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Anti-Gravity Q

  1. Feb 8, 2012 #1
    Im watching some documentary on alien spaecraft, it was said that propulsion for one of these crafts would need an anti-gravity device. My first question is it even possible for an anti-gravity device to work according to the laws of physics. Second, if the field turned on you would need to generate -gravity to of set the current pull of gravity of the ship. Does that mean you also generate -mass to 0, and if so then shouldnt faster than light travel be possible?

    I guess what Im getting at is can mass exist that gives off zero gravity?
     
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  3. Feb 8, 2012 #2

    DaveC426913

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    No.

    The answers to the rest of your questions follow from that.

    P.S. 'Documentary on alien spacecraft' is an oxymoron. The shows are complete fanciful hogwash.
     
  4. Feb 8, 2012 #3

    Chronos

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    Based on our current understanding, gravity has no equivalent anti force. The trouble with FTL travel is how do you stop? Turning inertia back 'on' while at superluminal velocity would probably be disasterous.
     
  5. Feb 8, 2012 #4
    When you say “the laws of physics” you probably mean “the conservation laws,” since we reserve that term for those factors that we find in equal quantities both before and after all observed experimental interactions. You’ve probably heard of many of these laws: conservation of mass-energy, conservation of momentum, conservation of electrical charge, and maybe conservation of angular momentum (the “spinning ballerina” conservation law) or others.

    You’re asking if any of those laws would be broken if two bodies were to accelerate away from one another instead of accelerating toward each other. Simply put, no. None of the conservation laws would be violated if gravity were found to exhibit repulsion as well as attraction. Just as electrically-charged bodies exhibit both attracting and repelling forces, gravitationally-charged bodies could hypothetically exhibit both forces without violating any of the conservation laws. See the recent theoretical papers by: J.M. Ripalda, F. Henry-Couannier, S. Hossenfelder, and M. Villata.

    The objection heard at this point is that gravity only has a positive “charge,” which is observed to be attractive, and is described elegantly by general relativity. But this growing wave of theorists, spurred by the observation of a kind of cosmic-scale “antigravity” effect that astronomers call “dark energy,” have postulated that general relativity is only half of a larger “bi-metric” theory of relativity. These physicists propose that the missing or “dark side” of general relativity describes the equal (but inversely signed) metric that applies to antimatter. These new models predict that antimatter would gravitationally attract other antimatter, but repel ordinary matter; i.e. antimatter would “fall up” in the Earth’s gravitational field.

    Measurements of the precisely equal and positive inertial masses of protons and antiprotons, and electrons and positrons…combined with our unquestioned assumption that positive inertial mass must equate to an attracting gravitational field…seemed to settle the question for decades. Conventional thought has been: “antimatter has positive mass just like matter, and therefore both must possess identical and always-attractive gravitational fields.”

    Then a series of devastating calamities befell the established theories: first, the intractable problem of “the annihilation catastrophe.” The elegant and eerily-prescient Standard Model, and all of our laboratory observations, failed to explain the (assumed) abundance of matter over antimatter in the universe. Some physicists, such as Nobel laureate and MIT science hunk Dr. Samuel Ting (designer and mission commander of the Alpha Magnetic Spectrometer 2, which he got installed on the International Space Station last year), aren’t convinced that equal numbers of antimatter galaxies clusters and matter clusters have been ruled out. If the AMS-02 detects a single antihelium nucleus (one of its primary mission objectives) then we’ll have to accept that the universe is probably matter/antimatter symmetric after all (because antihelium would probably only be created in detectible quantities within antihydrogen stars, which would probably only exist in antimatter galaxies).

    Next, the new millennium double-whammy to our established assumptions about the universe: “dark matter” and “dark energy.” When astronomers mapped the spinning motion of the galaxies they discovered that they didn’t spin as expected. The simplest way to “correct” this unexpected discrepancy was to assume some kind of very abundant new kind of matter, permeating the entire galaxy, which we haven’t yet observed directly for unknown reasons. Other theorists questioned the validity of our ideas about gravity at the galactic scale. The debate rages on.

    And finally, the “dark energy” problem: how do we explain the observation that the universe is expanding at an accelerating rate, if the gravitational field is always attractive? ''Right now, not only for cosmology but for elementary particle theory, this is the bone in our throat,'' said Nobel-winning theoretical physicist Dr. Steven Weinberg on the problem of “dark energy.”

    All of which leads to the growing appeal of a single, elegant explanation for all of these theoretical physics conundrums. And an antimatter/matter gravitational repulsion model might be able straighten out all these tangles without demanding new particles, new universes, or new N-branes in my M-branes.

    So, some of the most brilliant minds at the most respected laboratories around the world are racing to be the first to experimentally demonstrate whether antimatter falls up, or down, in the Earth’s gravitational field. This link at the Max Planck Institute for Nuclear Physics offers a marvelous overview of on-going research on the gravitational interaction of matter and antimatter: http://www.mpi-hd.mpg.de/kellerbauer/en/projects/antimatter.htm It is, of course, an outrageously difficult observation to achieve: forming antihydrogen is dicey enough without having to cool it down before it commits suicide with some enticing atom of ubiquitous matter, but also delicate observations must be made of the antihydrogen atoms in free-fall without disturbing their infinitesimal momentum.

    In any case, the smart money waits for the decisive experimental observations. That’s the proper scientific, skeptical position to take: make up your own mind, don’t believe the hype, and always remember:

    “Science is the belief in the ignorance of the experts.” – Richard Feynman

    /Demon out
     
  6. Feb 9, 2012 #5
    there is supposed to theoreticly be a graviton, right? so with most other things having anti counterparts isnt it possible there are anti gravitons too? maybe dark energy could be anti-gravity, that could explain why the universe is expanding exponentialy, gravities counterpart working against it.
     
  7. Feb 9, 2012 #6

    Nabeshin

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    The graviton is its own antiparticle (like the photon).
     
  8. Feb 9, 2012 #7
    Conventional physics cannot currently offer 'antigravity', as is posted in the replies above.

    On the other hand, 'dark energy' is posited to be a form of negative pressure
    that causes the acceleration of the universe:

    http://en.wikipedia.org/wiki/Dark_energy#Negative_pressure

    This is a feature of 'empty space', is unbelievably weak, yet over vast cosmological distances
    is powerful enough to apparently cause expansion of the uuniverse..... Nobody knows exactly what it is nor how it might someday, if ever, be harnessed. Today antigravity remains in the realm of science fiction.
     
  9. Feb 9, 2012 #8
  10. Feb 9, 2012 #9
    Apparently nobody is bothering to read other posts here before contributing to the thread, so this is more of a pulpit than a discussion forum.

    Currently, it *IS* theoretically possible that matter and antimatter repel one another gravitationally, ie, via "antigravity." Here's an article on the subject: http://www.physorg.com/news/2011-04-antigravity-dark-energy-universe-expansion.html

    And once again, here's a link to the page at the Max Planck Institute for Nuclear Physics, which discusses current experimental attempts to determine if antimatter falls up, or down, in the gravitational field of the Earth: http://www.mpi-hd.mpg.de/kellerbauer/en/projects/antimatter.htm

    As cited above and elsewhere, it's quite possible, given the available data set, that antimatter possesses an "inverse gravitational charge," just as antimatter particles possess an "inverse electrical charge."

    Only direct experimentation, and not our expectations, can determine the issue decisively.
     
    Last edited: Feb 9, 2012
  11. Feb 10, 2012 #10
    Hi Maxwell,

    I read the blurb under the picture...did not even see the physorg link off to the right.....

    The physorg paper itself had a nice clear summary regarding the nature of antimatter, and I am sure not expert by any stretch, but the idea of CPT parity reversal enabling 'antimatter' from matter doesn't seem like anything new: Changing parity and time affect gravity by reversing its sign. I wonder what's 'new' here.

    Anayway, It's a wonderful potential [theoretical] opportunity.

    Is there any experimental 'data' yet that supports this statement:

    I went looking around and found that last year there may have been experimental evidence of direct CP violation:

    http://en.wikipedia.org/wiki/CP_violation


    The article seems to have a synopsis of current experimental work, and links to the CERN
    CP violation experiments:

    http://en.wikipedia.org/wiki/LHCb

    No evidence of antigravity is mentioned. Wouldn't that make
    headlines around the world??

    So for now I'll stick with my earlier post:

    let's hope somebody finds 'antigravity'...the sooner the better!
     
    Last edited: Feb 10, 2012
  12. Feb 10, 2012 #11
    As already mentioned in this thread, photons are their own antiparticles. Photon trajectories are deflected toward normal mass, and only toward it. We see no sign of oppositely lensed "antiphotons", and photons show no sign of inconsistency in their behavior in gravitational fields...star images don't form double images or blurred streaks both toward and away from large masses.

    In addition, gravity is a function of mass-energy. Protons (and antiprotons) have mass consistent with the combination of the mass of their quarks with their binding energy, a hot object has greater mass than an identical but colder one, etc. If antimatter had opposite gravitational charge, a particle and antiparticle annihilating to form photons (which are modeled as their own antiparticles and observed to react to gravitational fields with the same sign as normal matter) would be a net zero gravitational charge suddenly becoming a positive one. Never mind antigravity, you could turn gravity on and off by alternately performing annihilation (capturing the released energy) and pair production. This badly breaks conservation laws (turn gravity off, lift a now-weightless mass, turn it back on, use the falling now-heavy mass to generate power!).

    It's a quick and easy solution that might be intuitively appealing, but it is almost certainly completely wrong.
     
  13. Feb 11, 2012 #12
    Agreed: it’s a fascinating and impertinent question. Its simplicity is almost embarrassing, and yet it touches on nearly every major cornerstone and controversy in contemporary physics: general relativity, quantum gravity, the Standard Model, vacuum energy, dark energy, the Big Bang and the annihilation catastrophe problem, yes…even ufo’s, and did I mention: “antimatter?” And not only all that, but we get to see the definitive experimental observation within a matter of months probably. I daresay, if you don’t absolutely *live* for historical scientific moments like these, then physics probably isn’t really your bailiwick.
    There’s no experimental data either way, which is why I said “quite possible” instead of “true” or “known.” But there are published papers by the theoretical physicists I mentioned previously, and others. The wiki offers additional citations:
    http://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

    The ATHENA consortium attempted the measurement a few years ago, but their findings were inconclusive. However, some of the theorists I mentioned offer the observed repulsive acceleration of the universe as proof of their ideas. They suggest that half of the universe could be antimatter galaxy clusters which are antigravitationally repelling matter galaxy clusters. And they say this could explain dark energy…and perhaps even dark matter:
    Quantum vacuum and dark matter, Hajdukovic, 2011
    http://arxiv.org/ftp/arxiv/papers/1111/1111.4884.pdf

    And I’m loathe to get into it, but I think a good argument can be made that the analogous physics of electromagnetism and gravitomagnetism, which behave by essentially identical mathematical equations in the weak field limit, makes a strong circumstantial case that gravitation also possesses a dipole nature. But I don’t lend much credence to circumstantial arguments.
    On the other hand, astronomers can’t seem to shut up about antigravity lately. Because we now know that *something* which acts just like antigravity is pushing the universe apart. Of course we *may* find some other kind of explanation, but frankly, if it looks like a duck, and quacks like a duck…
    I’m going to have to split a hair with you on this one, Naty1: conventional physics might not currently offer any accepted mainstream prospects for antigravity (if we’re willing to ignore the theoretical investigations by R. Forward and H. Bondi on negative mass – which I’m not willing to do, because they’re all consistent with “conventional theory”). But nowadays astronomy seems incapable of working without antigravity (ok ok, we can keep calling it “dark energy” for awhile longer). And conventional physics *can* offer intriguing possibilities of antigravity, since it’s not explicitly forbidden by any of the conservation laws. And at this point one could argue that the equivalence principle may need to be revised in this simple way: “the inertial mass of a body is equivalent to the [absolute] magnitude of its gravitational mass,” which would defeat the “but the equivalence principle says that inertial mass = gravitational mass” argument.
    Apparently we already have…in the motion of the galaxy clusters. The only part we haven’t resolved is the precise nature of the mechanism (and happily, that’s only a matter of time, and good ole human ingenuity).
    The AEGIS group will have the definitive observational results when they perform their experiment soon: they expect to measure the polarity and the magnitude of the gravitational acceleration of antihydrogen to around 1% accuracy. And you’re right; if antimatter falls up then I think it’ll steal headlines all over the world.
    Or...not. If photons (and neutrinos) have a net gravitational charge of zero, and particles with a net gravitational charge of zero accelerate toward matter and antimatter equally (analogous to electrostatic induction), then there is no logical inconsistency. But this is exactly why I don’t trust theory: every theory is ultimately ad hoc, and only ever as credible as the next observational challenge.
    Here, take these two papers and call me in the morning:
    CPT symmetry and antimatter gravity in general relativity, M Villata, 2011
    http://arxiv.org/pdf/1103.4937.pdf
    Time reversal and negative energies in general relativity, JM Ripalda, 1999
    http://arxiv.org/ftp/gr-qc/papers/9906/9906012.pdf
    I could make a list of the ways that didn’t make sense. And I could be wrong, but I think you just implied that a water wheel violates conservation of energy. I suggest that you think about the same example (whatever it is) and replace the idea of “gravity field” with “electrical field” and check to see if any conservation laws are broken, badly broken, or very badly broken. I can almost certainly assure you that dipole gravitational charge interactions (which would yield attractive and repulsive accelerations) are every bit as conservative as dipole electrical charge interactions (which also yield attractive and repulsive accelerations). They’re both conservative fields, gravitational repulsion does –not- imply free energy any more than electrical repulsion implies free energy.
    I love that: “almost certainly”…followed by…“completely wrong.” It’s not quite certainly, but nearly certainly…not just wrong…but completely wrong. In that case I am almost certainly completely unconvinced that it’s almost certainly completely wrong :)

    And maybe I’m shallow, but I think that quick, easy, and intuitively-appealing explanations are rather compelling, not intrinsically suspect.

    Honesty, and nothing personal, but if the world-class physics wunderkinds at the Max Planck Institute for Nuclear Physics *and* CERN think that the question of the sign of the antimatter/matter gravitational interaction is unresolved, and worth spending a few years of their lives and millions of dollars on testing, then I’m going to keep an open mind and let their data settle the question.
     
    Last edited: Feb 11, 2012
  14. Feb 11, 2012 #13
    Good post, lots to consider, but not this one:


    Positive (normal) gravity and dark matter, not antimatter, seems behind the observed
    rotation of galaxies.

    And 'dark energy or anti gravity or whatever you want to call it is hardly evident within a galaxy.

    http://en.wikipedia.org/wiki/Dark_matter#Observational_evidence
     
  15. Feb 11, 2012 #14

    DaveC426913

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    To bring clarity, he specifically said rotation of galaxy clusters, not rotation of galaxies themeselves.
     
  16. Feb 11, 2012 #15
    Antigravity is a misunderstood term. Nobody equates "Antibiotic" with poison do they?

    The decommissioned space shuttle had a propulsion system that overcame gravity as well.

    We call propulsion systems "Antigravity" when they don't fit one of the systems we already understand but that doesn't mean they literally counteract gravity itself. It just means we don't understand the engineering well enough to know how the reaction forces are balanced.

    Hypothetical alien propulsion systems most likely would not counteract gravity but would in fact obey all the laws of reaction. Think of a helicopter where the blades engage a fundamental physical field (as yet not understoid by man) instead of air.
     
  17. Feb 11, 2012 #16

    DaveC426913

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    I don't think you've put your finger on the commonly-used definition. Generally when people talk about antigravity, they are (i.e. unless stating otherwise) talking about a force that causes repulsion directly from mass.
     
  18. Feb 11, 2012 #17
    Generally I agree with you about that in this forum. Dark energy etc. But this thread started off being about the other kind (the coloquial meaning; non electromagnetic levitation) and morphed into what you mean (the "astrophysical" meaning).
     
  19. Feb 11, 2012 #18

    DaveC426913

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    Good point.

    The statement "would need to have an antigravity propulsion" is silly. All it needs is a propulsion system that we don't recognize.

    And it should serve as an example of why these shows should never be taken seriously. They have no more factual content than any sitcom or reality show.

    Like I said, 'documentary on alien spacecraft' is an oxymoron.
     
  20. Feb 11, 2012 #19
    Treat it as science fiction. That's legitimate.

    Until you see them with your own eyes. Then you're on your own.
     
  21. Feb 11, 2012 #20
    For those who are interested in the theoretical physics of antigravity, here are some credible contemporary papers about a possible matter/antimatter antigravitational interaction, how this concept may explain “dark energy” and “dark matter,” and new “bi-metric” theories of general relativity that may explain the nature of the dipole gravity theory:

    Is dark matter an illusion created by the gravitational polarization of the quantum vacuum?, Hajdukovic, 2011
    http://arxiv.org/ftp/arxiv/papers/1106/1106.0847.pdf

    A Bi-Metric Theory with Exchange Symmetry, S. Hossenfelder, 2008
    http://arxiv.org/pdf/0807.2838v1.pdf

    The Dark Side of Gravity, Frederic Henry-Couannier, 2010
    http://arxiv.org/abs/0807.2838

    CPT symmetry and antimatter gravity in general relativity, M. Villata 2011
    http://arxiv.org/pdf/1103.4937v1.pdf

    Comment to a paper [arXiv:1103.4937] of M. Villata on antigravity, Marcoen J.T.F. Cabbolet
    http://arxiv.org/pdf/1108.4543v1.pdf

    Reply to "Comment to a paper of M. Villata on antigravity," M. Villata, 2011
    http://arxiv.org/pdf/1109.1201v2.pdf
     
    Last edited: Feb 11, 2012
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