# Newtons Gravitational constant?

1. Mar 24, 2005

### rbj

many people have offered an explanation for why $$G$$ is what it is. it is what it is because of the units of time, length, and mass we humans have anthropocentrically decided to use. it is a fundamental quantity and if we adjust our definition of units appropriately, we can set it to whatever value we want it to be. you might want to check out the Planck units page at wikipedia: http://en.wikipedia.org/wiki/Planck_units . to ask why $$G$$ is what it is, is to ask why we are as tall (relative to the Planck length $$l_P$$) as we are, why we are as massive (relative to the Planck mass $$m_P$$) as we are and why our sense of time (relative to the Planck time $$t_P$$) is what it is. once you answer those questions, you have an answer to why $$G$$ is what it is or why $$c$$ is what it is or why $$\hbar$$ is what it is.

Frank Wilczek said it best (June 2001 Physics Today)*(http://www.physicstoday.org/pt/vol-54/iss-6/p12.html [Broken]):

...We see that the question [posed] is not, "Why is gravity so feeble?" but rather, "Why is the proton's mass so small?" For in Natural (Planck) Units, the strength of gravity simply is what it is, a primary quantity, while the proton's mass is the tiny number [1/(13 quintillion)]...

The strength of gravity is simply what it is and the strength of the electromagnetic force simply is what it is. The electromagnetic force operates on a different physical quantity (electric charge) than gravity (mass) so it cannot be compared directly to gravity. To note that gravity is an extremely weak force is, from the point-of-view of natural units, like comparing apples to oranges. It is true that the electrostatic repulsive force between two protons (alone in free space) greatly exceeds the gravitational attractive force between the same two protons, and that is because the charge on the protons are approximately a natural unit of charge but the mass of the protons are far, far less than the natural unit of mass.

r b-j

Last edited by a moderator: May 1, 2017
2. Mar 24, 2005

### Andrew Mason

G is just a number used to convert gravity to metric - m. kg. - units. If Planck units were used, Newton's law would be just: F = Mm/r^2

AM

3. Mar 25, 2005

### Andrew Mason

Or one could ask, why is the Planck mass so huge?! Or why is the proton/electron so gigantic? (10^28 Planck lengths). If we all lived in a world where the atom was 10^-28 times its size, we would think that gravity was a pretty big force because every proton would be a black hole. There is no right/wrong way to ask this question.

AM

Last edited by a moderator: May 2, 2017
4. Mar 25, 2005

### rbj

it becomes a sorta philosopical navel gazing, but there are concptually or pedagogically earlier questions to ask. the Planck units are derived from $$c, G, \hbar, 1/(4 \pi \epsilon_0)$$, which are properties of space without any consideration of any particles or objects or "things" to base the definitions of units on. (that's why i think this "gravitational fine-structure constant" is sorta bogus. also, if it were up to me, i would normalize $$4 \pi G$$ instead of $$G$$ and i would normalize $$\epsilon_0$$ instead of the Coulomb Force Constant as they did with the cgs system.) then you introduce these electrons and protons and positrons and neutrinos and whatever quark and other particles into the picture and ask why they have the size or the mass or the charge that they do. and, in terms of Planck units, you will get dimensionless numbers and those numbers are worth pondering. the dimensionful value of $$G$$ is not.

r b-j

5. Mar 26, 2005

### Ian

rbj,
I think the thread was closed because of the forum rules which say,
OK, rules are rules and this forum has its owners, but personally I feel this is a kind of jack-boot mentality. There is no 'expert' in the field of gravitation, neither has anyone been able to produce anything other than mathematical descriptions of gravitation and apply these to the cosmos. Math is not proof; reproduction of gravitational phenomena is proof and we have never seen anything of the sort.

The model I conceived predicts G perfectly and its simplicity makes it extremely difficult to argue against. However, if my name was Hawking, Penrose, Kaiku etc., everyone would listen to me. Its kind of a pharisaical doctrine that applies here.
This is such a great pity because with all the scientific jargon spoken everyone has missed something so simple (with respect to gravity) it defies belief.
AM commented on the Planck mass, but if you apply my thought to this quantity by a change of G at the proton density the Planck mass becomes equivalent to the proton mass, the Planck Length becomes the gravitational length of the proton mass and the planck time becomes the time for light to traverse the gravitational length of the proton mass.
Oh what the heck!

6. Mar 26, 2005

### Integral

Staff Emeritus
Ian,
When your "theory" has been accepted for publication in a peer reviewed journal we can have a discussion about it. Meanwhile it is our experience that the authors of theories such as yours are generally not open to criticism. They argue endlessly about the validity of their "theory", with their strongest suit simply being that they are ignorant of the theory they are attempting to revise. Thus we have terminated this practice as it is a waste of time.

The fact that you seem to be basing your theory on the rubber sheet analogy is an indication that you do not have in depth knowledge of Einstein' General Theory of Relativity.

Proceed with caution.

7. Mar 26, 2005

### rbj

no?

good math is mathematical proof. it is not confirmation of physical experiment, however, both SR and GR have had a few physical confirmations which moved it from the status that string theory has today to real physics.

i couldn't make any sense of it. and your premise of predicting a value for this dimensionful quantity is meaningless. G = 1 or whatever value you want it to be (by judicious choice of units).

i wouldn't attach the label "simplicity" to gobbledegook, but even so, there is a good quote from Einstein about simplicity.

when something is too good or incredible or wild to be true (that everybody just missed this beautiful and elegant idea that you caught), it usually isn't (true).

BTW, not being a physicist (i'm and electrical engineer that works with audio signal processing), i don't have any physics jargon. also there is a lot of modern physics i do not understand sufficiently. but i do understand the concepts of physical units and of dimensionless vs. dimensionful physical quantities and the meaning therein.

i think the terms "Planck mass", "Planck length" and "Planck time" have already been taken (and defined). unless your definitions are equivalent (they're not) you might call your units something else such as "Ian mass", "Ian length" and "Ian time". the proton mass does not ever equal the Planck mass, given the normal definition of the term.

r b-j

8. Mar 26, 2005

### rbj

gee, i would hope that we could talk here about ideas or theories without having to get them published in a real hard-core journal. after all, crappy ideas here only waste time and not trees.

i fully agree if someone is posting about a personal pet theory (i have mine about what are the most natural physical units and i think that Planck was off by a factor of $$\sqrt{4 \pi }$$, but it's picking nits), they need to be open to real discussion where they can potentially learn something from someone else. if Ian (or any of us) can't do that, then it's a waste of time.

i have to confess that, although i'm pretty good at a lot of UG and graduate level applied math, i have great trouble conceptually with tensors and barely understood in classical mechanics what good the Hamiltonian was over the elementary expression of Newtonian mechanics. i understand classical physics pretty good and SR and elementary QM (and a little bit of semiconductor physics), but don't have any idea where all these particles (leptons, etc.) come from and can't do anything serious with GR. i do understand the fundamental concepts (e.g. Equivalence Principle) of GR and am gratified that a limiting (in reasonably flat space-time) expression of GR can be made with something that looks like Maxwell's Eqs. (that seems natural to me since both E&M and gravitation are inverse-square law with speed of propagation equal to $c$.)

as always.

r b-j

9. Mar 26, 2005

### Integral

Staff Emeritus
Rbj
Note that my comments were directed at Ian, the one who posted the original opinion.

It was a common consensus among the mentors to disallow the discussions of personal theories. Simply because they tended to suck up huge amounts of time, reading the posts, attempting to understand them, and explaining the errors. Then, nearly universally, all of this work was rendered wasted simply because the originators of the "theories" had such a poor understanding of Physics in general that they could not understand what was wrong with their ideas. No amount of explaining can change this situation.

We would rather spend our time working with students who wish to learn, or discussing legitimate physical concepts with others, who do understand physics, or are making an honest effort to learn.

Most who bring a personal theory here have spend months or even years believing that they are thinking outside the box, when in reality they are wondering lost in a dark dusty corner of the box with no idea of where the box is. Having but this much effort into faulty thinking they are not eager or willing to change their views. There are many other forums on the web where such topics are discussed and argued endlessly, Personal theories should be taken to one of those sites.