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  • Post #35

James, I think that all one needs to understand Vesselin's reply is that " ... the particles' acceleration in the curved spacetime surrounding the Earth is zero ..." which is simple Galilean physics. That is, there is no other source of particle acceleration than gravity. How do we know? -- because we can test it.

An observer in an airplane that drops an unpowered bomb and travels without accelerating for a certain distance while the bomb falls will find that the bomb remains directly beneath the plane for the total time of its fall. In other words, there is no horizontal acceleration component acting on the bomb; the plane and the bomb are both experiencing zero acceleration in the curved spacetime. Another way to test this hypothesis is to fire a cannonball in a flat trajectory, and drop another cannonball from the same height simultaneously. One will find that the fired projectile and the dropped projectile impact the ground at the same moment, even though the fired projectile follows a curved trajectory in its descent, and the dropped projectile a straight trajectory -- again illustrating that there is no horizontal acceleration to the common plane, only the acceleration of gravity acting on each cannonball.

Now when this Galilean theory is extended to Newtonian mechanics and finally to relativity, one gets not only the beautiful mathematics by which we understand relative motion, one can also physically *feel* what it means to have no resistance to motion. I know this from long years of studying Einstein, and have known that one cannot truly grasp relativity without having this sensation. Vesselin brings the subject to life by reminding us that unquantized motion is one continuous quantum, that every particle is as free of resistance as every other.

Tom

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  • Post #36

Tom, I understand those things. They do not address the question of why does the freely falling person not feel the force of gravity. It is not because gravity is no force. The persons feeling is not evidence for that conclusion. I gave the reason why there is no feeling. The reason is because there is almost equal application of force to all parts of the body and almost equal acceleration for all the parts of the body. There is no reason to feel pulled or pushed whatever.

The orbiting example does involve acceleration in the vertical direction. The reason it accelerates toward the Earth is because is is being acted upon by the force of gravity. That force is acting in the vertical direction.

The Relativity arguments do not apply to solving this matter because of the level at which you are using them. It is the assumptions and choices that led to the development of the theory of relativity that apply. It is at that level, I can diffuse concepts such as space-time. When you use space-time as the crux of your argument, you are relying upon a theoretical concept as if it is real.

My point in addressing what Vesselin said regarding Einstin's elation about no feeling of force of gravity is that that recognition is not an example of some great discovery. The lack of the feeling of being pulled or pushed down is exactly what anyone sould expect to be the case.

James

James,

"I understand those things. They do not address the question of why does the freely falling person not feel the force of gravity."

Yes they do. No particle or system of particles is in a privileged inertial frame. Think about it.

"It is not because gravity is no force. The persons feeling is not evidence for that conclusion. I gave the reason why there is no feeling."

A person is a system of particles. The external evidence is not contradictory of the internal evidence.

Tom

Thank you Tom for trying to help to clarify this issue. I should stress two things - (i) I have no intention to argue with James that gravity is not a force since that is an established fact of modern physics (not just my personal opinion), and (ii) my true motivation for trying to respond promptly to the messages on this page (despite the extremely time consuming launching of a new academic publisher other deadlines) is to share the many-year struggle to understand this really difficult issue (since it is quite counter-intuitive) with everyone genuinely interested in gravitation.

James (if I may),

What you say about unevenly applied acceleration is irrelevant for the issue of resistance due to acceleration. I will make one last attempt to explain.

A falling accelerometer reads zero acceleration, that is, zero resistance (that is an experimental fact). If there were gravitational force that accelerated the accelerometer downwards it would resist its acceleration. Your argument, I guess, is that acceleration is evenly applied to all of its atoms and that is why the accelerometer does not resist its fall. The reason I said this argument is irrelevant is, I think, obvious - because every single atom (electron, quark, etc.) of the accelerometer would resist its acceleration, if that acceleration were caused by a gravitational force, then the whole accelerometer would also resist its fall. But it does not - so no gravitational force is causing its fall.

Let me summarize again the explanation given by general relativity (GR). GR showed that only spacetime physical quantities adequately represent the world. The four-dimensional (curved-spacetime) acceleration of the falling accelerometer is zero; that is why it is not subject to any force (as Tom nicely stressed) and moves by inertia (the observed apparent acceleration of the falling accelerometer is relative and is not caused by a force either since it is a manifestation of the spacetime curvature as explained in my post above). When the accelerometer hits the ground, it is prevented from moving by inertia and its four-dimensional curved-spacetime acceleration becomes different from zero and a resistance (inertial) force arises in the accelerometer as a reaction to the force with which the ground disturbs the inertial motion of the falling accelerometer.

You seem to be depriving yourself from properly understanding the general relativistic explanation since you regard spacetime as nothing more than a theoretical concept (as you clearly stated it above). The best way to see why such a view is not just wrong but contradicts the experimental evidence, assume that you are right - that spacetime is indeed a theoretical concept and what exists is the three-dimensional world that appears to follow from our perception data. Then analyze rigorously all kinematical relativistic effects and most importantly the experiments that confirmed them. You will see that those experiments are impossible in a three-dimensional world. I would suggest that you start with the Master - with Minkowski's explanation of length contraction shown in Fig. 1 of his famous paper "Space and Time" (it is contained in the free version of a book H. Minkowski, Space and Time: Minkowski's papers on relativity; the pdf file is available at: http://minkowskiinstitute.org/mip/books/minkowski.html).

If you decide to follow my suggestion, feel free to ask any questions about Minkowski's explanation or about Einstein's explanation of gravitation in GR.

Best wishes.

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    • Post #39

    Vesselin,

    Thank you for the advice. I already know what causes length contraction. The cause does not require relativity theory. Relativity effects are quite easy to replicate theoretically without relativity theory. I moved the conversation to my own blog in order to not cause any more disruption here. I appreciate your dedication and Tom's dedication to relativity theory. It is quite clear to me that it is based upon misconceptions and wrong decisions. The support for my statements exists in my own work available publicly. Whatever it is that I think, your blog is freed up. I think you for your conversation with me and wish you good luck in the contest. Your essay is ranked quite highly by the community votes.

    James

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    • Post #40

    Vesselin Petkov,

    "Divine Einstein" is enough - no need for "Divine Minkowski". The difference between the two deities is that the former, being a physicist, tries to give some phisical justification to relativistic absurdities from time to time while the latter is just a mathematical juggler. Look at this:

    http://minkowskiinstitute.org/mip/MinkowskiFreemium,%20MIP%202012.pdf

    Hermann Minkowski: "I want to make it quite clear what the value of c will be with which we will be finally dealing. c is the velocity of the propagation of light in empty space. To speak neither of space nor of emptiness, we can identify this magnitude with the ratio of the electromagnetic to the electrostatic unit of the quantity of electricity. (...) According to Lorentz every body moving at a velocity v must experience a reduction in the direction of its motion... (...) This hypothesis sounds extremely fantastical. Because the contraction is not to be thought of as a consequence of resistances in the ether, but merely as a gift from above, as an accompanying circumstance of the fact of motion. I now want to show on our figure that the Lorentzian hypothesis is completely equivalent to the new concept of space and time, which makes it much easier to understand."

    Now compare Minkowski's text with Banesh Hoffmann's text below. You may find that one of the texts is honest and the other extremely dishonest:

    http://www.amazon.com/Relativity-Its-Roots-Banesh-Hoffmann/dp/0486406768

    Relativity and Its Roots, Banesh Hoffmann: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether."

    Pentcho Valev pvalev@yahoo.com

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    • Post #41

    Vesselin, I don't blame you for declining debate with relativity deniers. We both know that relativity is controversial nowhere else where science is discussed, and there's no basis for debate.

    I've been fascinated by the apparently unlimited capacity in these forums to gin up alternative explanations for known physics in the name of "thinking outside the box," while ignoring that the box is part of the physics, too. Unless one has, like Einstein, built up a complete program of logically closed and experimentally validated judgments, from the earliest ancient knowledge of mechanics and geometry to Minkowski space and Riemannian geometry, I think one is unlikely to get the full import of what "the box" contains.

    That said, I know James to be honest in his efforts to deny every mechanical explanation of reality. I don't buy it, and I agree that such denial deprives one of the beautiful experience of comprehending a physically real spacetime.

    Best,

    Tom

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    • Post #42

    Tom and Vesselin,

    "...That said, I know James to be honest in his efforts to deny every mechanical explanation of reality. I don't buy it, and I agree that such denial deprives one of the beautiful experience of comprehending a physically real spacetime."

    There is no empirical evidence for the existence of space-time. There has never been an experiment or effect observed that involved only space or only time or space and time together. Your belief in the 'real' spacetie is based upon effects observed to occur to objects that are neither space nor time.

    The discussion about the reason for not feeling the force of gravity when falling freely has no need for disdain or denial. The fact is that there never was a reason to predict or expect or think that a freely falling person would feel uncrutched or undistorted or undisturbed.

    James

    Hi Vesselin:

    Thanks for your response. Some additional questions below.

    Are you saying that the following Einstein's Equivalence Principal of General Relativity is wrong? :

    "In the physics of general relativity, the equivalence principle is any of several related concepts dealing with the equivalence of gravitational and inertial mass, and to Albert Einstein's assertion that the gravitational "force" as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference."

    Even while standing on earth, the accelerometer reads zero. Does that mean there is no pull force of gravity on any bodies resting on earth? Then why the bodies resting on earth not fly away in all directions away from or tangent to earth? What holds them clinging to earth?

    Another question - if there is no force, then what makes a falling body fall - what causes the motion of falling? What determines the direction of fall - why does the body not fall backwards? What determines the amount of acceleration - why is it constant and not some other value than g??

    Could you please explain the answers to above to clarify your conclusion that gravity is not a force or gravitational potential energy does not exist?

    Please also look into another posted paper - -" Does Gravitational Collapse Lead to Singularities?" that recommends adding the potential energy (implying force) to the energy tensor -

    "According to conventional modelling by general relativity the collapse of radially symmetric gravitating objects may end in a singular state. But by inclusion of potential energy into the energy tensor, which is required to guarantee global energy conservation, the occurrence of singularities is avoided. Instead the final states of the collapse of mass concentrations of arbitrary size are nuclear matter objects, from which jets of matter can be recycled into space. The mysterious dark energy, supposed as the main constituent of the universe, may even be the potential energy of matter itself."

    I welcome and look forward to your answers and explanations.

    Regards and best of Luck

    Avtar

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    • Post #44

    James,

    "There is no empirical evidence for the existence of space-time."

    Of course there is. If Minkowski space were not physically real, light would not follow a curved path in the presence of a gravity source, and Einstein lensing would not be observed.

    Tom

    Tom,

    "If Minkowski space were not physically real, light would not follow a curved path in the presence of a gravity source, and Einstein lensing would not be observed."

    Yes the would. It would be the theoretical explanation that would change. The evidence remains what it is. The current theoretical explanation is based upon concepts that are empirically unsupported such as deformations of space and time. My message explained that neither space nor time have ever been parts of physics equations including those of relativity theory. The correct explanation will speak about objects and their behaviors. In other words, the correct explanation will be directly tied to actual empirical evidence.

    James

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    • Post #46

    James,

    Spacetime most certainly is described by Minkowski space; that's what Minkowski space *is.* You are correct in some sense that " ... neither space nor time have ever been parts of physics equations ..." in that neither space nor time independently are physically real. Only the Minkowski space model, which supports relativity, preserves space and time, and only by combining them. Spacetime is physically real, both theoretically and demonstrably. "By 'physically real,'" said Einstein, "we mean 'independent in its physical properties, having a physical effect but not itself influenced by physical conditions.'" (The Meaning of Relativity, 1956.)

    Tom

    Tom and Vesselin,

    And by 'physically real', I mean both the effect observed and the cause of it. Neither are naturally theoretical. Neither require nor should involve theoretical speculations. Neither involve space and time as cause nor as intermediaries between cause and effect.

    Either empirical evidence is the source of understanding or we become vulnerable to of flights of theoretical fancy. In my essay, I gave the first error of theory and showed that it is also the first error of relativity theory.

    Einstein did not explain the nature of the universe to us. He explained his theory. His abduction of space and time into his theory has no empirical justification. The correct explanation will have direct continuous connection to empirical evidence. It won't just fit with the patterns observed in empirical eidence. It will be rooted right from its start in empirical evidence.

    It will be expressed in the terms in which the empirical evidence is expressed. Those terms are the units of empirical evidence. The units are those of distance and duration. Everything that follows, in order to remain uncorrupted by theoretical inventions, will continue to be expressed in units of distance and duration no matter how complex the equations become.

    James

    Hello Avtar,

    Let me start by stressing that it is Einstein's "conclusion that gravity is not a force" (not mine) and this conclusion is an established fact in modern physics.

    I will answer your questions, but the best way to understand general relativity (GR) and gravitation is to answer those questions yourself by taking seriously the four-dimensional (spacetime) view of the world. Only in the framework of this view one can have genuine understanding of gravitational phenomena; GR showed that only spacetime physical quantities adequately represent the world. Einstein's initial reaction to Minkowski's spacetime physics was negative, but only after Einstein adopted spacetime he was able to arrive at GR.

    So your first question is answered - it was Einstein who introduced both the principle of equivalence and the explanation that gravity is not a force, which demonstrates that there is no contradiction between the two (see also the second paragraph in the quote below).

    I am sorry that I will have to post again part of what was already posted on this page, but the answers to your 2nd and 3rd question are given there:

    "The experimental fact that falling particles do not resist their fall confirmed the geodesic hypothesis in general relativity, which in turn explained why the particles do not resist their fall - the particles' acceleration in the curved spacetime surrounding the Earth is zero, which means that no force is acting on them and they move by inertia. The observed apparent acceleration of falling particles is relative, which is caused by the fact that the particles worldlines and the Earth's worldline converge toward one another (this is called geodesic deviation). Therefore the observed apparent (relative) acceleration of falling particles is caused by the non-Euclidean geometry of spacetime in the Earth's vicinity and is not caused by a force.

    When a falling particle hits the ground it is prevented from moving by inertia and it resists its curved-spacetime acceleration (that is why the force of weight is inertial in general relativity in full agreement that there is no gravitational force). The measure of that resistance is the particle's (passive gravitational) mass. So general relativity also nicely explains why inertial and passive gravitational masses are equal."

    I think the following analogy, often given to illustrate the essence of GR (that no gravitational force in involved in gravitational phenomena), is most helpful. Imagine that a distance separates two observers whose locations are exactly on the equator. They decide to move north by following a path that is perpendicular to the equator. As they move and monitor the distance between them they discover that they are approaching each other. If they are unaware that the Earth surface is spherical they would think that they move on a flat surface and the only explanation of their getting closer would be that they are subject to some force. The truth is that no force is acting on them; simply they move on the surface of a sphere.

    So the fact that the observers approach each other can be explained by two hypotheses - (i) either they live in a flat world and there is a force between them, or (ii) no force is causing their mutual attraction since they live on a curved surface (this analogy is best understood in terms of spacetime when you consider the worldlines of the observers which converge towards each other exactly like the meridians converge towards the North Pole). A crucial piece of evidence can help the observers determine which hypothesis is the correct one - the acceleration between the observers while they are approaching each other is exactly the same no matter what the masses of the observers are (by contrast, a given real force accelerates different masses differently). Falling bodies of different masses fall with the same acceleration.

    I hope this helps. Best wishes.

    Hi Vesselin:

    Thanks for the clear explanation.

    Why do you think general relativity is unable to explain dark energy and dark matter and suffer with the Black Hole singularity? What is missing? How it can be fixed?

    Thanks

    Avtar

    Hello Avtar,

    These are several (at least two) different issues whose resolutions have nothing to do with what is confirmed by experiment in GR. As you know a lot of approaches have been offered to deal with what is called dark matter and energy, but practically we know close to nothing certain about them.

    Regarding singularities (and this might apply to the above issue), we can have a better idea of them only when we direct our attention to what I think is the real open question in GR - how matter curves spacetime.

    I would like to stress one crucial point - our accepted theories are not universally valid; they have a domain of applicability / validity. They will never be disproved in their domains of validity (because their predictions have been repeatedly confirmed by experiment and one can't disprove experiments).

    A physical theory breaks down beyond the domain of its validity. It might turn out that this is the case with GR when applied beyond its domain to deal with singularities (since it is now assumed that the singularities might lie in the domain of quantum physics). We have a good example of such a case - special relativity breaks down (is not fully valid / applicable) at the quantum level since its equations of motion manifestly fail to describe the behaviour of quantum objects. However, that does not mean that special relativity is wrong; it is perfectly valid in its domain.

    The not fully studied issue of validity of physical theories is very important and interesting, but it is not the subject of my essay (and of the contest) and I do not like to participate in any discussion on it.

    All the best.

    Hi Vesselin:

    Thanks for your response. Please excuse me for some additional questions (I am trying to learn and clarify GR concepts) on your paper and I would greatly appreciate your answers in the light of general relativity:

    Q1: If gravity is not a force, why and how an apple detaches from the tree and accelerates its falling motion towards earth from the initial state of zero velocity. Does it not require a force of gravity to break the bond between the apple and tree? If there is no force of gravity, should the apple not stay put on the tree without breaking away from it?

    Q2: Why the upward lifting force of a rocket is required to lift a space shuttle or satellite of the launch base and into the orbit? Is it not true that the lifting force of the rocket is required to overcome the force of gravity?

    Thank you for your kind patience and responsiveness,

    Regards and best of Luck

    Avtar

    Hello Avtar,

    The answers of both questions are contained in what I wrote earlier (replying to one of your posts):

    "When a falling particle hits the ground it is prevented from moving by inertia and it resists its curved-spacetime acceleration (that is why the force of weight is inertial in general relativity in full agreement that there is no gravitational force)."

    In more detail: GR showed that only 4D quantities adequately represent physical phenomena. The 4D curved-spacetime acceleration (CSA) (representing the curvature or rather the deformation of a geodesic worldline which represents a free particle moving by inertia) of a falling particle is zero. So, like in Newtonian physics, zero acceleration => zero force; therefore a falling particle is not subject to any gravitational force in full agreement with the experimental fact that a falling particle does not resist its fall (which proves that no force is causing its fall). The falling particle moves by inertia (its 4D CSA = 0) and its worldline is geodesic (which is analog of a strait worldline in curved spacetime).

    When the particle reaches the ground... see the quote above. The worldline of a particle at rest on the ground is not geodesic, i.e. the worldline is deformed which gives rise to a static resistance / restoring force in the particle's worldline or rather worldtube (like the resistance / restoring force arising in a deformed rod). That restoring force is inertial (see the quote above) and has been traditionally called gravitational force or the weight of the particle. So the apple breaks the bond because of the force of its weight; or more correctly (in terms of GR) - the bond has been preventing the apple to move by inertia (i.e. to fall) and the inertial force arising in the apple breaks the bond; or even more correctly (in terms of spacetime) - the bond has been deforming the apple's geodesic worldtube (deformation => 4D CSA => 4D force) and the static restoring force in the deformed worldtube of the apple (the inertial force) breaks the bond.

    Your second question - the rocket deforms the worldtube more than the ground by making the rocket move upwards and the restoring force is even greater and has to be overcome.

    Genuine understanding of the world, not just SR and GR, is only possible when spacetime and worldlines (worldtubes) are taken seriously; they are the ultimate reality; the 3D object we observe in everyday life are only 3D images / light reflections from the worldtubes of physical objects. To see that this is really the case, assume that those worldlines (and spacetime) are nothing more than geometrical abstractions and rigorously analyze Minkowski's explanation of length contraction shown in Fig. 1 of his famous paper "Space and Time" (it is contained in the free version of a book H. Minkowski, Space and Time: Minkowski's papers on relativity; the pdf file is available at: http://minkowskiinstitute.org/mip/books/minkowski.html). You will see that length contraction is impossible in a 3D world. The same is also true for the other kinematical relativistic effects.

    Good luck.

    P.S. Much more detailed explanations of everything we discussed here are given in a book "Inertia and Gravitation" which I am now completing; it will appear by the end of September.

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    • Post #53

    " ... by 'physically real', I mean both the effect observed and the cause of it."

    Then you've condemned yourself to an irrational explanation of the physical world, James. Simultaneous observation of cause and effect is impossible in principle. Were it not so, rational correspondence of language to meaning (theory to result) would be superfluous, because mere observation would replace language -- in which case, how would one communicate the results of the observed phenomenon except by telepathy?

    Tom

    "one can't disprove experiments"?

    See references 20 to 30 of my essay, in particular Nimtz who measured superluminal propagation of light.

    Eckard Blumschein