Expert: James Gort - 7/21/2011

Question
Why all the planets and stars revolve around everything in an elliptical orbit rather circular? If you say, the planets are not moving at constant speed. Why? Big bang expelled everything out each at certain constant speed. right? If I'm wrong, please explain me. I'm waiting for your reply...

Answer
Hello Shameem,

First of all, I want to remind you that the origin of the universe by a "Big Bang" is very much still a theory, and there are alternative theories.  Some observations do not support an expanding universe or the Big Bang.  There are several references concerning this, but perhaps the most authoritative person is Halton Arp, a leading astronomer and researcher on galaxies, who wrote "Seeing Red".  That book is highly recommended to get an alternative view.  Or read "A Different Approach to Cosmology" by Hoyle, Burbidge, and Narlikar.  Another great book which gives a scientific view on how the universe has always been in a steady state.

But let's assume there WAS a Big Bang. That wasn't an "explosion" that occurred somewhere in space, but it was the start of the expansion of space-time itself. That expansion resulted in energy, elementary particles, atoms (hydrogen), gas clouds, stars, and galaxies - all receding from each other as space-time expanded, but all interacting with their mutual gravity. So the "speed" - if you can call it that - may have started out the same, but the interactions and random motions quickly changed things. Eventually, when stars formed and exploded, they released heavy elements (such as comprise the planets) into the expanding space. The release of heavy elements WAS a violent explosion, resulting in matter being expelled into clouds of gas and dust. Eventually, a large cloud of gas and dust would have enough gravity on its own to start collapsing. Unless conditions were PERFECT, it would be a rotating cloud (having angular momentum from the rotating galaxy or even from the stellar explosion that created it). That rotating cloud would eventually condense (gravitationally) to form the Sun, with the "left over" gas and dust forming the planets (still rotating). Again, unless conditions were PERFECT, the planets would assume orbits which were elliptical (only PERFECT conditions would result in circular orbits). There's usually too many random effects and gravitational interactions to create circular orbits. Some orbits may even have been parabolic or hyperbolic (like some comets), but these objects would only have been seen once, and would have left the Solar System forever. Only the stable, elliptical orbiting planets would have been left.

Hope that helps.

Prof. James Gort