Expert: Jayendra Upadhye - 7/23/2008

Question
The General theory of relativity was written based on a static universe without taking the big bang into account. So the heavy masses attract the lighter object and keep them in orbit around them with the help of their gravitational pull. If there were more objects, than due to their collective gravitational attraction the masses should attract each other and collide unlike objects put in the orbit. Einstein introduced that there should be an equal and opposite force acting on these objects to compensate gravity which keeps the masses in orbit.
He called it as Cosmological constant.
Now the according to big bang the universe is expanding.
My question is, could this cosmological constant be the effect due to expansion of the universe. Like a police chasing a thief, the expansion might keep the masses falling together due to the gravitational attraction. I mean there is a balance between these two, which Einstein called it as cosmological constant.
And if the big bang expansion stop what will happen to these masses, will the planets be in orbit around the Sun or attracted towards the Sun
Thanks for your answers in advance !

/Mohan

Answer
Hi Mohan,
Found this on the question pool.

1 - Einstein did not invent the Gravitational constant for reasons you have mentioned.
   That was to counter an expanding universe as suggested by friedmann (1922) against the "static universe" theory then in vogue.
   To do this, Einstein had to build a new constant into his equations which would ensure the universe would remain static.
   Only later when observational evidence began filtering in (Hubble and Shapley) that he rescinded, and admitted that
   That was his life's biggest blunder.
   
2 - Stable orbits dont rely on any gravitational constant, but they form when the gravitational centripetal acceleration is balanced by the
   centrifugal force due to their orbital velocities.
   or g = (Orbital Velocity squared) / orbital radius.
   Plain and simple newtonian mechanics is involved there.
   
3 - The expansion of the universe is accelerating!
   
4 - When the sun enters its red giant phase 5 billion years from now, its outer layers will extend to the orbit
   of mars! The inner planets will burn to cinders, then spiral into the sun, which will later end as a cooling white dwarf star.

regards
Jayen