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I Experiments about impact of mass in different areas

  1. Jul 31, 2018 #1
    There's important experiments showing the equivalence of inertial mass and gravitational mass ( the Eotvos experiments), but I couldn't really find many that show the equivalence of mass (or the stress-energy tensor) in other contexts.

    These are some of the variants of mass I'm interested in:
    - Inertial mass
    - 'passive' gravitational mass, as in: how much does an object get accelerated due to spacetime curvature?
    - 'active' gravitational mass, as in: how much does the object curve spacetime, with important sub-parts such as:
    - How much does the object impact gravitational acceleration of other objects
    - How much does the object impact gravitational time dillation
    - How much does the object impact gravitational lensing
    - How much does the object impact gravitational red/blueshift
    - How much does the object impact shapiro time delay

    Generally, these are assumed to be the same, and of course, everything is much more sensible and works out much neater if they are. We might even run into some issues with conservation laws if they weren't the same.
    But neatness aside, I'm wondering if there's any good experiments that show that these effects indeed do all use massenergy, and aren't influenced by some other attribute of the objects that cause them (like say, total particle count or the sum of the particles rest masses).

    The only solid experiment I could find that isn't just about inertial mass vs gravitational mass was this one by Kreuzer:
    https://journals.aps.org/pr/abstract/10.1103/PhysRev.169.1007
    Which is at least something, but it doesn't really cover all the bases
     
  2. jcsd
  3. Aug 1, 2018 #2

    mfb

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    • Eötvös links the inertial mass to the passive gravitational mass.
    • Cavendish-like experiments link passive and active gravitational mass for the acceleration (ACC) as the roles are interchangeable. Lunar laser ranging does the same.
    • GPS, Hafele–Keating and all the similar experiments link ACC and time dilation.
    • Various stellar measurements link ACC and red/blueshift
    • Time dilation and red/blueshift are the same thing anyway, just measured in a different way.
    • Measurements of galaxies link the Shapiro delay to lensing and they can link lensing to ACC.
    • Gaia will add gravitational lensing from planets (with known ACC).
    • ... and probably more.

    Measurements of the Sun include all types of active and passive gravity you listed. They all agree.
     
  4. Aug 1, 2018 #3
    Thank you! I will explore these!

    These are of course true, and it'd be extremely weird if it weren't the case that these are the same, but it's still interesting to see whether it has been experimentally shown whether they are. It might be worth some experiments just to remove that tiny bit of doubt.
    As far as I'm aware, Cavendish doesn't really test that, though it does test inertial mass vs acceleration.

    Do you know of any in particular that put bounds on this? I'm guessing you mean something like comparing the rotation behavior of binary stars to the shifts in their emission spectra?


    Do you know if there's any experiments that have tested whether it's the total massenergy or the rest mass of the particles that matters? Say by testing whether a heated object has a larger effect on spacetime curvature?

    I'm curious because I can imagine that in some unified quantum physics + GR/SR, things might work slightly different. Like say, if gravitons exist and are involved in gravitational acceleration but not in time dillation, then whatever creates gravitons may be slightly different from what causes time dillation. Perhaps time dillation is caused by mass energy, but gravitons are created by rest mass, or just by protons, or something like that. Many of these experiments don't really seem like they'd be able to tell that apart.



    Oh, for any googlers who get here. I found another paper handling 'active' vs 'passive' gravitational mass, though it seems to assume that the laws of conservation would be broken if they were different:
    https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.57.21
     
    Last edited: Aug 1, 2018
  5. Aug 3, 2018 #4

    mfb

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    The Cavendish experiment has been done with a large range of source masses of various materials and size and many of them have been used as test masses as well.
    I don't know, check the publications. Gravitational redshift measurements are routine. In binaries you know the average radial velocity of both is the same so you can remove the contribution from the Doppler effect.
    We don't have measurements precise enough to detect heat yet (~1-2 orders of magnitude missing), but objects of different composition (=> different contribution from electrons, quarks and binding energies) have been measured, in the lab, for the Earth/Moon system and for stars.
    That is ruled out by a few thousand standard deviations at least. All these measurements are looking for parts per million, parts per billion or sometimes part per trillion effects.
     
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