Make out the position of Andromeda

[marcus]

Incidently, the God I believe in is the author and guarantor of the laws of science, not the gaps in it.

Garth

that is a noble concept of the Deity

 

[marcus]

I don't take a stance either way and don't want to give any indication of a position pro or con. but I am impressed

 

[nightcleaner]

On re-reading this thread it occurs to me that there is a curious parallel between the AP and CNS. AP says the universe was made so as to benefit Man, and CNS says the universe was made to benefit black holes. It seems clear to me that the black holes win. They last a lot longer in this universe than do humans.

But I still want better information on this bent light idea. GR, I think, says light always travels in straight lines, but that gravity bends spacetime, so that light passing near a star will appear bent to an observer further up the gravity slope. Am I correct that SCC says spacetime is bent, which makes light look bent, but that light also experiences additonal bending due to gravitational attraction?

Bent spacetime is invoked in GR to explain gravitational attraction between masses. It doesn't make any difference if the attraction is due to rest mass or to kinetic energy. Light has lots of kinetic energy but no rest mass.

SCC says there is an additonal effect of gravitation on light...not only is it bent by bent spacetime, but it also experiences an additional attraction? Light is doubly bent?

And I still don't see where the evidence for this idea is, nor do I understand how gravity probe B is going to tell us the difference between the two theories.

nc

 

[Garth]

Hi nightcleaner!

But I still want better information on this bent light idea. GR, I think, says light always travels in straight lines, but that gravity bends spacetime, so that light passing near a star will appear bent to an observer further up the gravity slope. Am I correct that SCC says spacetime is bent, which makes light look bent, but that light also experiences additonal bending due to gravitational attraction?
Bent spacetime is invoked in GR to explain gravitational attraction between masses. It doesn't make any difference if the attraction is due to rest mass or to kinetic energy. Light has lots of kinetic energy but no rest mass.
SCC says there is an additonal effect of gravitation on light...not only is it bent by bent spacetime, but it also experiences an additional attraction? Light is doubly bent?
And I still don't see where the evidence for this idea is, nor do I understand how gravity probe B is going to tell us the difference between the two theories.

OK! Where do we start?

Think of the standard GR situation of a path of light being ‘bent’ by the Sun. You are probably familiar with the analogy of the gravitational field of a spherical object like the Sun represented by a round rubber sheet curving down to its centre by the presence of a large ball in the middle. ‘Straight’ lines (i.e. paths of the shortest distance) drawn on this surface will seem ‘curved’ because of the curvature of the surface on which they are drawn. Two adjacent initially ‘parallel’ lines will diverge or converge because of this curvature. The curvature of the surface of the rubber sheet can therefore be described intrinsically by such di/convergence without having to leave that surface.

Take the point of view of an observer co-moving with the centre of mass of the Sun and take a slice through space-time of simultaneous events in that frame of reference. That surface will be bent in towards the centre as in the analogy above.

Now consider the passage of a ray of light traveling in a straight line across that sheet and just grazing the central body. It will be deflected towards the body by the curvature of the surface on which it is travelling. This is the curvature of space.
However a photon in that ray of light will have energy and that energy has a mass equivalent so it will be gravitationally attracted towards the mass. It will fall towards the Sun, this is an effect of the equivalence principle.

Thus we can split the deflection of the path of light into two component effects, one is due to the ‘gravitational’ attraction (in the Newtonian sense) of the photon, the other is due to the curvature of space. In GR these two effects are both equal and individually give rise to half the total solar deflection of ½ + ½ = 1 x 1.75”, which is due to the curvature of space-time.

Now in Self Creation Cosmology there is a ‘Machian’ scalar field, which endows particles with inertial mass, and which both perturbs the curvature of space-time and causes a ‘upwards gravitational-type’ force that acts on particles (rest masses) but not photons. The true gravitational force (curvature) is 3/2 the GR value, but the total force felt by particles is the GR – Newtonian gravitational force. Photons therefore ‘fall’ at 3/2 the acceleration of particles – even so in a 2km light path the deflection is only about 1 Angstrom.

The amount of space curvature caused by the Sun in SCC is ½ that of GR, whereas the amount of ‘gravitational attraction is 3/2, so the total deflection is ½ x ½ + ½ x 3/2 = 1 x the GR deflection = 1.75” as observed. This is one case of many tests in which the presence of the scalar field force has the effect of exactly balancing the effect of the presence of the scalar field.

There are three tests, however, where this exact compensation does not hold, the GPB geodetic precession measurement being one of them; the other two are a direct comparison of the ‘rates of falling’ of light compared with a physical apparatus, these are described in Self Creation Cosmology - An Alternative Gravitational Theory .
As the GPB measurement is being carried out at this moment we shall see! (Apparently in about a year)

I hope this helps.

Garth

 

[nightcleaner]

Hi Garth

I have been less than happy with the rubber sheet model of gravity since I first read of it. It undertakes to describe the attractive force between masses in terms of deformation of a two dimensional plane. Gravity, however, acts in our three dimensions of space, and the two dimensional plane invoked in GR is not physically apparent.

The rubber sheet model uses an impenetrable membrane. Where is this membrane? I don't see it spreading out between real objects in real space. Why is it visible in two dimensions (the model) but not visible in real three dimensional space? What causes it to resist penetration so mightily? And there are two forces in counterbalance in the sheet model, that pushing down on the masses, causing the deformation, and that pushing up on the masses, preventing them from passing through the membrane, and incidentally causing them to attract each other. What is this second force in GR?

The questions are rhetorical and intended to highlight the problems with the model. It is a good model in so far as it reproduces the behavior of masses in which we are interested, but it is a bad model in so far as it consists of physical elements which mechanically act to mimic the real behavior we are interested in, and may or may not represent the real operations resulting in the behavior.

The sheet itself is one physical construct which is not present in the real three dimensional system. Because it is not present, it cannot be the source of the second, resisting force. There is no sheet, and there is nothing analogous to the sheet in the real system.

The masses are also artificial. We do see real masses at macroscopic scales and they do look more or less like bowling balls and so on. But the whole question is to do with why masses attract in the first place. Plunking a mass down in the middle of it is like defining a word as the opposite of its opposite. The answer may be true but it is trivial. We want to know why mass behaves as it does. Saying that mass behaves as mass behaves because it is mass is no use at all.

And then there is the force and the counter-force, which I have already discussed, as well as the resultant third force in the equation, which the one thing in the model we are actually interested in, the attractive force.

If we are to make any progress understanding the physical process that is going on in Gravity, we have to begin by abandoning this toy model of rubber sheets and bowling balls, and begin to work directly in three and higher dimensions.

In our usual three dimensions of space there is a component of change, in which time is irrevokably involved. There is no possibility of change in the absense of time. This leads us into the frozen instant, the image of timespace as a landscape, a physical place in which frozen instant after frozen instant may be displayed in sequence like the frames in a movie film, produceing motion as a sort of illusion. In this view the only kind of motion, or change, that is possible is the motion of the observer, who, disembodied, may float or race across the landscape, thus experiencing the "illusion" of local three dimensional time.

Notice however that the observor is not limited to the three dimensions of space and one of time, but can presumably turn and circle and choose to move into whatever part of the landscape that is of interest, past present and future all frozen into one eternal surface. This means that the observor has to have additional degrees of freedom beyond the three space and one time system that we commonly inhabit. We need more dimensions of spacetime to accommodate the freedom of the observer. We talk of the observer as being able to change from past to future or future to past at will, so it is clear that the one time line, past and future, is not enough. The observer has to be higher dimensional than the observed spacetime landscape.

We need to have a better understanding of these higher dimensional relationships before we can have an understanding of the gravitational mechanism.

Garth, I am still trying to make the double gravitation idea fit into my head. At this point I am still inclined to think that the idea is an artifact of the model and does not describe reality.

I need to understand the GPB experiment better. I think it has something to do with the precession of the axis of a gyroscope in free fall, but I have not gotten a clear idea of the question. My guess is that the spin axis of the gyroscope is taken to be a referential absolute, and any changes in the axis when it is in free fall must be attributable to curvature in timespace.

I appreciate any discussion or guidance on this.

I also want to take a moment to thank the moderators and participants on Physics Forums for giving me so many interesting things to think about.

Be well,

Richard T. Harbaugh,
Nightcleaner

 

[marcus]

I also want to take a moment to thank the moderators and participants on Physics Forums for giving me so many interesting things to think about.
...

thanks to you as well, nc, for the mind-mill's grist you contribute,
you give as good as you get, by my rough reckoning

 

[Kea]

Nightcleaner,

Your thoughts are an inspiration to us all.

 

[Spin_Network]

I agree! If for no other reason is right.

I am still fumbling with the wording of that CNS prediction. As Smolin stated it in a 1995 paper, it is put in a positive way:

(remember he wants to say that we have a parameters which are as good as they can get for prolific black hole production, so any change should make black holes less prevalent if it changes things at all, so he says)

"Any small change you could make in the parameters of the standard physics and cosmology models would cause black holes to be fewer, or leave their number unchanged."

One has to be careful of the vast number of predictions about Blackhole Production factories?..Black Holes are the singularity 'end' of certain Stella Mass Production lines?..if Stars create Blackholes as an emerging singularity phenomena, then either the standard model is wrong..or god forbid, Smolin is way off target?
prolific black hole production must be ongoing..as the Universe age's and wain's out..so must the Blackholes by fact of lack of Stella Source's, fewer Blackholes will always prevail at a distant future, by fact of above..the Universe past cannot therefore have 'Less' Blackholes.

I have to point out that a number of authors have papers detailing the that the Universe could not have produced a finite number of Stars at the same instant as a finite number of Blackholes?

 

[Garth]

nightcleaner - Thank you for your comments and questions.

The 'rubber sheet model' is only an analogy.

Three points.

First, in order to be able to picture it one space dimension has been suppressed.

Secondly this rubber sheet in the language of GR is the 3D space all around us.

Thirdly, and here I refer to "This leads us into the frozen instant", which is why I said, "take a slice through space-time of simultaneous events", you are right, such a slice is a frozen instant! The extra dimension you mention in Einstein's thought is the dimension of time, that is why you have to talk in terms of a 4D space-time and not just space or time. (Notice how I also highlighted these three separate concepts in my post above.)

If you do not want to picture the analogy by ‘standing outside the model’ consider the intrinsic curvature measured by the behaviour of ‘straight’ or ‘parallel lines’ drawn in the surface. It is this curvature that the ‘bent light ray’ observation was measuring.

There is a mystery in why the presence of mass should cause space-time curvature. Density can be connected to “the moment of rotation of the curvature” through the basic Einstein field equation; in the large textbook “Gravitation” by Misner, Thorne and Wheeler this is dealt with in chapters 15 and 17, but I cannot quickly deal with it here.

Does Einstein's concept of curved space-time work? Well it has been tested again and again and so far it seems to! GPB is the latest, and most expensive, (!) in a long line of experiments. However SCC also predicts the same results in all experiments up to the present date, so GPB could still be interesting!

Finally what is GPB measuring? As with the rubber sheet analogy all I can give you is a picture, the real explanation both for the gravitational field itself and the GPB experiment is to be found in the mathematics and the concepts they encapsulate. GPB measures two precessions of a gyro-compass (actually four of them) in a circular polar orbit predicted by GR (and SCC), the gravito-magnetic, or ‘frame-dragging’ (Lense-Thirring effect) precession in an E-W direction, and the geodetic precession in a N-S direction. The gravito-magnetic precession is caused by the spinning Earth dragging the inertial compass of space-time with it. The geodetic precession can perhaps be described by the inertial-compass, the gyro’s axis, being ‘tipped over’ in a N-S direction by the slope of that curved ‘rubber sheet’.

I hope this helps.

Garth

 

[nightcleaner]

Very helpful indeed, Garth, and thank you for being patient with my ignorance. I wish I could read the mathematics but that language is not yet fluent for me. I can make out bits here and there but still need help to get the story line.

So the two dimensional sheet is an analogy, of course, or as I said, a model. What does it mean in three dimensional space? Well, first off, the idea seems to be that the gravitating object "stretches" or somehow deforms space nearby, using the inverse square rule as a guide. Space close to the object is deformed more than space farther away from the object. We may imagine then a region of "free space" in which there is no deformation, and take that undeformed region as a place to establish our meter. When we take the meter from the undeformed region and compare it to the same meter in the deformed region, there is a difference, the difference of course being a measure of the amount of deformation.

The meter near the gravitational object is compressed compared to the meter in free space. This is apparent from the convergence of the lines in the model. It is a little hard to get the visualization correct since the gravitating object in the model stretches the lines, making them longer in the radial direction, but leaves them unchanged or even shorter in other directions. This seems to me to be an artifact of the model. In the real three dimensional space, the gauge lines must be compressed in all three dimensions.

That's why it seems to me to make more sense to speak of spacetime density near gravitating objects. Space and time, I think, are compressed by the gravity field, not stretched, and the compression is very nearly uniform in every direction from any point in the affected space. In this way gravity can be seen as an expansion of spacetime units as the observor moves outward through the gravitational field, and their expansion can be seen as identical with the expansion of the universe as an entire entity. Cosmic expansion and local gravitation seem to me to be two views of the same effect.

Hi Kea, thank you darling, I am becoming quite fond of you. And Marcus, of course, don't be jealous, and welcome to Spin network.

Be well,

Richard

 

[Garth]

The rubber sheet analogy or model allows us to visualise the concept of curvature 'from the outside'. However, as you point out, space-time is all around us, we are 'inside'. That is why I carefully explained that curvature can be described 'from the inside' by the intrinsic behaviour of 'parallel lines', actually two adjacent and initially parallel geodesics, the paths of two freely falling test particles. If they converge, or diverge, or rotate around each other, then although you may be also in a freely falling laboratory, and ‘weightless’, you may conclude that there is a gravitational field, and by measuring how these test particles are behaving relative to each other you detect curvature by measuring tidal forces.

Another way of measuring curvature is to parallel transport a vector around a closed circuit until it is back where it started. If you find that it has in fact rotated with respect to its initial direction then you again conclude that there is curvature i.e. a gravitational field. This is indeed what the GPB geodetic precession measurement is doing.

I am intrigued by your suggestion that a metre would be compressed when it is brought into a gravitational field. The question is, "How do you measure the change?" - by another metre rule? In which case it too will suffer the same deformation and you will not be able to detect a change. In GR the metre rule is defined to be ‘rigid’ i.e. of unchanging length.

However in SCC the metre rule does change, albeit in the opposite way; that is it is shortened when lifted out of the gravitational field. This is because, as it is lifted, it gains gravitational potential energy and hence (according to SCC) rest mass. As the diameter of an atom is inversely proportional to its mass, other things being equal, the ruler shrinks. Clocks also speed up.

But how do you measure these changes in SCC? By comparing the size of atoms and behaviour of clocks with the wavelength and frequency of a photon. What do you then observe? Gravitational red shift! But now interpreted, not as a loss of energy by the photon, but a gain of (P.E.) rest mass by the apparatus measuring it.

Garth

 

[nightcleaner]

Hi Garth

I came by the idea that spacetime is compressed near a gravitating object by means of considering what the idea of the word "bent" is. You take two points connected by a line, impose a force causing the line to "bend," and the result is that the original, unbent line is now longer than the distance between the two points. Hence, the resulting line is bent like a bow, and the new shortest distance between the two points is like the bowstring.

But that is just another model, we are not practicing archery. The "bend" could just as easily be seen as a compression or increase in density of the line.

I think when using these models we need to be more careful of our idea of dimensionality. If we start from the definition of the point in a space without undefined qualities (Machian space I think would fit this category) then two defined points make a straight line, since a straight line can be defined in the space from the two points.

It may be useful to ask how we came by two points. We started with a single defined point, in an otherwise undefined space. It has the quality of being, which means it has something within. It contains the category of itself. This requires the definition of the opposite of within, which is the undefined space outside the defined object, in this case, a point. You see, I hope, the sense of evolutionaly steps I am trying to establish for a higher dimensional geometry.

The second point is necessarily outside the first point, so that we may have a basis for counting. It initially could be anywhere outside the first point, and so everywhere outside the first point. It is a sense of representation of two conflicting ideas. One idea is that it is outside the first point, not further defined. The other idea is that it is somehow like the first point, so that a new category can be formed containing two points in otherwise undefined "Machian" space. Since it is outside and somehow like, there must be an outside that is somehow unlike, or else like has no meaning. In this way, by a self-reflective bending, a self creation if you will, the geometry of the universe can be mentally traced from the first point.

I refer the reader interested in details of geometric evolution up through the third dimension to Euclid.

My position then is that our universe, however many dimensions you count after that, is evolved according to geometric principles. The fundamental laws of the universe are all self evolved from geometry, and in no case is there an outside finger poking new holes in reality. A hole, in this idea, is just a point. Instead, the second point and all the points thereafter are evolved from within the first point.

Every point is the same, so there is no way to distinguish between the first and second point or any point evolved thereafter. Every point evolves the same way. In this way the universe is a self creating burgeoning of form into undefined space. It is expanding from every point in every possible dimension.

What is a possible dimension? Well, from the first point came the second point, which we have as a single dimension. The point itself is zero dimension. The line is one dimension. Bend the line, and you have another dimension, which you can confirm by laying a strung bow on a table. You see that the curve is in the dimension of the table top, which is two dimensional, having length and width. This is again, just a model, but with the caveat in place, it serves to communicate the geometric idea, as long as we stick to the math and don't get distracted by the archery.

I have gone on too long, but I hope you see that the notion that the "meter" in its "metric" can be usefully thought of as smaller when near gravitating objects. And then we can carry that image to its conclusion, which is that eventually the metric approaches zero in the presence of sufficient mass, which is where spacetime collapses into singularity.

The idea of a collapsing meter makes it very hard to talk about the radius of any space containing a black hole, if indeed a black hole can be contained. Its a paradox Zeno would recognise. We can, however, measure the radius of a black hole from the outside, with the understanding that the size of the hole will then be a variable dependent on the conditions we bring into play in the attempt to make a measurement. In a sense, the size of the hole depends on where you stand when you make the measurement!

You said "However in SCC the metre rule does change, albeit in the opposite way; that is it is shortened when lifted out of the gravitational field. This is because, as it is lifted, it gains gravitational potential energy and hence (according to SCC) rest mass."

I am not clear on your idea of rest mass. Are you saying that rest mass depends on distance to local gravitational objects?

Eager to hear more.

Thanks,

nc

 

[Garth]

I am not clear on your idea of rest mass. Are you saying that rest mass depends on distance to local gravitational objects?

In SCC there are two convariant frames of measurement.

In its Einstein conformal frame the rest mass of fundamental particles is constant and the theory reduces to General Relativity.

In its Jordan conformal frame the energy of a photon remains constant when measured in a preferred inertial frame selected by Mach's Principle, the co-moving Centre of Mass/Momentum frame.
In this frame the rest mass of a particle includes gravitational potential energy, so m = m₀exp(Phi_N) where m₀ is its mass at 'infinity' and Phi_N is the dimensionless Newtonian gravitational potential
Phi_N = GM/(rc²).

Garth

 

[nightcleaner]

This is interesting to me, and I hope my conversation is not boring you. I have looked at the idea of Machian space in the bucket problem. In my mind, I have retained the idea of Machian space as beginning point from which to proceed in an evolutionary fashion in building the geometries that should lead us to an understanding of the reasons for the standard models having so many seemingly arbitrary parameters.

Well let us assume a Mach kind of space, at least in the context of events which occur near the Planck scale, or perhaps just under the Fermi scale. These events are so local that nothing much at our scale affects them appreciably anyway. If I understand correctly, you are preferring an inertial frame in which all particles of interest possesses a co-moving center of mass and differ little from each other in terms of angular momentum. In my words, they are not spinning, orbiting, or translating through at relitivistic velocities. Does this seem to match up with your understanding?

We might think of a bunch of rocks that happen to be moving together somewhere out in the distant reaches of intergalactic space perhaps, where any local field is likely to be mostly pretty flat, so that perturbations can be ignored. These rocks are not spinning like tops nor orbiting around each other nor are they rushing toward or away from each other with any great velocity. Pardon me for repeating the landscape in different words but I want to get as clear an image as possible. We might then gedank an apparatus in such a space, such as a massive and very dense torus, and consider what light does as it passes near the center of mass, which of course would be in the hole. We can aim a laser beam of light as close to or on either side of the hole as we like, and see where it comes out the other side. Is it deflected by the center of mass?

I think it certainly should be.

If we substitute a beam of relitivistic particles for the beam of laser light, we can likewise measure where they come out on the other side.

If I understand correctly, you are saying that in this gedank tank light will be deflected more than will the relitivistic particles? That makes some sense to me. The light has no momentum and so will not have any inertial reason to resist being bent. The particles, having momentum, will be bent less. The more massive the particle, the less it will bend. Is this what you are talking about? Or have I missed the point completely again?

Thanks for being here, Garth. I am enjoying this conversation, and learining about the Jordan conformal frame.

nc

 

[Garth]

I'm not sure about your gedanken set up, however, there are one or two other things I would like to comment on.

First light does have momentum, but not rest mass, because light travels very quickly the deflection is very small compared to the deflection of a solid body such as a space craft. If we are talking about gravitational deflection then rather than talking about light (paths) being bent it is better to think that it is the space-time itself, in which their null-geodesics (world-lines) as embedded, that is curved by the presence of mass and energy.

The hypothesis of SCC, (in its Jordan frame), is that, whereas light travels along these (null) geodesic paths, non-relativistic matter is perturbed from them by the scalar field force. The result being that light 'falls' more quickly (at 3/2 the acceleration) than matter. In my post #34 I explained that because the measurement of the deflection of light measures two effects, one of which in SCC increases by a factor 3/2 whereas the other decreases by 1/2, the net result is the same as in GR.

Garth