"Long before it's in the papers"
January 27, 2015


First realistic universe simulation said to be created

May 9, 2014
Courtesy of 
and World Science staff

Move over, Ma­trix—as­tro­no­mers have done you one bet­ter, cre­at­ing what they call the first real­is­tic “vir­tual uni­verse” us­ing a com­put­er sim­ula­t­ion.

Be­fore, “no sin­gle sim­ula­t­ion was able to re­pro­duce the uni­verse on both large and small scales” at once, said astro­nom­er Mark Vo­gels­berg­er, a col­la­bo­ra­tor in the work. Called Il­lus­tris, it mim­ics a pe­ri­od of 13 bil­lion years, al­most the whole es­ti­mat­ed age of the uni­verse. 

A real pho­to of ga­lax­ies (top) com­pared with a view from the Il­lus­tris sim­u­la­tion (bot­tom), said to ac­cu­rate­ly re­pro­duce the sizes, types, and col­ors of ga­lax­ies in the uni­verse. The im­age on the home page is a com­pos­ite from the Il­lus­tris sim­u­la­tion, and cen­tered on the most mas­sive gal­axy clus­ter known to­day. It morphs from con­cen­tra­tions of dark mat­ter (at left in blue and pur­ple) to nor­mal mat­ter made most­ly of hy­dro­gen and he­li­um gas (at right in red, or­ange and yel­low) . (Credit: NA­SA / Il­lus­tris Col­lab.) 

Pre­vi­ous sim­ula­t­ions were ham­pered by lack of com­put­ing pow­er and the com­p­lex­i­ties of phys­ics, sci­en­tists said. As a re­sult they were lim­it­ed in de­tail, or in the space co­vered. They had trou­ble mi­mick­ing in­ter­ac­tions—thought to strongly af­fect how the uni­verse de­vel­oped—be­tween star form­a­t­ion, stel­lar ex­plo­sions, and gi­ant black holes.

Il­lus­tris ass­umes the pres­ence of “dark mat­ter,” ma­te­ri­al be­lieved by most as­tron­omers to be an un­seen in­gre­di­ent of the uni­verse though it is de­tected only through its gra­vity. 

The sim­ula­t­ion cu­be con­tains 12 bil­lion pix­els, or res­o­lu­tion points. The team ded­i­cat­ed five years to de­vel­op­ing the pro­gram. A sim­ula­t­ion run-through took three months, us­ing 8,000 com­put­er pro­ces­sors run­ning to­geth­er—an av­er­age desk­top com­put­er would have tak­en over 2,000 years to do it.

The dig­it­al re-enactment “be­gins” when the uni­verse was about a thou­sandth of its cur­rent es­ti­mat­ed age. 

When as­tro­no­mers ran it, by the time it reached “p­re­sen­t,” they counted more than 41,000 ga­lax­ies in the cu­be. There was a real­is­tic mix of gal­axy types, in­clud­ing spir­al ga­lax­ies like our Milky Way, they said. It al­so recre­ated large-scale struc­tures like gal­axy clus­ters and so-called “bub­bles” and “voids” of a cos­mic “we­b,” and, on a smaller scale, the chem­is­t­ries of in­di­vid­ual ga­lax­ies.

Since light trav­els at a fixed speed, the far­ther away as­tro­no­mers look, the far­ther back in time they can see. A gal­axy one bil­lion light-years away is seen as it was a bil­lion years ago. Tele­scopes can give us views of the early uni­verse by look­ing fur­ther out, but can’t show stages in one gal­ax­y’s ev­o­lu­tion. 

With Il­lus­tris, “we can go for­ward and back­ward in time. We can pause… and zoom in­to a sin­gle gal­axy or gal­axy clus­ter to see what’s really go­ing on,” said study co-au­thor Shy Genel of the Cen­ter for As­t­ro­phys­ics. It’s “like a time ma­chine.”

The team is re­leas­ing a high-definition vid­e­o, which morphs be­tween dif­fer­ent com­po­nents of the sim­ula­t­ion to high­light var­i­ous lay­ers. They’re al­so re­leas­ing sev­er­al smaller vid­e­os and im­ages at www.illustris-project.org. The re­sults are re­ported in the May 8 is­sue of the jour­nal Na­ture, with Vo­gels­berger, of the Ma­ssa­chu­setts Insti­tute of Tech­no­logy/Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics, as lead au­thor.

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Move over, Matrix—astronomers have done you one better, creating what they call the first realistic “virtual universe” using a computer simulation. Before, “no single simulation was able to reproduce the universe on both large and small scales” at once, said lead author and study collaborator Mark Vogelsberger. Called Illustris, it mimics a period of 13 billion years, almost all of the estimated age of the universe. Previous simulations were hampered by lack of computing power and the complexities of physics, scientists said. As a result they were limited in detail, or in the space covered. They had trouble modeling complex interactions—thought to strongly affect how the universe developed—between star formation, stellar explosions, and giant black holes. Illustris includes both normal matter and “dark matter,” material believed to be an unseen ingredient of the universe and detected only through its gravity. The simulation cube contains 12 billion pixels, or resolution points. The team dedicated five years to developing the program. A simulation run-through took three months, using 8,000 computer processors running together—an average desktop computer would have taken over 2,000 years to do it. The digital re-enactment “begins” when the universe was about a thousandth of its current estimated age. When astronomers ran it, by the time it reached “present,” they counted more than 41,000 galaxies in the cube. There was a realistic mix of galaxy types, including spiral galaxies like our Milky Way, they said. It also recreated large-scale structures like galaxy clusters and so-called “bubbles” and “voids” of a cosmic “web,” and, on a smaller scale, the chemistries of individual galaxies. Since light travels at a fixed speed, the farther away astronomers look, the farther back in time they can see. A galaxy one billion light-years away is seen as it was a billion years ago. Telescopes can give us views of the early universe by looking further out, but can’t show stages in one galaxy’s evolution. With Illustris, “we can go forward and backward in time. We can pause… and zoom into a single galaxy or galaxy cluster to see what’s really going on,” said study co-author Shy Genel of the Center for Astrophysics. It’s “like a time machine.” The team is releasing a high-definition video, which morphs between different components of the simulation to highlight various layers. They’re also releasing several smaller videos and images online at www.illustris-project.org. The results are reported in the May 8 issue of the journal Nature, with Vogelsberger, of the MIT/Harvard-Smithsonian Center for Astrophysics, as lead author.