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B Name of experiment confirming mass-gravitational attraction?

  1. Feb 5, 2016 #1
    Not sure where this particular question belongs.

    Do you know of any Cavendish type measurements of G, in which the mass (and ~density) of the attractors (gravitational sources) are controls, and the number of particles (fermions or maybe quarks+leptons) is the independent variable?

    The Eöt-Wash group has done Eötvös style tests of the WEP using test bodies of the same mass/density with different baryon/mass ratios, but this was a test of the WEP.

    I haven't been able to find any information about experiments to test whether gravitational acceleration (warping of spacetime) is more closely correlated with the number of particles of an attractor, or the mass of the attractor.

  2. jcsd
  3. Feb 12, 2016 #2
    I'm still curious if anyone has any information about any experimental measurements of G (the gravitational constant) in which mass of the attractor* is a control, and the number of particles (quarks, or quarks+ leptons) in the attractor is varied.

    *attractor being the "source" of the gravitational field
  4. Mar 17, 2016 #3
    I can't find the name of the experiment that confirms that gravitational attraction towards an object is correlated with the object's mass instead of being correlated with the number of particles in the object. I'm hitting a Google block, since I don't know the name of the experiment or theory (hope I don't have brain damage!#@#).

    Does anyone know the name of the experiment (similar to the below experiment) and the corresponding physical theory?

    The following diagram shows a torsion balance experiment similar to Cavendish experiments, that uses a laser reflected off a mirror attached to the torsion balance so that small deflections of the torsion balance can be detected on a "far away" wall.

    The cylinders are 100kg ~100% Al on one end, and 100kg ~100% Be on the other end because those substances have decent particle number difference for the same mass (there are more particles per mass in the Al than in the Be, so the deflection would be in the direction of the Al if gravitational acceleration is correlated with the number of particles in the sample, instead of the mass of the sample).

    There would be no deflection if gravitational acceleration was correlated with mass, instead of number of particles.


    To reiterate:

    I'd like to know the name of this experiment, and the name of the theory that gravitational acceleration is more closely correlated with mass than the number of particles in a volume of spacetime. I'm hitting a Google block...
  5. Mar 18, 2016 #4


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  6. Mar 18, 2016 #5
    I don't think the original Eötvös experiment, or the modern experiments by the Eöt Wash group answer this question.

    Both (I think) are focused on confirming that inertial mass and gravitational mass are the same, and that objects experience the same acceleration in a gravitational field regardless of their composition. In other words, the Eötvös type experiments confirmed that the force to accelerate a 100kg object at 9.8 m/s^2 is equal to the force that the object experiences in the Earth's gravitational field.

    The Eötvös type experiments didn't address whether a 100kg object with more particles in it caused greater acceleration towards it than a 100kg object with a lesser number of particles in it. The Eötvös type experiments confirmed that gravitational mass * acceleration = inertial mass * acceleration.

    So that's not the name of the experiment or theory that I'm looking for. I'm drawing a total blank here, and I can't Google it without a name for the experiment, or the theory associated with the results!!! Totally frustrating!@#!

    Thanks for your reply!
  7. Mar 18, 2016 #6

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    The Eötvös experiment tested, I believe, copper sulfate crystals and copper sulfate in solution. The former has thousands or millions of individual crystals, the latter 10^23-ish molecules in solution - many. many m ore particles. Does this do what you want?
  8. Mar 18, 2016 #7


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  9. Mar 18, 2016 #8

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  10. Mar 18, 2016 #9
    I want conversation, so yes, but it's not the answer I'm seeking (explained below comic).


    The Eötvös experiments did not measure the attraction towards the crystals or solution, instead they confirmed that equivalent masses with different numbers of particles experience the same attraction towards the gravitational sources (they confirm UFF: the universality of free fall, offhand I think the old Eötvös experiments used the Sun as an attractor??).

    So it's not the Eötvös experiment that I'm familiar with, unless there is another one? It's also not the Cavendish experiment that I'm familiar with.

    It might not be a "named" experiment, sort of like the experiment that confirmed the precession of Mercury doesn't have a name that I am aware of, but I can Google precession of Mercury and get the results I want.

    I can't figure out the Google search terms for this experiment... get way too many non-pertinent results, so I need the name of an experimenter or something along those lines to narrow down the search.
  11. Mar 18, 2016 #10

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    What do you mean by "particle"?

    It can't be elementary particle, because that would lead to a composition-dependent gravitational effect, and you repeatedly say the answser is not "Eötvös".

    It can't be the usual everyday macroscopic definition of "particle", because that leads to a round of name-calling on your part - and would also show up as a composition-dependent gravitational effect -- and you repeatedly say the answser is not "Eötvös".

    So what the heck is it?

    As an aside, the fact that you haven't asked a clear question is no reason to lash out at the people who are trying to help you.
  12. Mar 18, 2016 #11


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    Only because the Cavendish experiment, in its original form, used the same material for all the masses. But it seems like a Cavendish experiment that used different materials for the different masses--the same mass of each, but different composition, such as a lead sphere and an aluminum sphere of the same mass and size--would be what you are looking for.
  13. Mar 18, 2016 #12
    The mods combined this thread with a thread with a different set of questions, so please see post 3 for the question that I'm asking, since the first 2 posts are related but not pertinent.

    Elementary particle.
    I'm talking about the experiment that addresses the other (see below) composition dependent gravitational effect, so the answer is not Eötvös.

    The Eötvös experiments do not check whether there is a composition dependent gravitational effect by gravitational sources, since they are not designed to. They check the UFF, and confirm the WEP. The Eötvös experiments (modern Eöt Wash included) don't check whether a source with the same mass but a different number of particles causes the same deformation of spacetime. They do check whether objects of different compositions but the same mass experience the same acceleration towards the sources of gravitation.

    Eötvös Experiment (I have a Google search term): Confirmed* UFF, confirmed* WEP, confirmed* that objects with different composition but same mass experience the same acceleration towards a gravitational source, Google search term is Eötvös Experiment

    *within certain parameters

    "?" Experiment (I need a Google search term): Confirmed* or falsified* that gravitational sources of the same mass composed of different numbers of elementary particles cause the same deformation of spacetime, Google search term is "?"

    * Obviously it's confirmed because of all the publicly available material on gravitational acceleration being correlated with mass instead of number of particles, but since I can't cite the experiment I have to include "or falsified" until I know the name of the experiment because I don't like to pretend to know something I don't.

    The simplest "?" experiment is the one I described, and I can't find the name of it or figure out Google search terms that will lead me to the experiment, or what the "? principle" is called.

    It's something we were all probably taught in elementary school, which might be why we forget the name of the physicist who did the experiment.
  14. Mar 18, 2016 #13
    Hi, thanks! Unfortunately my current question was combined with some questions I asked earlier*. I'm looking for the name or information about a far more elementary, but related, experiment (described in post 3 and fleshed out in post 12).

    *The mods combined this thread with a thread with a different set of questions, so please see post 3 for the question that I'm asking, since the first 2 posts are related but not pertinent.
  15. Mar 18, 2016 #14


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    Um, the experiment you're describing in those posts is a Cavendish experiment with different materials for the different masses.
  16. Mar 18, 2016 #15

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    Exactly. The number of particles per kilogram is about 2% different for lead as paraffin.

    Sure they do, so long as the gravitational force of A on B is the same as B on A. If you question that, we should take a step back and address that - because the entire operation of these experiments relies on Newton's Laws. Give that up, and you have to explain what laws should be used instead to analyze the operation of these experiments. I should point out that if you allow the gravitational force of A on B to be different from B on A, gravitationally bound systems of different composition will experience an acceleration without an applied force, and go flitting away. We do not see that.
  17. Mar 18, 2016 #16
    Not exactly. The Al/Be masses are one object, instead of displaced like in the Cavendish experiment.
  18. Mar 18, 2016 #17


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    Ah, I see. I don't think there is a simple name for this experimental configuration. I don't know that an experiment with this configuration has actually been done.

    I also agree with other posters who have said that, if this experiment were to show a deflection, one would expect Eotvos experiments to show a deflection too. Here's why: in the Newtonian approximation, which is what you are implicitly assuming here, you can't say that one mass, such as the Earth or the Sun in Eotvos-type experiments, is a "source", so you are testing how its field depends on its mass and other properties, and the other mass, such as the test masses in Eotvos-type experiments, is not. Eotvos experiments compare the mutual attraction between the Earth or Sun and bodies of different composition. If test masses of different composition acted differently as sources, then they would produce a slightly different mutual attraction with the Earth or the Sun, because they are just as much "sources" as the Earth or the Sun is. So the fact that Eotvos experiments show no difference in behavior with test objects of the same mass but different composition is strong evidence that the behavior of an object as a "source" depends only on its mass.
  19. Mar 19, 2016 #18
    Maybe not this specific configuration (sharks with fricken lasers are hard to train), but an experiment to determine whether spacetime deformation is more closely correlated with mass than the number of particles in it has to have been done.
    That's precisely what the Eötvös type experiments do. The Eöt Wash group used/uses the sun, Earth, galactic center, and a 3 ton U238 source http://www.npl.washington.edu/eotwash/epdone [Broken]) for gravity to confirm the EP (and/or the UFF at the same time...). In other words, they tested whether gravitational/inertial mass were the same. The acceleration towards a source is the same no matter what substance they use (within the constraints of the various experiments they've conducted).

    If you use 100kg of Al in a field, it experiences the same acceleration as 100kg of Be. This doesn't mean that the Al and the Be create the same acceleration towards themselves, nor do their (neither Loránd Eötvös' nor the Eöt Wash group's) experiments do anything to check the effects of the Al and Be test masses as "sources" as far as I can parse. The bar in the Eötvös experiment isn't going to deflect because of the gravitational interaction between the objects on the end of it (it deflects because of inertia due to the Earth's rotation and the Earth's gravity (the forces acting on it), it might compress a negligible amount due to the gravitational force between the test masses on either end of it), and the Eöt Wash group's pendulum test masses detect effects from external bodies, not the acceleration due to the test masses themselves. The Eöt Wash group did do some measurements of G, but those don't satisfy my desire for certainty either (at least what I looked at).

    The test masses are only to test the equivalence of gravitational and inertial mass- they are not sources in the Eötvös experiments as far as I can tell.
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  20. Mar 19, 2016 #19


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    Yes, it does. The acceleration is not due to the Earth, Sun, galactic center, or whatever by itself. It is due to the mutual effect of the Earth, Sun, or whatever and the 100kg of Al or the 100kg of Be. The fact that both accelerations are the same does not just mean that the Sun accelerates both the same towards itself; it also means that both of them accelerate the Sun the same towards themselves.
  21. Mar 19, 2016 #20
    The experiments don't detect the negligible effect of the acceleration due to the test masses. In the original experiment, the only detectable effect the test masses could have on one another would be canceled out by the bar in between them.

    http://www.tat.physik.uni-tuebingen.de/~kokkotas/Teaching/Experimental_Gravity_files/EP_06_05.pdf <-- Original exp.

    http://arxiv.org/pdf/1207.2442v1.pdf <-Eot Wash exp.
  22. Mar 19, 2016 #21


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    They don't detect the effect of the interaction of the test masses with each other. But that's not what I'm talking about.

    The experiments most certainly do detect the effect of the interaction of the test masses with the Sun (or the Earth or whatever is being used as the "source"); if they didn't, they would be useless. More precisely, they detect whether there is any difference in that interaction from one test mass to the other. And my point is that both of those interactions are mutual interactions; they are not two instances of "the Sun pulling on a test mass", they are two instances of "the Sun and a test mass pulling on each other".

    Here's another way of putting it. The first pdf you link to describes (as is typical) an Eotvos-type experiment as testing the equality of inertial and gravitational mass. But "gravitational mass" is a "source" property as well as a "response" property; an object's gravitational mass determines its behavior as a source of gravity just as it determines its behavior when responding to gravity. So testing the latter is also testing the former.
  23. Mar 19, 2016 #22
    Thanks for the replies everyone. No need to pursue the Eötvös angle any further, unless someone has information about a different kind of Eötvös experiment that is sensitive enough and specifically set up to detect gravitational acceleration contributions from the test masses used (none of the experiments I provided links for, nor the original experiment were set up or even able to do so in any meaningful way).

    Anyone with further information about the matter:

    I'm still looking for the name of the experiment or experimenter (it isn't any of the Eötvös or Cavendish type experiments that I've read about) that confirmed or falsified that it is mass in a volume of spacetime rather than the number of particles in a volume of spacetime that causes the deformation of spacetime.

    See post #3 to get a better idea of what I'm asking about.
  24. Mar 19, 2016 #23


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    If you're talking about GR, it isn't just mass that causes spacetime curvature; it's stress-energy. This includes, for example, the kinetic energy of electrons in atoms; this has been analyzed by Steve Carlip, in the following paper:


    Also, in our current understanding of nucleons, a significant part of their observed mass is due to the kinetic energy of the quarks inside them. So a significant part of the mass of the Earth, Sun, etc. is due to kinetic energy. The same would be true of the Al and Be masses in the experimental setup you describe in post #3.

    In other words, I'm not sure how you could test experimentally that it is "mass rather than the number of particles" that acts as the source of spacetime curvature, because the model GR uses is more complicated than "mass" to begin with.
  25. Mar 19, 2016 #24
    Mass contributes to the total stress energy, however someone still had to confirm experimentally that mass <sic> stress energy in a volume of spacetime instead of the number of particles in a volume of spacetime is what causes the deformation of the volume of spacetime. I'd still like the name of whoever did the experiment so that I can read about it.
    I'm aware, and I don't see what that has to do with anything:

    I'm thinking that people worked backwards from detected accelerations (spacetime geometry) towards various astronomical bodies to determine what the mass (stress energy) of the Sun, Earth, Mercury, etc. are...

    You could also work backwards from detected acceleration (spacetime geometry) to determine the number of particles in them, assuming the number of particles is what determines warping of spacetime instead of mass.

    The geometry would be the same either way. Work backwards from the geometry to determine the number of particles, or the mass. You still need an experiment to tell you which of the 2 it is, which is why someone probably did the experiment to determine which it is.

    So, any experimental confirmations of GR that prove that spacetime deformation is due to the mass () instead of the number of particles in a volume of spacetime? I'm assuming there is one, because everyone says it's mass. That would be probably be the experiment name that I'm looking for. The easiest experiment I can think of is the one I mentioned in post 3, but undoubtedly someone did a better one than that.

  26. Mar 19, 2016 #25

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    Can we get away from GR? I know that PF loves to bring in GR at the drop of a hat, but the problem we are facing here is probably not that Newtonian gravity and mechanics just isn't complicated enough.

    Matt, I know you keep saying "not Cavendish or Eötvös", but unfortunately, those are exactly the kinds of experiments that show this. Newtonian gravity does not distinguish "source" and "target" masses. It's mutual attraction. Indeed, it's just better to say "larger mass" and "smaller mass" rather than "source" and "target".

    Here is the argument:

    1. A gravitational attraction due to particle number would manifest itself as a composition-dependent gravitational force.
    2. Strict limits on the magnitude of this have been obtained by Eötvös-type experiments.
    3. The gravitational attraction between A and B is mutual: the force on A due to B is the same as the force on B due to A.
    Do you disagree with any or all of these? If so, which one(s)?

    If not, how can you escape the conclusion that an experiment that shows no variation when varying the composition of the smaller mass also implies that there is no variation when varying the composition of the larger mass?
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