[jeffreyH (OP)]

Potential energy should be at a maximum value at infinity. This is exactly where, mathematically, gravity ceases to operate. So that in the absence of gravity any mass should therefore be infinite since there have been infinite contributions of potential energy. Does this sound sensible to you John?

[timey]

Oh look, Jeff's created a riddle!

Ok, hmmm...  Well, I think the answer has got to be, that where there is no gravity, there is also no mass.

Does this give indication that potential energy is only applicable where there is mass in relation to Mass?

[timey]

Since potential energy is the measure of kinetic energy required to 'get back' to (?) ...where you are calculating from...

... When gravity potential is set at infinity, in consideration that infinity potential energy is set at 0 gravity, 0 gravity being an absence of mass - can anyone tell me exactly 'what' it is from that reference frame that is mathematically being calculated as 'getting back'?

[jeffreyH (OP)]

Since potential energy is the measure of kinetic energy required to 'get back' to (?) ...where you are calculating from...

... When gravity potential is set at infinity, in consideration that infinity potential energy is set at 0 gravity, 0 gravity being an absence of mass - can anyone tell me exactly 'what' it is from that reference frame that is mathematically being calculated as 'getting back'?

You can't have a reference frame at infinity. It can only be used in mathematical procedures to demonstrate something. Since it is infinitely far away you can never get there in a finite amount of time.

[timey]

Which is exactly my point.

What is being demonstrated?

[guest4091]

As m rises gravity imparts ke downward until m stops and reverses direction and returns to the ground.

...and by what mechanism is gravity imparting ke downwards?

The mass M tranfers energy into the surrounding space via an unknown process, producing the g-field.
Remove the mass and you remove the field.

[timey]

Yes - and considering that the energy imparted by 'unknown process' to the g-field is greater near M than far from M, why is it thought that energy is greater in space at 0 gravity?

[guest4091]

Yes - and considering that the energy imparted by 'unknown process' to the g-field is greater near M than far from M, why is it thought that energy is greater in space at 0 gravity?

Who thinks that? Energy anywhere depends on a source and specifically gravity depends on the distribution of mass. 

[guest4091]

Ideally in the over simplistic classical illustrations of momentum vectors (which represent motion of the fictitious center of mass, there is a large arrow for M and a small arrow for m, and initially they are parallel. If m (a rocket) departs M with mV, then M should react with Mv in the opposite direction to balance the 2 body system. In the 'real' world M does not react in that manner since the coordinated momenta of the exhaust disperses as heat.

 
If the strength of gravity decreases as the inverse square of distance then at large  astronomical distances, it would approach zero. This is another ideal concept involving an isolated earth-object system. It is only necessary to leave the local sun system and approach another star system and it would dominate the gravitational effects. Selecting a random volume of 'empty' space a few 1000 ly distant, any contribution from Earth would be washed out by the g-noise from all the masses of the universe with a net effect of zero.
Is there really an image moving across your computer screen?

[timey]

Yes - and considering that the energy imparted by 'unknown process' to the g-field is greater near M than far from M, why is it thought that energy is greater in space at 0 gravity?

Who thinks that? Energy anywhere depends on a source and specifically gravity depends on the distribution of mass. 

Current physics thinks that via gravity potential energy which is set at infinity in a 0 gravity field.

Via the inverse square law it's virtually impossible to arrive at 0 gravity mathematically.

Yes - mass distribution would indeed have a bearing on what the g field in space, and outer space will be doing, and where there is less mass, the energy of the g field would be less, right?

[guest4091]

Current physics thinks that via gravity potential energy which is set at infinity in a 0 gravity field.

Via the inverse square law it's virtually impossible to arrive at 0 gravity mathematically.

Yes - mass distribution would indeed have a bearing on what the g field in space, and outer space will be doing, and where there is less mass, the energy of the g field would be less, right?

Infinity has no value in any possible situation. It's a relation/state/property, literally 'without limit'. The  gravitational relation is probably more complex than 1/d^2. If it is quantized, then it can reach a saturation level which avoids 'infinite' binding.

[timey]

So - if one uses this infinity as a basis for ones mathematics, in relation to gravity = 0, for the weak field - then is it any surprise that where gravity is at the far greater value such as found in black holes, and the far weaker fields of individual particles, that these mathematics will result back to infinities?

[guest4091]

So - if one uses this infinity as a basis for ones mathematics, in relation to gravity = 0, for the weak field - then is it any surprise that where gravity is at the far greater value such as found in black holes, and the far weaker fields of individual particles, that these mathematics will result back to infinities?

Not sure I understand what you're saying. In general "infinities" lead to illogical conclusions. An inverse square rule at zero distance resulting in an "infinite" force? Where would the energy come from? At the other end, a particle only needs to be at a large (but not 'infinite') distance to not have any significant effect on nearby particles. Water contracts as it cools except when within a degree of freezing, when it expands. The mind would prefer a simple linear behavior, but reality is more complex.

[timey]

What I refer to is that potential energy and time dilation are set at infinity at 0 gravity, but time dilation and energy 'cease' before infinite gravity is reached.

[Petrochemicals]

From an engineering point of view, 2 bodies exert a force upon each other, if they have enough kinetic energy between them, they escape the attractive power of gravity. If however they do not have enough kinetic energy gravity becomes dominant and therefore they combine. Newtons inverse square law says gravitational attraction is inversley proportional to the square of the radius between them (i will stand to be corrected on that!) . Both bodies attract towards each other,to the gravitational centre . If the bodies had kinetic energy to begin with(one or both) the energywill cobine/counter the other, or have an effect upon to put it another way. If neither had initial energy neither will loose to or gain from the other,  so initial energy cannot be required for gravitational attraction.  The potential energy of each body is dependant upon the gravitational pull of the other, more potential energy for an apple attracted to earth than an apple to the moon When the bodies attract, the mass of the combined body determines the gravitational force. To seperate these bodies once more, will  require energy on both bodies, ie does the apple move the earth or the earth move the apple? That means to conserve energy the problem is that 1) counteracting initial energies has to be accounted for 2)the gravitational centre of each body is not reached 3)Energy is required to seperate the bodies when none was removed initially from the bodies when individualy viewed
The initial energy if on collision  can be accounted for by   a big impact that kills the dinosaurs in a fireball, or if similar by orbiting around/combining in a centre of gravity in a combined directon , the path is altered.  (if you can understand this with a bit o' leeway)
The kinetic gained by the  attraction from the potential energy of the created gravitational field is concerved in the gravitational field, the bodies moving towards the centre of gravity The gravitational centres is not reached as both bodies wish to centre over it,  it results in a bump, ie expended in heat light /molecular fracturingm  . The kinetic energy of the attraction also transferred to a tragectory in the combined resultant mass. The potential energy to the gravitational centre is conserved and the kinetic energy conserved
The energy required to seperate the bodies is the same that was gained through the attraction plus the potential energy, you have to put energy in to overcome gravity. This is conserved by each body being freed from the combined specific field of gravity, the bodies tragectory are altered back to there original and the energy is conserved.

[chiralSPO]

Potential energy should be at a maximum value at infinity. This is exactly where, mathematically, gravity ceases to operate. So that in the absence of gravity any mass should therefore be infinite since there have been infinite contributions of potential energy. Does this sound sensible to you John?

The maximal potential energy is attained infinitely far from the source of the gravity well, but the potential energy is always finite. Because the gravitational field falls off with the square of the radial distance, the integral of the change in potential energy converges as you rise from surface to infinite distance. It is actually very useful to treat this infinite distance limit as 0 potential energy, and then potential energy goes negative as the object is subjected to attractive fields (gravity or electrostatic).

[jeffreyH (OP)]

Potential energy should be at a maximum value at infinity. This is exactly where, mathematically, gravity ceases to operate. So that in the absence of gravity any mass should therefore be infinite since there have been infinite contributions of potential energy. Does this sound sensible to you John?

The maximal potential energy is attained infinitely far from the source of the gravity well, but the potential energy is always finite. Because the gravitational field falls off with the square of the radial distance, the integral of the change in potential energy converges as you rise from surface to infinite distance. It is actually very useful to treat this infinite distance limit as 0 potential energy, and then potential energy goes negative as the object is subjected to attractive fields (gravity or electrostatic).

Yes of course with an infinite series you can get a finite limit. It still doesn't make John's assertion right.

[timey]

ChiralSPO - I agree that it is useful to suggest that gravity potential energy is set at 0 in a 0 gravity field at infinite distance from M, but unless you have an m to apply gravity potential to, the statement is meaningless - unless applied to the reference frame of the g-field of space without mass. ie: 0 gravity

Taking m to an infinitely far distance from M, m has its own mass and gravity will not be 0...
Therefore m in a near 0 gravity field will have a very high gravity potential, but not infinitely high, and 0 gravity potential for m in relation to M would be at centre of body of M.

[PmbPhy]

An object moving away from a large mass has an initial kinetic energy. Gravity removes this positive kinetic energy until it reaches a value of zero. It then continues to remove kinetic energy so that the object now travels towards the centre of the force with increasing negative kinetic energy. Where does the kinetic energy go? Is it conserved?

No. Kinetic energy is not conserved. Only total energy is conserved. In this case its the total mechanical energy that's conserved. I.e. the sum of potential and kinetic energy.

[timey]

Pete - Then how can it be said that the frequency and therefore energy of a caesium atomic clock in a differing gravity potential is observer dependent?