Freethought & Rationalism Archive

08-08-2002, 03:46 AM

We know there is a force G. This is the force of two masses on each other.

Why is this force the way it is?

How did it come about?

Why is it no less or no more?

Even socalled dark matter has this property.

Do we know how it works or do we just know its characteristics?

[ August 08, 2002: Message edited by: raindropple ]

Kevin Dorner · 08-08-2002, 03:57 AM

Though the possible implication of this thread is that there is design to the constants of nature, therefore to the products of nature (ie living things) its connection to evolutionary biology and/or creationism is tenuous at best as it only relates to physics; it would seem to fit more into Science and Skepticism.

[ August 08, 2002: Message edited by: Kevin Dorner ]

08-08-2002, 04:07 AM

Do we know how it works or do we just know its characteristics?

Philosoft · 08-08-2002, 05:56 AM

Superstring theory predicts a "gravity particle," called a graviton that produces force interactions between matter particles similar in execution to bosons and gluons for nuclear forces. Since gravity is the weakest of the four fundamental forces, it is speculated that gravitons have never been experimentally observed because our particle accelerators lack the ability to create enough total energy.

String theory also predicts that the distinct force energies of electromagnetism, weak and strong nuclear, and gravity, are "unified" in a single force at extremely high temperature.

This is as detailed as I can get, however, as I am no physicist. I strongly recommend Brian Greene's The Elegant Universe as a layman's starting point for understanding superstring theory.

Secular Pinoy · 08-08-2002, 08:24 AM

I always thought that gravity is the local deformation of spacetime caused by a massive object, and that bodies that seem to be attracted to each other are really just traversing the path of least resistance. I assume that this is a classical interpretation of gravity, grossly oversimplified. I'm no physics guy.

Philosoft · 08-08-2002, 08:35 AM

Quote:

Originally posted by Secular Pinoy:
I always thought that gravity is the local deformation of spacetime caused by a massive object, and that bodies that seem to be attracted to each other are really just traversing the path of least resistance. I assume that this is a classical interpretation of gravity, grossly oversimplified. I'm no physics guy.

Actually, this is the relativistic theory of gravity. Relativity does make some odd predictions about the behavior of light in the presence of gravity that have been experimentally confirmed. This is a problem for quantum mechanics because photons are theoretically massless. Superstring theory was born, in part at least, in an attempt to reconcile gravity and quantum mechanics.

ohwilleke · 08-08-2002, 10:27 AM

The short answer to the OP is that the constant G is simply a measured quanity, and, in fact, is the least accurately known of the measured physical constants. We do not know "why it exists", "how it came about", or what its mechanism is beyond its observed characteristics. In fact, we may never know. In fact, the questions may not be particularly meaningful. Some of these questions may as understanding grows increasingly seem like a "Why aren't flat things round?", kind of question, and I suspect that they will.

Classical gravity theory does not propose a mechanism or a reason that gravity is what it is, it simply states that experiment indicates that the force of gravity exists and can be fully explained by a very simple formula (M1)*(M2)*G/r^2=Force of Gravity, where M1 and M2 are the respective masses of two objects, G is the gravity constant, and r is the distance between the two objects.

Relativistic gravity (which is part of General, rather than Special relativity), interprets gravity as a curvature in space-time caused by an individual mass, rather than according to the simple theory. Relativity is closer to the truth than the classical formula, but the results are in most circumstances very similar. Two of the most famous examples of the differences between the two theories are that (1) photons are affected by gravity despite not having mass (contrary to the Classical formula) which produces effects such as gravitational lensing of light, and (2) that the orbit of Mercury around the sun differs slightly with the prediction of classical gravity but agrees with the relativistic expression of the theory. Even general relativity, simply provides a "heuristic meachinism" (i.e. one that allows for understanding but isn't based on direct knowledge of a mechanism).

The theory of the graviton, while a nice quantum mechanical speculation, is just that, informed speculation. It would make various parts of different theories work better together if it was true, but the fundamental unsolved issue in modern physics today is how, if at all, the theory of relativity which has the relativistic theory of gravity as one of its core elements, relates to quantum physics. The dozens of books on Theories of Everything and research in modern physics are a testiment to the fact that there has been no satisfactory resolution of the issue. Quantum mechanics provides a plausible mechanism for gravity, but not one that has been proven in any way.

[ August 08, 2002: Message edited by: ohwilleke ]

Friar Bellows · 08-08-2002, 02:56 PM

Quote:

Originally posted by Philosoft:
Relativity does make some odd predictions about the behavior of light in the presence of gravity that have been experimentally confirmed. This is a problem for quantum mechanics because photons are theoretically massless.

So what? I mean, why is this, specifically, a problem for quantum mecahnics?

Philosoft · 08-08-2002, 06:13 PM

Quote:

I said:

Relativity does make some odd predictions about the behavior of light in the presence of gravity that have been experimentally confirmed. This is a problem for quantum mechanics because photons are theoretically massless.

Quote:

Friar Bellows replied:


So what? I mean, why is this, specifically, a problem for quantum mecahnics?

Quantum mechanics predicts that the graviton facilitates interaction between certain particles that have mass. When it was shown that light is in fact affected by gravity, this was a problem because the massless photon can't interact with the graviton under QM.

Bill · 08-08-2002, 10:12 PM

Quote:

Originally posted by Philosoft:
Quantum mechanics predicts that the graviton facilitates interaction between certain particles that have mass. When it was shown that light is in fact affected by gravity, this was a problem because the massless photon can't interact with the graviton under QM.

And yet, the issue of whether or not photons have a small (but definitely non-zero) mass is still an open question (the last I heard). The classical view of the photon having a zero mass is given on <a href="http://www.weburbia.demon.co.uk/physics/photon_mass.html" target="_blank">THIS PAGE</a>. However, as is explained on <a href="http://www.phys.virginia.edu/classes/252/Bohr_to_Waves/Bohr_to_Waves.html" target="_blank">THIS PAGE</a>, even as long ago as 1924, Prince Louis de Broglie showed "that the photon might well be a particle with a rest mass." All we have managed to do so far with experimental results is to limit the possible rest mass of the photon to a very small value indeed, on the order of <a href="http://www.weburbia.demon.co.uk/physics/photon_mass.html" target="_blank">7x10-17 eV</a>.

The limits on photon mass quoted above are many orders of magnatude smaller than the limits that are even anticipated to be measurable using modern experimental techniques, such as those using <a href="http://research.spinweb.com/_tp/00000403.htm" target="_blank">so-called "frozen light" experiments</a>:

Quote:

Regarding the mass of the photon issue, relativistic theory supports a minute (a.k.a small) mass for a photon given certain other variables. If light has a mass less than 10E-50kg, relativistically, it can reach speeds of 0.9999999999c in a pure vacuum without an observable energy change. Does anyone have measurement instrumentation that can measure the 0.0000000001c difference in speed? No, but you can measure these relatively small changes in a Bose-Einstein condensate which is why they are doing these experiments in the first place!

As far as I'm concerned, the jury is still out on what the real rest mass of the photon might actually be.

== Bill

08-08-2002, 03:46 AM	#1
raindropple Guest Posts: n/a	Why is the G, G? We know there is a force G. This is the force of two masses on each other. Why is this force the way it is? How did it come about? Why is it no less or no more? Even socalled dark matter has this property. Do we know how it works or do we just know its characteristics? [ August 08, 2002: Message edited by: raindropple ]</p>

08-08-2002, 03:57 AM	#2
Kevin Dorner Senior Member Join Date: Dec 2001 Location: Toronto, Ontario, Canada Posts: 762	Though the possible implication of this thread is that there is design to the constants of nature, therefore to the products of nature (ie living things) its connection to evolutionary biology and/or creationism is tenuous at best as it only relates to physics; it would seem to fit more into Science and Skepticism. [ August 08, 2002: Message edited by: Kevin Dorner ]</p>

08-08-2002, 10:27 AM	#7
ohwilleke Veteran Member Join Date: Jun 2000 Location: Denver, Colorado, USA Posts: 4,834	The short answer to the OP is that the constant G is simply a measured quanity, and, in fact, is the least accurately known of the measured physical constants. We do not know "why it exists", "how it came about", or what its mechanism is beyond its observed characteristics. In fact, we may never know. In fact, the questions may not be particularly meaningful. Some of these questions may as understanding grows increasingly seem like a "Why aren't flat things round?", kind of question, and I suspect that they will. Classical gravity theory does not propose a mechanism or a reason that gravity is what it is, it simply states that experiment indicates that the force of gravity exists and can be fully explained by a very simple formula (M1)(M2)G/r^2=Force of Gravity, where M1 and M2 are the respective masses of two objects, G is the gravity constant, and r is the distance between the two objects. Relativistic gravity (which is part of General, rather than Special relativity), interprets gravity as a curvature in space-time caused by an individual mass, rather than according to the simple theory. Relativity is closer to the truth than the classical formula, but the results are in most circumstances very similar. Two of the most famous examples of the differences between the two theories are that (1) photons are affected by gravity despite not having mass (contrary to the Classical formula) which produces effects such as gravitational lensing of light, and (2) that the orbit of Mercury around the sun differs slightly with the prediction of classical gravity but agrees with the relativistic expression of the theory. Even general relativity, simply provides a "heuristic meachinism" (i.e. one that allows for understanding but isn't based on direct knowledge of a mechanism). The theory of the graviton, while a nice quantum mechanical speculation, is just that, informed speculation. It would make various parts of different theories work better together if it was true, but the fundamental unsolved issue in modern physics today is how, if at all, the theory of relativity which has the relativistic theory of gravity as one of its core elements, relates to quantum physics. The dozens of books on Theories of Everything and research in modern physics are a testiment to the fact that there has been no satisfactory resolution of the issue. Quantum mechanics provides a plausible mechanism for gravity, but not one that has been proven in any way. [ August 08, 2002: Message edited by: ohwilleke ]</p>

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08-08-2002, 04:07 AM	#3
raindropple Guest Posts: n/a	Do we know how it works or do we just know its characteristics?

08-08-2002, 05:56 AM	#4
Philosoft Veteran Member Join Date: Feb 2002 Location: Southeast of disorder Posts: 6,829	Superstring theory predicts a "gravity particle," called a graviton that produces force interactions between matter particles similar in execution to bosons and gluons for nuclear forces. Since gravity is the weakest of the four fundamental forces, it is speculated that gravitons have never been experimentally observed because our particle accelerators lack the ability to create enough total energy. String theory also predicts that the distinct force energies of electromagnetism, weak and strong nuclear, and gravity, are "unified" in a single force at extremely high temperature. This is as detailed as I can get, however, as I am no physicist. I strongly recommend Brian Greene's The Elegant Universe as a layman's starting point for understanding superstring theory.

08-08-2002, 08:24 AM	#5
Secular Pinoy Veteran Member Join Date: Feb 2001 Location: Quezon City, Philippines Posts: 1,994	I always thought that gravity is the local deformation of spacetime caused by a massive object, and that bodies that seem to be attracted to each other are really just traversing the path of least resistance. I assume that this is a classical interpretation of gravity, grossly oversimplified. I'm no physics guy.

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