How gravity works

[Farsight]

I have edited this opening post and deleted several follow up posts since this is simply republishing a lot of material that has already been published in multiple places on the WWW. This is a breach of Rule 4 (see:http://www.internationalskeptics.com/forums/showthread.php?postid=5669795#post5669795).

Sites where this has previously been published include: http://www.bautforum.com/against-mainstream/96659-einsteins-gravity.html#post1623158 and http://www.physforum.com/index.php?showtopic=13122

Replying to this modbox in thread will be off topic  Posted By: Darat

 

[paiute]

When telling a story, it is always good to have a point.

Point.

Get to it.

 

[Kwalish Kid]

People tend to see the word velocity in the translations without seeing the context and without noticing that he’s repeatedly referring to “the principle”.

Just like you ignore that he wrote "the principle"? It is obvious that he is referring to principle 2 of "On the Electrodynamics of Moving Bodies". That principle is based on a simple definition of intervals that uses a synchronization of clocks that GR does not fully support. If one works through the contents of the theory rather than stick to the introructory sections and the popular science works, that this is Einstein's meaning becomes obvious.

If you want to learn what Einstein meant, learn the theory, don't try to merely do a literary analysis on the parts without mathematics.

 

[Farsight]

OK, that's the gravity thread as requested. Over to you.

 

[Kwalish Kid]

People often react badly this, like creationists confronted with strata and fossils and carbon dating.

People also react badly when someone makes bold claims and insults about their field while obviously not knowling the details.

Einstein talking about the variable speed of light does not fit with the relativity they've been taught. They cannot conceive that the “modern interpretation” is different to Einstein's relativity, as described by Peter M Brown’s Einstein’s Gravitational Field.

Why would anyone want to trust this citation?

The paper is in the general physics section, a bad sign given that if it was worthwhile it would be in a specific section. There is no evidence it was ever published in a peer reviewed journal.

The author seems to have no institutional affiliation or publications.

The paper is cited by one paper, a paper that is itself cited by one paper, a paper written by that author!

This is a crackpot paper. Why can't you find a real scientist who supports your wild claims?

People swear on oath that Einstein told us about curved spacetime, but when you read The Foundation of the General Theory of Relativity it's just not there. Yes, he talks about geometry and curvature and space-time, but he's giving the equations of motion, through space.

If one actually learns the mathematics of differential geometry, what Einstein is discussing is clear. Poor literary analysis is no substitute for working through the physics. Heck, even historical analysis on Reimann and Gauss would reveal that Einstein was discussing curved geometry.

He doesn't talk about "motion through spacetime" like people do these days.

Nobody does this.

. See http://www.rebelscience.org/Crackpots/notorious.htm where you can read this:

This is the tu quoque fallacy, Farsight; just because some people had some crazy ideas doesn't mean that we have to accept their crazy ideas or yours.

There's other things that people don’t know. Such as how Einstein was still derided by many theoreticians even in 1923.

This is not relevant to the strength of general relativty or to the rejection of you by others.

Nor do most people know that in 1949 Einstein and Godel worked out that time is cofounded with motion through space, not with space.

People do not know this because it is not true.

But perhaps the signal most important thing most people don't know, is that whilst aether is a taboo word which is sneered at by people who consider themselves to be mainstream, Einstein's gave his Leyden address in 1920. And the title is Ether and the theory of relativity. There's Einstein, talking about space and calling it an aether:

As many people, including the author of your citation, point out, it is incorrect to say that Einstein is offering an ether theory. You merely cherry-pick a specific quotation while ignoring all the things that Einstein says about the difference between the ether he discussed and traditional ether theories. Also, since Einstein later rejected Mach's approach, do you think that he also reject the ether theory?

And what’s really surprising is how similar it is to the way Newton described it in Opticks:

In the alchemy section of the Opticks. Now it may be that some parts of alchemy bear a resemblance to some of the conclusions of physics, but we do not think that alchemical theories were good science, even if they happen to produce the occaisional statement that looks like the truth.

The language is different, but the underlying concept is the same.

No, it isn't. Would you like to explain how Newton's alchemy relates to contemporary particle physics using actual science rather than literary theory?

It doesn't matter that it comes from Einstein and Newton and is supported by experimental evidence, they refuse to believe it. They are outraged.

So far you have yet to bring up a single experiment.

 

[Hellbound]

Actually, if you read the book on relativity that Einstein wrote himself (called, oddly enough, "Relativity"), he specifically states that the speed of light in vacuum is a constant, and does not change. No ifs, ands, or buts. People claiming otherwise have not done their research and are, quite frankly, either dishonest or incompetant (unless you can thing of some third alternative for someone stating a "fact" that even a minor amount of research will disprove).

Not to mention that things such as time dilation has been tested, and General relativity has been shown to give accurate results. For example, GPS satellites have to correct for the dilation effects of differing gravity to give correct answers, IAW GR.

And just another addition, the definition of a second in terms of light motion came about only after it had been shown that the speed of light was constant.

Not to mention you destroy your own arguments. You claim Eisntein was not talking about velocity, but speed. Yet you then go on to talk about light curving (which is a change in velocity, no matter the speed value).

So, do you have an argument where you don't contradict yourself?

 

[Farsight]

Actually, if you read the book on relativity that Einstein wrote himself (called, oddly enough, "Relativity"), he specifically states that the speed of light in vacuum is a constant, and does not change. No ifs, ands, or buts. People claiming otherwise have not done their research and are, quite frankly, either dishonest or incompetant (unless you can thing of some third alternative for someone stating a "fact" that even a minor amount of research will disprove).

Give the link, and give the quote. Like I did. Then I'll show you the ifs and buts.

Not to mention that things such as time dilation has been tested, and General relativity has been shown to give accurate results. For example, GPS satellites have to correct for the dilation effects of differing gravity to give correct answers, IAW GR.

Of course time dilation has been tested. I even talked about GPS.

And just another addition, the definition of a second in terms of light motion came about only after it had been shown that the speed of light was constant.

And before that it was defined on the motion of the earth. It always comes down to motion.

Not to mention you destroy your own arguments. You claim Eisntein was not talking about velocity, but speed. Yet you then go on to talk about light curving (which is a change in velocity, no matter the speed value).

No I don't. He said a curvature of rays of light can only take place when the speed of light varies with the locality. That's why he was referring to the postulate of the constant speed of light. If you try to apply the vector-quantity meaning of velocity the statement is reduced to a nonsensical tautology: light curves because it curves.

 

[Kwalish Kid]

You probably think of gravity as “curved spacetime”, but that's the effect, not the cause. Curved spacetime is just curvilinear motion, and to see the cause you have to take a derivative of that curved spacetime. What you get is a gradient. It’s a g_μν gradient, essentially a gradient in the properties of space. And this gradient in space is caused in turn by the central energy locked up in the matter of the planet or star that “conditions” the surrounding space. It’s all to do with stress-energy and pressure, and the best way to conceptualize it is to start with an old favourite.

Can you run through an example with numbers and compare this to the standard Reimannian way of doing GR?

People don't quite understand these terms because they don't understand the electromagnetic field. They forget about the dualism of Jefimenko's equations, and about Minkowski's wrench, which is two pages from the end of Space and Time:

"Then in the description of the field produced by the electron we see that the separation of the field into electric and magnetic force is a relative one with regard to the underlying time axis; the most perspicuous way of describing the two forces together is on a certain analogy with the wrench in mechanics, though the analogy is not complete".

This is a quotation that you have refused to explain in any detail. What is the analogy that Minkowski is making? Does the mathematical theory that Minkowski is doing have anything to do with Jefimenko's equations? Does the mathematical theory that Minkowski is discussing have anything to do with stress gradients in space?

A moving electric field doesn't generate a magnetic field, it is a magnetic field, because Minkowski's wrench is referring to a screw mechanism.

Why should we not take Minkowski as saying that in SR, the components of electromagnetism break down into two fields based on a choice in a way analogous to how we can represent a wrench (a force transmitted to a solid object at a single point) as a combination of forces based on choice of force vectors? You need to defend your literary analysis here, even if you cannot follow Minkowski's mathematics.

Hence when a photon passes a massive body, it's travelling through inhomogeneous vacuum where there's a gradient in c across the photon wave-front. Hence it veers towards the body a little.

I note that this is a citation to an obscure physics journal promoting a speculative idea that has only been tested in one very limited application. Are there any other references supporting this speculative idea or verifying that it works for other applications of GR?

Let's ask an expert, somebody who was right on the money:

“That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it”.

Now what does Newton say right after that quotation? And how does Newton develop his theory despite saying that? This is the problem with cherry-picking quotations: a quick read dispels the illusion.

That's a no from Sir Isaac Newton, and he should know.

Why should he know? Do you trust his alchemical theory to give us the truth?

Let’s take a look at an electron to see why things fall down. It has angular momentum aka spin and a magnetic dipole moment, and this evidence along with electron-positron annihilation tells us its something like a self-trapped 511keV photon going round and round in circles.

Can you show, using a proper mathematic description of the photon, that a photon can become self-trapped and that it has the proper spin? Before you try to weasel out of things and say that mathematics do not matter, let me point out that spin is a mathematical quantity, so you need mathematical evidence to use it.

And note that it’s energy that causes gravity, not matter. See The Foundation of the General Theory of Relativity. On page 185 Einstein says the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". A gravitational field is a region of space that contains extra energy and in itself causes gravity, hence an integration approach is required, as per page 201. But we don't consider a gravitational field to be dark matter. We don’t go looking for WIMPs. Yes, space is "dark", and the mass of a system is a measure of its energy content, so if you defined the space around a planet as a system, it has a mass of sorts. But it isn’t matter. It’s just space.

Can you do a calsulation with an actual galaxy rotation curve to demonstrate that it is this gravitational energy that is causing the change in rotation curves. Can you address someone like Bekenstein that demonstrates that a deviation from GR is required to account for these curves?

What did Einstein say about space? Neither homogeneous nor isotropic.

Now you are simply not telling the truth.

What does the FLRW metric say?

”The FLRW metric starts with the assumption of homogeneity and isotropy of space.”

But the FLRW model (the metric is simply RW) is not the only source of evidence for dark matter. It is not involved in galaxy rotation curves.

And what about Einstein's cosmological models, models that are all FLRW models? Was Einstein so inconsistent? Or can you show how his models were not FLRW model?

The universe expands, but the space within the galaxies doesn’t, because galaxies are gravitationally bound. So each and every galaxy is surrounded by a halo of inhomogeneous space. That’s a dark-energy density gradient, and a g_μν gradient. It’s a gravitational field without any matter on the end of it.

So, please, show us the calculation with any galaxy you would like.

 

[Farsight]

Professor Yaffle: Sorry about the image hotlinks to sites that don't expressly permit them. I guess I didn't read the forum rules properly. I'll see if there's some wiki commons images that I can use as replacements.

 

[sol invictus]

That wall of text starts off with the issue of whether the speed of light is constant in GR. So, for any interested lurkers, I'll summarize what's actually true about that.

The theory of general relativity is based on a few fundamental principles. The most important is called the principle of equivalence, which states that in any sufficiently small region, the laws of physics in a freely-falling reference frame are simply those of special relativity (i.e. no gravity). What that means is that if you are inside a sealed lab that's falling through some gravity field, you won't be able to detect that field unless your lab is big enough that the field varies significantly inside the lab (if it does there will be so-called "tidal" forces you can detect, forces like the ones that cause the tides on earth).

Now, as everyone knows, one of the laws of physics according to special relativity is that the speed (and velocity) of light in vacuum is constant. Therefore, according to general relativity, the speed of light measured in any sufficiently small vacuum region is constant.

However: we're not always restricted to small laboratories. We can measure the speed of light over long distances, over distances where the gravity field varies a lot. What then?

The answer is a little bit subtle, because "speed" is no longer uniquely defined (hence the quotes). To measure speed you need to measure a distance and a time, then take the ratio. But it turns out that neither distance nor time is uniquely defined over such long distances, and depending on your definition you could find either that the speed of light is constant or that it isn't.

Just to give one concrete example where the "speed" of light would vary: if you define distance using the area of a sphere (e.g. the distance through the sphere along a diameter is the square root of its surface area/pi), and time by ordinary clocks positioned on the surface of the sphere, then you will find that the speed of light varies depending on how much mass there is inside the sphere. The extreme example is when there's a black hole inside, in which case the speed of light defined that way goes to zero (because the crossing time goes to infinity - the light falls into the hole and never comes out).

 

[uruk]

I may be stating the obvious here but it is a well known fact that the speed of light varies as it passes through transparent media. Look up Jean Foucault, Snell's law, Cherenkov radiation. Not to mention red/blue shift phenomena.

We coudn't send data down optical fibers if the speed light doesn't vary in a transparent media.

Here is an article by a professor from the University of California concerning the consistancy of the speed of light.

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html

What I get from this is that the variances of the speed of light in a vacuum could have something to do with the methods of measurement, the question of the mass of a photon, and the nature of our definitions of space, time, velocity and how we measure them.

Interesting read either way.

 

[Hellbound]

You're missing another point, as well, which I'll type will finding the relevent quotes for you.

Why, if Einstein claimed the speed of light changed, do none of his equations and none of the mathematics lead to changes in the speed of light? Why is it always a constant?

In fact, if you go through the book, the entirety of Relativity was built on the idea that the speed of light had to be constant, or physical laws would change besed on your movement rate and other factors. This is evident throughout the entire book, as Einstein uses this to build his theory, and take the reader through the steps. It's hard to pick out a single statement, but his meaning is clear by reading.

You can download a PDF copy of the book at http://www.relativitybook.com/resources/relativity_pdf.html

Chapter 7 is probably a better area to look at. The last paragraph:

At this juncture the theory of relativity entered the arena. As a result of an analysis of the physical conceptions of time and space, it became evident that​

​

​

​

in reality there is not the least incompatibility between the principle of relativity and the law of propagation of light, and that
by systematically holding fast to both these laws a logically rigid theory could be arrived at. This theory has been called the special theory of relativity to distinguish it from the extended theory, with which we shall deal later. In the following pages we shall present the fundamental​

ideas of the special theory of relativity.

Pay close attention to the red italicized statement. The earlier discussion in this chapter is perfectly clear about the law of propogation of light: the speed of light is constant in vacuum.

For Gneeral Relativity, let's try Chapter 22 (starting bottom of page 42 in the PDF linked above), which is where your quote comes from, but we'll put it into context here:

In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already

frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity: its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (​

​

​

​

e.g. of light).
Since it has often been contended by opponents of the theory of relativity that the special theory of relativity is overthrown by the general theory of relativity, it is perhaps advisable to make the facts of the case clearer by means of an appropriate comparison.

Before the development of electrodynamics the laws of electrostatics were looked upon as the laws of electricity. At the present time we know that electric fields can be derived correctly from electrostatic connsiderations only for the case, which is never strictly realised, in which
the electrical masses are quite at rest relatively to each other, and to the co-ordinate system. Should we be justified in saying that for this reason electrostatics is overthrown by the fieldequations of Maxwell in electrodynamics? Not in the least.
​

Now, if we assume he means speed, as you do, then the staement is obviously false. A curvature can occur without a change in speed, but is by definition a change in velocity. Not to mention he specifically states that Maxwell's equations hold true, and it is these equations that "fix" the velocity of light as a constant value.​

 

[Hellbound]

An addendum to my earlier post:

I will defer to sol invictus on this, as he's like a professional and stuff. Me, I'm just an interested layman

ETA: And for Uruk, yes, this is involving the speed of light in vacuum. Typically the "in vacuum" part is assumed to be understood..so for any others out there who might be confused, that's the point of contention here.

 

[Farsight]

Why, if Einstein claimed the speed of light changed, do none of his equations and none of the mathematics lead to changes in the speed of light? Why is it always a constant?

Because we define time using the motion of light. Like I said:

“Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom...”

You sit there counting microwave peaks going by, and when you get to 9,192,631,770 you tick off a second. So if the light moves slower, the second is bigger. Then you use it to measure the speed of light!

In fact, if you go through the book, the entirety of Relativity was built on the idea that the speed of light had to be constant, or physical laws would change besed on your movement rate and other factors...

That's not quite right. It's the locally measured speed of light that's constant.

For General Relativity, let's try Chapter 22 (starting bottom of page 42 in the PDF linked above), which is where your quote comes from, but we'll put it into context here... Now, if we assume he means speed, as you do, then the statement is obviously false. A curvature can occur without a change in speed, but is by definition a change in velocity. Not to mention he specifically states that Maxwell's equations hold true, and it is these equations that "fix" the velocity of light as a constant value.

There's nothing there that changes the sense of what Einstein said or alters the context. He said a curvature of rays of light can only take place when die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert. It's in black and white.

 

[Hellbound]

Farsight:

So, you claim that Einstein stated light cannot curve unless it's speed changes? Let's be clear on this, because by your interpretation that is the statement.

 

[Vorpal]

WHAT EINSTEIN SAID

People say the speed of light is constant, and Einstein said it. But that’s... not... entirely... true, Mr President. Yes, Einstein started with this as a postulate in 1905, but in 1911 he wrote On the Influence of Gravitation on the Propagation of Light, where we can see his ideas evolving. He gives the expression c = c₀ (1 + Φ/c²), which is c varying with gravitational potential.

What you have here is a confusion about who is doing the measurement and how. When a (modern) relativist says a speed of light is constant, what is meant is that a local measurement will always yield c. And it's quite obvious what going on: the factor (1 + Φ/c²) is the gravitational time dilation (in the Newtonian approximation, to first order). So if a local observer measures the light ray as moving with speed c, then:
-- c = dx/[dt_loc] = dx/[dt_far(1 + Φ/c²)],
so the far observer will be under the impression that the "speed of light" is dx/dt_far = c(1 + Φ/c²). Exactly as Einstein said.

___Addendum:
If you care for the details, here's the Newtonian approximation from MTW (the first in a sequence of approximations to higher orders):
[1] ds² = -(1+2Φ/c²)(cdt)² + (dx²+dy²+dz²)
A light-like geodesic has ds = 0, so that:
[2] (dx²+dy²+dz²)/(dt²) = c²(1+2Φ/c²).
Identifying the right-hand term as v² and using the Taylor series expansion sqrt(1+x) = 1 + x/2 + O(x²), we have a speed of light:
[3] |v| = c(1 + Φ/c²) + (higher order terms).
Same result.

 

[Farsight]

Farsight: So, you claim that Einstein stated light cannot curve unless it's speed changes? Let's be clear on this, because by your interpretation that is the statement.

Yes. It's passing through a region where there's a gradient in g_μν which causes the curvilinear motion. Think of it in these terms:

Imagine a swimming pool. Every morning you swim from one end to the other in a straight line. In the dead of night I truck in a load of gelatine powder and tip it all down the left hand side. This starts diffusing across the breadth of the pool, imparting a viscosity gradient from left to right. The next morning when you go for your swim, something's not right, and you find that you're veering to the left. If you could see your wake, you'd notice it was curved. That's your curved spacetime, because the pool is the space round a planet, the viscosity gradient is Einstein's non-constant gμν, and you're a photon. As to how the gradient attracts matter, consider a single electron. We can make an electron along with a positron from light, via pair production. Since the electron also has spin, think of it as light trapped in a circular path. So if you're swimming round and round in circles, whenever you're swimming up or down the pool you're veering left. Hence you find yourself working over to the left. That's why things fall down.

Vorpal: yes, the locally measured speed of light appears to be unchanged. It’s like you’ve plunged a mechanical clock into an oil-bath. The local environment is different, the viscosity makes the cogs and gears move slower. Only you’re like a clockwork man, and you’ve jumped in after it. So you don’t notice it locally.

 

[Pixie of key]

How pressure works?

It is better to ask how Pressure works!

There is no drawing force at all! No gravity at all!

We allready know how pushing force / power works, born and move!

So, why we dont try to make theory with only pushing force.

Same relativity expanding / exploding quarks and then you can explain everything with Pressure of changing!

Energyconcentration exploding in space who dont expanding at all!


http://www.youtube.com/results?search_query=Etimespace&search_type=&aq=f


No gravity.

http://www.youtube.com/watch?v=eFPYHdllHa4


I found one reason more. Before i had five reason and now 6 reason for "gravity" with out drawing force!


Lets think about all this particle who moving and coming to here. Moving direction go centre of earth. When this particle is moving half way here, they are two times closer eachother and after half way to here, this particle are again two times closer etc.

This is good to remember when you are making some theory, you know!

.

 

[Dave Rogers]

I think the problem is that you're neglecting time dilation. It seems intuitively obvious to me that a gravitational potential gradient will produce a varying time dilation, and that a wavefront propagating perpendicularly to this gradient will therefore describe a curved course despite its local velocity being invariant. Although one side of the wavefront travels at the same local velocity as the other, the distance travelled differs between them because the time differences are not the same. Therefore, light can describe a curved path with no requirement for velocity variance.

Dave

 

[sol invictus]

Farsight:

So, you claim that Einstein stated light cannot curve unless it's speed changes? Let's be clear on this, because by your interpretation that is the statement.

Yes.

That's obviously not true, and it's trivial to falsify with a counterexample. There are closed orbits for light around black holes. That is, a photon or pulse of light can orbit a black hole in a circle at a certain fixed radius. The speed of light by any definition cannot change on that orbit because of spherical symmetry (the black hole is a sphere, so its potential energy depends only on radial distance from the center of the sphere, but the orbit I'm talking about is at constant radius).

More generally it's just the wrong way to think about things. In general relativity light always follows geodesics, which are the closest analogue to straight lines that exist in a curved space. So light doesn't really curve; it just always follows the shortest possible path between any two points on its trajectory.