Einstein's GR passes extreme test

messagenews:487d22d3$0$25503$ snipped-for-privacy@news.coretel.net...

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Hi Martin and fella's, here's a sample of the parameter complexities I was referring to,

Ok, you disagree with the theory.

I don't follow your thinking here. If space/time is curved by gravity, how does that show that gravity is not a force?

Yes, but how does that show that gravity is not a force?

Ok, but I don't yet understand what you have in mind. It sounds like momemtum and works fine until you introduce gravity (whether you consider it a force or not) or some other force into the mix. Are you thinking of momentium?

Whether or not the curvature of spacetime is involved, our ability to measure has nothing to do with whether or not a force exists. In your mind, does stipulating that spacetime can be curved by mass logically preclude stipulating that mass exerts an attraction on mass?

And the thing that initiated the acceleration toward the pavement was ? The force upward that keeps the remains on the surface counteracts and equal and opposite force. You call it weight, which classical teaching says is the result of gravity pulling the mass toward the center of the mass of the planet. You have an idea that says that gravity does not do that pulling. Ok - what is the force that counteracts the upward force, if not gravity?

My problem is trying to understand what you have in mind. Are you saying that every observable effect of gravity is due to curvature of spacetime?

Ed

See my comments below Bob

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"ehsjr" wrote in message news:nFVfk.33$0p1.24@trndny08...

Newton's gravitational formula is:

F = G*m1*m2 / d^2

where F is the net force between two massive objects G is the gravitational constant m1 and m2 are the masses of the two objects involved d is the distance between the two objects

If either M1 or M2 is equal to zero then F is equal to zero. If we accept that fact that photons have no mass then they aren't affected by a gravitational force. However, they are. You need to read about gravitational lensing and what an enormous impact its confirmation had on the scientific community.

See above. Also, beyond that, you cannot measure any net external forces acting on a freefalling object -- regardless of whether it's way out in deep space or hurtling toward a planet's surface.

You're missing the major point. The thing falling toward the pavement is NOT undergoing acceleration because there are NO net external forces acting on it. Certainly, there is an equal and opposite force between the "thing" and the pavement, but there is still a net force (upwards) on the thing once it has landed.

You (and the rest of us) need to not think of the Earth as the reference point for universal velocity and/or change in velocity. Read up on Special Relativity as a starting point. It's easier to grasp (imho) than General Relativity.

Just because an object is changing its velocity with respect to the surface of the Earth does not automatically imply that the object is undergoing acceleration.

Ed -- the best thing for you to do is to read some books on General Relativity. You should be able to get the basics without having to learn the math (unless you're already good at things like tensor calculus).

Here's a website that's a good starter, and an excerpt that should whet your appetite:

"Because gravity is not a force in GR..."

Bob

"ehsjr" wrote in message news:nFVfk.33$0p1.24@trndny08...

It must. Consider that gravity is the curvature of spacetime AND that it exerts a force ala Newtonian gravitation. Consider an object with mass travelling past another massive object. Then, there would be a force pulling the object in, and it would no longer follow its geodesic. Therefore, Newtonian gravity (gravity as a force) and General Relativity cannot be used simultaneously.

One might argue that they can be, if the constants are split in half, so the total path comes out correctly. But G.R. is fixed by the speed of light, and I don't think that can be done. Therefore, Einstein was right and Newton only formulated an apparent approximation of what's really going on.

It's still fine to use Newtonian gravitation, and classical mechanics instead of quantum mechanics, because they are approximations which can be derived from the overarching theories. As with using any approximation, do keep in mind their limitations.

Tim

If you are going to top post it is terminally dumb to include a signature separator.

Regards, Martin Brown

Yes. General Relativity which also works correctly in more extreme situations than we experience on Earth. Although it is a bit overkill for apples falling to the ground and periodic pendulums.

It is a bit like the old fictitious centrifugal force in a rotating frame. They are convenient for doing the simpler calculations, but eventually you have to understand all the properties of a rotating coordinate system to fully appreciate all the subtleties.

Gravity as a classical attractive force between objects has a nasty property that even Newton found somewhat abhorrent. That is action at a distance - if the force of gravity does not act instantaneously along the radius vector between the sun and the Earth then our orbit would be instable. Essentially the "force" has to be instantaneous or angular momentum is not conserved. And invariants of motion are very precious. GR still has a logical equivalent of this classical invariant.

Einsteins special relativity precludes faster than light transfer of information on causality grounds and so you end up with a new theory which is more complex to grasp but also more generally applicable. And where changes in the gravitational field have to propogate at the speed of light, but the established field in inherent in the structure of space time itself.

We invented a fictitious force to explain the way things move due to the distribution of masses. And it works well enough until you get really close to a rapidly spinning massive object. Even the sun manages to make Mercury's orbit precess due to relativistic frame dragging.

Yes. In essence a particle moving under the influence of other masses follows a path that is dictated by the shape of spacetime itself in the vicinity of those other masses. It gives the same results as classical gravity in the limiting cases but it extends the applicability right up to the event horzons of black holes.

That is exactly it. The problem with treating gravity as a fictitious force is that it has to work instantaneously over any distance. The Earth would see Newtonian gravitational force from the sun with a light travel time of about 9 minutes allowing for relativistic corrections. We know that this is wrong because angular momentum is conserved, our orbit is stable and we do not spiral into the sun.

Regards, Martin Brown

at:

I can't point you at the paper free access but their poster on the eclipse study itself is online at:

The original article is in Science magazine for July PPV

You might. I would be more worried about the interactions of their extremely strong magnetospheres at such close quarters, but they seem to have it under control. The fact that one eclispes the other and both are observable high precision clocks in mutual orbit does make things rather well constrained. The only real uncertainty is how much they are spinning with a component along our line of sight.

They have even used the evolution of the orbital parameters to map out the beam profile of the pulsar beam (on one of the others).

Hi Ken, once long ago I was a radio astronomer.

It is mentioned in the pulsar zoo page of this J0737-3039a,b. The discovery paper of B is online free access at:

Double pulsars are thought to be rare.

Regards, Martin Brown

at:

PPV

Yeah, even leaning optimistically, the scientific method requires an independent verification, that has so far eluded GP-b (frame dragging) and LIGO (g-waves). (more below)

Super, you certainly type knowledgeably, probably hit you up with some questions on that.

I have a few briefs on GR here,

It demo's how alternative solutions produce differing results.

Yes, my thinking is they are an older population of star and so would be more frequent near the core of the galaxy.

Regards Ken S. Tucker

GR is fully consistent with a model that treats gravity as being a "conventional" force. That is, the idea that *all* forces are due to momentum exchange of some particle is not at odds to a curved space model of gravitation.

This argument can not be true.

It is well known that the GR field equations can be derived by momentum exchange of gravitons (spin 2 particles). See for example, "Gravitation" by Misner, Thorne and Wheeler.

Ho..hummm again, it is well known that the eclipse of 1919 had such experimental uncertainties, that after the fact, showed that this particular observation did not confirm of refute GR at all. Of course, the bending effect of EM due to gravity has been adequately verified since then, but as for as the original experiment was concerned, it was completely meaningless.

It should noted that the curved space model of gravitation is just one particular model that has the Einstein field equations. The spin 2 graviton momentum exchange model is another equally valid model which also has the identical field equations. So whether you wish to believe in conventional (quantum) forces or curved space, appears to be simply a matter of taste.

Kevin Aylward snipped-for-privacy@kevinaylward.co.uk

Not at all.

This misses the point. As I indicate in another post in this thread, GR is entirely explainable by a momentum exchange force model, however, its not Newtonian. It requires quantum mechanics, not Newtonian mechanics, to explain how the spin 2 graviton can produce an attractive force, in much the same way as QED explains the attraction due to unlike charges by momentum exchange of photons.

Kevin Aylward snipped-for-privacy@kevinaylward.co.uk

Nice site Kevin, enjoyed the humor too. You should check out "sci.physics.foundations". Ken

Thanks.

Ok.

I would recommend checking out

Kevin Aylward snipped-for-privacy@kevinaylward.co.uk

out

Thanks, I'm on dial-up, and in canukistan that's bytes/hour :-). However, if you have an abbreviated edition (

Wierd - when I click on reply, all of your post, except the above, disappears from the reply window. No matter, I'll paste what I am replying to below between the lines of asterisks:

Ed -- the best thing for you to do is to read some books on General Relativity. You should be able to get the basics without having to learn the math (unless you're already good at things like tensor calculus).

Here's a website that's a good starter, and an excerpt that should whet your appetite:

"Because gravity is not a force in GR..."

Bob

Thanks! Now I see what you have in mind.

And thanks also to the others who replied.

Ed

GC == General Covariance.

The Article is an exposition of confusion on the part of the theoreticians to realize there is a distinct difference between the General PRINCIPLE of Relativity (GPoR) and the General THEORY of Relativity (GToR), although many seem to think those terms are interchangeable, they certainly are not, the logical progression is as follows,

GPoR + MATH => GToR

where the best commonly used MATH so far is the conventional Tensor Analysis designed for static n-dimensional geometry with the continuum assumption (differentiable) applied to a dynamic 4D spacetime, that uses quantized photons in measurement.

The definition of the GPoR is the relativity of "position", with the caveat that any point may be regarded as the universal center of the universe, at rest, independent of the effects of acceleration.

Concerning the PoE (Principle of Equivalence), using the above MATH, I find the best definition is the vanishing of the covariant derivative of the metric tensor,

g_uv;w = 0 (1)

Late Prof. Grueb (UofT), a geometrist, taught me that when I confidently entered that into my mathematical argument with him, and was corrected. He explained Eq.(1) is a tight condition imposed on the geometry. IOW's in all possible universes, Eq.(1) applies to the one we inhabit, so it is a fundamental assumption and condition imposed by physical experiment. Regards Ken S. Tucker

attractive force between objects. In fact if it were, it would not be able to have any effect on (massless) photons -- but it most certainly does (look up "gravitational lensing"). The ability of gravity to affect photons (electromagnetic radiation) was predicted by Einstein. When it was finally observed, Einstein instantly became a lot smarter than he was previously. It was huge.

If they had nonzero *rest mass* they would travel slower than C. They have mass, 100% of it "relativistic mass". Other particles also can have relativistic mass. For example, electrons gain mass when accelerated.

That is also true.

- Don Klipstein ( snipped-for-privacy@misty.com)

Hence the reason for a dynamic focus anode supply on a CRT tube with a large, curved face.

or a flat face, for that matter... moreso even.