Results 1 to 26 of 26

Thread: Negative masses

  1. #1
    Join Date
    Jun 2011
    Posts
    913

    Negative masses

    Firstly I wanted to apologize to everybody from drifting away from the rules of CQ previously. So I will keep my questions extremely simple.

    Secondly I know Physical Review Letters is much more valuable than arXiv where we can find the following paper on negative masses:
    https://journals.aps.org/prl/abstrac...ett.118.155301

    Thirdly the questions I have are:
    - does General Relativity allow for negative masses?
    - are negative masses repulsive towards positive masses?


    Regards,
    philippeb8

  2. #2
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    21,639
    The link is broken...

    As to the final question, I think we could only answer that after empirical tests.
    Forming opinions as we speak

  3. #3
    Join Date
    Jun 2011
    Posts
    913
    Quote Originally Posted by antoniseb View Post
    The link is broken...

    As to the final question, I think we could only answer that after empirical tests.
    Sorry:
    https://journals.aps.org/prl/abstrac...ett.118.155301

    But theoretically speaking General Relativity doesn't disallow negative masses? Thanks.

  4. #4
    Join Date
    Jan 2005
    Location
    Anzakistan
    Posts
    10,643
    Quote Originally Posted by philippeb8 View Post
    Firstly I wanted to apologize to everybody from drifting away from the rules of CQ previously. So I will keep my questions extremely simple.

    Secondly I know Physical Review Letters is much more valuable than arXiv where we can find the following paper on negative masses:
    https://journals.aps.org/prl/abstrac...ett.118.155301

    Thirdly the questions I have are:
    - does General Relativity allow for negative masses?
    - are negative masses repulsive towards positive masses?


    Regards,
    philippeb8
    Do you mean this?

    https://journals.aps.org/prl/abstrac...ett.118.155301

    (When a long link is displayed, it may be visually shortened with "..." showing the removed bits. If you copy the visual (shortened) representation, you'll get a link that does not work.)
    Attached Images Attached Images
    Last edited by pzkpfw; 2017-Apr-17 at 10:36 PM.
    Measure once, cut twice. Practice makes perfect.

  5. #5
    Join Date
    Jun 2011
    Posts
    913
    Quote Originally Posted by pzkpfw View Post
    Do you mean this?

    https://journals.aps.org/prl/abstrac...ett.118.155301

    (When a long link is displayed, it may be visually shortened with "..." showing the removed bits. If you copy the visual (shortened) representation, you'll get a link that does not work.)
    Yes exactly.

  6. #6
    Join Date
    Oct 2009
    Location
    a long way away
    Posts
    9,989
    Quote Originally Posted by philippeb8 View Post
    Firstly I wanted to apologize to everybody from drifting away from the rules of CQ previously. So I will keep my questions extremely simple.

    Secondly I know Physical Review Letters is much more valuable than arXiv where we can find the following paper on negative masses:
    https://journals.aps.org/prl/abstrac...ett.118.155301
    Note that the paper is about "effective mass". This is not quite the same thing as mass. For example, in semiconductors "holes" as charge carriers (the absence of an electron) can have a high effective mass, even though there is nothing there.

    - does General Relativity allow for negative masses?
    As far as I know, the equations would work equally well with negative values for the mass-energy terms.

    - are negative masses repulsive towards positive masses?
    I think this was stated in another thread, but it depends on what type of mass you are talking about (inertial, gravitational, etc).

    There is an ongoing experiment at CERN (the ALPHA experiment) to collect enough anti-hydrogen to test how it responds to gravity.

  7. #7
    Join Date
    Dec 2004
    Location
    UK
    Posts
    8,169
    Quote Originally Posted by Strange View Post
    Note that the paper is about "effective mass". This is not quite the same thing as mass. For example, in semiconductors "holes" as charge carriers (the absence of an electron) can have a high effective mass, even though there is nothing there.



    As far as I know, the equations would work equally well with negative values for the mass-energy terms.



    I think this was stated in another thread, but it depends on what type of mass you are talking about (inertial, gravitational, etc).

    There is an ongoing experiment at CERN (the ALPHA experiment) to collect enough anti-hydrogen to test how it responds to gravity.

    anti-hydrogen isn't negative mass is it?
    Formerly Frog march..............

    She was only a farmer's daughter, but she was outstanding in her field.

  8. #8
    Join Date
    Oct 2009
    Location
    a long way away
    Posts
    9,989
    Quote Originally Posted by Frog march View Post
    anti-hydrogen isn't negative mass is it?
    No one expects it to be, but that is what they are checking.

  9. #9
    Join Date
    Jun 2011
    Posts
    913
    Fascinating. Thanks!


    Sent from my iPhone using Tapatalk

  10. #10
    Join Date
    Aug 2008
    Location
    Wellington, New Zealand
    Posts
    3,547
    What Negative-Mass Hydrodynamics in a Spin-Orbit–Coupled Bose-Einstein Condensate describes is an experiment that creates negative effective mass in laboratory conditions. This is not actual negative mass. It is mass that acts as if it were negative under these conditions. This gives insights into how negative mass would act if it actually existed.

  11. #11
    Join Date
    Jun 2007
    Posts
    5,478
    Note that this is negative "effective mass" in a condensed matter experiment. These sometimes use condensed matter systems as physical analogs for exploring more fundamental phenomena. For example, some experiments have been done reproducing the behavior of event horizons and Hawking radiation...this doesn't mean they actually bent spacetime into a light-trapping black hole, they just reproduced the behavior in an ultra-cold gas:
    http://www.nature.com/nphys/journal/...nphys3104.html

    Basically, they are verifying mathematical models by checking them against a physical system that is expected to behave similarly to the one being modeled, and using it to explore phenomena that may translate back to the system being modeled.

    GR and QM do allow for negative energy density. It's complicated. Note that consistency and conservation laws require that all three forms of mass be negated: inertial, active gravitational, and passive gravitational. Gravitational force on a negative mass particle would be reversed, but so would its response to force, so it'd still behave like a particle with positive mass.

    https://en.wikipedia.org/wiki/Wormho...able_wormholes
    https://en.wikipedia.org/wiki/Negative_mass

  12. #12
    Join Date
    Jun 2005
    Posts
    12,465
    But actually I think there is a very good reason to assume that there is nothing with negative mass. The issue is, if you have two positive masses, they attract one another, which is fine. If you have two negative masses, they will repel one another. But if you have a positive and negative object with the same magnitude of mass, but opposite, then the the positive one will be repelled by the negative one, but the negative one will be attracted to the positive one. So the negative one will end up running after the positive one, which will run away at ever increasing speed.
    As above, so below

  13. #13
    Join Date
    Jun 2011
    Posts
    913
    Quote Originally Posted by Reality Check View Post
    What Negative-Mass Hydrodynamics in a Spin-Orbit–Coupled Bose-Einstein Condensate describes is an experiment that creates negative effective mass in laboratory conditions. This is not actual negative mass. It is mass that acts as if it were negative under these conditions. This gives insights into how negative mass would act if it actually existed.
    Order of Kilopi? Congrats.

    So I guess that means we cannot harness this.

  14. #14
    Join Date
    May 2003
    Posts
    5,784
    We've had multiple conversations about this, the most recent I'm aware of are here and here.

    Thinking about all the possibilities, there are at least three important things determined by mass. One is inertia, or how an object accelerates when you apply a force. One is the active gravitational mass, which is how strong of a gravitational field an object generates. And the third is the passive gravitational mass, which is what kind of force an object experiences in a gravitational field. For all objects that we've studied, all three types of mass are not only positive, but equal to each other. So we generally don't draw any kind of distinction between these "types" of mass (because they're all the same), except in discussions of hypothetical particles that might have different values.

    Whether "negative mass" is a problem for general relativity, and whether it is attracted to or repelled from normal mass depends on which type or types of mass you make negative. If inertial mass and passive gravitational mass are different, then the principle of equivalence breaks, and so general relativity (as well as a number of similar ideas) won't work. If active and passive gravitational mass are different from each other, that breaks conservation of momentum.

    So if you like general relativity and conservation of momentum, and you flip all three types of mass to negative, you end up with a kind of matter that moves in the opposite direction that you push on it. If you have a chunk of normal matter and a chunk of negative matter, the negative matter accelerates toward the normal matter, while the normal matter accelerates away from the negative matter. It would make a great space drive, since it will accelerate indefinitely without having to use any reaction mass. Sadly, there's no evidence that the stuff actually exists. As others have noted, this experiment only behaves like an effectively negative mass in certain specific ways, not in general.
    Conserve energy. Commute with the Hamiltonian.

  15. #15
    Join Date
    Jun 2011
    Posts
    913
    Quote Originally Posted by Grey View Post
    We've had multiple conversations about this, the most recent I'm aware of are here and here.
    (I'm waiting for the subject to be published first before bringing up the question; this way I'm sure it is mainstream)

    Thinking about all the possibilities, there are at least three important things determined by mass. One is inertia, or how an object accelerates when you apply a force. One is the active gravitational mass, which is how strong of a gravitational field an object generates. And the third is the passive gravitational mass, which is what kind of force an object experiences in a gravitational field. For all objects that we've studied, all three types of mass are not only positive, but equal to each other. So we generally don't draw any kind of distinction between these "types" of mass (because they're all the same), except in discussions of hypothetical particles that might have different values.

    Whether "negative mass" is a problem for general relativity, and whether it is attracted to or repelled from normal mass depends on which type or types of mass you make negative. If inertial mass and passive gravitational mass are different, then the principle of equivalence breaks, and so general relativity (as well as a number of similar ideas) won't work. If active and passive gravitational mass are different from each other, that breaks conservation of momentum.

    So if you like general relativity and conservation of momentum, and you flip all three types of mass to negative, you end up with a kind of matter that moves in the opposite direction that you push on it. If you have a chunk of normal matter and a chunk of negative matter, the negative matter accelerates toward the normal matter, while the normal matter accelerates away from the negative matter. It would make a great space drive, since it will accelerate indefinitely without having to use any reaction mass. Sadly, there's no evidence that the stuff actually exists. As others have noted, this experiment only behaves like an effectively negative mass in certain specific ways, not in general.
    I thought about that "turbine" engine but I think there's something we're missing because it sounds unreal.

    But thank you all for your answers.

  16. #16
    Join Date
    Jun 2009
    Posts
    2,128
    Quote Originally Posted by philippeb8 View Post
    (I'm waiting for the subject to be published first before bringing up the question; this way I'm sure it is mainstream)



    I thought about that "turbine" engine but I think there's something we're missing because it sounds unreal.

    But thank you all for your answers.
    It's definitely unreal. Since it doesn't conserve momentum, you could get free energy from it, forever.

    It violates conservation of momentum. It violates conservation of energy. It violates thermodynamics. I expect to see flying unicorns before I see negative mass.

  17. #17
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    46,501
    Quote Originally Posted by philippeb8 View Post
    (I'm waiting for the subject to be published first before bringing up the question; this way I'm sure it is mainstream)
    philippeb8

    I know you didn't ask for any clarification on this, but I'm going to give it anyway...

    Just because something is published, doesn't make it mainstream. Just because something is published in a mainstream, referred, well-respected journal like Physical Review Letters, doesn't make it mainstream. Einstein had a first publication of special relativity, but it wasn't mainstream just because of one publication.

    Then the question is... when is it mainstream? I can't give you a simple answer to that. When it is accepted by a preponderance of scientists in the discipline? When it is published in physics textbooks? I don't know.

    For the vast majority of science, this isn't really an issue. We know it when we see it. Unfortunately for moderators, a significant percentage of the CQ membership likes "exploring" (pushing) the edge of the mainstream envelope, and there is no simple definition where the boundary is.

    Last edited by Swift; 2017-Apr-19 at 03:18 AM. Reason: big typo
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  18. #18
    Join Date
    Jun 2011
    Posts
    913
    Quote Originally Posted by Swift View Post

    For the vast majority of science, this isn't really an issue. We know it when we see it. Unfortunately for moderators, a significant percentage of the CQ membership likes "exploring" (pushing) the edge of the mainstream envelope, and there is a simple definition where the boundary is.
    Pushing the edges is in our nature and CQ is a great but strict platform at the same time so there's always going to be a clash there unfortunately.

    Anyway thank you all again, that was my last question (for a while).

  19. #19
    Join Date
    Oct 2005
    Posts
    25,700
    Quote Originally Posted by Grey View Post
    So if you like general relativity and conservation of momentum, and you flip all three types of mass to negative, you end up with a kind of matter that moves in the opposite direction that you push on it. If you have a chunk of normal matter and a chunk of negative matter, the negative matter accelerates toward the normal matter, while the normal matter accelerates away from the negative matter. It would make a great space drive, since it will accelerate indefinitely without having to use any reaction mass. Sadly, there's no evidence that the stuff actually exists.
    Yeah, the problem with that kind of matter is that, in combination with regular matter, it would completely break our concept of "where the system is," in connection with "where its parts are." If you have a system with very nearly equal parts of this strictly positive and negative matter we are speculating about, you can still have the equivalence principle and conservation of momentum, as you say, but the "center of mass" of a system like that could be vastly distant from the system itself. Gravitationally, the system zooming off in one direction is a manifestation of a motion that is really an oscillation about that distant center of mass. But having such a distant center of mass does violence with intuitive notions of "where the system is", so the fact that the laws of physics seem so built around describing the motion of the center of mass of a system, having that center of mass location bear so little resemblance to what we think of as where the system exists, would surely cause significant issues.

    So perhaps we can say this. The idea that the inertial mass, the active gravitational mass, and the passive gravitational mass, are not only equal to each other for a given object, but also are all positive, is a manifestation of the principle of equivalence, the principle of action/reaction, the principle of inertia, and the principle that the location of a system is related to "where the system is." It's a bit like a fourth Newton's law, one that no one ever felt necessary to verbalize because alternatives seem so pathological. That doesn't mean such mass couldn't exist-- indeed it suggests some parallels with the oft-used concept of "virtual particles", which have no net energy and a very loose concept of location, yet can be regarded as having consequences. In fact, I wonder if a classical analog of a virtual particle might be nearly-overlapping identical positive and negative masses, but a model like that would need a lot of work to be usable. Negative mass might also be a good way to cancel the needed 100+ orders of magnitude of zero point energy. It's also a concept that appears in Hawking's way of talking about Hawking radiation, though I never understood why the negative mass is the one that is supposed to go inward and the positive outward. But with all this potential for the idea, we might be wise to not completely reject the notion!
    Last edited by Ken G; 2017-Apr-21 at 05:36 PM.

  20. #20
    Join Date
    Oct 2013
    Posts
    100

  21. #21
    Join Date
    Mar 2004
    Posts
    15,781
    Closer to being from the horse's mouth: Washington State University News: ‘Negative mass’ created at Washington State University

    Washington State University physicists have created a fluid with negative mass, which is exactly what it sounds like. Push it, and unlike every physical object in the world we know, it doesn’t accelerate in the direction it was pushed. It accelerates backwards.
    [...]
    “What’s a first here is the exquisite control we have over the nature of this negative mass, without any other complications” said [Michael] Forbes. Their research clarifies, in terms of negative mass, similar behavior seen in other systems.
    0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...
    Skepticism enables us to distinguish fancy from fact, to test our speculations. --Carl Sagan

  22. #22
    Join Date
    Oct 2005
    Posts
    25,700
    But keep in mind that these condensed-matter analogs are never really the same as the genuine article!

  23. #23
    Join Date
    Jun 2005
    Posts
    12,465
    Quote Originally Posted by Ken G View Post
    But keep in mind that these condensed-matter analogs are never really the same as the genuine article!
    Yes, these are very special conditions. But it's still pretty amazing work. I only read the abstract but I think I'll look at the paper when I get to work.
    As above, so below

  24. #24
    Join Date
    Apr 2017
    Posts
    4
    Quote Originally Posted by Strange View Post
    Note that the paper is about "effective mass". This is not quite the same thing as mass. For example, in semiconductors "holes" as charge carriers (the absence of an electron) can have a high effective mass, even though there is nothing there.



    As far as I know, the equations would work equally well with negative values for the mass-energy terms.



    I think this was stated in another thread, but it depends on what type of mass you are talking about (inertial, gravitational, etc).

    There is an ongoing experiment at CERN (the ALPHA experiment) to collect enough anti-hydrogen to test how it responds to gravity.
    Yes, but then anti-matter is not negative gravity.

  25. #25
    Join Date
    Oct 2009
    Location
    a long way away
    Posts
    9,989
    Quote Originally Posted by dgjohnsonstein View Post
    Yes, but then anti-matter is not negative gravity.
    That is the assumption to be tested.

  26. #26
    Join Date
    Jun 2006
    Posts
    4,543
    Quote Originally Posted by philippeb8 View Post
    Pushing the edges is in our nature and CQ is a great but strict platform at the same time so there's always going to be a clash there unfortunately.

    Anyway thank you all again, that was my last question (for a while).
    phillippe, the link below is a ood example of how an idea in competition with other idea wins out:

    https://en.wikipedia.org/wiki/Cosmic...ave_background

    It doesn't happen by assertions, or by a single publihed paper, but by the work of many, many people. Look at the quote from korjik below.
    Last edited by John Mendenhall; 2017-Apr-26 at 01:11 AM.
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •