The text discusses the process of simulating the universe on a computer, starting with the Swedish astronomer Eric Holmberg's first simulation in 1941 using light bulbs to represent stars in a galaxy disk. The text also mentions the three-body problem and the need for numerical calculations or n-body simulations in astrophysics. It highlights the computational challenges in simulating the universe, especially for large-scale structures like galaxies. It also mentions the use of tree codes and particle mesh methods to reduce the number of calculations needed. The text talks about the use of smoothed particle hydrodynamics (SPH) for simulating flows of gas in astrophysical situations. It also mentions the use of these simulations to observe phenomena like star formation, planet formation, and galaxy formation. The text concludes by discussing the limitations of these simulations and the potential for future advancements in the field.
1. The text discusses the event of the Andromeda galaxy and our Milky Way colliding in around four and a half billion years.
2. The delicate spiral arms of the galaxies will be yanked almost out of their sockets.
3. The denizens of the galaxies may look back with relief as the dislocated galaxies retreat from their future night skies.
4. The galaxies will pause for a hundred thousand years before falling back together in a series of whirl and collisions.
5. All spiral structure will be obliterated, gas will be compacted to produce waves of supernovae.
6. The giant Milky Dromeda Galaxy will have been born from the event described.
7. This event will happen as surely as the sun will rise tomorrow.
8. The chaotic gravitational and hydrodynamic interactions with countless stars, gas, and dark matter particles have been calculated over billions of future years.
9. Simulations of Galaxy collisions are just the beginning.
10. The text mentions that it is possible to build a universe in a computer and to see whether there's a limit to what we can simulate.
11. The first simulation of the universe was conducted by the Swedish astronomer Eric Holmberg in 1941 when the first programmable computers were being assembled.
12. Holmberg didn't use a computer, but theoretically 37 light bulbs on a plane, each one representing billions of stars in a spiral galaxy disk.
13. The light from each bulb was its gravity.
14. A galvanic cell could determine in which direction the intensity of light was strongest.
15. Holmberg started with a pair of these light bulb galaxies next to each other and then moved the bulbs according to their new velocities.
16. The two galaxies collided just as with our modern supercomputer simulations.
17. The text discusses the three-body problem, which is the problem of writing down equations describing the trajectories of a pair of massive bodies moving in each other's gravitational fields.
18. The three-body problem doesn't have any simple set of equations describing their future evolution under gravity.
19. Holmberg had to solve the problem with light bulbs and did what we call a numerical calculation.
20. This particular type of numerical calculation is called an n-body simulation.
21. Newton's laws of motion and gravity are applied over a series of time steps each step is short enough that we can assume that the global gravitational field is constant.
22. The text mentions that the room-sized computer used to calculate the Apollo trajectories had about the computing power of your smartphone.
23. The text discusses the method of doing end-body simulations of entire galaxies using the method that was described.
24. In the simplest type of end-body simulation, you need to compute the effect of every particle on every other particle.
25. In the real challenge in astrophysics, we often have to deal with huge ranges in scale.
26. The text mentions the original approaches to doing this is a so-called tree code.
27. The tree code works by starting with a volume full of particles each with its starting position and velocity.
28. The text discusses the particle mesh method in which particles are converted into a density distribution and a gravitational potential across the grid.
29. The text mentions that modern mesh codes also do classic particle-particle interactions at short ranges to improve accuracy at small scales.
30. The text discusses how modern simulations often use an amalgam of these methods.
31. The text mentions that astrophysicists often inject all sorts of other physics into their simulations.
32. The text discusses the complexity of including magnetic fields or of Einstein's general relativity when the gravitational field becomes very strong.
33. The text mentions that using parallelized code on modern computing clusters, we can compute some pretty insane simulations.
34. The text discusses how we can see how stars form in multitudes from collapsing gas clouds and how planets then coalesce in the disks surrounding those stars.
35. The text mentions that we can watch as galaxies form with gas and dark matter interacting to produce waves of star formation and supernovae.
36. The text discusses the possibility of simulating a real Universe in which creatures evolve that can themselves