Has any Prominent Physicist Ever Admitted to Not Understanding Magnetism?

Discussion in 'Physics & Math' started by Eugene Shubert, Sep 17, 2015.

  1. OnlyMe Valued Senior Member

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    Part of the problem is in the above bold text. Science seldom really answers the fundamental how and why's, most lay persons ask about. Most of the time where theoretical physics is involved it doesn't even try. At least not within a context anyone could consider a consensus view.

    Rpenner, in another thread made a statement that was so succinct on this issue I saved it,

    Any attempt to introduce speculation about any fundamental how or why, even if it springs from peer reviewed sources, is generally met with dismissal as fringe or crank, or labeled in some other dismissive way, so why bother presenting independent speculation?.... It would not amount to a credible response to a lay question anyway.

    There does seem to have been an increase in the number of posters who just want to argue or have some other hidden agenda. There were in the past more who did try and explain. Some seem to have been run off by the constant bickering or just moved on. Others do the best they can, when they can.., but threads devolve into mud slinging so fast that it is hard to turn a discussion back to into a discussion.

    An open forum like this, has both advantages and disadvantages. Of late it seems more of the disadvantages have dominated...
     
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  3. James R Just this guy, you know? Staff Member

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    Yazata:

    I think that what we often see is a reaction to how the initial question is phrased.

    If somebody starts with "Physics must be wrong because I don't understand how ..." that will likely get quite a different response to a genuine query like "Can you please explain to me how we know that ..." or "How do physicists know that ..."?

    Sure, but you can't expect endless patience. If somebody shows they have no real desire to engage in a learning process or an honest exchange of ideas then it is a wasted effort to try to teach them.

    The field model gets around the problem of action at a distance by postulating that changes to the field happen locally and then propagate outwards through the field to distant locations, where their effects are felt at some later time.

    Yes. It's pointless to talk over the head of a student. The teacher must talk at a level the student can understand.

    I can't comment on that particular example. Perhaps the "advanced" response was due to a misunderstanding of the question, or of the questioner's level of competence.

    If I have an electric charge here at point A and give it a shake, the field around the charge changes as I shake it. Those changes propagate outwards at the speed of light, and later affect the charge at point B.

    This isn't metaphysics.

    Like what?

    I tried to explain above. The acceleration of something like an electron in an electrical field depends not just on its electrical charge but also on its mass. In contrast, the acceleration of an electron in a gravitational field depends only on its mass. It is the equivalence between inertial mass and gravitational charge (which we also confusingly call "mass") that allows gravitation to be formulated as spacetime curvature. But inertial mass and electric charge are not equivalent, so we can't use the same trick for electromagnetism.
     
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  5. James R Just this guy, you know? Staff Member

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    P.S. Regarding "mechanisms":

    Physical models are just that: mathematical models of how a system works. They aim to predict, quantitatively, what will happen in a particular experiment or if you make a particular observation. In so doing, physical theories often make use of undetectable entities and unmeasurable properties - that is, properties that are not directly observable but are observable only through their indirect effects.

    The only way to determine whether one physical theory's unmeasurables is superior to another's is to compare the predictions of each theory against actual outcomes of measurements or observations. Having done that, we still don't know whether the unmeasurables of the superior theory are real or not. All we know is that one theory is better than the other at making useful, accurate predictions.

    Complaining that a physical theory doesn't provide a satisfying "mechanism" is, in one sense, to misunderstand what a physical theory is for. It is also to misunderstand the limits of science. There is no magic crystal we can look into to tell us how nature really is, at the fundamental level. We only have our models of how it might be - and those are constantly being revised to improve their predictive power, as well as their parsimony.

    Ultimate "why?" questions are always open ended.

    Why does an apple fall from a tree?
    - Because of a mysterious force we call "gravity". Gravity is a field.
    Ok. How long will it take to fall to the ground from a given height?
    - Use Newton's laws of gravity and motion to model the problem.
    Why is gravity a field?
    - Because Newton said it was (in effect).
    Is Newton's law of gravity accurate?
    - Well, not in all circumstances, as it turns out. Einstein's model is more powerful, but conceptually very different from Newton's.
    Einstein says spacetime is curved, and not a field after all. Why it is curved, and what happened to Newton's field?
    - Because Einstein's model says it is curved and that gives the correct answers to problems. We replaced the old, less powerful model with a new, more powerful one.
    What is the mechanism that curves spacetime?
    - In the model, the curvature is due to mass/energy.
    Why does mass curve spacetime?
    - Because that's the model we're using.
    But is spacetime really curved?
    - How would we tell either way? We can't directly measure curvature. That's a feature of a particular physical model.
    But that's unsatisfactory. Why does gravity obey Einstein's theory?
    - You have things the wrong way around. Einstein's theory is a model of how gravity works.
    Yes, but what is the mechanism for one object attracting another?
    - According to the model, or are you looking for some kind of unobservable ultimate reality?
    I want to know about the ultimate reality!
    - Then you might be better off consulting a priest or a philosopher, or meditating or something, rather than talking to a physicist.
     
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  7. Farsight

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    Why is gravity a field? Because a field is a state of space, and a concentration of energy "conditions" the surrounding space, akin to setting up a pressure-gradient in it. Hence the energy-pressure diagonal in the stress-energy-momentum tensor.

    Einstein says spacetime is curved, and not a field after all. Why it is curved, and what happened to Newton's field? Einstein said gravity is a field, see the Einstein digital papers. He didn't actually say it's curved spacetime. Instead he described a gravitational field as space that's neither homogeneous nor isotropic. And his description wasn't all that different to Newton's. See Opticks query 20.

    Why does mass curve spacetime? Because energy effectively exerts an outward pressure on space, such that motion through space over time is curved.

    But is spacetime really curved? No. Instead space is really inhomogeneous, and when you plot this inhomogeneity using light clocks in an equatorial slice through the Earth, your plot looks like the Riemann curvature depiction.

    We can't directly measure curvature. Oh yes we can, with light clocks. But we aren't measuring a curvature of space, we're measuring a curvature in the inhomogeneity of space.

    What is the mechanism for one object attracting another? The wave nature of matter. Light curves towards a massive body because the speed of light varies with position, just like Einstein said. It "veers", rather like sonar. We make electrons and positrons out of light in pair production, and we can diffract electrons. So think of the electron as light going round and round, simplify it to a square path, then draw it:

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    The electron falls down, and the deflection of light is twice the Newtonian deflection of matter, just like Einstein said.
     
  8. krash661 [MK6] transitioning scifi to reality Valued Senior Member

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    • Please do not taunt or flame other members.
    LIM.... hilarious..... you remind me of a schizophrenic name craig.
     
  9. rpenner Fully Wired Registered Senior Member

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    Wrong. This is not the correct definition of "field" in physics and to the extent this definition is compatible with physical theory, only toy theories like electrostatics and analogous static field configurations apply.

    Um, wrong. All 10 symmetric components of the stress-energy-momentum tensor are in play and there will be off-diagonal elements if either the local electric or magnetic field is not parallel to one of the spatial directions. The error in your conclusion makes one doubt you conveyed anything correct in your description of a field.

    What? All of them? <citation required>
    While you have have linked to a search page of results, in many of these he is making deliberate use of Newtonian gravitational theory and language that was in use in the day.
    Except in his published scientific papers where he used geometric language. Also, Einstein died in 1955 while General Relativity didn't really come into its own until the 1970's.

    A good example is Einstein's lecture of 1921-05-12 which was summarized correctly as “The fourth lecture was devoted to the mathematical development of the general theory of relativity. Beginning with the analogy of Gauss’s theory of curved surfaces, Prof. Einstein shows how the methods of the absolute differential calculus developed by Riemann and other led to a formation of the principle of equivalence, by means of which the gravitational field could be interpreted in terms of the invariant properties of four dimensional space.
    He finally showed the form the the equations of motions of a material point take in a gravitational field, and also how the path of light rays in a gravitational fields can be determined.”

    http://einsteinpapers.press.princeton.edu/vol7-trans/331 through 384.
    Uh oh. You've done it now.

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    1) If it is so easy to push on space, what happens to Newton's 3rd law? 2) How exactly does all this pushing explain the features of Mercury's orbit namely that a) it is concave, b) nearly elliptical, c) has anomalous precession of the perihelion.

    Incorrect. Ignores cosmological evidence and GPS evidence that supernova light curves are time-stretched proportional to their redshift factors and GPS clocks tick faster than on the ground.
     
    Last edited: Oct 13, 2015
  10. John Connellan Valued Senior Member

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    I agree, and to add an important point - misunderstanding the limits of the human mind/imagination. There is only so far our minds can go in imagining what nature is really like at it's most fundamental level. I would be very very surprised if evolution has bestowed upon us, an ability to comprehend all of nature in terms that we are familiar with. What advantage would that have given us as an African primate?
    after a certain point, the best we will ever do will be mathematical models. We just have to live with that.
     
  11. Farsight

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    3,492
    Not so. See Einstein talking about field theory in 1929 and note this: "The two types of field are causally linked in this theory, but still not fused to an identity. It can, however, scarcely be imagined that empty space has conditions or states of two essentially different kinds, and it is natural to suspect that this only appears to be so because the structure of the physical continuum is not completely described by the Riemannian metric". This is Einstein saying a field is a state of space.

    Take that up with Einstein.

    A field is a state of space. The state of space in the room you're in is inhomogeneous. Hence your pencil falls down.

    No I haven't. Follow my link, and read what Einstein said. You can issue him a ticket if you like, but it won't get you very far.

    Nothing. The simplest situation we can describe is a photon. It has a non-zero "active gravitational mass" because any concentration of energy causes gravity. The photon energy is E=hf, and the resultant gravitational field is the reaction to action h.

    See the existing material for that, and remember that I did't invent that energy-pressure diagonal.

    It's correct. Place optical clocks throughout an equatorial slice through the Earth and the surrounding space, then plot the clock rates. You depict lower slower clocks as lower down in a 3D image, and higher faster clock rates higher up. What your plot looks like, is this:

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    GNUFDL image by Johnstone, see Wikipedia
     
  12. Farsight

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    No we don't. When you read what Einstein actually said in the digital papers, gravity is fairly simple actually. There is a satisfying mechanism. Don't give up.
     
  13. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    Oh great, farsight, the Einstein quote generator is back...
     
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  14. exchemist Valued Senior Member

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    Oh dear.
     
  15. rpenner Fully Wired Registered Senior Member

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    Your statement still does not adaquately define what a field is. Importantly, your false dichotomy between the terms space and space-time in discussions of relativity leaves the reader with the distinct impression that you have described only static fields. A more generic definition of a physical field is a smoothly varying geometric quantity (scalar, vector, tensor, etc) associated with every point in space and time. Maxwell relied on such a definition when he takes both space- and time-derivatives of the fields in his theory of electrodynamics.

    Einstein's unified field theory (the topic of the paragraph you quote from) never took off because the nature of radioactivity revealed that there were other forces than just electromagnetism and gravity.

    I'm not the necrophiliac in this discussion. Regardless of what you think Einstein may have meant, the electromagnetic stress-energy tensor in Cartesian coordinates in approximately empty spacetime is (modulo choice of space-time signature):
    \( T^{\mu\nu} = \begin{pmatrix} \frac{\epsilon_0}{2} ( E_x^2 + E_y^2 + E_z^2) + \frac{1}{2 \mu_0} (B_x^2 + B_y^2 + B_z^2) & \frac{1}{c \mu_0} ( E_y B_z - E_z B_y ) & \frac{1}{c \mu_0} ( E_z B_x - E_x B_z ) & \frac{1}{c \mu_0} ( E_x B_y - E_y B_x ) \\ \frac{1}{c \mu_0} ( E_y B_z - E_z B_y ) & \frac{\epsilon_0}{2} ( -E_x^2 + E_y^2 + E_z^2) + \frac{1}{2 \mu_0} ( - B_x^2 + B_y^2 + B_z^2) & -\epsilon_0 E_x E_y - \frac{1}{\mu_0} B_x B_y & -\epsilon_0 E_x E_z - \frac{1}{\mu_0} B_x B_z \\ \frac{1}{c \mu_0} ( E_z B_x - E_x B_z ) & -\epsilon_0 E_x E_y - \frac{1}{\mu_0} B_x B_y & \frac{\epsilon_0}{2} ( E_x^2 - E_y^2 + E_z^2) + \frac{1}{2 \mu_0} (B_x^2 - B_y^2 + B_z^2) & -\epsilon_0 E_y E_z - \frac{1}{\mu_0} B_y B_z \\ \frac{1}{c \mu_0} ( E_x B_y - E_y B_x ) & -\epsilon_0 E_x E_z - \frac{1}{\mu_0} B_x B_z & -\epsilon_0 E_y E_z - \frac{1}{\mu_0} B_y B_z & \frac{\epsilon_0}{2} ( E_x^2 + E_y^2 - E_z^2) + \frac{1}{2 \mu_0} (B_x^2 + B_y^2 - B_z^2) \end{pmatrix}\)
    So because of symmetry, it has 10 independent components, 6 of which are off-diagonal.


    The fact that I can point to a direction called down just indicates that I have chosen a local set of coordinates where my origin doesn't obey the geodesic conditions. The whole reason Einstein used Riemann's tensor calculus is so that he could ignore the choice of curvilinear space-time coordinates and talk about geometry. He said so in the 1921 lecture I linked to.

    Not really an argument.

    Not a response to what was asked.

    Not a response to what was asked. The diagonal does not tell the whole story of Einstein's theory. You've thrown away 6 of Einstein's 10 components.

    Your source for that image does not support you. Your proposed methodology throws away 9 of Einstein's 10 components. Cosmology doesn't allow you to lump all objects at high redshift as having peculiar properties, so the most parsimonious way to think about this is that space-time is curved and they see us at high redshift.
     
    Last edited: Oct 13, 2015
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  16. John Connellan Valued Senior Member

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    I was talking generally though. I just think it would be very coincidental if nature at the most fundamental level was perfectly understandable to human brains and that we would be able to imagine all of it in terms we are familiar with. There is absolutely no reason to believe this - unless you believe that God created the universe as one big puzzle for us to solve

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    I do believe in the possibility of getting a unified mathematical description of nature but not necessarily that we can imagine what the mathematics means with our limited imagination. We see these limits already with Quantum theory.
     
  17. Farsight

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    Understanding all of it is a tall order. But understanding gravity isn't. Have a look at threads like this. Sadly there are people who will try to tell you that you can never understand any of it, and that you shouldn't read what Einstein said, or that you should utterly dismiss what he said. I find it rather strange myself.
     
  18. paddoboy Valued Senior Member

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    Of course people should read what Einstein said.
    But people such as cranks alternative nuts, those that claim to have TOE's, [just as you have] Take what Einstein said out of context.
    Also worth remembering that Einstein formulated GR 100 years ago, and we know a lot more today [well most of us do] than even Einstein its formulator knew a 100 years ago.
    Spacetime most certainly is curved in the presence of mass, and that has been evidenced many times culminating in the GP-B results.

    Actually someone like yourself that has claimed to have a TOE, yet will never answer questions about it, sees one as concluding that you are another fraud on a forum open to any Tom, Dick or Harry.
    Elsewhere of course you are banned.


    http://www.staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

    STRANGE MISCONCEPTIONS OF GENERAL RELATIVITY

    G. ’t Hooft:

    Indeed, it often happens in science that a minority of dissenters try to dispute accepted wisdom. There’s nothing wrong with that; it keeps us sharp, and, very occasionally, accepted wisdom might need modifications. Usually however, the dissenters have it totally wrong, and when the theory in question is Special or General Relativity, this is practically always the case. Fortunately, science needs not defend itself. Wrong papers won’t make it through history, and totally ignoring them suffices. Yet, there are reasons for a sketchy analysis of the mistakes commonly made. They are instructive for students of the subject, and I also want to learn from these mistakes myself, because making errors is only human, and it is important to be able to recognize erroneous thinking from as far away as one can ...

    Examples of the themes that we regularly encounter are:- "Einstein’s equations for gravity are incorrect";
    - "Einstein’s equivalence principle is incorrect or not correctly understood";
    - "Black holes do not exist";
    - "Einstein’s equations have no dynamical solutions";
    - "Gravitational waves do not exist";
    - "The Standard Model is wrong";
    - "Cosmic background radiation does not exist";and so on.

    "They find some support from ancient publications by famous physicists; in the first decades of the 20th century, indeed, Karl Schwarzschild, Hermann Weyl, and even Albert Einstein, had misconceptions about the theory, which at that time was brand new, and these pioneers indeed had not yet grasped the full implications. They can be excused for that, but today’s professional scientists know better".

    more at the link:
     
  19. Farsight

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    Do remember paddoboy, that I'm the guy who quotes Einstein, and you're the guy who dismisses Einstein because you think you know better. And note that 't Hooft peddles the holographic principle. That flatly contradicts general relativity. So there's a certain irony to his polemic bitching about Crothers.
     
  20. OnlyMe Valued Senior Member

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    Sometimes it is more like, you are the guy who constantly takes Einstein quotes out of context. You don't seem to have any grasp of the fact that Einstein did not make any of the quotes.., you often misquote by interpretation.., yesterday!
     
  21. Kristoffer Giant Hyrax Valued Senior Member

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    People should also remember that Farsight has the great honour of having a page dedicated to him on Rationalwiki.

    He might not like it, though.
     
  22. billvon Valued Senior Member

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    Well, given that we don't understand nature at a fundamental level yet, and that most people don't even understand the basics - I'd have to say your assumption is incorrect.
     
  23. Farsight

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