Answerer

Hi guys, we all know there is a upper range for strong and weak nuclear force. But what about the gravitional force? While it is claimed that the range of gravitional force is infinite. I tend to think that it is, at the maximum, the diameter of our universe(assuming that the universe is spherical for simplicity).

There are a few reasons for my claim. First of all, according to GR, our universe is a four dimensional spacetime reality in which gravitional force exists. And we don't know whats outside our universe, chances(high) are, it could be the other higher dimensional spacetime which forbids the eistence of gravitional force.

Next, assuming that there are infinite(or close to it) number of parallel universes that do exist outside our universe and the range of gravitional force is inifnite. Then our universe will have experienced great acceleration of its expansion straight after the big bang rather than now. So to prevent the above scenario(which is apparently not the case), our gravitional force must have a range.

Anyway guys, I just suggesting, don't get too over-agitated by my views.

Bob K

Who is claiming that the gravitational force is infinite in range?

What are their premises?

Consider this: If the effect of a gravitational force is inversely related to the distance from its source, a kinda-sorta ‘half-the-distance-to-the-goal-line’ phenomenon, there will occur a point in the range at which the effect of the gravitational force will diminish to ineffectiveness and, thus, the range of gravity has a practical limit, a limit you can kinda-sorta physically observe or imagine by the metaphor of a football game of infinite duration in which a referee keeps penalizing an infinitely inept football team and he appears to get to a point wherein although he picks up the ball and appears to move it eventually he stops actually moving the ball and, thus, the ball never gets to the goal line.

http://www.bobkwebsite.com/opdefuniverse.html

Answerer

Well, here are the websites who claim that gravitational force has an infinite range(of course numerous of textbooks state the same thing as well):


http://www.chembio.uoguelph.ca/educm...t/gravitat.htm


http://hyperphysics.phy-astr.gsu.edu...grav.html#grav

http://www.neutron.anl.gov/hyper-physics/force.html


Anyway, mathematically, gravitational force has an infinite range as there are no pre-conditions to limit it.

Late_Cretaceous

What if the whole universe consisted of only two massive, but neutral,subatomic partilces that they were located 100 trillion light years apart. WOuld gravitational force not attract them to one another? They would eventually meet because of gravity.

Psycho Economist

Given any finite distance and sufficient time... I can't imagine why they would not eventually collide.

Bob K

Answerer:And yet, as I have shown, there is a practical limit wherein the gravitational range becomes ineffective at causing observable effects because of the limits of the inverse square law.

Therefore, the Theory of the Practical Limits of the Inverse Square Law proves there are pre-conditions to limit the range of a gravitational field.

And, because the universe is a closed system insofar as matter/energy, there being no place for matter/energy to ‘go’ beyond the space of this one-and-only universe, and there is no other source of matter/energy within or beyond this one-and-only universe from which matter/energy could be added to the matter/energy present in this one-and-only universe, the sum total of matter/energy in this one-and-only universe is a constant, a finite number, and, since the finite quantity of matter/energy cannot be infinitely dispersed into infinite space, again, because of the Theory of the Practical Limits of the Inverse Square Law, there have to be areas of space in which there is no matter/energy present, and, since gravitational fields are forms of matter/energy, forms of energy, as are electromagnetic fields, they are subject to the inverse square law and, therefore, the practical limit to their effectiveness and therefore their range.

In case you are wondering if I am reading someone else’s words regarding the Theory of the Practical Limits of the Inverse Square Law, I am not, therefore I have no URLs/websites to point you to.

I am capable of independent intuitive thought, and the Theory of the Practical Limits of the Inverse Square Law I have articulated was generated by me 2/14/03 by the results of discussions on this and other Topics. Someone else may have generated this conclusion, possibly from other premises, but I am not aware of who they may be at this timepoint.

Again, the sports metaphor wherein in football the half-the-distance-to-the-goal-line penalty can be readily observed to have a practical limit, as does the inverse square law.

Thanks for the URLs. I’ll check them out.

Late_Cretaceous:Not if the spatial interval/distance between them were beyond the inverse square limits and thus beyond the practical gravitational range.

Undercurrent

What I was always taught that forces operating with an inverse square law were considered "long range" forces while anything with an inverse higher-power law (e.g. 1/r^(2.0000001)) is a "short range" force.

This is because if you use the Schrodinger equation to model a particle escaping form the centre of short range (as defined above) field, the wave function far away from the field centre is asymptotically similar to the wavefunction of a free particle. That is, the wavefunction 100 km away from the disturbance does not contain information about the distubance being there, (except for a finite phase shift, which is impossible to detect.)

The wavefunction of a particle scattered by an inverse square (or lower power) force does not, however, return asmptotically to the free particle state. It has a phase shift that increases logarithmically (read: slowly, but approaching infinity rather than any finite number) with distance from the disturbance.

The important thing is, even though all forces (I'm pretty sure even the stong and weak forces) have non-zero strength at any finite distance, terms like "short range" and "long range" still have some meaning.

Tim Thompson

All of the classical forces are mathematically infinite in range, but they are described by different formulas. The force of gravity is proportional to 1/r^2, where r is the distance to the source of gravity. The strong force falls off much more rapidly, and is described by what is called a "Yukawa potential"; the force is proportional to (e^-r)/r^2 (the force is the gradient of the potential, which looks like (e^-r)/r). That's why it falls off in range so fast by comparison to gravity, which falls off as r^(-2).

The "sports metaphor" is a false analogy, and so has no relevance to the discussion. So long as r is a finite number less than infinity, then so will 1/r^2 be a finite number greater than zero, and the force of gravity will be finite and greater than zero for all possible non-infinite values of r. The same argument applies to the Yukawa potential

The correct source of a practical limit on the range of any force is the physical limit based on a finite size for the universe. So while the range is mathematically infinite, it may not be physically infinite, if the universe is itself not physically infinite.

Also keep in mind that in classical general relativity, there is no "force" of gravity at all. Rather, the phenomenon of gravity is a manifestation of the local geometry of space time. However, in a quantum theory of gravity, then there must be a true "force" of gravity. the challenge is finding something that can unite these seemingly disparate views of nature into one model (string theory and loop quantum gravity are popular these days).

• The Fundamental Forces - From Hyperphysics.
• Fundamental Forces - From the American Institute of Physics.
• Fundamental Forces - From the World of Physics (Eric Weisstein).

enigma555

[/engineer hat]
[mathematician hat]

Well, if they were the only two things in the universe, weren't moving at the start, the universe wasn't expanding, they were neutrally charged, and you had infinite time, then they would.

[/mathematician hat]
[engineer hat]

tronvillain

Answerer:
Do we all know that? While there is a practical upper range for the strong and weak nuclear forces since they fall off so quickly, I was unaware that there was any absolute upper range to the forces. At significant distance they are simply so small as to be completely irrelevant, but I was not under the impression that they did not exist at all.

[/quote]But what about the gravitional force? While it is claimed that the range of gravitional force is infinite. I tend to think that it is, at the maximum, the diameter of our universe(assuming that the universe is spherical for simplicity).[/quote]

Well, like the other forces its range is theoretically infinite, but at extremely long distances it too will be so small as to be completely irrelevant.

Yes, they would eventually meet, and it would only require a finite amount of time. The only reason I can think of that they would not meet would be some kind of quantization - perhaps a minimum amount of force is required to overcome intertia and the mass of the two particles would be insufficient to generate that amount of force for particles of their mass.