Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dark Matter & Energy/Mass of False Vacuum

  1. Mar 20, 2005 #1
    I'm not trying to advance a pet theory here .. it's really just a question.

    Why don't physicists serious consider the possibilty of energy/mass contained in the false vacuum as the source of Dark Matter? At least I've never heard of a serious one in these terms. Real particles and their anti-particles are said to be created & annihilated constantly. Also virtual particles are supposed to be exchanged all the time. I would think the mass equivalent of the energy needed for these things is significant.

    Maybe there is some constraint of not feeling the gravitation as these things happen underneath the limits of the HUP?
  2. jcsd
  3. Mar 20, 2005 #2
    This is similar to asking "why isn't dark matter just black holes?". The reply is "why do you think we believe in dark matter?".

    The main reason for believing in dark matter is that we observe galaxies and clusters of galaxies to have systematically higher than expected rotation rates and energies, telling us there must be a lot of dark matter distributed in a very specific way.

    The key thing about vacuum energy is that it should be the same energy density everywhere in the universe. Cosmologist believe it is constant through time also, the vacuum energy is called the cosmological constant.
  4. Mar 20, 2005 #3

    Are you saying that "very specific way" has been tested to be more specific than the general distribution vacuum energy/mass would be?
  5. Mar 20, 2005 #4


    User Avatar
    Gold Member

    This is where I believe the misunderstandings regarding vacuum energy begin. Even many of the top people researching ZPE fall into this trap, and it shows in their papers. ZPE is expressed through fields, and fields can be polarized, densified, or rarified. Even at absolute zero, the vacuum is swarming with particle-antiparticle pairs. The pairs can be prevented from arising by the simple expedient of physical exclusion. A Casimir device demonstrates this by physically preventing some wavelengths of the ZPE field from arising simply by restricting the space in which the pairs can form. Solid matter physically prevents particle-antiparticle pairs of many more (but perhaps not all) of the wavelengths of the ZPE from forming.

    As for polarization: If the alignment of these virtual pairs can be affected by the presence of matter, then the ZPE field will be both polarized and densified. At the quantum level, the behavior of particles is not straightforward and the chance of finding a particle at a certain place at a certain time between point A and point B is a matter of summing amplitudes of probability of the various paths that the particle could take from A to B. See the wonderful Feynman lecture series at VEGA:

    http://www.vega.org.uk/series/lectures/feynman/ [Broken]

    If matter and antimatter are attracted to one another, virtual particle pairs will arise preferentially oriented with the antiparticle closer to the dominant local mass, and with respect to the local polarized ZPE field. It takes less energy for the pairs to arise in this orientation and therefore quantum physics tells us that a preponderance of the pairs in the field will be so oriented. In this scenario, the ZPE field has been polarized, and because that orientation promotes packing, the field is also densified. The Athena Project (link below) is dedicated to producing experimentally-useful electrically neutral antihydrogen. If the gravitational infall rates of antihydrogen and hydrogen are not equal, the simplest, most intuitive method of polarizing the vacuum fields will have been discovered.


    Another common misunderstanding relates to the total energy of the vacuum, with a nice overview here:

    http://arxiv.org/PS_cache/astro-ph/pdf/0005/0005265.pdf [Broken]

    The ZPE field theoretically contains 120 OOM more energy than required by the cosmological constant, BUT this is only if we calculate this energy in relation to a perfect vacuum, as envisioned in quantum theory. The problem here is that the ZPE is the Ground State of our universe, and there is no perfect vacuum. Since we can only sense and exploit energy differences, the 120 OOM energy problem is a moot point. As an example that even young children can understand:

    Q: How can a bird perch on a high-voltage wire without being fried?
    A: The bird comes to the same voltage potential as the wire on which it perches. Without reference to a higher or lower voltage reference, the bird is safe. If she should be able to touch an object that is referenced to a much higher or lower voltage (like a grounded utility tower), though, POOF!

    We are in exactly the same situation with ZPE. Theoretically, the vacuum has incredible potential energy, but since it is the ground state of our universe, there is no way that we will be able to exploit it unless we find a way to either densify or rarify a ZPE field so we can exploit that differential.
    Last edited by a moderator: May 1, 2017
  6. Mar 20, 2005 #5


    User Avatar
    Gold Member

    I'm not Crosson, but yes. A uniform distribution of energy/mass would not do the job. We have to accept that like any other field, the ZPE fields of the vacuum can be polarized, densified or rarified.

    Inferred dark matter has to be distributed in quite specific ways to perform the various jobs that it is invoked for, like explaining flat galactic rotation curves, excess cluster binding and excess cluster lensing. It is quite puzzling how something as evasive, invisible, and undetectable as "non-baryonic dark matter" manages to arrange itself so nicely wherever the behavior of visible matter violates the gravitational theories of GR.
  7. Mar 21, 2005 #6


    User Avatar
    Gold Member

    There is a big chasm between seriously considering something and adopting it as the mainstream view. The issue has been seriously considered. There are physicists who have explored the idea seriously. But, it is an idea that has not yet won mainstream acceptance, and may never win that kind of acceptance.
  8. Mar 21, 2005 #7
    That's what I was wanting .. a direct reply.

    I think in the end it may well boil down to: Take a not-so-well defined problem and pick a not-so-well defined solution off the top of your head, and see if you can tweek either or both to satisfy both.
  9. Mar 21, 2005 #8


    User Avatar
    Gold Member

    Turbo 1
    http://athena.web.cern.ch/athena/ most of the pages on this site
    come up blank, can you tell if progress has been made with production
    of cold anti hydrogen.
  10. Mar 21, 2005 #9
    Thanks. It sounds like you know a little bit more about Dark Matter. I'm wondering if you could give a little bit more on how DM must be distributed to give the flat galactic rotation curves, and the excess cluster binding and excess cluster lensing. Thanks.
  11. Mar 21, 2005 #10
    We have to talk about two functions of radius; velocity V(r) and density p(r).

    Using Newton's mechanics, it is possible to show the following:

    If all the mass is in the middle (a big black hole) we expect a Keplarian velocity distribution, V drops proportional to r^-(1/2).

    If the matter is distributed evenly, we get V(r) proportional to r.

    The visibly matter in a Galaxy is usually fit well by p(r) = e^-r. We notice that the rotation of the Galaxy is like V(r) = constant, so we infer that the Galaxies actual mass distribution is closer to p(r) = r^2.

    A different test of dark matter involves the Virial theorem, which states that in any self gravitating system, the energies are related by:

    Potential = -2*kinetic

    But we can measure the potential (GMm/r) and kinetic energy independently. When we do this, we find systematically (everywhere we look) that based on kinetic energy, there should be more mass than we can see (by the same order of magnitude as the mass distribution argument.)

    In Einstien's GTR, the cosmological constant is a constant. In recent years, some people have identified the cosmological constant with the vacuum energy of particle physics. It doesn't matter (for constancy sake) that there are small scale variations in the field, if the universe is homogeneous on a cosmological scale then the cosmological constant is a constant.

    The sad truth is that QFT has stalled on progress on understanding the vacuum energy, and current techniques predict a cosmological constant that is off by 120 orders of magnitude.
  12. Mar 21, 2005 #11

    But, does the signature of Dark Matter needed to keep galaxies from flying apart match exactly the signature of Dark Matter needed to keep clusters of galaxies from flying apart? .. within limits of measurement.
  13. Mar 21, 2005 #12


    User Avatar
    Gold Member

    Here is an example of the genre: http://xxx.lanl.gov/abs/physics/0402007 discussing dark energy and zero point fields (the link is to the abstract).

    Another paper which examines what room there is to tweak current GR theory given current observational limitations in here: http://arxiv.org/abs/gr-qc/9306025
  14. Mar 21, 2005 #13
    In terms of the amount of mass, all different shaped galaxies and clusters of galaxies agree that about 90% of the mass must be dark matter.

    Clusters do not have a well defined v(r) because the velocities are randomly distributed, so it is not really possible to guess the distribution of dark matter in a cluster very well (limited by experiment). This is also true for galaxies that are not spiral or spherical shaped.
  15. Mar 21, 2005 #14


    User Avatar
    Gold Member

    There have been technical problems with the project, as discussed on the papers page of that site. Here is the most recent.

    http://athena-positrons.web.cern.ch/ATHENA-positrons/wwwathena/Documents/madsen2005.pdf [Broken]
    Last edited by a moderator: May 1, 2017
  16. Mar 22, 2005 #15


    User Avatar
    Gold Member

    There has been a difference of perception, fueled by those (quantum physicists) who believe that we should be able to somehow measure the energy of the quantum vacuum relative to a theoretical pure vacuum - which they have told us cannot exist in our universe. This 120 OOM disconnect is disconcerting until we come to grips with the fact that the vacuum energy is the ground state of our universe, and that we would have to have access to a pure vacuum in order to exploit the theoretical potential energy. The understatement police are hauling me away, so please bail me out! :eek:

    https://www.physicsforums.com/journal.php?s=&journalid=13790&action=view#NEW%20PLANET%20DISCOVERED%20!!! [Broken]
    Last edited by a moderator: May 1, 2017
  17. Mar 24, 2005 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Measuring DM in clusters is done by gravitational lensing (of more distant objects, seen through the cluster), by assuming the IGM is in equilibrium (X-ray temperature and intensity profiles), and from application of the Virial Theorem (intra-cluster motion of galaxies, from their redshifts). Of course, all these tell you is the mass (and its distribution), not whether that mass is DM or baryonic (BTW, the three independent methods give consistent results, one reason why we think it's DM and not some new physics, for example). Estimates of baryonic mass come from Mass/Luminosity estimates (galaxies), X-ray intensity ('count the electrons, assume there are as many protons'), and the SZE. A minus B gives an estimate of the amount of DM in the cluster (again, consistency suggests DM is a good thing to assume).
  18. Mar 25, 2005 #17
    :blushing:Stupid questions for 100: what is Dark Matter? What is it do? What is meant by vacuum? Because I think I might be thinking of vacuum in the wrong context?

    Sorry if I upset anyone with my questions :redface:, but I seriously want to know about this stuff because its interesting.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook