Does gravity violate the second law of Thermodynamics?

Question

Thermodynamics states that it is almost impossible for all the gas particles in a room to gather themselves into one side of the room, as this would decrease the number of microstates (by 2^n), violating the second law of thermodynamics(spontaneous reduction of entropy cannot occur).
What explanation is given for gravity which can attract particles to one another in large scales, reducing microstates? i.e. a massive cloud of H2 condensing under gravity to form a star? What happens to the entropy?

I might add that H2 under the collapse of gravity gains heat from the increase in kinetic energy (and loss of gravitational potential energy).
If gravity is a force, how does it do work to decrease entropy? Ultimately, does gravity increase order? Does this violate the second law?

Answer 1

I like your question. In short, no, gravity can't cantradict the second law--otherwise it would not be a law. If you could prove that it does, that's nobel laureate material. In effect, gravity can be considered analogous to a compression. Now, when you think of a microstate--keep in mind that's of the dimension of the state in question, e.g. phase space. For a monoatomic gas, that's x and p, or six dimensions. Sure, as you crush the gas down, the number of states in x (space) decreases, but the gas now has more collisions, and heats up, which means the states available to p (momentum) increase.

Answer 2

Gravity Thermodynamics

Answer 3

Consider this.
Imagine an apple hanging from a tree.
We hollow out the apple and put an accelerometer inside.
We see the apple hanging motionlessly in the tree, yet the accelerometer indicates that the apple is accelerating upward.
Q: If the apple were accelerating upward what would be causing this acceleration? A: The tension on the stem.
When the stem breaks we see the apple accelerating toward the ground, yet now the accelerometer indicates zero acceleration.
The only "work" being done here is the stem holding the apple up against the "pull" of gravity.
That work is measured in newtons of tension on the stem.
When the stem breaks the tension goes to zero and the "work" stops.
Gravity is not a force. Gravity is simply a "space modifier".
(In the case of the collapsing cloud of gas, entropy still increases (heat)).

Answer 4

The gravitational collapse of a gas cloud involves a mechanical force - gravity - acting on the gas. The gravitational potential energy is converted into thermal energy as the gas collapses. This doesn't violate the laws of thermodynamics any more than compressing the gas with a piston or turbine. The second law of thermodynamics merely assures you that you won't be able to recover all the energy that was put into the gas.

Answer 5

You said it yourself that the second law of thermodynamics states that SPONTANEOUS reduction of entropy cannot occur. Gravity causes the atmosphere to "clump" around the earth because it is a force. It is an explainable (yet not totally understood) phenomena and therefore is not spontaneous.

Answer 6

Gravity is a force, that's the explanation. The example you give of the gas in a room is assuming that there is no special force acting on the gas.

We don't know the mechanism of gravity, but it is a force that we can measure.

Answer 7

When gas contracts to form a star, enormous quantities of entropy are generated in the form of heat.