Galaxies in bullet-time

Our ancestors, lacking artificial lights and thus light pollution, would have seen the stars in the sky more clearly than most people today can. A few of them would have seemed to move continuously, what we now call planets, but most of the stars were fixed, never moving from their place in the solid, rotating canopy. Apart from the occasional falling meteor or comet, this wonderful canopy of stars would remain the most constant and unchanging part of their world.

The canopy itself is for the most part darkest black, with some lighter smudges in places. In tribal legends, some anthropomorphic invisible giant would have spilled milk while moving over the perfectly black background, creating what we still call the Milky Way.

the flowing movement that we intuitively recognize in the spilling of the Milky Way never stopped

Since then, we have discovered that there is no solid canopy, and the stars are not fixed to anything at all. The universe by and large is not solid, and the flowing movement that we intuitively recognize in the spilling of the Milky Way never stopped, it is ongoing and continuous.

Perspective affects the way we perceive motion. To a human child looking up, a flying bird seems faster than an airliner, when in fact a jumbo jet is hundred times bigger than the bird, flying hundred times faster, hundred times more distant. Our senses are simply not equipped to grasp how big and how distant the objects we see in the night sky really are.

Even though the stars are actually moving faster than any bird or aeroplane, they are so distant from us that their angular velocity is negligible from our point of view. Luckily, they are also bright enough to shine over the vast distance, serving our ancestors as beacons to navigate their vessels; although the beacons were in fact moving faster than the vessels.

Everything in the sky is falling. But because there is no universal “down” or “up”, objects either fall in all directions, possibly colliding with others, or end up falling round and round each other, in rotating patterns.

Turbulent flow produces cloud-like shapes that we recognize, in vastly varying scales of magnitude, provided that the timescale is suitable. Stellar nurseries, planetary nebulae, supernova remnants, all have provided spectacular images through modern telescopes. The original exposure times have been in minutes, and many of the famous images are also false-color combinations of several exposures at different wavelengths. Yet these images look to our eyes more like short exposures of flow on Earth, than long exposures, because of the difference in scale of the flow.

Based on these astronomical images, special effects artists have produced dazzling visualizations of galaxies and nebulae, for TV shows like “Cosmos: A Spacetime Odyssey”. To break the illusion of a fixed 2D canopy, zooming into a static picture of the sky has been replaced with flying the camera into a computerized 3D model of a galaxy. This apparent motion can make the size of these celestial objects more magnificent to the human viewer, but the timescale of these fly shots is problematic.

Movement of the camera usually implies passing of time. When the imaginary camera slowly flies into the computer model of a galaxy, it moves the equivalent of thousands of light years a second. Yet the computer simulation of the galaxy in these shots is as static as the astronomical images they are based on, with no movement in the relative positions of the stars. The resulting fly shot looks as artificial as bullet-time, a galaxy frozen in mid-sneeze, with only the camera capable of any motion.

If instead the computer simulation was good enough to realistically animate long-term changes within the galaxy, time could be shown at the same enormous scale as distance in these computer generated shots. By compressing tens of thousands of years of galactic evolution into a few seconds, while the camera moves tens of thousands of light years, the fly shots would certainly look more lively. The apparent speed of ten thousand years a second would be long enough to make visible the proper motion of all the stars, along with multiple exploding stars, sparkling along turbulently flowing spirals. Like in the solar system, the fastest motion would occur near the center of the galaxy,  blurring the orbits of star systems into lines. At this timescale, a galaxy might resemble a cyclonic storm of sparkling fire.

It is unfortunately not possible to say how realistic such an animation would actually be. We humans have known about the existence of galaxies outside of our own for about a century now, so we cannot have any long-term data about how galaxies change. We don’t even know for certain how galaxies came to have the different shapes they do, and can only make plausible guesses. It also does not help that our current physics fails at simulating galaxies with any stability unless fudge factors are used.

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