Quote:
Originally Posted by N0B0DY  Also, why would gravity overcome expansion when it is the cause of expansion according to Kirchoff's law? I would think that the denser the matter, the greater the expansion would be, no? |
I don't understand the reference to Kirchoff's Law. I had to learn it as an apprentice electrician many years ago and to me it is forever associated with the current balance in a circuit.
Hmmmm ... Nob, please be aware that I don't really know what I'm talking about from here on.
Lets accept that the gravitational force consists of Mass, Energy and Pressure as described by Einsteins General Relativity. The greatest contributor of course is Mass.
Mass is always positive. Energy I'm not so sure about, but Pressure can be positive or negative. Now where ever Mass is present in large quantities then 'positive' gravity dominates. We know by the blue-shift that all the galaxies in the local cluster, known as the local group, are hurtling towards each other. Why, because Mass, in the form of stars, is the dominant contributor to gravity inside the local group.
But, out in space Mass is no longer the dominant contributor to gravity. Space consists of energy and pressure and virtual 'Rascal' particles but very little Mass. If the dominant contributor is now pressure, and that pressure is positive then gravity will be attractive. But if the pressure is negative then gravity will be repulsive.
You can quickly see from this that Gravity can be both attractive and Repulsive. Within a galaxy, group of galaxies, or cluster of groups attractive gravity rules, drawing them closer and closer together.
But outside that region, space is being created by repulsive gravity between that cluster and the next. Why is the pressure negative? I'm not sure but Einstein had to have a negative Cosmological Constant to develop a stationary state (static) Universe which he then abandoned. So an expanding Universe would also have to have a negative cosmological constant. Possibly Lloyd or Dave might know this?
The effect of positive gravity can be seen in the blue-shift of galaxies. The effect of negative gravity can be seen in the red-shift.
As I explained in the previous post, when referring to the 100m distance between me, you and Lloyd, negative pressure is
cumulative because it is acting everywhere at once so that the further apart two objects are the greater their rate of separation.
This also is confirmed in the red-shift, the greater the distance, the greater the red-shift. There are three methods of determining the recession between galaxies, red-shift is only one of them. Importantly all three agree on the recession of distant galaxies and all three are independant of each other.
This means as the Universe gets older we (the milky-way kids) are going to huddle closer and closer together as we become more and more isolated until eventually the only stars in our sky will be the stars of the milky-way. (And Andromeda of course, which will have carved through the milky-way like a circular saw blade by then).
Don't take this as gospel
cool bananas ... greg
