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What is gravity?
Posted: 20 October 2011 12:55 PM   [ Ignore ]
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The effect of gravity i.e. the attraction between two macro physical objects is a fact. On the earth, all free falling objects is due to gravity. Newton characterized gravity as a force and derived his law of gravitation.  However, he had reservations wrt how there could be “action at a distance”.

From the wiki on Newton’s law of gravitation

“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 another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it.”

Einstein came up with a solution:

In general relativity, the gravitational force is a fictitious force due to the curvature of spacetime, because the gravitational acceleration of a body in free fall is due to its world line being a geodesic of spacetime.

However, even though if one can conceive of massive objects like planets or stars doing that, it still remains quite ridiculous for small objects like apples to fall just like that, notwithstanding Einsteinian physics. In that respect, Newton’s gravitational force makes more sense but “action at a distance” is clearly absurd. How about mediating gravitons, the Higgs boson etc. Very esoteric indeed.  cheese

OTOH, in describing micro quantum objects, QM do not consider gravity at all. 

Apparently, QM is incompatible with general relativity because one intractable issue is gravity.

Does quantum gravity exist or is there no gravity at the quantum scale and if so, why is it so?

What is gravity and why does it do what it does in the macro realm?

According to Erik Verlinde, gravity is an emerging “entropic force” on the macro scale.

From the wiki on entropic gravity

Entropic gravity is a hypothesis in modern physics that describes gravity as an entropic force; not a fundamental interaction mediated by a particle, but a probabilistic consequence of physical systems’ tendency to increase their entropy.

Also, from this article at the
NYT

What is gravity?

Forget curved space or the spooky attraction at a distance described by Isaac Newton’s equations well enough to let us navigate the rings of Saturn, the force we call gravity is simply a byproduct of nature’s propensity to maximize disorder.

Einstein’s equations of general relativity are fundamentally about thermodynamics:

In a provocative calculation in 1995, Ted Jacobson, a theorist from the University of Maryland, showed that given a few of these holographic ideas, Einstein’s equations of general relativity are just a another way of stating the laws of thermodynamics.

His concept of gravity is interesting and controversial. Nevertheless, from the wiki HERE

It appears that Verlinde’s approach to explaining gravity leads naturally to the correct observed strength of dark energy. In June 2011, he was awarded the prestigious Spinoza Prize with a 2.5 million euro grant for this work, including his paper.

If gravity is an emerging macro entropic force and is deterministic, the question which arises is, at the micro level where quantum objects interact randomly and indeterministically, is there any quantum gravity at all?

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Posted: 20 October 2011 01:00 PM   [ Ignore ]   [ # 1 ]
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What does gravity have to do with philosophy?

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Posted: 20 October 2011 01:40 PM   [ Ignore ]   [ # 2 ]
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George - 20 October 2011 01:00 PM

What does gravity have to do with philosophy?

Plenty George.

Is gravity contingent? Is it a brute fact? Is gravity a force? Does It govern what stuff does? Is it a man made scientific law? Is it something that exists independently of us and our science? What is space/ time? (Remember space/ time is not physical)

And lots more, these are all philosophical questions.

All science does is measures it, which to me is the dull bit, though I’m sure the scientifically minded will disagree.

Stephen

[ Edited: 20 October 2011 01:45 PM by StephenLawrence ]
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Posted: 20 October 2011 01:51 PM   [ Ignore ]   [ # 3 ]
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As far as I can tell, those are all scientific questions.

[ Edited: 20 October 2011 01:54 PM by George ]
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Posted: 20 October 2011 02:30 PM   [ Ignore ]   [ # 4 ]
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George - 20 October 2011 01:51 PM

As far as I can tell, those are all scientific questions.

Can’t see why George?

I do think if kkwan had posted in the science section, he’d have been directed to the philosophy section. grin

Stephen

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Posted: 20 October 2011 03:40 PM   [ Ignore ]   [ # 5 ]
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Of course, George, gravity has a great deal to do with philosophy here.  Haven’t you noticed that this sub-forum is completely bereft of humor, that is, completely immersed in gravity. LOL   See, I even had to hide that in white.

(Damn, this stupid program won’t print smileys in white.)

Occam

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Posted: 20 October 2011 08:40 PM   [ Ignore ]   [ # 6 ]
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Forget curved space or the spooky attraction at a distance described by Isaac Newton’s equations well enough to let us navigate the rings of Saturn, the force we call gravity is simply a byproduct of nature’s propensity to maximize disorder.

Who wrote that??

If anything, gravity is a byproduct of nature’s propensity for ORDER.  How can a planetary system be considered an expression in disorder? Apparently the positor has forgotten that if it weren’t for gravity, we’d still have chaos (inflation). Perhaps the universe is still expanding, but it is an orderly expansion and restricted by several universal constants, i.e. Gravity, SOL, Mathematical functions.
Entropy may well seem to defy gravity, but that is due to the limitations of gravity itself. Lest we forget, there are 4 types of gravity (including electro magnetism).

[ Edited: 20 October 2011 09:23 PM by Write4U ]
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Posted: 20 October 2011 09:07 PM   [ Ignore ]   [ # 7 ]
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Stephen,
Is gravity contingent? Is it a brute fact? Is gravity a force? Does It govern what stuff does? Is it a man made scientific law? Is it something that exists independently of us and our science? What is space/ time? (Remember space/ time is not physical)

IMO, perhaps spacetime is not physical, thus in and of itself has no causality except that its constituents, space and time, are interdependent. Without space there is no time, without time there is no space.  But not being physical does not mean it has no functionality. Within spacetime, things must behave in very specific ways, i.e. speed (time) and location (space).
Without physical/energetic objects there would be no spacetime. This is why we have an “event horizon” (the limits of spacetime function). IMO, spacetime was created as a result of BB. Before then there was no spacetime, i.e. spacetime is also a contingency.

And so is gravity a contingency. Within the metaphysical structure of spacetime, things must behave as they do. Gravity is an expression of the impact a massive object has on the fabric of spacetime, affecting all things within that gravitational field (spacetime warp).

[ Edited: 20 October 2011 09:19 PM by Write4U ]
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Posted: 20 October 2011 09:44 PM   [ Ignore ]   [ # 8 ]
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kkwan - 20 October 2011 12:55 PM

However, even though if one can conceive of massive objects like planets or stars doing that, it still remains quite ridiculous for small objects like apples to fall just like that, notwithstanding Einsteinian physics.

No, it doesn’t remain ridiculous at all. Although, this might be a good case of showing how human intuition about how things ‘should’ work don’t actually line up with how things really work.

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Posted: 20 October 2011 10:31 PM   [ Ignore ]   [ # 9 ]
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What i find fascinating is the concept of a “hot-air balloon” in regard to gravity. It so clearly illustrates the relationship of size and mass to gravity. Small size with great mass produces an acute (forcing) spacetime warp. The man in the basket does not feel any lighter.
Great size with small mass produces a spacetime “tendency”. The balloon “floats” in spite of gravity because it is lighter than air by volume (size), not by weight (mass). A bubble.

[ Edited: 20 October 2011 11:08 PM by Write4U ]
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Posted: 20 October 2011 11:00 PM   [ Ignore ]   [ # 10 ]
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George - 20 October 2011 01:00 PM

What does gravity have to do with philosophy?

The ideas and concepts of what is the nature of gravity are philosophical. However, physicists and cosmologists do consider the elucidation of gravity as a scientific endeavor.

There is philosophy behind all areas of science.

From this paper HERE

The Philosophy behind Quantum Gravity

From the abstract:

This paper investigates some of the philosophical and conceptual issues raised by the search for a quantum theory of gravity. It is critically discussed whether such a theory is necessary in the first place, and how much would be accomplished if it is eventually constructed. I argue that the motivations behind, and expectations to, a theory of quantum gravity are entangled with central themes in the philosophy of science, in particular unification, reductionism, and the interpretation of quantum mechanics.

Also, from this essay in the SEP on Newton’s philosophy

If we interpret Newton solely as a “scientist” whose work spawned discussion by canonical philosophical figures, we run the risk of ignoring his own contributions to the philosophical conversation in England and the Continent in the late seventeenth and early eighteenth century.

Historically, all the greatest scientists from Newton, Bohr, Heisenberg, Schroedinger to Einstein were philosophers/scientists who grappled with the philosophical issues wrt science in their respective world views. Similarly, contemporary scientists cannot just simply divorce science from philosophy, notwithstanding if they consider philosophy as dead/useless. (cf. Stephen Hawking)

From this article HERE

Is Philosophy Dead?

Many eminent physicists, from Einstein to Lee Smolin, have questioned the kind of interpretation of quantum theory assumed by Hawking and Mlodinow, whose discussion of multiple universes is through-and-through philosophical, not straightforwardly scientific in the way they pretend. Like string theory on which it is based, it is difficult to find direct experimental support for M-theory. Hence Hawking and Mlodinow are deriving philosophical conclusions from a shaky interpretation of a controversial scientific theory.

Why Stephen Hawking is wrong:

Hawking and Mlodinow repeat the Kantian philosophical error of inferring from the fact that we need minds to develop knowledge of reality to supposing that there is no reality independent of minds and the models they produce.

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Posted: 20 October 2011 11:21 PM   [ Ignore ]   [ # 11 ]
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I like string theory, it has a certain symphonic quality and harmony to it. Perhaps there are other symphonies elsewhere.
“To the symphony of life no one has the score”

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Posted: 20 October 2011 11:45 PM   [ Ignore ]   [ # 12 ]
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StephenLawrence - 20 October 2011 02:30 PM

I do think if kkwan had posted in the science section, he’d have been directed to the philosophy section. grin

Quite so, Stephen.  smile

As it is, gravity conceived as an “entropic force” is more in the realm of philosophy and not science per se, though the entanglement between philosophy and science cannot be ignored.

As such, it should be investigated if the concept has any merits wrt observed reality.

What is intriguing is that dark energy (a repulsive force) in the universe as distinct from gravity (an attractive force) can, from “Verlinde’s approach to explaining gravity leads naturally to the correct observed strength of dark energy.”

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Posted: 21 October 2011 12:22 AM   [ Ignore ]   [ # 13 ]
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I lean toward Plasma Cosmology - an Electric current in a plasma is all the force needed - exceedingly more powerful than gravity. No dark energy, matter, black holes, space-time, etc. Observations should preceed beautiful mythamatics and made-up entities. Trying to model the universe on gravity only modles is well - so passe. smile

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Posted: 21 October 2011 01:56 AM   [ Ignore ]   [ # 14 ]
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TromboneAndrew - 20 October 2011 09:44 PM

No, it doesn’t remain ridiculous at all. Although, this might be a good case of showing how human intuition about how things ‘should’ work don’t actually line up with how things really work.

The concept that space-time has a geometry that can be distorted or curved by objects with mass and it thereby determines the falling as well as the path of the falling object in it is neither intuitive nor credible.

For instance, when an apple falls to earth does the curved space-time due to the earth’s mass cause it to fall and to fall along a geodesic which is measurable at all or what? What makes it fall directly instead of it leisurely floating down along a geodesic instead if there is no initial force exerted on it?  It makes no sense. grin

OTOH, in reality, the apple falls straight down as though there is an attractive force between it and the earth and that’s it. Newton’s concept of gravity as a force makes more sense.

In other words, invoking the curvature of space-time to account for the fall and the path of falling of small objects like apples, is ridiculous.

Einstein himself rejected this predominance of geometry over physics.

From this article HERE

Relation Between Geometry and Physics

Although many people continue to hold this view of Einstein’s accomplishment and attribute it to him, Einstein explicitly rejected it. In 1928 he wrote: “I cannot agree that the assertion relativity reduces physics to geometry has a clear meaning. One can more correctly say that it follows from the theory of relativity that (metric) geometry has lost its independent existence with respect to the laws usually classified as physical.

Hence, for massive objects like planets or stars, they behave gravitationally as though the geometry of space-time is curved and not vice versa, i.e. it is physics which is predominant at all times.

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Posted: 21 October 2011 04:36 AM   [ Ignore ]   [ # 15 ]
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kkwan - 21 October 2011 01:56 AM
TromboneAndrew - 20 October 2011 09:44 PM

No, it doesn’t remain ridiculous at all. Although, this might be a good case of showing how human intuition about how things ‘should’ work don’t actually line up with how things really work.

The concept that space-time has a geometry that can be distorted or curved by objects with mass and it thereby determines the falling as well as the path of the falling object in it is neither intuitive nor credible.

I felt comfortable with that metaphysical aspect of spacetime. When proving Einstein’s GTOR the light was clearly observed to curve along a curved geometric path, only it’s speed (momentum) preventing it from falling into the star.

For instance, when an apple falls to earth does the curved space-time due to the earth’s mass cause it to fall and to fall along a geodesic which is measurable at all or what? What makes it fall directly instead of it leisurely floating down along a geodesic instead if there is no initial force exerted on it?  It makes no sense. grin

OTOH, in reality, the apple falls straight down as though there is an attractive force between it and the earth and that’s it. Newton’s concept of gravity as a force makes more sense.

In other words, invoking the curvature of space-time to account for the fall and the path of falling of small objects like apples, is ridiculous.

How so?
a) How large is the warped spacetime cone to center of the earth relative to the apple? It is straight down from any point.
b) Spacetime is 4 dimensional. What appears to fall in a straight line is in fact following a curved spacetime path. Moreover, when we throw the apple like a baseball, the curvature of spacetime becomes readily visible. The apple does not fall diagonally, it follows a trajectory along spacetime curvature in direct relationship to its speed and mass.

Einstein himself rejected this predominance of geometry over physics.

From this article HERE

Relation Between Geometry and Physics

Although many people continue to hold this view of Einstein’s accomplishment and attribute it to him, Einstein explicitly rejected it. In 1928 he wrote: “I cannot agree that the assertion relativity reduces physics to geometry has a clear meaning. One can more correctly say that it follows from the theory of relativity that (metric) geometry has lost its independent existence with respect to the laws usually classified as physical.

Hence, for massive objects like planets or stars, they behave gravitationally as though the geometry of space-time is curved and not vice versa, i.e. it is physics which is predominant at all times.

I understand Einstein’s quote to mean the interdependence of gravity and 4 dimensional spacetime geometry. Neither may be prominent over the other, but one cannot function without the other. Spacetime (a universal) is a metaphysical (latent) geometry, i.e. it is founded on the abstract concepts of speed and location in spacetime. Gravity is also a universal (a latent constant). Gravitational action between two massive bodies reveals this geometry which mathematically determines the paths they must follow in relation to each other.

I may well be wrong, but intuitively I feel comfortable with these concepts of potential inherent in the geometric structure of spacetime, which becomes disturbed in the presence of massive objects.

[ Edited: 21 October 2011 12:49 PM by Write4U ]
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