the absurd implied density of moons kills gravity

[marengo]

No he didn't. He created an approximation of what it does--not what it is or how or why it exists.

It is absurd to expect anyone to know everything about the Universe. Newton made a great step forward.
It is also absurd to expect physicists to explain WHY things exist.

Yes I agree--you effectively said nothing factual and contradicted yourself in the same sentence.

You are a great one for being pedantic. Gravity EFFECTIVELY acts from the centre point of a massive sphere. That is the physics of it. Why dont you stick to physics rather than lexicography.

LOL ok How can anyone read your paper for a "more complete understanding" of gravity when you agree with me that gravity cannot be entirely understood!

So you equate more understanding with a complete understanding. In your dictionary MORE and COMPLETE have the same meaning???

In agreeing with me you just contradicted your own assertion that gravity acts as a "point source"..

I never said that. I said EFFECTIVELY acts as a point source. Would you like to borrow my spectacles?

[marengo]

Well, it does not work at cosmic scales, witness the need for the ad hoc addition of a supposition that the majority of matter in the universe is Dark (unseen, undetectable, non baryonic) Matter.
And there are problems with the solar system as a gravitational system too. The little fact that Newtonian calculations of a multi planet solar system tend toward unpredictability over time is often ignored by those who seem to prefer to regard the Solar System as a perpetual clock.
recommended reading:

Yes, Nick, I did say except for extreme cases.
Of course we must accept the modification of Relativity to Newtons law.
I do not , however accept General Relativity as a theory although I do accept some of its predictions. See my paper on Gravity.

[marengo]

The density doesn't enter into the calculation of the orbital characteristics of the Moon. But once the gravitational attraction is estimated, then we "think" we know the mass of the Moon. And we definitely know the radius, so we can calculate the volume. And just for the fun of it, we can find the density, as the mass/volume. The problem with that is that the density comes out lighter than water, when a rocky moon should be heavier than water. This means that one of our assumptions is false. Having been there, we're pretty sure of the distance, and the radius, and we're sure of the mass of the Earth. There are only two assumptions in there: 1) that gravity is the only force operative at the astronomical scale, and 2) that a rocky moon could be lighter than water. One of those assumptions is false.

How do you calculate the mass of the Moon? Your thoughts all depend upon that.

[marengo]

Yes. On Earth, we can experimentally isolate all of the forces, including gravity, inertia, and electric charge. We can see the 1:1 correspondence of gravity and inertia, hence the concept of mass as something that gives rise to both gravitational and inertial forces, though gravity varies with the distance between the bodies, while inertia is integral to the body itself, so that doesn't change. When we send rockets out into space, we can measure the distance from Earth, and the force of gravity diminishes as expected. So the Earth is a well-established benchmark.

That isn't to say that it's the only force, and there are anomalies, even here on Earth. I'm convinced that all of the anomalies are evidence of the electric force. But the force of gravity can be measured independent of the electric force here on Earth, so I'm not convinced that all gravity reduces to the electric force. Gravity is a force. It's just that it isn't the only force. And the problem in calculating orbits is that they're all predicated on the Earth's mass. Even the mass of the Sun was derived from the mass of the Earth, which we couldn't calculate accurately until the Space Age, when we gained the ability to measure gravity at varying distances. And in space, the gravitational anomalies are a bit more extreme. I'm convinced that there is an electrostatic attraction between celestial bodies, due to their net charges.

Before you start looking for modifications to Newtons law I think you should first explain exactly why you need them.

Just a side issue. There is no such thing as inertia. You are talking here of mass.
Just another side issue. How does your idea of gravity operate upon light? See my paper on Gravity for an explanation. In Aether Physics the gravitational potential is the speed of light.

[CharlesChandler]

How do you calculate the mass of the Moon? Your thoughts all depend upon that.

Exactly.

Before you start looking for modifications to Newtons law I think you should first explain exactly why you need them.

The OP identified an anomaly. As I said previously, "There are only two assumptions in there: 1) that gravity is the only force operative at the astronomical scale, and 2) that a rocky moon could be lighter than water. One of those assumptions is false."

There is no such thing as inertia.

So you're rejecting Newton's First Law of Motion? Do you have a substitute?

How does your idea of gravity operate upon light?

Before I commit to reading your paper, do you provide evidence of gravity operating on light? Or do you just take Eddington's "gravitational lensing" on faith?

[marengo]

The OP identified an anomaly. As I said previously, "There are only two assumptions in there: 1) that gravity is the only force operative at the astronomical scale, and 2) that a rocky moon could be lighter than water. One of those assumptions is false."

Wiki states that the mean density of the Moon is 3.35 times that of water. Are you saying that the Moon is bigger or lighter than the figures that Wiki employs. And why?

So you're rejecting Newton's First Law of Motion? Do you have a substitute?

I am not rejecting the First Law of Motion. Please explain why you think that I am.

Before I commit to reading your paper, do you provide evidence of gravity operating on light? Or do you just take Eddington's "gravitational lensing" on faith?

I predict the effects of gravity from calculations based upon the properties of my Aether model. Observations such as Eddingtons and gravitational redshift merely confirm my predictions.

[CharlesChandler]

Wiki states that the mean density of the Moon is 3.35 times that of water. Are you saying that the Moon is bigger or lighter than the figures that Wiki employs. And why?

I didn't track down the actual numbers, much less run the calcs. I was just suggesting that the thread get back on the topic of the OP, which wasn't a philosophical debate on whether or not a point exists.

I am not rejecting the First Law of Motion. Please explain why you think that I am.

Ummm, you said, "There is no such thing as inertia." Are you familiar with the First Law of Motion?

I predict the effects of gravity from calculations based upon the properties of my Aether model. Observations such as Eddingtons and gravitational redshift merely confirm my predictions.

And what did Eddington observe? A couple of arc-seconds of deflection? Did he have the instrumentation to make such an accurate measurement? Mind you that in all of the cases in which gravitational lensing supposedly occurs, there is also a mirage effect, where light passing through a gas with a density gradient (as is always the case in a gravity field) is deflected toward the higher density. So to estimate the "gravitational lensing", you first have to factor out the mirage effect, to a degree of accuracy finer than your proposed GL effect. So...

Here on Earth, we can observe mirage effects where the light is getting deflected several degrees when traveling over a distance of just a couple of kilometers, and where the gradient responsible for the deflection is just the difference of a couple percent. Do you think that we have the instrumentation necessary to predict such deflections within a couple of arc-seconds? If we sampled the atmosphere at a thousand places along the path, to get the actual density, I don't think that it would be enough for arc-second accuracy. When Eddington "observed" gravitational lensing, he had NO in situ sampling of the atmosphere through which the light was passing. He could only guess at it, from the degree of scattering. So here on Earth, if we were to guess at the density of the gas through which the light was passing just on the basis of scattering, would that enable predictions of deflections to arc-second precision? That's laughable, and so is all work based on it, for the same reason.

[viscount aero]

No he didn't. He created an approximation of what it does--not what it is or how or why it exists.

It is absurd to expect anyone to know everything about the Universe. Newton made a great step forward.
It is also absurd to expect physicists to explain WHY things exist.

I believe you said "Newton was right" and he wasn't. He created only an approximation for calculating gravitational effects in local space. Yes it was a big discovery. Nobody denies that. Who has denied that his discovery was big? But he wasn't aware of the bigger picture for gravity. He was stuck in his time. Despite its usefulness to this day, it is time to move beyond Newton's world to new things.

Yes I agree--you effectively said nothing factual and contradicted yourself in the same sentence.

You are a great one for being pedantic. Gravity EFFECTIVELY acts from the centre point of a massive sphere. That is the physics of it. Why dont you stick to physics rather than lexicography.

The origins of falsehood begin in language particularly when all we have here is texting. Because you are also known to construe what you say to mean whatever you want when faced with rebuttals you must be treated accordingly. Grammatical vagueness is your middle name.

Again 1: As in the case of Newton's entrapment in his own time and paradigm: you don't know that gravity acts that way 2: There is no such thing as a "point source" (particularly if at Earth's center there are no gravitational effects). For that matter you might as well say "all of the cosmos arose from a point source"--and that, too, is probably a falsehood.

LOL ok How can anyone read your paper for a "more complete understanding" of gravity when you agree with me that gravity cannot be entirely understood!

So you equate more understanding with a complete understanding. In your dictionary MORE and COMPLETE have the same meaning???

This is what you wrote: "marengo wrote:
Try reading my paper on gravity for a more complete understanding..."

More modifies "Complete" but incorrectly. Something cannot be "more complete." Regardless, you imply a false authoritative voice on the nature of gravity. You claim to guide the reader down a path to some level of completeness, clarity, truth. That is the implicit and greater POINT.

It is particularly false in light of how we don't know how gravity actually works (and you admitted that). But you then immediately disqualified it by telling me to refer to your papers for a "more complete understanding" of gravity that "acts as a point source."

Again, there is no such thing as a point. So why become enraptured in this visualization? We don't know that gravity acts that way. Therefore why should anyone take that idea seriously as a "more complete understanding." A point source, real or mathematically abstract, may not be at all how gravity originates, bears, or radiates its influence.

In agreeing with me you just contradicted your own assertion that gravity acts as a "point source"..

I never said that. I said EFFECTIVELY acts as a point source. Would you like to borrow my spectacles?

But what if it doesn't act this way? I would move away from using a "point source from the center of the Sun/Earth" to describe gravitational effects. Gravity appears to behave more as a field, a gross effect, and not a point.

[Aardwolf]

Out of interest, whats your explanation for Mars and Mercury having the same surface gravity?

I cannot believe that you are asking this question.
Simply,the surface is at a different distance from the effective point source at the center of the planets.
The planet with greatest mass also has a larger radius.Are you forgetting that acc = GM/r^2.

Then please explain why they have the SAME surface gravity?

If, as you state, only the distance from the centre matters, then why do two significantly different planets in radius, have the same surface gravity?

[viscount aero]

This is a very mainstream article on the Moon (and uses typical "impactor" logic for explaining the physics) but it admits to the supposed variable density problem as related to the Moon's variable gravity:

Moon’s Variable Gravity
http://www.universetoday.com/102576/

and this:
The Moon reveals its weirder side--SELENE mission reports on gravity anomalies:
http://www.nature.com/news/2009/090212/ ... 9.100.html

excerpt:
"Because the Moon has no atmosphere or weather to speak of, its geology has remained almost unchanged since it formed. So unpicking its structure could offer information about how the early Solar System — including Earth — developed. But the Moon has some unusual traits that have so far proved tricky to study: its gravity and the thickness of its crust vary from the near side that faces Earth to the far side.

Mapping the gravity field on the far side of the Moon for the first time is the "most transformative piece of information" that the SELENE mission has provided, Zuber adds. "What they have managed to find is that there are differences between the near and far side. It underscores and quantifies the asymmetry of the Moon."

[viscount aero]

And this:

NEWTON’S LUNAR MASS ERROR
http://dioi.org/kn/newtonmoonerror.htm

excerpt:
"An important mistake in Newton’s lunar computa­tions, not hitherto detected, is the overestimation of the Moon’s mass by 100%. The Moon : Earth mass ratio is inferred to be 1 : 40 (Principia Book III Prop. 37, Cor. IV) when in fact it is 1 : 81; and the mean lunar density to be 1-5 times that of Earth (System of the World’, 56) whereas it is 0-6 that of Earth’s mean density.

In what follows, the means by which Newton arrived at the erroneous estimate is first described by way of a comparison of the solar and lunar tide­raising components. Then, the effect of the error upon his estimation of the barycentre of the Earth­Moon system is examined, and it will be seen how his error in positioning the barycentre affected his gravity computation. Lastly, it is asked why such a prominent error has not hitherto been detected."

[meemoe_uk]

that A rocky moon could be lighter than water.

Wiki states that the mean density of THE Moon is 3.35 times that of water. Are you saying that the Moon is bigger or lighter than the figures that Wiki employs. And why?

Watch the As and the THEs, they make all the difference.
My OP was about the rocky moons of Saturn, some of which have an assumed density less than water.

Our own moon is assumed denser, but its surface is much more dense than Earths, which is interesting.

[marengo]

Ummm, you said, "There is no such thing as inertia." Are you familiar with the First Law of Motion?

Yes. There is no point to the First Law. The second Law states F = ma. Thus if F = 0 then there is no acceleration. That is not inertia. It is merely a consequence of no force. I repeat; the word inertia is pointless.

And what did Eddington observe? A couple of arc-seconds of deflection? Did he have the instrumentation to make such an accurate measurement? Mind you that in all of the cases in which gravitational lensing supposedly occurs, there is also a mirage effect, where light passing through a gas with a density gradient (as is always the case in a gravity field) is deflected toward the higher density. So to estimate the "gravitational lensing", you first have to factor out the mirage effect, to a degree of accuracy finer than your proposed GL effect. So.

You are forgetting Gravitational Redshift.
You are also forgetting that my theory predicts these effects.
It is not good enough to doubt observations without providing a theory which predicts what you alternatively suggest is happening. You have not done that.

You seem to have forgotten that you were once predicting the density of the Moon to be less than 1 when it is given by Wiki at 3.35. The mass of the Moon can be calculated from the orbit of a spaceship round the Moon.
So where do you get this low density from?

[marengo]

I believe you said "Newton was right" and he wasn't. He created only an approximation for calculating gravitational effects in local space. Yes it was a big discovery. Nobody denies that. Who has denied that his discovery was big? But he wasn't aware of the bigger picture for gravity. He was stuck in his time. Despite its usefulness to this day, it is time to move beyond Newton's world to new things.

I dont understand you. You say there is a bigger picture of Gravity than Newtons, yet you fail to explain what it is.

[marengo]

Then please explain why they have the SAME surface gravity?

If, as you state, only the distance from the centre matters, then why do two significantly different planets in radius, have the same surface gravity?

I have explained it. It is not my fault that you cannot understand the explanation.
But here is another go, m/r^2 = M/R^2 for the two planets