Gravity: Newton or Einstein

Discussion in 'Physics & Math' started by Xmo1, Apr 27, 2017.

  1. Xmo1 Registered Senior Member

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    I know you didn't answer this, but is there a spacetime density factor relative to massive objects? If so, what is it's name? Is it rather referred to as a gravitational field, or a Higgs field density? What are the language terms when discussing this relationship between massive objects and spacetime? I should probably let this rest, and get back to reading.
     
    Last edited: Apr 29, 2017
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  3. danshawen Valued Senior Member

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    Now THAT (density of space, gravitation field, etc.) is a really interesting question.

    Because of the Banach-Tarski paradox, (volume of sphere = 2 x volume of sphere), all bets are off the table in terms of whether density means anything at all, physically.

    rpenner once pointed out to me, the same argument goes against a fairly simple-minded interpretation of Special Relativity being compliant with Maxwell's equations involving the magnetic field between two current carrying wires and charge density. It works in that very limited one dimensional case, but ever since, I have never resolved whether or not it is possible to do anything with the determination of physics to make anything related to density mean anything as concrete as that ancient Greek geometry everyone in physics is so very, very fond of. You are unlikely to find any really satisfactory answers from an analysis of density, at any scale of physics.
     
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  5. Xmo1 Registered Senior Member

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    I think rpenner told me something about time: For massive particles we have the elapsed proper time which can be written as (ddλτ)2=(ddλt(λ))2−(ddλx(λ))2−(ddλy(λ))2−(ddλz(λ))2(ddλτ)2=(ddλt(λ))2−(ddλx(λ))2−(ddλy(λ))2−(ddλz(λ))2 which is a physically measurable metrical property of these space-time curves.
    He also said spacetime is a metrical environment. So I'm learning. Yes, I need to read rpenner's posts twice, and sometimes that is not enough.
     
    Last edited: Apr 29, 2017
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  7. rpenner Fully Wired Staff Member

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    Not really. Quantum filed theory defines defines excitations of fundamental quantum fields that carry such-and-such an intrinsic angular momentum and in plane-wave approximation obey \(E^2 - p^2 = m^2\) for such-and-such a mass and interact with other fields at points with such-and-such coupling constants. That's description of behavior but it doesn't tell you what a fundamental quantum field "is."

    We talk about "blue" without defining it. As such we will encounter cases where people talk about "blue" in incompatible ways. Famously, the Japanese use the same word, 「青い」, for the color of the sky, the color of spring growth and the change in tone when a person loses blood flow to the face. So too, from examples of phenomena of time, we can generalize to come to a commonly shared meaning. As the above discussion related, different physics models had different concepts of time. Today we distinguish between the "coordinate time" which is used as part of a algebraic framework to assign coordinate quadruples to all events in a region of space-time and "elapsed proper time" which is the trajectory-and-location-dependent phenomena which clocks actually measure.

    "Elapsed proper time" is a phenomenon — a metrical phenomenon which can be divided into hours, minutes, seconds and finer pieces apparently without human-encountered limits. "Coordinate time" is a human-adopted convention to facilitate agreement on what "it happened then and there" or "let's meet then and there" mean.

    "Elapsed proper time" is a phenomenon, "proper distance" of comoving objects is a phenomenon, "length contraction" and "limiting speed of c" are phenomena, so spacetime is a physical model which operates as framework for precisely describing a wide field of related phenomena. Spacetime is physics. Arguing about what spacetime "really is" is metaphysical.

    Quite possibly there are more layers to peel back, but since I never claimed present day physics is reality, why would I expect tomorrow's physics to be reality? Even if it was all that was knowable about reality, how could you be sure there wasn't a deeper level yet? Instead of worrying about tomorrow's physics, why not master what we know of physics today so when a gap opens up between how we think reality behaves and how it actually behaves we will be able to recognize that gap as a need for new physics? What's the point of worrying about directionless "could-be" physics when we have zero information if it is even steps in the correct direction? There are infinitely more ways to be wrong than right, so physics confines itself, parsimoniously, to descriptions of behaviors of observable phenomena so that when it is wrong it is a matter of fractional accuracy or only new-to-humanity phenomena even if the entire conceptual world is rewritten.

    Metaphysics has no such fetters of economy so all sorts of "could-bes" and "should-bes" fill metaphysical works, with little or no application to reality since saying things about reality has no track record of success on changing how reality behaves.

    Since you have not defined "time particle" nor given examples of it to generalize from, this term doesn't communicate much. Since "coordinate time" is a human convention modeled on the reals, there is no smallest bit of "coordinate time". Since "elapsed proper time" is a physical phenomena without evidence of a smallest bit, the proposal that "elapsed proper time" has indivisible components is without empirical basis.

    Again, the Standard Model of Particle Physics and General Relativity describe how the universe behaves, not what it "is". Also, we've had the Standard Model since the 1970's so the existence of the Higgs is a predicted by the Standard Model based on the way the weak force behaves at high energy. If I parsed his public lecture correctly, John Ellis thinks the particular mass of the discovered Higgs makes the idea of the phenomena of supersymmetry seem more likely, but the Higgs boson itself is not new to physics. A bigger change to the Standard Model was the discover that neutrinos oscillate and thus behave like they have tiny masses.

    The only concrete definitions I would want are of how time and spacetime are modeled in a particular framework so that I could make the predictions of that physics model the same way everyone else does. Then I could compare those predictions to experiment and observation. Reality doesn't care what definitions I use, but when I cross the street if my predictions of space and time are bad, reality bites me on the ass.
     
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  8. danshawen Valued Senior Member

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    Well stated.

    The sphere volume paradox mentioned in my last post has not been satisfactorily resolved by means of mathematics, to my knowledge. But it makes perfect sense that if your mathematical system of reasoning has either failed to sufficiently define what constitutes an infinitesimal amount of volume, nor an infinite amount of curvature for the space around said volume, then you are probably going to get all sorts of strange and inconsistent answers when you try to apply those ideas to volumes large enough to have physical meaning, like density, for instance.

    rpenner and I differ somewhat of our assessment of the importance of the discovery of the Higgs boson. The paper Peter Higgs wanted to publish was originally rejected by a peer reviewed science journal. It actually does sound like something of an outlandish idea at first, but it grows on you if you allow it.

    If you get all of your science knowledge about inertia from how matter or energy travels in straight lines <c, you are missing consideration of a rather large arena of energetic events that possess both inertia and energy because they have angular momentum. It is possible to understand how the two domains exchange inertia, even on a quantum scale, and there is power in understanding what inertia is.
     
  9. Xmo1 Registered Senior Member

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    It bothers me when people reply with thank you after I've written well thought out paragraphs. Still, I am left only to absorb what you have said within the context of my own questions. So, thank you again rpenner for taking the time to respond to my posts.
     
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  10. danshawen Valued Senior Member

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    Thanks indeed. Those were very well written responses, and I see no real need to improve on any of them.

    It's kind of funny, actually. When I started posting here, there seemed to be heated discussions about whether there was actually a smallest interval of time, and the answer most gave involved the interval of time it took for light to traverse Planck's length, which was a popular answer at the time. Now, there seems to be no doubt that there is no lower limit to the discrete nature of time, and I think that is a better answer in every way imaginable.

    If light is propagating, in any frame of reference, something else needs to be moving or changing faster in order for that motion or amplitude variations of EM fields to occur.
     
  11. rpenner Fully Wired Staff Member

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    The Planck time \( \sqrt{\frac{\hbar G}{c^5} } \approx 5.4 \times 10^{-44} \, \textrm{s}\) makes sense as part of a natural set of units in which to describe the universe without the anthropocentric bias of meters, seconds and kilograms and also the approximate scale where quantum mechanics can't be ignored in a theory of gravity. Since we don't have a quantum theory of gravity the details of how space and time and gravity become different are unknown, but even if they get very weird what is 1 Planck time to a proton can be about 7000 Planck times \( \approx 3.8 \times 10^{-40} \, \textrm{s}\) and 7000 Planck lengths \( \approx 1.1 \times 10^{-31} \, \textrm{m}\) at the Large Hadron collider due to Special Relativity. For this reason, thinking of it as a grain of time seems like a view uninformed of relativity.

    https://en.wikipedia.org/wiki/Planck_time
     
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  12. danshawen Valued Senior Member

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    True. But I will expand this a little so that the other thread participants understand what we are talking about.

    Given the appropriate relativistic time dilated frame of reference in relative motion to the known universe (appropriately close, but not equal to c), every event that has occurred in the known universe since the Big Bang could be fit into a time interval no longer than the Planck time <interval> in the frame that was at rest relative to to the Big Bang at the very beginning.

    If this realization does not suggest strongly enough that time itself <or even a time interval> is not something that is actually based on direct proportion to the propagation of light, I don't know what would. Perhaps the best reasoning that could be applied to demonstrate this is that while a time interval may be maintatined to be proportional to a velocity, a single instant of time cannot. A single instant of time nevertheless has meaning, to quantum entanglement state changes, for starters.

    And although absolute space has no real physical meaning, absolute time <an instant, not an interval> evidently, makes perfect physical sense if simultaneous events exist. And they do.

    Or to put it another way that is closer to the heart of particle physics, all of the events that have occurred since the Big Bang and all of the events that are ever likely to occur until each and every star in the known universe winks out will not see the spontaneous decay of even a single proton. Very likely, there is some measure of temporal connection between the permanence of both measures of time, and that connection may well turn out to be related to the quantum spin / entanglement equivalent of time dilation. Some of this is of course, highly speculative.
     
    Last edited: Apr 30, 2017
  13. The God Valued Senior Member

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    Once the Meter, kilogram and second is defined then the universal constancy of h c G would ensure a fixed value for Planck's time, unless of course relativity claims to change the values of h c G based on observer.

    Secondly talking of relativity at Planck's level itself is bad, we really do not know about its workability in that domain.

    But nonetheless you raise a nice debatable point. Assuming that time is discrete should the least discrete quanta of time change on account of dilation? On the face of it, appears so but why? A process which was taking 100tp, may take 101tp or 99tp on account of variability of time without changing tp as such.
     
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  14. danshawen Valued Senior Member

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    My central point of the previous post is that both the infinite and the infinitesimal, in concrete terms where time is concerned, BOTH have real, physical meaning that is independent of whether someone has a complete or consistent system of reasoning to deal with them symbolically or not. That system is only complete if you are willing to ignore something inconsistent but important that lies outside of it. The true nature of time would be that something.

    This is why it would be foolhardy to make an assumption that time itself is somehow proportional to the speed of propagation of light and to run with it, as Minkowski did. It is akin to dividing by zero, and doing so right from the off.

    Neither Pythagorus nor Euclid's geometry have anything physical to do with inertialess, or position-less empty space, or inertia, or most particularly TIME. The Lorentz relationships so tediously tended to yield time interval dilation fail utterly if the roadbed itself moves, even in small geometrical or physical measure. I think perhaps the only reason this works to compute the time dilation effect is ONLY because of the nature of time dilation itself. Absolute time actually does exist, and the roadbed only needs to be stationary for the briefest of time intervals. But at least the Lorentz relationship derived involving time has actual, physical meaning that we use every day in GPS technology.

    Minkowski's formulation requires that the speed of light not only be Lorentz invariant, but that it is somehow distinguished among other invariants, like rest mass, or for that matter, the frame 'at rest' in which important energy events such as pair photon creation and quantum entanglement actually take place. It also requires that simultanaeity for two events separated by light travel time not exist anywhere in this universe. To this I call 'foul'. In any reference frame, the speed of light is no more or less meaningful than the rest frame, without which a velocity cannot even be measured. Even the speed of light is relative to another velocity, or else it is meaningless. To dictate that events separated by light travel time cannot interact simultaneously ignores an entire physical universe in which they do.

    Give it up. This idea about time corresponding to the propagation of light does not possess a one-to-one correspondence to independent physical reality. Nor does Euclid's geometry and physical measurement of space and time. If you fail to understand the nature of inertia, the power of which has been demonstrated only thrice in human history, then you will never understand that time and energy are intimately related in a way Minkowski's hasty supposition is incapable of supporting.
     
    Last edited: Apr 30, 2017
  15. The God Valued Senior Member

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    Dhansawen,

    But do we understand inertia?
    I have read about your bound energy, any further progress? in my opinion Machian stuff is still haunting us.
     
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  16. danshawen Valued Senior Member

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    As I have explained numerous times before, it seems to extend itself more easily if I am allowed to discuss it. I don't know where it comes from, but not all of it comes from me.

    Machian stuff should bother anyone who does not think the universe as a whole does not spin because the quantum field it encompasses it does not possess the property of zero quantum spin angular momentum. Only one boson of quantum spin zero exists.
     
  17. The God Valued Senior Member

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    Universe as a whole cannot spin, simply because it is not bound. Some works suggest spin of universe, all speculative.

    People will love Mach one day, because the inertia of the whole universe is zero.
     
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  18. danshawen Valued Senior Member

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    And I love that kind of talk! Don't stop thinking about inertia of any variety, and there are several to consider.

    If you are speaking of the universe as a whole has total quantum spin angular momentum = o, of course. And if it were not the case, the Higgs boson would not be distinguished as the only quantum spin = o boson. It's a rather BIG deal, in the grand scheme of things. Fermions with ± fractional positive or negative quantum spins could not exist. This includes electrons and quarks and their antiparicles.

    Everywhere and anywhere there is matter, there is entanglement, quantum spin angular momentum, and time. AND anywhere there are subatomic particles or atomic structure, there is the Higgs mechanism, courteously provided by a universal quantum field, to provide inertia to certain kinds of particles and to bind atomic structure where conditions are right for it to exist.

    Although photons "appear" to propagate through the entangled quantum field permeating space, it is far more likely that it is simply chained interaction, like a falling row of dominos, everywhere localized, and is nothing like a bulk inertial mass movement other than the transfer of energy from one region of the field to another, and with linear inertia mostly in a single direction.
     
    Last edited: Apr 30, 2017
  19. hansda Valued Senior Member

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    Newton and Einstein developed two models of gravity. There are still many other models of gravity https://en.wikipedia.org/wiki/Alternatives_to_general_relativity . Though these models may not be so much successful. I think these models also can be co-related.
     

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