Tidal forces of a black hole

  1. Hi!
    New here. Be gentle.

    Kinda an idea that popped into my head a little while ago:

    Are the tidal forces of some black holes powerful enough to separate quark groups? Google seems to be a bit iffy on the subject.
    Last edited: Jun 19, 2014
  2. jcsd
  3. Matterwave

    Matterwave 3,865
    Science Advisor
    Gold Member

    This is an unanswered question in physics. Quark confinement, or color confinement, is not currently completely understood. On top of that, there is no quantum theory of gravity at the moment. Add on top of that, there's no current way to experimentally test for this hypothesis. The result is, there's really no way to know at this point.

    Probably some calculations can be done, but the reliability of those calculations would be suspect.
  4. Well, if black holes do separate quark pairs... wouldnt the resulting mesons and its electons, neutrinos, and photons be the result of the gravitational energy of the black hole? Beyond that, wouldnt those particles being pulled into the black hole literally be the black hole feeding on its own gravitational energy? Doesnt that break conservation of energy?
  5. mfb

    Staff: Mentor

    No, as the additional energy from a particle deep inside the gravity well is lower than the additional energy from the same particle far away.

    The tidal forces within the diameter of hadrons are tiny for large (stellar mass) black holes, so in the region where current physics works, nothing problematic happens. Smaller black holes give larger tidal forces, but it is unclear if they exist at all.
  6. forgive me im somewhat of a layman.

    Why is the energy lower? Are you talking about potential energy?
  7. Cus I don't think potential energy would come into play here. New mass is created. Unless its a photon I guess XD.
    Last edited: Jun 19, 2014
  8. mfb

    Staff: Mentor

    The total energy matters, and potential energy is a part of it.
    As seen from far away (!), creating particles close to a black hole needs less energy. In the same way, an annihilation gives less energy - if you want to get produced photons out, for example, they get redshifted.
  9. Isnt the red shift caused by interactions with the gravitational forces (and time dialation) of a black hole? That doesnt mean there is less energy, it just means measurement of energy over time is lower because time moves faster away from the massive body. Since frequency is a direct inverse of time, as time "speeds up", frequency slows down. No energy is removed from the system. Or is that wrong x.x

    Yes. according to wikipedia this is correct. Total energy of the photon remains constant.

    Oh I think I see what you are saying when it comes to less energy... huh... I have to think about it more.... I still think there is a discrepancy...

    Yeah. Even if the energy of particles the black hole "system" is lower for a far away observer, there is still an increase of energy caused by the black holes gravitational energy beyond potential energy. The creation of these new particles does not diminish energy from anywhere else in the system or the universe for that matter. Plus those new particles have potential energy of their own to add to the system. The black hole would still be feeding on itself. It still seems like energy is being added to the system from within the system.

    Wouldnt the total mass-energy of a particle within a gravity well, correcting for th negative energy from gravity (there is probably a better way to state this), be the same as that particle far away without that negative energy? (assuming the particle did not reach the event horizon). i mean it would have to be to conserve energy...
    Last edited: Jun 21, 2014
  10. UltrafastPED

    UltrafastPED 1,912
    Science Advisor
    Gold Member

    The strength of tidal forces depends upon your distance from the effective center of the mass; so for a very large black hole they would be relatively weak at the surface. The smaller the black hole, the greater the tidal forces near the surface.

    Practically speaking, tidal forces appear because the force of gravity is different at one end of the object than it is at the other ... so for very small objects (like a person) you would need to be in a very situation where the force of gravity is very different at your head than at your feet - different enough that you would actually feel the difference as a stretching force.

    As you look for these effects in smaller and smaller objects it becomes clear that the gravitational force must be changing more and more rapidly with distance. Classically this is 1/r^2 for the force, though a calculation shows that the tidal forces change as 1/r^3.

    See http://en.wikipedia.org/wiki/Tidal_force
    and http://spacemath.gsfc.nasa.gov/weekly/4Page33.pdf

    At atomic scales the distances are on the scale of 10^-10 meters; the nucleus is 10^-15 meters. So given the strength of the nuclear forces it requires an immense "gravitational field gradient" to pull apart the nuclei.

    Of course, this actually happens, and results in neutron stars - if an object is compressed all the way, but does not become a black hole, then it will become a neutron star.

    See http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html

    The science fiction author Larry Niven wrote an excellent story called "Neutron Star". He helps you visualize what is going on in detail, in a very entertaining way.
  11. mfb

    Staff: Mentor

    It does, as two particles separated by some distance have a lower potential as the particles closer together (this is exactly the effect of tidal forces). This difference has to be significant (order of GeV/fm) to notice tidal effects in hadrons - if it is small (and therefore not relevant), nothing happens. Separating the quarks by a fm would give ~1 GeV of available energy.

    To get those tidal forces, you would have to be extremely close to a microscopic black hole. And then you'll probably want a theory of quantum gravity.
  12. i dont understand (repeating pattern eh?)

    yes but wouldnt the total system of particles have the same potential? The differences in potential energy between the two particles directly reflected by the strong force field forming between the two (three) quarks? The energy of course being generated by the gravitational tidal forces which does not grow weaker as more energy is exerted? Thats the whole problem.
    Last edited: Jun 21, 2014
  13. hmmmm
  14. mfb

    Staff: Mentor

    I don't understand your question :(.
  15. potential energy is a direct result of gravitational energy. Even if the energy to form the new particle came from the potential energy of the particle closer to the singularity, that potential energy comes from a gravitational field which does not deminish as these new particles form, thus violating conservation, yeah?.
    Last edited: Jun 21, 2014
  16. It is new mass created from gravitational energy. Things get even weirder if the black hole engulfs the new particle. The black hole's mass would be increasing from its own gravitational energy instead of canceling out like it would under conservation...
    Last edited: Jun 21, 2014
  17. mfb

    Staff: Mentor

    The gravitational field does not change (significantly), but the particle positions inside change, that is enough.

    No, its mass is always linked to its gravity.
  18. but the new particle would have an equal (or greater) potential energy to the energy that was taken to create it. Plus the energy of the particle itself.

    i dont understand what you mean. Of course its linked to its gravity, but its gravity (and mass) would increase when it engulfs this new mass created from its own gravity instead of canceling out the energy used to create it like it should under conservation of energy.
    Last edited: Jun 21, 2014
  19. interesting question I too would love to hear the answer , my take would be that the energy to form these new particles comes from the pressure and gravity of the Black hole which comes from the mass it gains. If I understand Soule correctly.
  20. Oh uh no. When a quark is separated from its particle, two new particles are formed from the energy used to separate them. When it comes to a proton, when one of its quarks are removed, a new quark forms in the proton and a meson as well, leaving you with the origional particle an the meson. Thats just how it works according to the internet rofl.

    Did i misunderstand what you are asking? Cus i do that... a lot... rofl
    Last edited: Jun 21, 2014
  21. mfb

    Staff: Mentor

    Potential energy is negative.

    I made a mistake earlier - for the calculation I used two quarks 1fm apart and the tidal forces at a fixed distance from the black hole. That does not work, however - to get tidal forces strong enough, the whole hadron would have to be significantly closer than 1fm to the black hole. That does not work with the above assumption.

    The graviational potential for quarks does not exceed their rest energy outside the black hole. For light quarks (!) any differences in this are not enough to form new particles. For heavy quarks, this could be different. But even then, it happens only at black holes with a size of at most the diameter of hadrons, and then I really think we need quantum gravity to tell what would happen.
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