Amusing musings...

[LAW (Murphy)]

So...I was thinking. Matter and energy are interchangeable (more or less), all the matter in the universe is just condensed energy from the 'big bang', matter 'exerts' gravity which has the power to affect the momentum of any any mass or energy nearby. Ability to alter an object's momentum is measured by Force (f=ma), so where does the 'gravitational energy' which is exerted by mass come from?

Some of the finite energy from the 'big bang' is converted into matter (E=mc^2) and that matter is exerting gravity on surrounding mass (f=ma) and the body is not losing mass but energy cannot be created or destroyed, so where does this energy come from?

It seems that as long as there is mass, gravity will be exerted. Think of the angular momentum of the earth as it orbits the sun, there is energy required to overcome the earth's inertia, that energy is not 'generated' anywhere, it simply 'exists' because of mass. The sun performs nuclear fusion, this exerts energy and the fuel is burned up, but long after Vulcan's fires are cold gravity will still exist. Why?

My head hurts

Sorry if this doesn't make sense, I'm trying to write my thoughts down but I don't think in words and I can't type as fast as my brain throws ideas at me.

[malclocke (Malc)]

The zero-energy universe hypothesis proposes that the total energy of the universe is zero, and that matter is essentially 'positive energy', and the gravitational field represents 'negative energy', and over the scale of the universe the two cancel each other out.

Hunted through 'A Brief History of Time', which I was sure mentioned this concept, and found this:

Two pieces of matter which are close to each other have less energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together. Thus, in a sense, the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels out the positive energy represented by the matter. So the total energy of the universe is zero.

[LAW (Murphy)]

Riiiight... So the gravitational potential is offset by the inertial mass of the object. *lightbulb* this is why orbits are ellipses! Because speed (inertia) increases with the inverse square of distance (field strength) which balances out the energies. They don't have to lose mass because they can lose energy instead by getting closer at the cost of exchanging gravitational potential for inertia.

Thank you, I just needed another way of looking at it. I guess the permanent nature of gravity is no more baffling than the permanent nature of matter.

Sorry, I just realised I put this in the wrong forum, I got a bit distracted.

[sheeny (Al)]

The gravitational potential energy also "comes from" the big bang. It may have been in the form of kinetic energy of fast moving mass, for example, in the early universe. The work done by gravity over the eons slowing the matter down is exactly equal to the gravitational potential energy.

Al.