
Originally Posted by
Graybeard
First I will try to explain Gravity as I see it.
According to Newton, the gravitational attraction between two objects depends on two things, the distance between the two objects and their combined mass. According to Newton an object's mass was 'particulate in quantity'. Meaning that the gravitational attraction of an apple is equal to the sum total of the individual gravitational attractions of each atom making up the apple. The total gravitational attraction of a planet equals the sum total of the individual gravitational attractions of each atom making up the planet.
The planet does not attract the apple because its 'gravity' is stronger than the apple's gravity, but just because it has more atoms of the same 'gravity'. More atoms means more of the same gravity, not stronger gravity.
Listen to this old fart, "Hitherto we have explained the phaenomena of the heavens and of our sea by the power of gravity, but we have not yet assigned the cause of this power. This is certain, that it must proceed from a cause that penetrates to the very centres of the sun and planets, without suffering the least diminution of its force; that operates not according to the quantity of the surfaces of the particles upon which it acts but according to the quantity of the solid matter which they contain, and propagates its virtue on all sides to immense distances, decreasing always in the duplicate proportions of the distances.
Gravitation towards the sun is made up of the gravitations towards the several particles of which the body of the sun is composed ... " from Newton's Principia, 1726 edition.
So gravity depends on two things, mass and distance of separation.
So if we have a block of iron composed of 1,000,000 iron atoms (10^6 atoms) then its total mass would equal 1,000,000 times the mass of one iron atom and it would weigh 1,000,000 times the weight of one iron atom. According to Newton !
But not according to Einstein. E = mc^2. If you add kinetic energy to the block of iron lets say by heating it, then you are increasing 'E' which translates into more 'm'. So this is a different definition of mass. If you heat a block of iron composed of 10^6 atoms it will weigh (mass will increase) more than it did when it was cold but it still only has the same number (10^6) of atoms. Newton would not have believed this.
To keep this in perspective, if the iron weighed 1/2 kilogram and you heated it by 10-20 degrees centigrade you would only increase its 'weight' by a millionth of a billionth of a kilogram. Not much, otherwise Newton would have found it .. lol.
So now the total gravitational force within a region depends on the total mass and the total energy within that region. Energy adds to the total gravitational field.
But thats not all, pressure does the same, but this is harder to explain because it does it in two ways.
a .. The easiest way to explain it is with a spring. Take a coil spring from the front strut of your car (left or right .. I don't care .. lol) and weigh it and record the weight. Now compress it down and tie it with a few cable ties. Subtract the weight of the cable ties and the spring will still be found to weigh more. Because you have increased the potential kinetic energy of the spring as evidenced by the strain on the cable ties (perhaps you call them zip ties or something). So the spring has more gravitational attraction when its compressed than when it is uncompressed.
But this is not the only secret of pressure and its ties to gravity
b .. . The 'presence' of pressure creates its own gravitational force which adds to total gravity within a region. I don't mean that pressure, by exerting its force increases the gravitational field (as described above in 'a') but just the presence of pressure adds to the gravitational force. In 'a' above the energy was added by pressure differences, the compressed and uncompressed spring, which equates to energy.
Pressure differences exert forces, but the gravitational force contributed by pressure in 'b' does not change by differing pressure values within the region, but by the pressure in the region, and its constant according to that pressure, regardless of that pressure's fluctuating values within the region. It's a pure gravitational force and does not exert a pressure differential force.
So now the total gravitational force within a region depends on the total mass within that region, total energy within that region as well as the total pressure within that region. Energy adds to the total gravitational field. Pressure adds to the total gravitational field via its energy, as well as via its presence.
Why am I trying to ineptly explain all this ?
Because our universe is old. If you go by a tick tock clock then the universe is very young. But if you cumulatively increment time by the number of events occurring (Event driven time) then most of the universe's events, presuming the number is finite, have already occurred in the first few minutes. What we take to be the 'norm' is at the very remote skewed end of the scale.
The reason pressure and energy contribute such a little insignificant amount to gravity's total value is because we are living in a very very old, very very cold, dispersed universe. Our universe has run down. The temp outside in space is 2.7 degrees above absolute zero.
But back when the universe was young, (Event driven time) it was hot, squillions of degrees, and compressed, a teaspoon of matter would have weighed squillions of tonnes. In fact the universe would have fitted into a full stop. And temperature, and pressure, and especially pressure, not only contributed large amounts to the gravitational field but were by far the bigger contributors.
And this is the secret that drove inflation, no outside forces will be required (such as collisions ... lol) because Pressure like Matter and Energy can have a positive value, but unlike Matter and Energy, Pressure can have a negative value ... ???
Our view of gravity is a local perception, a perception of this time and place in the cosmos. It was never the 'norm'.
Are you still with me, or have I lost everyone ... lol
cool bananas ...greg