I've always thought of a geologist as a guy who gets a pot of boiling stew, plunges it into liquid nitrogen, and then starts picking at the hard cold block that results and tries to figure out how the ingredients were added, in what order, when, and how much.

A photograph of a spiral galaxy resembles a satellite image of the rain bands of a hurricane, but the two processes which form the same morphology couldn't be more different.

The stars and gas clouds rotating about the galactic center interact gravitationally, and eventually the randomly distributed elliptical orbits become coupled like this. Its almost a stroboscopic epiphenomenon. I guess you could call it a kind of resonance, a standing wave slightly out of phase and drifting in frequency.

These are the density waves which form the spiral arms. Nothing is "flowing towards the center", the arms may not even be rotating in the same direction the galaxy is, or at the same speed. That spiral structure is not real at all, its a wave whose component atoms do not travel along with, they are washed over by it like a wave at sea moves through the water but no drop of water is moving along with it.

The stellar density (stars/cubic parsec)isn't any different in the arms than it is in the spaces between them, in fact, the stars are too massive to be affected by the wave as it sweeps by. So just what is it that we see?

As the wave sweeps through the disk, the great molecular clouds scattered randomly in the galactic plane are momentarily compressed as the wave rolls through them. The compression causes stars to condense out of the interstellar medium, like the mist that forms on the wing edges of a jet fighter. Most of these stars are small, run of the mill stars like the sun, or smaller, but a very few of them are massive blue supergiants that flare with the light of a thousand suns. These giants burn brightly, but briefly, and as the wave moves on they quickly burn out. When we look at the spiral arm of a galaxy we are seeing the bright stars that formed as the arm passed. These stars burn for only a few million years, and the galaxy as a whole rotates in a few hundred million years, so we are seeing only an instantaneous snapshot of a continuous rolling explosion of star formation.

The arms form and dissolve, reform, and sometimes splinter or break. They shimmer, like standing waves in a coffee cup dragged across a rough tabletop. And yet, many galaxies show no trace of spiral stucture at all. The whole system is a quivering mass of interference patterns and ripples that play out in extreme slow motion--like a still photograph of a forest in transition to its climax stage. We can't see it unfolding because it happens so slowly in our time frame.

And this is just the kinematics and dynamics. There are also chemical, radiation, magnetic, even acoustic phenomena going on, a continuous evolution of interacting matter and energy. The galaxy is alive. Is it evolving consciousness?

Maybe we're it.