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Purported Relativity Paradox Resolved 128

Posted by timothy
from the disappears-in-a-puff-of-logic dept.
sciencehabit writes "A purported conflict between the century-old theory of classical electrodynamics and Einstein's theory of special relativity doesn't exist, a chorus of physicists says. Last April, an electrical engineer claimed that the equation that determines the force exerted on an electrically charged particle by electric and magnetic fields — the Lorentz force law — clashes with relativity, the theory that centers on how observers moving at a constant speed relative to one another will view the same events. To prove it, he concocted a simple 'thought experiment' in which the Lorentz force law seemed to lead to a paradox. Now, four physicists independently say that they have resolved the paradox."
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Purported Relativity Paradox Resolved

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  • by CodeBuster (516420) on Saturday January 26, 2013 @05:04AM (#42699347)
    The four physicists waived their hands over the box containing Schrödinger's cat while repeating, "omine, omine, omine" before walking away without looking inside and thus the conjecture was false and the paradox is resolved.
    • Re: (Score:2, Funny)

      by Anonymous Coward
      So they refrained from using their hands?
  • by thephydes (727739) on Saturday January 26, 2013 @05:16AM (#42699373)
    Science is alive and well in at least the Physics community. Whilst I won't even pretend to understand General Relativity, the questioning of it and discussion about those questions is the true essence of science. facts ->theory->more facts->questions->revised theory. Beautiful!
    • by Anonymous Coward

      This is in the range of a practise problem in special relativity, not something for a scientific paper.

    • by Anonymous Coward on Saturday January 26, 2013 @06:30AM (#42699521)

      Science is alive and well in at least the Physics community. Whilst I won't even pretend to understand General Relativity, the questioning of it and discussion about those questions is the true essence of science.

      Sigh. General Relativity was not even at question here. Perhaps commenting on Slashdot should require a minimum amount of knowing what one is talking about. AAAHAHAHAHAHAHAHAHHAHAHAHA. Sigh.

      At any rate, electrical engineers tend to view parts of Special Relativity in isolation. That makes them easier to handle and "visualize" in some respects, but much harder to deal with interactions. Minkovsky vectors and tensors are what theoretical physicists use instead, grouping several codependent field parts into one entity that can then be transformed as a whole.

      So the physicists will most likely just have employed a better mathematical toolbox for resolving the "paradox". I've not actually read the original Einstein papers, but I would not be much surprised if his equations were closer to what Electrical Engineers get to deal with than what Theoretical Physicists do. Shaking out all that tensor stuff is more or less elegant wrapup work.

      That sort of approach was, however, at the core of General Relativity, and mastering it took quite a bit more time for Einstein. I seem to remember that he discussed the underpinnings with Hilbert, and Hilbert came up with the general equations independently within something like a week, but retracted his papers out of respect for Einstein doing all the visionary groundwork as well as shouldering the math (though being quite slower at it than well-versed mathematicians).

      • I've not actually read the original Einstein papers, but I would not be much surprised if his equations were closer to what Electrical Engineers get to deal with than what Theoretical Physicists do.

        Indeed. When Minkowski reformulated it with 4D tensors, Einstein complained that he didn't recognize his own theory any more.

        However, for General Relativity, Einstein had to go that path as well, and learned to love the power of it.

      • by BitterOak (537666)

        Science is alive and well in at least the Physics community. Whilst I won't even pretend to understand General Relativity, the questioning of it and discussion about those questions is the true essence of science.

        Sigh. General Relativity was not even at question here. Perhaps commenting on Slashdot should require a minimum amount of knowing what one is talking about. AAAHAHAHAHAHAHAHAHHAHAHAHA. Sigh.

        Wow, somebody took their grumpy pill this morning. Can't a person simply point out that it's great to see issues like this being discussed without someone tearing them apart for confusing the special and general theories of relativity? By the way, I have a Ph.D. in physics. Does that make me qualified to post a reply to your comment?

        • by BitZtream (692029)

          By the way, I have a Ph.D. in physics.

          No. Having a Ph.D. in physics means nothing more than you have a Ph.D. in physics. It does not, contrary to what you assume, mean you know what you're talking about. Having a Ph.D. just means you did the same shit grunt work those before you did so now you've got a certificate from the Good Ole' Boys club saying you did the same shit they did. That is not science, thats Academia and while most associate Academia with knowledge, that is also silly and more often than not, wrong.

          A Ph.D. means you paid you

          • Bullshit. If you have a Ph.D., you've published original research papers, so you know your field as well as anyone. Sounds like someone never got theirs, but still thinks they should be considered to be in the same league as someone who did?
            • Bullshit. If you have a Ph.D., you've published original research papers, so you know your field as well as anyone. Sounds like someone never got theirs, but still thinks they should be considered to be in the same league as someone who did?

              And yet he could have published in completely unrelated areas of physics to the discussion at hand, thus making him no more qualified for the discussion and a high school student.

    • by Anonymous Coward
      /. is the last place I expected to see, "isn't science great" Facebook-type posts.
      • /. is the last place I expected to see, "isn't science great" Facebook-type posts.

        Not everybody here is a depressed curmudgeon.

        • by Anonymous Coward

          Perhaps the previous AC meant that science being great is a given and doesn't need to be stated here.

    • Science is alive and well in at least the Physics community. Whilst I won't even pretend to understand General Relativity, the questioning of it and discussion about those questions is the true essence of science. facts ->theory->more facts->questions->revised theory. Beautiful!

      Did you mean trueFacts, or goodFacts? Anything can be politicized, even physics. Humans, as a rule, don't care about "facts" when they conflict with personal beliefs. If the algorithm starts with "facts", you are setting up a conflict between trueFacts and goodFacts, which allows personal beliefs to corrupt the entire process. Let me propose a slightly different algorithm that takes personal belief out of the way of the pursuit for knowledge:

      model -> hypothesis -> measurement -> failure of h

      • You have to start with facts because without facts you don't even know that you have something you need a model for. You don't just invent models and then look if you can find something in nature which fits that model. You start with facts you find, and try to make a model which reproduces those facts. You generally try to be compatible with existing models in regimes where those didn't fail, so that would be the first test of your model (well, you might at the very first also do some consistency check). Th

        • by lgw (121541)

          Starting with "facts" really adds nothing to the process, except perhaps expediency. If a model accurately predicts new measurements it's a good model. If a model accurately fits the set of known measurements ("facts") - that actually means very little! Necessary, but not even close to sufficient. That's the "data mining fallacy", and why people tend to do such a poor job at modelling the stock market.

          • Without having facts, you don't even know what to model. If someone told me to model the solar system and I had no facts about the solar system, my model might look like "a=b+c" where a is the a-ness of the solar system, b is the b-ness and c is the c-ness. Of course that has nothing to do at all with the solar system. But I can't know that without any facts about the solar system.

            • by lgw (121541)

              Perhps, in that most general sense, sure. But Newton wasn't really trying to explain a set of measurements with his reasoning about gravity - he was trying to deduce what it must be, what the most attractive model was. Unlike most of his writings, which were comically bad, he happened to be right about gravity. We don't teach the rest of his ideas because he really wasn't very concerned with facts

              But mostly I was just warning of the natural inclination to prefer theories for their explanatory power (of fa

              • Perhps, in that most general sense, sure. But Newton wasn't really trying to explain a set of measurements with his reasoning about gravity - he was trying to deduce what it must be, what the most attractive model was. Unlike most of his writings, which were comically bad, he happened to be right about gravity. We don't teach the rest of his ideas because he really wasn't very concerned with facts

                Newton certainly wanted to reproduce Kepler's laws which at the time were the best description of the solar syst

      • No, it's not about facts.

        It's about epistemologies: How you arrive at those facts. Most scientists follow an empirical empistemology. The rest of the world usually follows a more rational one, or historical (i.e. something is true because a book says so).

        A rational epistemology holds that anything that can be proved logically is true. An empiricist holds that anything that can be demonstrated experimentally is true. Some statements can be true in either paradigm, but it can make a big difference as to how y

        • I don't think "rational" means what you think it means...there is nothing rational about an epistemology that requires faith to espouse. Faith is the acceptance of truth without evidence. The wikipedia entry for faith and rationality [wikipedia.org] explicitly calls out faith as being incompatible with rational, evidence-based reasoning.
          • Actually in the context of epistemology [wikipedia.org], it means exactly what I said it means. The wikipedia article you refer to conflates rationalism and empiricism, I refer you to my previous post for an explanation of the differences.

            You're also ignoring centuries of christian apologists and philosophers, scores of whom were better logicians than either of us: I may single out Descartes and Kant. Faith is an axiom, not necessarily an irrationality. The axioms of Christianity and those of mathematics may differ, but th

            • Hmmm...I had to go back and re-read your post. When I first read it, I saw "something is true because a book said it's true" being equated with rationality and pretty much dismissed the rest of the post as equally flawed. I'm glad I went back, though. I am indeed ignoring centuries of christian apologists and philosophers, largely because apologizing for a fallacy doesn't correct the fallacy. Faith is not compatible with reason, despite Augustine's and Aquinas' elegant arguments to the contrary. Descar
    • by bill_mcgonigle (4333) * on Saturday January 26, 2013 @10:23AM (#42700237) Homepage Journal

      And it's a healthy sign that some random guy can say, "look Special Relativity seems to be broken," and nobody starts screaming about golden idols or anything, but rather four smart guys kindly consider what he has to say and show him where he went wrong. Everybody learns something, egos remain intact, and nobody starts swinging guns. Science FTW.

      • by Anonymous Coward
        This is actually surprisingly easy to do with physicists in my experience. As long as you are polite, and don't make it look like you are trying to feed your ego by "beating" physicists with no effort, you can sometimes get a remarkable amount of effort and response to questions. In other words, physicists are very nerd-snipe-able, and will before they know it, spend a weekend working on a problem just because of something a student, coworker, or random person said or asked in idle conversation.
  • by Anonymous Coward

    How strange that even I understand the "hidden momentum" concept (I think!). Time for a car analogy:
    Imagine a car driving past you. At first you're looking at its front, then side, then it rear. So the car actually rotated from your frame of reference, and at the time it was passing right next to you it had an angular momentum.
    Since the car was not actually rotating, those physicists call it a "hidden angular momentum".

    This electrical engineer claims that such angular momentum is just a kludge concept added

    • Re: (Score:2, Flamebait)

      by expatriot (903070)

      Whenever there are any really tough questions about relativity, the world waits for an electrical engineer to comment. Unfortunately their comments are not correct.

      • Re: (Score:2, Interesting)

        by Anonymous Coward

        Well, "hunt the paradox" is a standard exercise in Theoretical Physics 101, special relativity. There are quite a number of them, and not too few involve understandings of "orthogonal" and "simultaneous" and other conceptual geometric invariants that are not actually invariant.

        Electrical engineers don't go through that enfuriating and embarrassing spectacle of "ok, what did I take for granted now again" of relativity initiation.

  • Read original paper (Score:4, Informative)

    by Janek Kozicki (722688) on Saturday January 26, 2013 @07:46AM (#42699727) Journal
    http://prl.aps.org/toc/PRL/v108/i19 [aps.org]

    Scroll down to "Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation", there you can get the pdf, if you have university access. Whew, it took me more than 20 minutes to find it. Why those journalists do not include the cited source?!

    This paper is actually quite interesting, and I remember my ED teacher complaining about the Lorentz Law incompatibility during his lectures too. Whether "hidden moment" exists or not - maybe is a matter of performing the right experiments :)

    And what about the proton radius problem?
    • it is slashdotted now...
      • by 0111 1110 (518466)

        Ah. Sometimes denial of service attacks are a good thing then. Locking away pure information in such a way that only rich people from rich countries can view them is so not the way for science to move forward.

    • Re: (Score:3, Informative)

      by henryteighth (2488844)
      http://arxiv.org/abs/1205.0096 [arxiv.org] Many physics papers are also uploaded to the arxiv where they are freely accessible.
  • by Anonymous Coward

    Since a paradox is not a feature of the Universe; it is a feature of a limited mind trying to understand the Universe.

    • Since a paradox is not a feature of the Universe; it is a feature of a limited mind trying to understand the Universe.

      Physics is all about understanding the universe with our limited mind.

  • by forand (530402) on Saturday January 26, 2013 @08:36AM (#42699857) Homepage
    Glad to see that others are noticing that in Physics we are still willing to entertain questioning of the foundations of modern Physics by those outside the field. Another great thing about our field is that most every paper is openly available on one of the abstract services. The original article noting the apparent paradox can be found here [harvard.edu]. While the subsequent discussion can be seen by looking at the papers citing the original, found here [harvard.edu]. Some of the commentaries have yet to be released from their embargo and are thus not yet available but will likely be so soon.
  • It's not a paradox (Score:5, Insightful)

    by mocm (141920) on Saturday January 26, 2013 @09:40AM (#42700041) Homepage

    if you forget part of the energy-momentum tensor when you transform your coordinates from a stationary into a moving frame of reference.
    Special relativity really cannot "clash" with the Lorentz force law, because it is based on the Lorentz invariance of Maxwell's equations. I think a "paradox" like this keeps coming up ever so often in discussions of special relativity, form people who don't understand it. I just don't see how PRL can accept such a paper.
    I admit it would make a nice problem for a physics test, but not much more.

    • I just don't see how PRL can accept such a paper.

      Simple: The referees they sent it to for peer review didn't understand it either.

    • by tinkerton (199273)

      I think your position is too radical. Understanding is more than knowing what the result will be. Understanding is about - to put it in James Maxwell's words - knowing the particular go of it. And that is valid science. The twins paradox in special relativity can easily be dismissed on general principles but that isn't the same as understanding how it goes.

      When someone proposes a perpetuum mobile it can instantly be dismissed by slapping a physics law on it, but that is a limited form of understanding. It's

    • Re: (Score:3, Informative)

      by daaxix (218354)

      Read his paper and his rebuttal. He is basically saying that if the Lorentz law of force is replaced with a more elegant equation (Einstein-Laub), then you naturally obtain the "hidden momentum" terms that are inserted under a covariant transformation. Furthermore, there is another candidate equation, Helmholtz force, which is different but takes care of the "hidden momentum" in a similar way. Predictions in differences in experiments can be made and Mansuripur is attempting to realize these experiments.

  • by exploder (196936) on Saturday January 26, 2013 @10:34AM (#42700291) Homepage

    First of all, this post is aimed not at the engineer from the article, but at some of the posters to this story and others like it. What is it about physics in particular that attracts so many uneducated crackpots? It seems to be the sweet spot for cranks on the XKCD spectrum--they don't go all the way over to math, and try to promote their pet tensor analysis theory ("this is how we really should compute the induced map on the cotangent bundle!"), and even less often are we treated to their "revolutionary" theories of hydrocarbon structure or ribosomal protein synthesis.

    Nope, they gravitate straight to physics. Is it that concepts are (relatively) familiar, like light, gravity, time, particles, etc? Is it Star Trek? Must drive physicists nuts.

    • by ceoyoyo (59147)

      I suspect it's because classical physics is something we're all reasonably familiar with from our everyday experience but modern physics departs from our expectations in many ways. We know our intuition doesn't work very well with tensor analysis or hydrocarbon structure or protein synthesis, but we expect it to work well with bits of matter flying around. Cranks are just people who mistake their intuition, or deeply held beliefs, for "truth."

    • I'd say it is the philosophical side of physics. Physics, sometimes more than the other sciences focuses on the big picture and hence, meaning of equations and less of plain facts, or at least that's what I gather from the pre-meds I tutor. It's not that meaning isn't important in biology or chemistry, it is just is that with so much information, going too deep into one topic can be a waste of time that misses the point. For physics, depending where you are on the experimental to theoretical spectrum, depth

    • by Sigg3.net (886486)

      Any expert field suffer fools.

      Take philosophy, which I study. People get frustrated just by my saying that I study philosophy. Why ?Because everyone's opinion is supposed to be equal. So I usually stick to empirical evidence and pick apart the arguments.

      After a while they calm down. It is the "so you think you are smart" kind of prejudice. If not that, then it's the "you can't tell me what the meaning of my life is". Yes, I can, several meanings from several philosophers which can help us frame the question

  • Executive Summary
    If you have a paradox in a thought experiment, you can think your way out of it.

    • Re:Cognition (Score:5, Informative)

      by thegreatemu (1457577) on Saturday January 26, 2013 @01:01PM (#42700993)

      Not by any means. For probably the best example, look at the Einstein-Rosen-Podalsky paradox , a simple thought experiment used an attempt to disprove the so-called Copenhagen interpretation of quantum mechanics because it would require the instantaneous transmission of quantum states in such a way that would violate special relativity. People did try to think their way out of it, until Bell's theorem "thought" everyone back into the paradoxical corner - leading to the modern sciences of quantum entanglement.

      In fact if you look back, many of the advances in modern physics have come about specifically because of paradoxes arising from thought experiments. See also the ultraviolet catastrophe, or even Schrodinger's cat for that matter.

  • Mansuripur's papers are readable on Archive.org, while the replies of his critics are on paywalled journals. I do not have 30 or 40 dollars to observe their handwaving. Since he's out in the open, while their supposed 'replies' are hiding behind the bulwarks of protectionist convention, I'm awarding the decision to Mansuripur. All hail Swartz.

  • "In your face, engineers !"

    -- Physicists

  • For those not interested in the fine detail, there's a very simple explanation as to why there isn't any real paradox involved.

    Let's start with a quote from the article (looks like the paper is a bit more subtle, but the upshot is the same): "Now imagine how things look from a "moving frame of reference" in which the charge and magnet both glide by at a steady speed. Thanks to the weird effects of relativity, the magnet appears to have more positive charge on one side and more negative charge on the other."

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