusion! Could it be really possible? I would like to learn more about your facts so could you please help me.. please visit my site at
    http://shortstoriess.webs.com .. I also have blogs there, you could post a comment if you want! THANK YOU SO MUCH! :)

  5. #5 anon.
    February 11, 2010

    “But there’s problems, too. There ought to be “air resistance” from the particles as the planets move through space. Then there’s the fact that the force is proportional to surface area hit by the particles, not to the mass. This can be remedied by assuming a tiny interaction cross-section due to the particles, but if this is true they must be moving very fast indeed to produce the required force – many times the speed of light. And in that case the heating due to the “air resistance” of the particles would be impossibly high. Furthermore, if the particle shadows of two planets overlapped, the sun’s gravity on the farther planet should be shielded. No such effect has been observed.

    “For these and other reasons Fatio’s theory had to be rejected as unworkable.”

    Wikipedia is a bit unreliable on this subject: Fatio assumed on-shell (“real”) particles, not a quantum field of off-shell virtual gauge bosons. The exchange of gravitons between masses in the universe would cause the heating, drag, etc., regardless of spin if the radiation were real. So it would dismiss spin-2 gravitons of attraction, since they’d have to be everywhere in the universe between masses, just like Fatio’s particles. But in fact the objections don’t apply to gauge boson radiations since they’re off-shell. Fatio didn’t know about relativity or quantum field theory.

    Thanks anyway, your post is pretty funny and could be spoofed by writing a fictitious attack on “evolution” by ignoring Darwin’s work and just pointing out errors in Lamarke’s theory of evolution (which was wrong)…

  6. #6 Nige Cook
    February 11, 2010

    “This can be remedied by assuming a tiny interaction cross-section due to the particles, but if this is true they must be moving very fast indeed to produce the required force – many times the speed of light.”

    Or just increasing the flux of spin-1 gravitons when you decrease the cross-section …

  7. #7 Uncle Al
    February 11, 2010

    http://arXiv.org/abs/0706.2031
    Physics Today 57(7) 40 (2004)
    http://physicstoday.org/vol-57/iss-7/p40.shtml
    http://cfa-www.harvard.edu/Walsworth/pdf/PT_Romalis0704.pdf
    No aether

    http://relativity.livingreviews.org/Articles/lrr-2005-5/index.html
    Phys. Rev. D 81 022003 (2010)
    http://arxiv.org/abs/0801.0287
    No Lorentz violation

    There is no vacuum background drift in the massless sector (photons) to 10^(-16) difference/average over a year’s observation, simultaneous opposite latitude and longitude sites at Berlin, Germany 52°31′N 13°20′E (optical) and Perth, Australia 31°53′S 115°53E (microwave).

    The unconscionably omitted massed sector is easily examined with enantiomorphic atomic mass distributions. Two solid single crystal spheres: one each space groups P3(1)21 and P3(2)21 quartz or P3(1) and P3(2) glycine gamma-polymorph. Niobium plate (Type I superconductor), cool, Meissner levitate in hard vacuum. If there is any background vacuum interaction of any kind, the balls will spin in opposite directions (oppositely handed propellers in a flow).

    Glycine has 1.6 times more atoms/volume than quartz (7.869 vs. 12.556 A^3/atom), 0.6 times the density of quartz (1.584 vs. 2.649 g/cm^3), and all glycine dipoles H3N(+)-CH2-COO(-) are aligned parallel head-to-tail. Single crystal quartz is commercial, easier to fabricate, has zero vapor pressure, and is electrically unpolarized. (Google “glycine density” 1.1607 g/cm^3 should be 1.6107 g/cm^3, for the alpha-polymorph.)

    Somebody should look.

  8. #8 RWA
    February 11, 2010

    This is totally off-topic, but Vernon Ehlers, the first physicist in Congress, is retiring this year, which will be a tremendous blow to science in the House. But since Ehlers is a Republican, every other science blogger is choosing to ignore the news.

  9. #9 andy
    February 12, 2010

    very interesting, thanks :)

  10. #10 Jerjoshy
    February 12, 2010

    Do you think why is this happening?
    It is something to do with PHYSICS!!!

  11. #11 robert
    February 12, 2010

    Interesting,wish I went to college to learn more about physics…thanks

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