Formation of Structure in the Universe

prodigious; but computers are always improving and, fortunately, many aspects of such a simulation are "parallelizable." This means that many separate processors can work together to solve the same problem.

When such a program is run, structures are, indeed, seen to arise and evolve, often in a way that, to the eye, reminds one of structures observed in today's universe. And, while these simulations are still very much in a state of "fine-tuning," they have taught us much about what kinds of structures arise in what kinds of universes.

Simulators are working to include more elements of physics than simply gravity, such as gas dynamics and radiative processes, so that they can "predict" what kinds of structures should be visible in the universe today. While they have had some success in this area, they are chiefly limited by "microscopic" processes such as the formation of individual stars within galaxies. This is already very difficult to understand, but it is totally impossible to simulate every individual star's forming and evolving within a computer model meant to represent the entire universe.

This "resolution" problem remains an active area of research and promises many advances. As successful as such simulations are and might become, we are still left with the nagging problem of "What is the dark matter?" It would be embarassing to learn that the nature of the dark matter is nothing like CDM, because a great fraction of the excellent effort in computer simulations would seem at once, frivolous.

Understanding the structure in the universe remains the largest problem in cosmology today: our computers aren't powerful enough, and we have no idea what the dark matter is.

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