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General Relativity Is At Least 99.95% Right

Posted by ryuzaki0 on from the happy-hair dept.

ultracool writes to mention a ScienceDaily piece on compelling proof of general relativity. A team at the University of Manchester have used three years' worth of data on a pair of pulsars as a litmus test, against which they've benchmarked Einstein's theory. From the article: "Though all the independent tests available in the double pulsar system agree with Einstein's theory, the one that gives the most precise result is the time delay, known as the Shapiro Delay, which the signals suffer as they pass through the curved space-time surrounding the two neutron stars. It is close to 90 millionths of a second and the ratio of the observed and predicted values is 1.0001 +/- 0.0005 - a precision of 0.05%. A number of other relativistic effects predicted by Einstein can also be observed. 'We see that, due to its mass, the fabric of space-time around a pulsar is curved. We also see that the pulsar clock runs slower when it is deeper in the gravitational field of its massive companion, an effect known as "time dilation."'"

6 of 223 comments (clear)

  1. General Relativity Is At Least 99.95% Right by Anonymous Coward · · Score: 4, Insightful

    Observations that support a theory are nice, but they are not a proof.

    1. Re: General Relativity Is At Least 99.95% Right by smash · · Score: 4, Insightful

      You can never *prove* a theory, you can merely disprove it by finding evidence which does not support it.

      --
      I run: Windows, OS X, Linux, FreeBSD. Just because you have a hammer, doesn't mean everything is a nail.
    2. Re: General Relativity Is At Least 99.95% Right by kfg · · Score: 5, Insightful

      . . .they are not a proof.

      Only mathematics has proofs, but observations that support a theory demonstrate that the model has predictive value. Observations that do not support a theory demonstrate that the model is, at best, incomplete.

      Ignoring the predictive value of a model, whether it is complete or not, demonstrates that you are an idiot. Within its limits of significance Newton's theory of gravitation is still just as "correct" as Relativity.

      Facts are not proofs, but they are facts.

      KFG

    3. Re: General Relativity Is At Least 99.95% Right by QuantumFTL · · Score: 4, Insightful

      Within its limits of significance Newton's theory of gravitation is still just as "correct" as Relativity.

      That's like saying "for whatever region of the hypothesis space a given theory gives usably correct predictions, it's useful." Of course that's true, however part of using a theory correctly is knowing how far it goes. Quantum theory has demonstrated that the fundamental concepts in newtonian physics (position, momentum, energy, time, etc) are not really meaningful when you boil things down to the lowest levels we can observe.

      I mean, you can tell someone that a VCR works because there's a little man in there that knows when you said you wanted something taped and writes all the TV programs down on tape. I mean, I don't think people actually believe this, but their black-box model of a VCR is essentially equivilent to this. The reality of how a VCR works, of course, is much more complex in many ways, and involves failure modes that non-electronic type people will likely fail to predict because of their incomplete view of the situation.

      Newtonian physics is not merely an appoximation error, the fundamental set of concepts and intuitions are just completely unhelpful at any scale but mezoscale (that on which we exist, somewhere between atom and star).

    4. Re: General Relativity Is At Least 99.95% Right by QuantumFTL · · Score: 4, Insightful

      You can't measure position in quantum physics - you can only use device which responds probabilistically to a quantum 'waveform' (yes, I know it's not exactly a wave, I do have a degree in physics despite not being a physicist myself). As far as we known, the "particle" *NEVER* has an exact position or momentum, but rather is at an infinite set of locations (more strongly than others) with an infinite set of momenta, and the same with energy/time (yes, I'm abstracting away light cones and plank space/time).

      Yes the position/momentum/energy/time *operators* themselves have meaning, but giving a particle these properties, which it doesn't strictly even appear to have... that's simply ridiculous. Our intuitions don't work at these levels, the best we can do is trust to the math and come up with great ideas based on the equations we find in QM.

      Relativity is still "classical" physics in that it's deterministic, but its very concepts of mass, energy, time, space, and propagation of information are fundamentally different. I'm sorry, but it's just so very different from what Newton had in mind.

  2. Re:Maybe, but I don't think so! by Anonymous Coward · · Score: 5, Insightful

    there is no such thing as "fabric of space-time". It's a convenient buzzword but it doesn't mean anything

    Of course it means something: it is a summary of the distance and time measurements we make, and can be described in terms of geometrical curvature. If it didn't mean anything, then it wouldn't have any observable consequences.

    Things work as if Einstein was right, but there is no evidence that he was right.

    You're splitting hairs that don't exist. "Working as if Einstein was right" is "evidence that he was right". It's the only kind of evidence possible.

    If you pass a current through a wire it generates a magnetic field. If that field crosses another wire it generates a current in that wire.

    That's not necessarily true. A static magnetic field doesn't induce a current in a wire. You might be talking about alternating current, which produces a time-varying magnetic field.

    It's exactly as if the magnetic field moved from one wire across the other.

    I don't know what you mean by a magnetic field "moving", but certainly the magnetic field of one wire can intersect the position of another wire.

    The flaw is that if you wrap both wires through an iron donut all the field is inside the iron - absolutely NO field is detected anywhere around either wire.

    Perhaps I'm visualizing the geometry wrong, but your statement appears to be false.

    The theory is false, but it is "exactly as if" it were true.

    What theory? That the (time-varying) magnetic field produced by one current can induce a current in another wire? That theory is always true. (Of course, you have to take into account induction from other objects which may cancel that current.)

    Likewise, Einstein's theory may give correct answers even though nobody actually knows why.

    It is not possible to know "why" a theory is true, at least if that theory regards some fundamental phenomenon. It's possible to explain "why" some approximate theory is true by deriving it from a more fundamental one, assuming the more fundamental theory is true.

    For one thing, plasma physicists can easily explain a lot of effects in electrical terms, relying on laboratory observations instead of imagined theories.

    Nonsense. Plasma physicists use theories just like any other physicist does. Those theories of course are electromagnetic in nature.

    Astronomers ignore plasma physics because nobody ever taught it to them.

    More nonsense. Plenty of astronomers use plasma physics. What are you, an Alfven plasma cosmology crackpot?