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#240 by spupeng7 on 13 Jun, 2017 04:42
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Spupeng7,
The "gravity is entropic" argument was offered only as an example to show that the type of cause is universal and unique. As such, entropy is only our "rocket way" to deal with gravity. We can do better with EM waves in producing a differential in the rate of the time-process.
Unruh's "lesson" is in fact a partial metaphysical rendering of GR. He doesn't say why this unequable flow of time from place to place makes things to exist more (move) toward slower time. On the other hand, he reifies or makes real "time" as something already existing here and there waiting for us to measure it, i.e. he makes it a substance!
In order to abide by truth, your discourse must sit entirely either in physics or metaphysics and don't be intimidated by those who see it as still a matter of fairies and unicorns. Philosophy is too important to be left to philosophers (Einstein)
Marcel,
Marcel,
the concept of time lacks brevity. The term 'development' may be a better descriptor for what time does, than is 'flow'. Circumstances for an individual charge, develop at a rate relative to everything with which it is connected, ie; all other charges at separation ict.
'Time' is a name for a regular measure of that development against known rates of chemical and mechanical reaction. In my opinion, the divergence in the rate of development of time which we know as gravity causes acceleration of mass by altering the motion of electrons within the atom, extending and reducing their duration at the extremes of vertical displacement.
If inertia is a an inductive relationship with the universe, then it should act within the atom also
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#241 by Rodal on 13 Jun, 2017 14:02
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...
Einstein's way to look at this, which is still the prevalent way to look at this by most people in General Relativity, is as, beautifully and succently stated by John Wheeler:
I say that things have a higher probability to exist or be where the rate of time is relatively slower because they can stay there longer. This perspective consists in changing "motion", which is an observation related to us, by "existence", which is only due to the "thing" itself. This way, we may understand why the universe works the way it does without us in the picture.
Marcel,Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve.
[Wheeler's succinct summary of Einstein's theory of general relativity, in "Geons, Black Holes, and Quantum Foam" (2000), p. 235]
Please notice that matter (or energy in general, since m = E/c2) curves spacetime: matter (energy) curves both time (what you are referring to) and curves space as well. Both space and time get warped by matter-energy. The magnitude of matter dictates the amount of warping of time and warping of space in the vicinity of the matter.
As you get close to a matter source (whether the Sun, a Neutron star, or a black hole for example), time slows down (time gets curved) and space gets curved as well.
Both things are going on, both things (curvature of space and curvature of time) have to be taken into account when one calculates the geodesic motion of an object near the source of matter-energy (the geodesic is the "straightest" path in curved spacetime).
Credit for last image (curvature of space, warping of time): Prof. Kip Thorne (Caltech)
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#242 by M.LeBel on 13 Jun, 2017 14:43
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Spupeng7,
The "gravity is entropic" argument was offered only as an example to show that the type of cause is universal and unique. As such, entropy is only our "rocket way" to deal with gravity. We can do better with EM waves in producing a differential in the rate of the time-process.
Unruh's "lesson" is in fact a partial metaphysical rendering of GR. He doesn't say why this unequable flow of time from place to place makes things to exist more (move) toward slower time. On the other hand, he reifies or makes real "time" as something already existing here and there waiting for us to measure it, i.e. he makes it a substance!
In order to abide by truth, your discourse must sit entirely either in physics or metaphysics and don't be intimidated by those who see it as still a matter of fairies and unicorns. Philosophy is too important to be left to philosophers (Einstein)
Marcel,
Marcel,
the concept of time lacks brevity. The term 'development' may be a better descriptor for what time does, than is 'flow'. Circumstances for an individual charge, develop at a rate relative to everything with which it is connected, ie; all other charges at separation ict.
'Time' is a name for a regular measure of that development against known rates of chemical and mechanical reaction. In my opinion, the divergence in the rate of development of time which we know as gravity causes acceleration of mass by altering the motion of electrons within the atom, extending and reducing their duration at the extremes of vertical displacement.
If inertia is a an inductive relationship with the universe, then it should act within the atom also
--- First, let`s not do what philosophers do; invent a new word when there is already a good one that does the job. I call it the “time-process” in order to differentiate it from all other matter of meaning associated with the word “time”.
Second, this time-process and its variations make the whole universe. So, it is not surprising to find out we already had a name for it in one form or another. Time is a substance, not an experience, so we do not perceive time directly. We deduce it from motion and change.
Third, electricity and magnetism are variations of the time-process.
Fourth, the simple rule of logic that drives the universe is the cause which tells where things to exist; toward a place (gravity), away from a place (anti-gravity) or stay (structures, atoms, galaxies etc.). The only way time can logically affect a clock is if they are both operational i.e. they are of the same nature/substance or, the clock is also made of time!
Fifth, inertia is a higher probability of existence in one direction resulting from the associated differential in the rate of the time-process i.e. the associated wave (pilot wave).
The question is this. We have on one hand electricity, magnetism and electro-magnetism which we control and on the other hand we have the time-process which we don’t understand, but that makes everything and that is what we must control in order to get things going. How do we connect the dots? The time-process/causal structure of the photon with its classic electromagnetic representation is the Rosetta Stone for achieving this translation. Meaning, what forms of the time-process makes electricity and magnetism.
Marcel,
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#243 by M.LeBel on 13 Jun, 2017 18:39
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...
Einstein's way to look at this, which is still the prevalent way to look at this by most people in General Relativity, is as, beautifully and succently stated by John Wheeler:
I say that things have a higher probability to exist or be where the rate of time is relatively slower because they can stay there longer. This perspective consists in changing "motion", which is an observation related to us, by "existence", which is only due to the "thing" itself. This way, we may understand why the universe works the way it does without us in the picture.
Marcel,Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve.
[Wheeler's succinct summary of Einstein's theory of general relativity, in "Geons, Black Holes, and Quantum Foam" (2000), p. 235]
Please notice that matter (or energy in general, since m = E/c2) curves spacetime: matter (energy) curves both time (what you are referring to) and curves space as well. Both space and time get warped by matter-energy. The magnitude of matter dictates the amount of warping of time and warping of space in the vicinity of the matter.
As you get close to a matter source (whether the Sun, a Neutron star, or a black hole for example), time slows down (time gets curved) and space gets curved as well.
Both things are going on, both things (curvature of space and curvature of time) have to be taken into account when one calculates the geodesic motion of an object near the source of matter-energy (the geodesic is the "straightest" path in curved spacetime).
Credit for last image (curvature of space, warping of time): Prof. Kip Thorne (Caltech)
Thank you Dr Rodal for the nice and well illustrated expression of our present state of knowledge. As physics is concerned, I agree with it.
At the frontier between knowledge and ignorance, great men and women recognize being there by using philosophy or poetry to express the still unknown before them.
Space doesn’t really exist because it is a representation in one moment (drawing, illustrations etc.) of points that are not at the same moment (spacetime) except in our minds. The Earth-Moon “distance” is approximately 1 light second. No two points of this “distance” are at the same moment, or else light would not take any time to travel the distance. We may use kilometers (or geodesics) for convenience but it doesn’t make space real. “Space” is a dimension of consciousness, not a dimension of the universe. So, we may forget the poetics of “curving space” or “this telling that” what to do.
In conclusion, “space” is a necessary tool for representing concepts of physical knowledge but it plays no part in the universe since it doesn’t exist. IMO, we should replace the “false cause” for motion as “curvature” or “geodesics” by the true and logical cause for motion, a higher probability of existence due to a differential in the rate of time. I don’t dispute any of the representations used in physics. Here, I only want to remind us to carefully remove our own observer contributions from our knowledge before we say that the universe is this or that.
Marcel,
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#244 by OnlyMe on 13 Jun, 2017 19:12
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....
Einstein's way to look at this, which is still the prevalent way to look at this by most people in General Relativity, is as, beautifully and succently stated by John Wheeler:Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve.
[Wheeler's succinct summary of Einstein's theory of general relativity, in "Geons, Black Holes, and Quantum Foam" (2000), p. 235]
Please notice that matter (or energy in general, since m = E/c2) curves spacetime: matter (energy) curves both time (what you are referring to) and curves space as well. Both space and time get warped by matter-energy. The magnitude of matter dictates the amount of warping of time and warping of space in the vicinity of the matter.
As you get close to a matter source (whether the Sun, a Neutron star, or a black hole for example), time slows down (time gets curved) and space gets curved as well.
Both things are going on, both things (curvature of space and curvature of time) have to be taken into account when one calculates the geodesic motion of an object near the source of matter-energy (the geodesic is the "straightest" path in curved spacetime).
Dr. Rodal,
I have long felt that Wheeler's choice of phrasing in the above quote, was unfortunate. Out of the context of the greater discussion.., of GR itself.., it lends itself to a misunderstanding, which it seems you (subtlety) clean up in your later explanation.
I believe it would have been more accurate had Wheeler phrased that as, "Spacetime describes how matter moves; matter tells Spacetime how to curve." Out of the greater context that first portion of the quote, "Spacetime tells matter how to move;..." implies both, that Spacetime has some independent substance of its own and that describing how objects interact gravitationally, is the cause of gravitation... at least in many lay oriented discussions, and even some not so lay...
GR and thus Spacetime in the context of GR, is a geometric description of how massive objects interact due to gravitation. We could say that the presence of matter is the cause of gravity, because that is observable, and still not know what the underlying mechanism is. IOW Spacetime curvature is descriptive not causative and the presence of matter is at least a component of the underlying mechanism, that remains unknown.
The curvature of both space and time are descriptive of observable changes, in the way objects move and the rate of change, relative to an object's location in or motion through a gravity well. That is not the same as saying that curvature, another way of describing a location within a gravity well or perhaps the location specific effect of a gravity well on an object, is the cause of either.
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#245 by M.LeBel on 13 Jun, 2017 19:31
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In summary, keep "space" for what it is, just a tool. But don’t let “space” play any part in the working of the universe because it doesn’t exist. This means removing “space” from any explanatory or causality schemes.
Marcel, -
#246 by Rodal on 13 Jun, 2017 19:36
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...
Wheeler wrote that
Dr. Rodal,
I have long felt that Wheeler's choice of phrasing in the above quote, was unfortunate. Out of the context of the greater discussion.., of GR itself.., it lends itself to a misunderstanding, which it seems you (subtlety) clean up in your later explanation.
I believe it would have been more accurate had Wheeler phrased that as, "Spacetime describes how matter moves; matter tells Spacetime how to curve." Out of the greater context that first portion of the quote, "Spacetime tells matter how to move;..." implies both, that Spacetime has some independent substance of its own and that describing how objects interact gravitationally, is the cause of gravitation... at least in many lay oriented discussions, and even some not so lay...
...Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve
Referring to the General Relativity's field equation:
To understand what Wheeler means by "Spacetime tells matter how to move" one has to set the source terms on the right hand side to zero, so that all you have left are the Ricci curvature tensor, the curvature scalar, and the cosmological constant.
Einstein's field equations admit dynamic solutions of the field equations even with no source: without any matter whatsoever in spacetime to be responsible for the spacetime disturbance.
These solutions are gravitational waves. (Of course, the majority of gravitational waves are supposed to be due to matter sources, and certainly the gravitational waves that have been measured have been due to massive black hole collisions, but it is theoretically tenable in GR to have gravitational wave disturbances that are not due to matter sources.) Theoretically (this has not been experimentally proven of course), gravitational waves can occur in spacetime without being due to a matter source.
In any case, certainly gravitational waves transport energy through space empty of matter.
Now, envision gravitational wave disturbances in spacetime (traveling in space empty of matter, such that it is not relevant whether these gravitational waves were sourced by matter or not, what matters is that they transport energy in empty space), and suddenly a body with matter m travels in the path of such gravitational wave. In such a case, spacetime (the gravitational wave) will tell matter how to move (albeit usually infinitesimally since such gravitational waves in empty space have small amplitude). This fulfills Wheeler's statement, which I share (as well as being shared by much more important people
like Leonard Susskind and many others).
Now, I do know that you may prefer to adopt a Machian viewpoint: under a Machian viewpoint any gravitational wave can only occur if it is due to matter (as in Hoyle Narlikar's theory for example). Under a Machian viewpoint, without matter there is no spacetime.
But even under a Machian viewpoint, where the gravitational wave originated due to a matter source (for example black hole collision), when the gravitational wave encounters a body with mass m, the gravitational wave will tell the body how to move (actually it will produce a small strain on the body), thus fulfilling Wheeler's statement, since the gravitational wave is just a disturbance in spacetime. -
#247 by Star One on 13 Jun, 2017 20:26
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This could be relevant here.
Cosmology at at Crossroads: Tension with the Hubble ConstantQuoteWe are at an interesting juncture in cosmology. With new methods and technology, the accuracy in measurement of the Hubble constant has vastly improved, but a recent tension has arisen that is either signaling new physics or as-yet unrecognized uncertainties.
https://arxiv.org/abs/1706.02739 -
#248 by OnlyMe on 14 Jun, 2017 00:25
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...
Wheeler wrote that
Dr. Rodal,
I have long felt that Wheeler's choice of phrasing in the above quote, was unfortunate. Out of the context of the greater discussion.., of GR itself.., it lends itself to a misunderstanding, which it seems you (subtlety) clean up in your later explanation.
I believe it would have been more accurate had Wheeler phrased that as, "Spacetime describes how matter moves; matter tells Spacetime how to curve." Out of the greater context that first portion of the quote, "Spacetime tells matter how to move;..." implies both, that Spacetime has some independent substance of its own and that describing how objects interact gravitationally, is the cause of gravitation... at least in many lay oriented discussions, and even some not so lay...
...Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve
Referring to the General Relativity's field equation:
To understand what Wheeler means by "Spacetime tells matter how to move" one has to set the source terms on the right hand side to zero, so that all you have left are the Ricci curvature tensor, the curvature scalar, and the cosmological constant.
Einstein's field equations admit dynamic solutions of the field equations even with no source: without any matter whatsoever in spacetime to be responsible for the spacetime disturbance.
These solutions are gravitational waves. (Of course, the majority of gravitational waves are supposed to be due to matter sources, and certainly the gravitational waves that have been measured have been due to massive black hole collisions, but it is theoretically tenable in GR to have gravitational wave disturbances that are not due to matter sources.) Theoretically (this has not been experimentally proven of course), gravitational waves can occur in spacetime without being due to a matter source.
In any case, certainly gravitational waves transport energy through space empty of matter.
Now, envision gravitational wave disturbances in spacetime (traveling in space empty of matter, such that it is not relevant whether these gravitational waves were sourced by matter or not, what matters is that they transport energy in empty space), and suddenly a body with matter m travels in the path of such gravitational wave. In such a case, spacetime (the gravitational wave) will tell matter how to move (albeit usually infinitesimally since such gravitational waves in empty space have small amplitude). This fulfills Wheeler's statement, which I share (as well as being shared by much more important people like Leonard Susskind and many others).
Now, I do know that you may prefer to adopt a Machian viewpoint: under a Machian viewpoint any gravitational wave can only occur if it is due to matter (as in Hoyle Narlikar's theory for example). Under a Machian viewpoint, without matter there is no spacetime.
But even under a Machian viewpoint, where the gravitational wave originated due to a matter source (for example black hole collision), when the gravitational wave encounters a body with mass m, the gravitational wave will tell the body how to move (actually it will produce a small strain on the body), thus fulfilling Wheeler's statement, since the gravitational wave is just a disturbance in spacetime.
".... since the gravitational wave is just a disturbance in spacetime.
My point was that instead of the above in bold, it would be better to say, (my words) "since a gravitational wave is described by Spacetime." And yes both a gravitational field and gravitional waves, exist and/or propagate through space empty of matter, without respect to their fundamental source.
I did not start out there but I do tend toward a more (loosely) Machian view of late, but that really is not a significant issue. What I would contend is that whether a gravitational field (or wave) is or can originate from the presence of a massive source or in the absence of a massive component, GR (and Spacetime within the context of GR) are descriptive, rather than causative. The underlying casitive mechanism remains unknown, even while our theoretical model(s) accurately describe the observable (and unobserved) dynamics. The wave itself may just be descriptive of some aspect of the fundamental mechanism.
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#249 by Rodal on 14 Jun, 2017 01:27
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...
In General Relativity there is energy in both sides of the equation: there is energy in the left hand side of the equation that deals with the curvature of spacetime. Even when the left hand side of the equation is zero, when the Ricci tensor is zero, there still can be curvature in 4-dimensional spacetime because the Riemann curvature tensor can be non-zero when the Ricci tensor is zero. This is why energy conservation issues are particularly difficult in General Relativity. The energy is not only associated with the source, but is also present in spacetime itself. This is the reason for Wheeler's description, and that's why many physicists also like it and repeat it.
".... since the gravitational wave is just a disturbance in spacetime.
My point was that instead of the above in bold, it would be better to say, (my words) "since a gravitational wave is described by Spacetime." And yes both a gravitational field and gravitional waves, exist and/or propagate through space empty of matter, without respect to their fundamental source.
I did not start out there but I do tend toward a more (loosely) Machian view of late, but that really is not a significant issue. What I would contend is that whether a gravitational field (or wave) is or can originate from the presence of a massive source or in the absence of a massive component, GR (and Spacetime within the context of GR) are descriptive, rather than causative. The underlying casitive mechanism remains unknown, even while our theoretical model(s) accurately describe the observable (and unobserved) dynamics. The wave itself may just be descriptive of some aspect of the fundamental mechanism.
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#250 by M.LeBel on 14 Jun, 2017 03:07
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My second point will address this general repulsion for the fact of “substance”. This situation is exactly the same as before Galileo, when there was this sense of being at the center of the universe. Physics is also anthropocentric because of its empirical credo which only recognizes the experience of things and events as criteria for existence. Strangely, the universe has existed and evolved by itself for the past 13.7 billion years before we ever showed up to “experience it.” The universe is not made of our experience of it. The universe is made of substance that exists without the need for our experience. In other words, the universe is impossible without a substance. The substance is the source of our experience and is what guarantees that things do not disappear outside our experience.
Granted, by definition, physics specifically studies our experience of the universe. But physics must realize the meaning of these limits and shall overcome them by understanding what it is missing, the substance that supports both his experience and the existence of the universe. Although it was originally ascribed to philosophy, the concept of substance and existence are too important to keep them separated from science. This early analytic partitioning has no place anymore and the substance has to be made part of a synthesis greater than physics. The universe is what exists and happens by itself, not what is experienced. Sure, science, physics, astronomy, cosmology etc. have done great advances in our experience of the universe. But, we can do much better than that. We can understand logically what we are actually doing, not just empirically.
Marcel,
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#251 by Peter Lauwer on 14 Jun, 2017 16:32
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Mode frequency change due to loops
-- advice needed (I will mention you in my Acknowledgements!) --
I have an adaptable cavity with a loop on both endplates. One of the endplates is not in contact with the cavity wall and can be moved in order to change the length. I measured the transmission (S21) with a network analyzer (I posted about this earlier). The loops have a diameter of 15 mm and a separation from the endplate of 32 mm.
(these loops are not usable for exciting frustums etc., not narrow band enough)
My problem is now: I am uncertain which modes I am seeing.
E.g., the following (cavity diam. 98 mm, length 98 mm):
Frequency
[MHz] Mode F calculated [MHz]
3617 TE112? 3546
3251 TE211? 3344
2948 TM011? 2779
I expect them to be mainly TE-modes, due to the exciting loops. And, since they shift with changing cavity length, p≠0 (TE_mnp).
Or do I also see an interaction with 'the other cavity'? (behind the movable endplate)
More on this project later, I first need to know what modes it are.
Thanks, Peter
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#252 by Peter Lauwer on 14 Jun, 2017 16:34
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Mode frequency change due to loops
-- advice needed (I will mention you in my Acknowledgements!) --
I have an adaptable cavity with a loop on both endplates. One of the endplates is not in contact with the cavity wall and can be moved in order to change the length. I measured the transmission (S21) with a network analyzer (I posted about this earlier). The loops have a diameter of 15 mm and a separation from the endplate of 32 mm.
(these loops are not usable for exciting frustums etc., not narrow band enough)
My problem is now: I am uncertain which modes I am seeing.
E.g., the following (cavity diam. 98 mm, length 98 mm):
Frequency
[MHz] Mode F calculated [MHz]
3617 TE112? 3546
3251 TE211? 3344
2948 TM011? 2779
I expect them to be mainly TE-modes, due to the exciting loops. And, since they shift with changing cavity length, p≠0 (TE_mnp).
Or do I also see an interaction with 'the other cavity'? (behind the movable endplate)
More on this project later, I first need to know what modes it are.
Thanks, Peter
The spectrum.
[the frequencies differ a little from one measurement to another at the same given cavity lenght, since this latter parameter is not completely reproducable).
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#253 by Bob012345 on 14 Jun, 2017 18:57
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I was listening to the Estes Park discussions and frequency scaling comes up. What do people think is the practical limit to frequency scaling in a device? Thanks.
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#254 by Rodal on 14 Jun, 2017 21:10
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There is another issue that just occurred to me that makes Wheeler's statement...
Wheeler wrote that
Dr. Rodal,
I have long felt that Wheeler's choice of phrasing in the above quote, was unfortunate. Out of the context of the greater discussion.., of GR itself.., it lends itself to a misunderstanding, which it seems you (subtlety) clean up in your later explanation.
I believe it would have been more accurate had Wheeler phrased that as, "Spacetime describes how matter moves; matter tells Spacetime how to curve." Out of the greater context that first portion of the quote, "Spacetime tells matter how to move;..." implies both, that Spacetime has some independent substance of its own and that describing how objects interact gravitationally, is the cause of gravitation... at least in many lay oriented discussions, and even some not so lay...
...Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve
Referring to the General Relativity's field equation:
To understand what Wheeler means by "Spacetime tells matter how to move" one has to set the source terms on the right hand side to zero, so that all you have left are the Ricci curvature tensor, the curvature scalar, and the cosmological constant.
Einstein's field equations admit dynamic solutions of the field equations even with no source: without any matter whatsoever in spacetime to be responsible for the spacetime disturbance.
These solutions are gravitational waves. (Of course, the majority of gravitational waves are supposed to be due to matter sources, and certainly the gravitational waves that have been measured have been due to massive black hole collisions, but it is theoretically tenable in GR to have gravitational wave disturbances that are not due to matter sources.) Theoretically (this has not been experimentally proven of course), gravitational waves can occur in spacetime without being due to a matter source.
In any case, certainly gravitational waves transport energy through space empty of matter.
Now, envision gravitational wave disturbances in spacetime (traveling in space empty of matter, such that it is not relevant whether these gravitational waves were sourced by matter or not, what matters is that they transport energy in empty space), and suddenly a body with matter m travels in the path of such gravitational wave. In such a case, spacetime (the gravitational wave) will tell matter how to move (albeit usually infinitesimally since such gravitational waves in empty space have small amplitude). This fulfills Wheeler's statement, which I share (as well as being shared by much more important people like Leonard Susskind and many others).
Now, I do know that you may prefer to adopt a Machian viewpoint: under a Machian viewpoint any gravitational wave can only occur if it is due to matter (as in Hoyle Narlikar's theory for example). Under a Machian viewpoint, without matter there is no spacetime.
But even under a Machian viewpoint, where the gravitational wave originated due to a matter source (for example black hole collision), when the gravitational wave encounters a body with mass m, the gravitational wave will tell the body how to move (actually it will produce a small strain on the body), thus fulfilling Wheeler's statement, since the gravitational wave is just a disturbance in spacetime.Quote from: WheelerSpacetime tells matter how to move; matter tells spacetime how to curve
particularly true, now that we know for a fact (from cosmological measurements) that the expansion of the universe is accelerating and that the cosmological constant is real (and so is dark energy).
Referring again to the General Relativity's field equation:
A spacetime completely free of any matter sources (Tμν=0) with a positive cosmological constant Λ>0 must always be curved , because for Tμν=0, the Ricci tensor Rμν will not vanish.
For Tμν=0, we have
Rμν - ˝ R g μν = - Λ g μν
In essence, you can think of the cosmological constant Λ as a source of energy, by bringing this Λ term to the right hand side. That is one of the reasons is it called dark energy, it curves space.
Thus Wheeler was right once again, considering dark energy, spacetime tells matter how to move: it tells matter to move as spacetime accelerates its expansion and carries matter with it.
General Relativity is not just a geometric description of gravity: spacetime itself has energy (both dark energy and is capable of having gravitational waves carrying energy). That is why Wheeler, Kip Thorne and others refer to General Relativity as "Geometrodynamics". Spacetime without matter in General Relativity is not empty (it has gravitational waves and dark energy). Spacetime tells matter how to move [due to dark energy and due to gravitational waves]; and matter tells spacetime how to curve as well (gravitation due to matter).
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#255 by Peter Lauwer on 14 Jun, 2017 21:22
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...
General Relativity is not just a geometric description of gravity: spacetime itself has energy (both dark energy and is capable of having gravitational waves carrying energy).
...
But... dark energy does not follow from GR, if I am right. For the rest you are right, good to emphasize: GR is not just a geometric description of gravity.
[or you must take the cosmological term to be dark energy] -
#256 by Rodal on 14 Jun, 2017 21:25
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It depends on what definition of dark energy you ascribe to. Prof. Leonard Susskind and others conceive of dark energy as just the cosmological constant. According to this view, it is easy to see my argument above, as a non-zero lambda curves space and tells matter how to move (it carries matter with it as spacetime expands)....
General Relativity is not just a geometric description of gravity: spacetime itself has energy (both dark energy and is capable of having gravitational waves carrying energy).
...
But... dark energy does not follow from GR, if I am right. For the rest you are right, good to emphasize: GR is not just a geometric description of gravity.
However, others, for example those suscribing to the Chameleon field, propose this field, and hence a 5th force field as the nature of dark energy. (See http://www.skyandtelescope.com/astronomy-news/is-dark-energy-a-chameleon-0824201523/ ).
There is no definite experimental confirmation yet as to which view is correct. Prof. Leonard Susskind (last time I heard him give a lecture) expressed the firm opinion about the cosmological constant viewpoint. Of course an outstanding problem to be explained is that quantum field theories predict a huge cosmological constant, more than 100 orders of magnitude too large. But that is a problem with quantum theory, not a problem with General Relativity. People in General Relativity and Cosmology take the experimental value of the cosmological constant as an experimental fact in Cosmology and the calculation problem with quantum mechanics as something that will only be resolved once there is an acceptable theory of quantum gravity. So, this view takes the cosmological constant as an experimental fact. After all the nature of the Gravitation constant G, is also taken as an experimental fact of nature, and there is still no definite explanation as to the size of G.
When I was last week at the NIAC Orientation meeting at NASA Washington DC, I found this project most fascinating:
https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Dark_energy_interactions_solar_system_laboratory
I talked to Dr. Nan Yu (https://scienceandtechnology.jpl.nasa.gov/people/n_yu) , from NASA Jet Propulsion Laboratory. His proposal is fascinating, very impressive, as it would provide experimental confirmation as to whether dark energy is not just the cosmological constant but whether it is a separate field. One of the ways it would verify this experimentally is by placing spaceship(s) at the saddle gravitational point between the Moon, the Earth (and the Sun), that lies between the Moon and the Earth, and conduct experiments (with lasers) with screened atomic particles inside a shielded container and with unscreened atomic particles outside the spaceship in free space.
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#257 by spupeng7 on 15 Jun, 2017 03:10
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from Reply #242,
Space doesn’t really exist because it is a representation in one moment (drawing, illustrations etc.) of points that are not at the same moment (spacetime) except in our minds. The Earth-Moon “distance” is approximately 1 light second. No two points of this “distance” are at the same moment, or else light would not take any time to travel the distance. We may use kilometers (or geodesics) for convenience but it doesn’t make space real. “Space” is a dimension of consciousness, not a dimension of the universe. So, we may forget the poetics of “curving space” or “this telling that” what to do.
(...)
from Reply #244,
In summary, keep "space" for what it is, just a tool. But don’t let “space” play any part in the working of the universe because it doesn’t exist. This means removing “space” from any explanatory or causality schemes.
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from Reply #249,
My second point will address this general repulsion for the fact of “substance”. This situation is exactly the same as before Galileo, when there was this sense of being at the center of the universe. Physics is also anthropocentric because of its empirical credo which only recognizes the experience of things and events as criteria for existence. Strangely, the universe has existed and evolved by itself for the past 13.7 billion years before we ever showed up to “experience it.” The universe is not made of our experience of it. The universe is made of substance that exists without the need for our experience. In other words, the universe is impossible without a substance. The substance is the source of our experience and is what guarantees that things do not disappear outside our experience.
Granted, by definition, physics specifically studies our experience of the universe. But physics must realize the meaning of these limits and shall overcome them by understanding what it is missing, the substance that supports both his experience and the existence of the universe. Although it was originally ascribed to philosophy, the concept of substance and existence are too important to keep them separated from science. This early analytic partitioning has no place anymore and the substance has to be made part of a synthesis greater than physics. The universe is what exists and happens by itself, not what is experienced. Sure, science, physics, astronomy, cosmology etc. have done great advances in our experience of the universe. But, we can do much better than that. We can understand logically what we are actually doing, not just empirically.
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Marcel,
Good points in a fabulous discussion (pinching self to believe that I am a part of this) but...
to state that space does not exist, is such an immense leap of logic that it will not be logical at all to the unconvinced. Can we agree that human perception, the empirical experience, is valid yet incomplete within strict physical reality. If we accept GR then we owe it to the discussion to understand it. If we believe in a Machian universe it may help to agree that the vacuum is empty of anything other than charges.
Maybe we need a method of declaring our standpoints, so that we may defend them in a more transparent manner. I am a Machian, I don't believe in photons, I think that charge interactions explain inertia, gravity and electromagnetic action by coincidence of location in complex time. This allows me to interpret polarization and fringe effects as alignments through the dilations of spacetime that exist in the path that a photon would take if it had extension in time from any other than a single remote point perspective with an undefinable stationary location.
No, I do not expect anyone else to jump on board this twisted set of beliefs but I pursue them because they are the only ones that make any sense to me. Space exists in human perception and cannot be removed without destruction of our own argument. If energy conservation within GR is so complex then maybe there exists an explanation for emdrive thrust within GR but if that is not the case, we must explore every other logically feasible reality to make sense of it, in preference to throwing the baby out with the bathwater...
Well done everyone, all this is valid debate. jmn.. -
#258 by M.LeBel on 15 Jun, 2017 04:36
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Thanks JMM (spupeng7)
Allow me to repeat myself. The universe is logical and works according to logic. This fact requires that it be made of only one type of “stuff” or substance in order to work or be “operational” under logic. This means that the magnetic field, the electric field (and charges), the EM fields and Time are all various forms of this single substance. This is why I said earlier that in order for time to affect a clock, they both must be logically operational i.e. they must be of the same nature or same stuff i.e. the clock is made of time.
This is essentially why logic based mathematics are so efficient in describing natural processes (Wigner 1963). Up to now we didn’t need to know what the identity of the stuff is because it is all the same everywhere in various forms. Numbers, not identity mattered. But when our computations extend to the whole universe, we need to know what the stuff (substance) is because we are missing a lot of it i.e. dark energy, dark matter. We now need to know the identity of that stuff so that we can factor it into our computations
Marcel, -
#259 by WarpTech on 15 Jun, 2017 05:47
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Thanks JMM (spupeng7)
Allow me to repeat myself. The universe is logical and works according to logic. This fact requires that it be made of only one type of “stuff” or substance in order to work or be “operational” under logic. This means that the magnetic field, the electric field (and charges), the EM fields and Time are all various forms of this single substance. This is why I said earlier that in order for time to affect a clock, they both must be logically operational i.e. they must be of the same nature or same stuff i.e. the clock is made of time.
This is essentially why logic based mathematics are so efficient in describing natural processes (Wigner 1963). Up to now we didn’t need to know what the identity of the stuff is because it is all the same everywhere in various forms. Numbers, not identity mattered. But when our computations extend to the whole universe, we need to know what the stuff (substance) is because we are missing a lot of it i.e. dark energy, dark matter. We now need to know the identity of that stuff so that we can factor it into our computations
Marcel,
My 2 cents...
I appreciate the desire to insist that the universe be logical and things work according to logic. IMO however, statements like "the clock is made of time" or "in order for time to affect a clock", are highly illogical to me. The very notion that spacetime is more than a mathematical convenience, seems to me to be absurd.
Let's try to find some common ground, based on logic. As a scientific community, we have a perfectly good quantum field theory (QFT) referred to as; The Standard Model of Particle Physics. It describes what makes up all observable matter and energy in the Universe, i.e., Quantum Fields, not classical particles and waves.
Is this acceptable?
With this in mind, I offer you to choose anything by which to measure space and time. In other words; Choose your ruler and your clock.
I guarantee that whatever you choose, it can be tediously described by the Standard Model, or more simply by the macroscopic, classical approximation to it. It doesn't matter if you choose a wooden ruler or a laser beam, it's all the same. All Rulers and clocks are made of quantum fields and may be described by the QFT.
Logically, Space is what we measure with our ruler and Time is what we measure with our clock. There is no other choice. Therefore, variations in spacetime (i.e. curvature, waves, etc.) are variations in the quantum fields that Set The Scale of our Rulers and Clocks.
In my own theory, the interaction between quantum fields leads to power dissipation, which affects the scale of our instruments. The more densely packed the matter and energy becomes, the more dissipation there will be and this causes rulers to contract and oscillators (clocks) to slow down.
There is no need to quantize gravity. It is simply the natural evolution of the SM. I think, what is missing from GR is the notion that matter and vacuum are in equilibrium. Quantum fields are not billiard balls in an empty box. It is a dynamical system where the quantum vacuum and the matter fields are constantly exchanging photons, electrons, gluons and quarks, in equilibrium. (Power Radiated = Power Absorbed) When the power is not in a long term equilibrium state, we have gravitational drift (acceleration).
Todd
like Leonard Susskind and many others).