« on: Yesterday at 19:44:37 »
But surely, if Space is "expanding", it must be doing so throughout the entire Universe. Including within the Solar System.It does. Relative to the sun, Earth is not orbiting the same 'space' as it was long ago. That orbit has expanded to closer to where Mars is now, and Earth, not having any additional energy imparted by said expansion, has been pulled back to its original distance from the sun as determined by the mass of the sun and the tangential velocity of Earth, neither of which is effected by said expansion.
Wouldn't that make planets in the Solar System, get further apart, as the Space between them expands?It only moves away the space through which the planets used to orbit. Gravity keeps the planets at their relatively constant* orbital distance.
* Not including actual changes to orbital energy that I enumerated in my prior post.
I notice that you refer to "Gravitational Binding". But doesn't Gravitational "binding" , ie "attraction" operate through Space, following the "Inverse Square" law.Binding refers to things in orbit around each other, which requires them to be within the hill radius of the primary. So the moon is gravitationally bound to Earth, not to the sun, despite the sun exerting a stronger force on it. But Mars is not gravitationally bound to Earth despite its finite distance from Earth. Yes, our planet does alter the trajectory of the other planets and the stars, but only the one natural object is bound to us.
Earth is bound to the sun. The sun is bound to the galaxy, possibly indirectly.
If the expansion rate increases enough, it can disrupt this binding and pull the planets away. In such a scenaro, the sun exits the galaxy, then the planets get pulled away, you get pulled off the surface of Earth, your arms get pulled off you, and finally the nucleus of every atom gets pulled apart because expansion works quicker than even the nuclear strong force can overcome. This is the big-rip scenario, and it seems the universe is not headed for such a fate.
So if Space expands, won't the "binding" or "attraction" correspondingly reduce?Binding is not a function of what the space is doing. It is a Newton/Kepler concept.
Which would result, in the case of the Solar System, in reduced gravitational force from the Sun on the planets.If the gravity didn't keep the planets at a constant distance despite expansion, then yes, it would reduce the force between such objects. They would cease to be bound in that case, and each planet in turn would simply exit the solar system, staring with the outside ones. This again is the rip scenario where expansion takes place faster (say 1025 times more than the current rate) than forces can compensate over the distances involved.
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