1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

About Negative Mass

  1. Jun 5, 2013 #1
    I'm aware that this Topic is generally considered hypothetical, but at least I'm not talking about
    something that someone can say, "hey, that's your personal theory". A decent number of
    respected physicists have published papers on one aspect of the subject, or another.

    There is a Question, though, that has been nagging me for some time, and because it is about
    particles, that's why I chose this particular category for this Message Thread.

    Some background information:
    No examples of negative mass are known to exist.
    There is no known theoretical reason why the stuff couldn't exist.
    If we did have a sample of negative mass, it is expected to exhibit certain distinctive behavior.
    For example, if a sample of iron had negative mass instead of ordinary mass,
    and we tried attracting it with a magnet, we expect it would actually be repelled.
    That's because the equation F=(m)(a), when a negative mass is involved, becomes F=(-m)(-a).

    Now, regarding some particles:
    Most ordinary mass-possessing particles also have an electric charge associated with them.
    The neutron, for example, contains some charged quarks, and those charges happen to
    balance each other out, leaving the neutron with zero net electric charge.
    About the only particles that I'm aware of, that might possess mass without any hint
    of associated electric charge, are the Z boson and the neutrino. For the purpose of the
    Question I want to ask, I'll choose to use the neutrino in my lead-up. I don't want any
    unnecessary forces, such as might be associated with interacting electric charges,
    to interfere with the description that follows.

    Let us assume that a particle equivalent to the neutrino, except possessing negative
    mass instead of ordinary mass, might be able to exist. My Question relates to an
    examination of what might happen if that negative-mass neutrino (-m) collides with an
    ordinary neutrino (+m).

    Here is a simple sketch of the event: (+m)(+v)--->*<---(-m)(-v)
    If we assume the two particles have equal magnitudes of mass, despite their opposite
    signs, and we assume they are moving in opposite directions at equal speed, then
    when the collision is done, we might expect the mass to be "cancelled out" or
    "nullified" (this word courtesy of the late Dr. Robert L. Forward). We also can expect
    that there will be Zero Kinetic Energy left over (since equal and opposite magnitudes
    of KE are carried into the interaction).

    However! It looks like there will be Momentum left over, since we all learn in about the
    4th grade of school that two negative numbers, multiplied together, make a positive number
    (and so both particles bring positive amounts of Momentum to the interaction).
    What form can that Momentum have, after the nullification event completely
    dissociates it from both mass and kinetic energy???

    That's my Question. For anyone with an Answer, Thanks In Advance!
  2. jcsd
  3. Jun 6, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    First question: are you aware of the negative effective mass that is commonly used in solid state physics?

  4. Jun 6, 2013 #3


    Staff: Mentor

    Please post one of those papers, which we can discuss. We cannot discuss personal speculation, but we can discuss scientific literature on the topic.
  5. Jun 6, 2013 #4
    Negative Mass reference

    Bondi, H. (July 1957). "Negative Mass in General Relativity". Rev. Mod. Phys. 29 (3): 423. Bibcode:1957RvMP...29..423B. doi:10.1103/RevModPhys.29.423.
  6. Jun 6, 2013 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Unless you are the OP who opened another account and violated our rules, in general, please let the OP respond directly to the question. You have no way of knowing what publications he/she was referring to when he/she made the statement in question.

  7. Jun 7, 2013 #6
    No, I wasn't the one who mentioned the Bondi paper, although I think it was the first of the lot (about negative mass).
    Note I did happen to mention Dr. Robert L. Forward as someone who added something to the field --example:
    A few minutes ago as I write this, I did a Google search for [paper journal "negative mass"] (the brackets represent
    the search-entry box). There were "about 147,000" results, although I'm sure many of them were actually not related
    to what we actually want to see. But, here (example):
    <<Removed URL>>
    Then there are places in "advanced speculative physics" where, if negative mass-energy was available, certain things
    like "stabilizing the mouths of a wormhole" would be possible.
    <<Removed URL>>

    So, no, I'm not talking about an overall topic that hasn't been seriously considered by others; I'm only asking a
    Question based on what appears to be a simple logical consequence, within that topic.

    Oh, and no, I haven't heard about negative mass in solid-state systems. I suspect it is just a handy mathematical
    trick, and not a real thing.
    Last edited by a moderator: Jun 7, 2013
  8. Jun 7, 2013 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    You should not dismiss something that easily, especially when you are ignorant of it. However, I was expected that kind of a response.

    Condensed matter system is where some of the most clearest examples of various aspects of quantum field theory manifest themselves. In case you didn't know (and from the looks of it, you don't), various exotica of QFT have already been discovered from these condensed matter systems. The Higgs mechanism (symmetry breaking) came out of condensed matter, so much so that Phil Anderson has been mentioned as a strong candidate to receive a Nobel Prize, along with Peter Higgs, for the Higgs physics. Examples also includes the discovery of Majorana fermions, analogues to the magnetic monopole, fractional charges, etc.. etc. These are all phenomena that either were first discovered in condensed matter, or were the result of advances made in them. So for you to dismiss it out of hand as a "mathematical trick" is laughable.

    If you wish to know what would be the physics associated with something having a negative mass, and you are not aware of what has already been known about such things in condensed matter, then you have missed a lot of physics. If someone as distinguished as Frank Wilczek acknowledges the fundamental importance of condensed matter phenomena such as superconductivity, who are you to dismiss such a thing?

    Last edited: Jun 7, 2013
  9. Jun 7, 2013 #8


    Staff: Mentor

    Yes, I am aware of that, which is why I did not close the thread immediately. This topic is right on the edge, the aspects you are interested in are clearly speculative (as you recognize), but it is speculation which is part of the professional scientific literature. In order to stay within the forum rules we need to confine the speculation to the specific topics which are part of the scientific literature, so we need specific references to discuss.

    This is an acceptable reference. Do you have a specific question about this paper? Note, it is behind a paywall, so my comments below are taken from the first page only.

    Neither of these are valid journals. The list of valid journals is given in the forum rules. We should stick with the Forward paper.

    Your question in the OP does not appear to be a simple logical consequence of the paper. Forward does not seem to speculate that negative matter forms particles, and he specifically mentions that "Negative matter is not antimatter" which would seem to indicate that he is NOT suggesting the possibility of such an anhilation reaction as you are considering. (at least not on the first page)

    So we cannot discuss your OP question, but if you have other questions that do directly stem from the article then we can discuss those. (a brief quote might help if it is a topic in the later pages)
    Last edited: Jun 7, 2013
  10. Jun 7, 2013 #9
    Regarding the math-trick thing, consider the use of imaginary numbers in electromagnetic engineering.
    It is a handy way to keep magnetic-field data separated from electric-field data; nobody considers the
    data to actually have an imaginary component. So, because I knew such tricks do get used, that is
    why I wrote "I suspect...". I won't mind being mistaken, but it appears rather more data is needed before
    a conclusion about it can be reached.

    If you need specific articles about negative mass or negative matter in the scientific literature, then
    you should include the Bondi paper as well as the Forward paper. While I can't access the whole
    Forward paper, I'm almost certain (because he wrote other articles that appeared in "popular"-type magazines,
    which had references) that it references the Bondi paper.

    Regardless, I am quite certain that Forward, somewhere, applied the term "nullification" for an interaction
    between negative and ordinary matter/mass, specifically to distinguish it from a matter/anti-matter annihilation.
    My Question arises from a very simple examination of a nullification event, so I don't quite see how it can be
    horribly distinct from the stuff that Bondi and Forward published in physics journals.

    As it happens (I suppose this is an "aside" in terms of the forum rules), I actually wrote a letter (not an email)
    to Forward about my Question, years ago, and receieved an equally non-emailed reply. That response denied
    that there would be any leftover Momentum in a nullification event. Which I don't understand --he appeared to
    be violating 4th-grade math-- and so I decided to ask about it here. I could dig out the letter and quote it,
    but it would probably not count, per the forum rules....
  11. Jun 7, 2013 #10
    fyi...here is a 1997 paper by Millis on negative mass from the same journal discussed in OP for the R. Forward paper, so it should enter the discussion, especially since it is published after Forward:



    Also, I do not understand why a concept of negative mass could not be related to the Dirac equation experimentally verified 'anti-matter' ? Why must negative mass only carry an electron e- and not positron e+ ? Why not either e- or e+ (or both simultaneously) depending on the quantum system under investigation ?
  12. Jun 7, 2013 #11


    Staff: Mentor

    If the OP is amenable I would prefer to discuss the Millis paper as it is not behind a paywall. Although it seems to cover a wide variety of topics in not much depth, so the OP may not be interested in it for his specific question, particularly since it doesn't seem to discuss "nullification".
    Last edited: Jun 7, 2013
  13. Jun 7, 2013 #12


    Staff: Mentor

    Yes, but the exact "somewhere" is very important. If it is in a pop-sci book or an interview or something then it is outside of the rules. If it is in a scientific paper then we can discuss that specifically.

    I do hope that you can find a suitable reference, because I think that it would be enjoyable to discuss.
  14. Jun 7, 2013 #13


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    What more data? The concept of negative effective mass is very well-tested in condensed matter physics because we can engineer different materials to have such properties! If you look at the definition of an effective mass, you'll notice that it involves the curvature of the dispersion curve. By simply changing doping levels, for example, I can chance where the Fermi energy crosses the dispersion curve and I can obtain different 'sign' on the effective mass.

    The effect of having a negative effective mass has been measured in many different systems, whereby it shows an opposite reaction to an applied field. Do a search before you make comments on things you haven't put the time and effort to understand.

  15. Jun 7, 2013 #14


    Staff: Mentor

    Please, people. There is a list of journals that are usually acceptable on the rules page. For this topic we must stick to those.

    VernonNemitz, please PM me with the SPECIFIC reference that you would like to discuss. There have been multiple unacceptable replies recently, so the thread is temporarily closed. I would very much like to re-open it if it can be made to conform with our rules.
    Last edited: Jun 7, 2013
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Negative Mass Date
B Positive and negative mass Nov 5, 2017
I Can gravity be negative? Sep 18, 2017
B Can Negative Mass at near Speed of Light go Back in Time? Jul 15, 2017
Physicists create 'negative mass'? Apr 18, 2017