A few comments on Gravity

Yeah that's who you think it is. Quarkhead must have had some interaction with pmb. LOL.

 

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Quarkhead: See what I said above, and note this section of Einstein's Leyden Address:

"This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that "empty space" in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gmn), has, I think, finally disposed of the view that space is physically empty."

Also see this paper http://cpl.iphy.ac.cn/EN/Y2008/V25/I5/1571 which relates curved spacetime to inhomogeneous space. The important thing to notice is that spacetime isn't the same thing as space. Light moves through space, and we draw worldlines in spacetime to depict this motion through space over time. But spacetime depicts all times, it's the "block universe". There's no motion through spacetime because you'd need meta-time for that. So light doesn't curve because it moves through curved spacetime. Instead it curves because it moves through inhomogeneous space. Einstein actually said light curves because the speed of light varies with position, see Baez:

 

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There is no meaningful difference between what we call space and what we call spacetime.

Space is the 3D Universe in which events take place. In the Einstein view, space and time are united inextricably in the 4D "spacetime continuum".

 

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Either Farsight is truly deranged or even he knows that this isn't true.

Farsight, you and I and pretty much everyone else know that you can't do Einstein's physics, so we all know that you are merely presenting your textual analysis of a few things Einstein said or wrote rather than anything to do with the science he practiced.

 

Yes, see this obscure paper from an obscure journal that Farsight hasn't read that only tries to recreate one limited result.

Farsight, if you can show us how to calculate the fall of a pencil with your inhomogeneous space, then do it. If you can't (as we all know you can't), then give up telling people that your fantasy metaphysics is physics.

 

That paper was written by a very confused person. It's kinda funny in this case since the two citations [in blogs] are both cited by Farsight. In one blog he cites the paper and exclaims "It isn't peer reviewed but as far as I can tell it's right." What an endorsement. The citations are in the comments section for readers. Farsight probably formulated half his bullshit nonsense from a couple of papers Peter Brown has in the archive.

 

Paddoboy, that was an excellent quote for purposes of argument you probably did not intend.

Farsight, pay special attention to that last sentence.., "The idea of motion may not be applied to it.", and since you expect that everything Einstein said must be a true and accurate account of GR, tell me how it can be that the GP-B experiment measured a predicted motion, of that very thing that the idea of motion may not be applied to.

Even Einstein's understanding of GR changed over time, just as it has continued to change....., even after his death. Especially, as its implications were pointed out, scrutinized and debated by his peers.
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Context is the most important aspect when reading any historical account.., of anything. In a class on the history of religion some near fifty years back now, the class instructor made a special point of the fact that much of the information we were studying, and discussing in that class had originated during a time in our history when the general population was mythopoetic.., illiterate. They passed on knowledge in stories and parables, which when read as literal accounts today, did not communicate the same information intented at the time from which they originated.

I keep emphasizing context to you, because you continue to make a similar mistake. Instead of reading a historical lecture with any understanding of the time it was presented and the audience it was intended for, you wind up misunderstanding the original substance and intent.

 

Yes there is. Space is space, spacetime is a mathematical abstraction that models space at all times, wherein motion through space is depicted as a worldline in spacetime. Space is not the same as spacetime. Hence on the Baez website you can read this:

"Similarly, in general relativity gravity is not really a 'force', but just a manifestation of the curvature of spacetime. Note: not the curvature of space, but of spacetime. The distinction is crucial."

Gravity-probe B detected geodetic drift and frame dragging, see for example this website. Frame dragging is where space is effectively twisted, see NASA. It isn't moving, but motion through it is altered. This is how it is for a straightforward gravitational field. Space isn't moving, but motion through it is altered.

Do not be persuaded to dismiss what Einstein said by GR has moved on flummery. And do note that geodetic drift was predicted by Willem de Sitter in 1916, whilst frame dragging was predicted by Lense and Thirring in 1918.

Your religious example is not relevant to Einstein's scientific papers, and nor is it cause to dismiss what Newton and Einstein said and produce popscience articles that claim they said something they didn't.

I'm not making any mistake or misunderstanding the original substance and intent. What Newton said is clear, ditto for Einstein.

 

Of course the distinction is crucial. It is crucial because one has to learn how to do the mathematics properly.

But in GR one can decompose spacetime into space and time into different ways. So some of the curvature of spacetime can be represented as purely spatial curvature, depending on the particular spacetime region. You, of course, hold on to a fantasy that space "really exists" as a Euclidean entity. The evidence does not lie with your fantasy.

This passage is a great example of how you cherry-pick without concern for the actual science. You just said that spacetime curves, and space never does, but now you are relying on an article that says that space curves. Then you tell us a falsehood about your citation, claiming that it does not say that space curves.

At best, this is your interpretation. At worst (in reality), it is unsupported fantasy that you spam everywhere.

Yes, please do not believe Farsight's interpretation and actually read through Einstein's science. This is more than Farsight has ever done.

Farsight, you are doing textual analysis. In order to do that properly (which you do not), one must take into account the context in which texts were created. You are the one citing pop science articles again and again (you love wikipedia) and you are the one refusing to ever produce a single example of how your fantasy hyoptheses work.

 

I've said repeatedly on previous occasions that a gravitational field is inhomogeneous space rather than curved space, referring to Inhomogeneous Vacuum: An Alternative Interpretation of Curved Spacetime, as well as Einstein's Leyden Address where he said this:

"This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that "empty space" in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions..."

I've also referred to Percy Hammond, saying electromagnetism relates to curved space. See The role of the potentials in electromagnetism and note this:

"We conclude that the field describes the curvature that characterizes the electromagnetic interaction."

Electromagnetism and gravitomagnetism are of course somewhat related.

 

Ok, so show us how to describe the fall of a simple object using inhomogeneous space. If you can't do this, then your claims are based on nothing but your personal dogma and bad textual analysis.

 

I did that in this thread. It's very simple. Armed with knowledge of pair production and electron diffraction and spin and magnetic moment and the wave nature of matter, you think of the electron as a wave going round and round, then you simplify it to a wave going round a square path, then you draw the horizontals "bending gradually in curve lines", like this:

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Note that only the horizontals curve downwards. See Ned Wright's deflection and delay of light, the Newtonian deflection of matter is half the GR deflection of light.

 

brucep is right that I do this too often, and I plan to stop, right after this last post.

Newton and Einstein: Geometry is all they had to work with to explain the effects of gravity, and given that fact, they did quite well. They describe the way it behaves from the point of view of something composed of "solid" matter, which is, by the way, MOSTLY space and just a tiny bit of energy, relatively speaking, added to hold it all together.

You all can do better than this. You not only know that there is vacuum energy, but the particle that imparts inertia to mass has been discovered, is part of that vacuum energy and confirmed to a higher degree of certainty than any particles known to quantum theory previously were. Do you have any idea how much Newton or Einstein would have appreciated knowing even a fraction of what I just reminded you?

Now, don't you all think it's time someone tossed the fine geometry lessons and replaced it with something about which we previously had no knowledge? Space not only can't have geometry; it doesn't even exist on its own, any more than matter can exist without energy. This is fundamentally why space behaves so strangely when things move. Only energy and time are fundamental, and neither of those actually need "space" to exist.

 

That is a sad, sad reply.

Can you not try to give us a physics example? With numbers like in a text book? It's bad enough that you are showing us dumb drawings like you were in short pants, but really, how deluded does one have to be to thing that you are showing us anything?

Please show us how to use inhomogeneous space to actually calculate a trajectory for a simple body falling.

If you hadn't been spending over the last decade saying that all physicists had been making basic mathematical errors, for example in calculating galaxy rotation curves, then I might give you a pass. But since you insult others about their physics ability and you claim to be an expert, let's see your expertise at work.

On the other hand, I am willing to accept an apology from you for your behavior. If you admit that you can't actually do the physics and that you have been doing textual analysis, then we can forgive you and move on.

 

You asked me to describe the fall of a simple object using inhomogeneous space. That's what I've done. An explanation of how gravity works is a physics example. Calculating trajectories doesn't add anything to that. We already know how to calculate trajectories. Your reply is sad. I gave you what you asked for, and now you're attempting to move the goalposts.

 

In a "Physics and Math" forum.

You have given us something that we might expect from a 4-year old. That is the level of analysis you have given us so far.

Well, we're all pretty sure here that you can't calculate a trajectory.

So far, it seems pretty clear that you can't use inhomogeneous space in calculating a trajectory. So that indicates that it plays no role in physics, just like you play no role in physics.

This is not the first time that I or others have asked you for a specific example with numbers. I am glad that people can see your bald-faced dishonesty here along with your absolute incompetence.

 

Look, Faright,differential geometry is a hard, hard subject, so there is no shame attached to getting some of it wrong some of the time. What IS a shame is coming out, in an authoritative manner, with stuff like this

which to quote Wolfgang Pauli "isn't even wrong"

There is and never can be, neither in semi-Riemann or even Euclidean geometry, such a thing as "curvature in the metric"

It has no meaning, in spite of your arrogantly didactic tone.

I would offer to show you how to derive the metric tensor (it's actually a tensor field) but I fear you would not understand and dismiss my efforts as "mathematical woo" or something equally compementary

 

It's true. The metric is not space, it's related to "what you measure". That might be unfamiliar to you, but look at Wikipedia where you can see this depiction of the metric tensor:

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Now look again at Einstein's Leyden Address and pay attention to this:

"This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that "empty space" in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gmn), has, I think, finally disposed of the view that space is physically empty."

We describe the state of space using the metric tensor, and we talk of curved spacetime. But as per the Baez article, space isn't curved. Instead there's a curvature in the inhomogeneity of space.

The metric IS to do with what you measure.

There's a curvature in your plot of measurements. You plot light-clock rates in an equatorial slice through the Earth and surrounding space, and what you end up with looks like this:

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That's a depiction of Newtonian gravitational potential, but it's similar to the depictions of curved spacetime. The force of gravity relates to the slope, which is the first derivative of potential. The curvature you can see at some location relates to the tidal force or second derivative of potential which relates to Riemann curvature. It's the defining feature of a real gravitational field because without it your plot can't get off the flat and level in the middle.

Of course it has meaning. Light curves, and it doesn't do it because spacetime is curved. It does it because the speed of light varies with position. That's what Einstein said. The plot above is showing you light-clock rates, it's a plot of the "coordinate" speed of light.

It's a discussion forum, contribute whatever you think fit. But do try to make a useful contribution instead of merely dismissing something new to you. I'm not just making this stuff up. I refer to Newton and Einstein and others, some contemporary. It isn't my fault if some people have only learned some popscience version of general relativity and have never studied the original material.

 

I would have been tempted to respond to most what you believe... But while I slept others have beat me to it. Still the following and your comment seems to me to emphasize exactly my point.

How you took the above as a religious example, demonstrates two things; first you cherry picked a few words as categorizing the whole of the comment and then you quit thinking. Though the class was one segment of a history class, dealing with the history of religion, the point was about how the context associated with the time and audience affects the original intent of anything you read. Something you continue to miss, as I was pointing out into the following.

Which you again prove in the following.

While interpretaions and translations of Newton's writings are generally understandable in today's context, most of what you probably never read in Newton's own hand is not as clear, sometimes not even coherent, without making allowance for when it was written. You almost have to have the right secret decoder ring to make sense of some of what he writes. I tried to read through an original hand written copy of his Principia. Somewhere around halfway through, I finally decided it would be more useful to read a translation by someone with more patience and historical understanding than I.

I know, I know.., you have been repeating this garbage to yourself for so long you can see nothing else... A sad state of affairs!

At least when I go off the reservation, which I do, I know the difference between my speculations and the bits and pieces of a (the) more mainstream view, from where I started. You don't seem to recognize when you have stepped off the edge of reality, even as you fall into the abyss.

 

I haven't. Newton said what he said, so did Einstein. And when Newton said light curves because of a density gradient, it's recognisable as something akin to Einstein's explanation wherein light curves because the speed of light varies with position. And to Ned Wright's explanation wherein in a very real sense, the delay experienced by light passing a massive object is responsible for the deflection of the light:

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You're dismissing all these people in favour of some popscience you've picked up. Don't do it. I'm not some my-theory guy, I'm the guy who has read what Newton and Einstein etc said. You should do the same.