Cooking a Universe
According to Dr. Felipe Menanteau, all of human learning is driven by two fundamental questions.
“‘Where did everything come from?’ and ‘Are we alone?’ are what we humans are asking all of the time,” he says.
Menanteau (right) is a Research Scientist at the National Center for Supercomputing Applications (NCSA) and Research Associate Professor of Astronomy at the University of Illinois. He studies the Universe, so he spends a lot of time thinking about these questions and devising ways to answer them.
He has some good news. We’ve made tremendous progress on answering the first one. And we’re inching ever closer to the second. In the next fifty years, Menanteau says, scientists will launch space missions that will make it possible to use powerful telescopes and other technologies to search for life signatures in the atmospheres of distant planets. In our lifetime, then, we’ll know if humans are the only ones looking up into the great, wide dark.
But there’s a lot of work between here and the not-too-distant future. Menanteau, the Dark Energy Survey team, and a supercomputer are helping light the way to this brave new world, one sky mapping exercise at a time.
There is an old Buddhist parable about the sky. Bruce Lee fans have certainly heard it before.
In a famous scene from Enter the Dragon, Lee trains his young protégé in martial arts. The child kicks out at Lee, but he does so in rage. Lee rebukes him, and when the child strikes with controlled energy rather than passion, Lee asks him if he can feel the difference.
The child begins intellectualizing the experience. “Let me think,” he says, which prompts Lee to deliver one of the most classic lines in American film:
“Don't think. Feel. It is like a finger pointing away to the moon. Don't concentrate on the finger or you will miss all that heavenly glory. Do you understand?”
Parables are parables because they aren’t meant to be taken literally. Instead, parables are stories about physical things that are then abstracted into lessons about larger concerns like life or wisdom or faith.
But this parable turns the genre on its head.
We can understand the finger pointing toward the moon in a traditional way. The finger is a physical thing pointing to a larger idea--glory, wonder, wholeness--here embodied by the moon.
But the moon, we know, is no less physical than the finger. It’s a hunk of rock. It is also a hunk of rock that shines above us, drawing our eyes ever upward. The moon is thus both physical and philosophical, both known thing and burning mystery, at the same time. The danger comes when we stop looking up at that real, beautiful moon and instead get lost in the tools that exist only to remind us to keep looking up.
“The heart of science isn’t technology; it’s philosophy,” says Menanteau.
It all comes back to answering those two guiding questions, as old and as weighty as the moon itself. And to do that, we need to recreate the Universe.
Cooking a universe
In the southern hemisphere is a cluster of galaxies known as El Gordo, the fat one. Menanteau, originally from Chile, could have just called the galaxy cluster by the standard numbering classification system: ACT-CL 0102-4915.
But that seemed too weak a name to support all that heavenly glory.
Instead, when he and his collaborators at Rutgers University found El Gordo four years ago, the phrase immediately popped into his mind. “It’s the fattest galaxy we know of, El Gordo,” he says with a laugh. “It is so massive that it is at the limit that is allowed at the very limits of our models.”
Galaxy Clusters MACS J0416.1-2403 and MACS J0717.5+3745 (Hubble, Chandra, and JVLA). Image provided by http://hubblesite.org/images/news/release/2016-08.
El Gordo is a galaxy cluster. It’s made up of thousands of galaxies bound up together by gravity. The sheer girth of El Gordo is impressive for its own sake, but it’s also important for science.
Questions like why do galaxies look the way they do, how do they form, and how do they evolve (do they go from smaller to bigger or bigger to smaller) inform all of our models of how the Universe formed. Cluster galaxies are the biggest structures in the Universe. And the number and size of them as a function of cosmic time make our models more accurate and get us closer to answers.
Cosmologists just need a supercomputer and a few good food metaphors.
“We know how you make a Universe. We know the ingredients that we need to start, such as the amount of normal matter, dark matter, cosmological constant, fluctuations of matter, ionization optical depth and the expansion rate. We feed these ingredients into a supercomputer and cook a Universe, essentially. To change the recipe, we move the parameters just a little bit at a time, and cook again,” Menanteau explains.
They will keep cooking, adding bits of new information, removing bits of the old, until the model matches what we know of the Universe and fills in the gaps of what we don’t.
Despite (almost) popping the paradigms we have for galaxy models, El Gordo was found using these standard methods.
The night sky is not static. Things move slightly as the earth spins, clouds shift and scurry, and light seems brighter or fainter depending upon time, weather, and pollution. To spot galaxies, however, you have to be able to account for these changes. Menanteau is part of the Dark Energy Survey Collaboration, which is observing the southern sky over Chile for a total of five hundred nights over five years. They take picture after picture with a state-of-the-art camera, and then every night they funnel these data back to NCSA and to their nodes on the Illinois Campus Cluster Program (ICCP) for processing. The supercomputer then tells them if they need to retake any photos, or if they have enough good data to continue with the project.
What they’re looking for is light. Light helps them understand darkness, specifically, dark matter and dark energy. As it turns out, light and dark are both crucial ingredients in building a galaxy, which themselves are the building blocks of the Universe.
Members of the Dark Energy Survey also look for what are known as “standard candles”: type Ia supernovas.
Type Ia supernovas are a type of star explosion that occurs in a close binary system, where one of the stars is a white dwarf. As the gas of the companion star accumulates onto the white dwarf, the white dwarf sets off a runaway nuclear reaction that eventually leads to a cataclysmic supernova outburst. Because the explosion occurs when the accretion reaches a typical critical mass, when they explode, Type Ia do so with the same luminosity. As such, we can use them to measure distances. For more information on Ia supernovas, see http://hubblesite.org/hubble_discoveries/dark_energy/de-type_ia_supernovae.php.
For Menanteau, looking up into the sky is a lot like looking down into the ground. The Dark Energy Survey team is not dissimilar from the archaeologists who unearthed Pompeii, brushing off layers and layers of strata to find perfectly preserved loaves of bread still sitting in 2,000-year-old ovens.
There is one notable difference, however. When Pompeii was buried, everything stopped. The earth upon which Pompeii grew continued to spin, but it, too, exists in a kind of frozen state, limited as it is to a certain size, shape, and brightness. We will never be more than what we are right now.
But the Universe is expanding. And it’s getting darker.
The Universe is a lot like cake batter. Our galaxy, then, is like a raisin in the batter. (Why anyone would ruin cake with raisins is perhaps the most vexing question in the Universe.) When the cake is baked, the batter expands in the heat. But the raisin stays the same.
As the Universe expands, all of the galaxies are moving away from each other.
This is a delicious rendering of what happened about 14 thousand millions of years ago, when the Universe started through what is known as the Big Bang. The title of the event is somewhat disingenuous; the Universe didn’t explode like the word “bang” might lead us to believe. It expanded. And it hasn’t stopped since.
“Ever since the 1930s, when we discovered the Universe is full of galaxies, we’ve known that objects in the Universe are moving away from each other,” Menanteau explains. “Something is pushing them apart and with tremendous force.”
What’s more, this push is happening at a faster rate. Remember those supernovas? They’re very bright, so we can see them from very far away. But they’re fainter now than they used to be, because the Universe is bigger than it used to be.
(Image at right: Orion's Nebula (DECam, DES Collaboration). Image provided by https://www.darkenergysurvey.org/multimedia/photo-gallery/)
What’s growing the dark? It’s the other force besides gravity that shapes galaxies and clusters of galaxies: dark energy.
Dark energy has us a bit in the dark right now. The Universe is made up of things that we don’t understand. We can’t see them but we know that they’re there because we can feel them.
“Less than 5% of energy in the Universe is made up of normal matter. That’s our planet, it’s us, it’s all of the atoms in the periodic table. But around 25% is made up of dark matter. It doesn’t emit at any wavelength in the electromagnetic spectrum and it doesn’t interact with other particles. But we can feel its gravitational potential,” Menanteau says.
We only know the mass of a lot of objects in the Universe--galaxies like El Gordo, for example--because of things we can’t see. Cosmologists take indirect measurements of how these objects interact with others and determine mass from these interactions. But dark matter is cold; it is non-interactive. Dark energy, on the other hand, is toasty by comparison.
Where there is gravity, there, too, is dark energy. But it moves on objects in ways opposite to gravity. Like a galactic version of former First Lady Michelle Obama, when gravity goes low, dark energy goes high.
“Imagine throwing a ball up in the air and, somehow, instead of coming back to you, it keeps going up faster and faster,” explained Menanteau.
All structures in the Universe, from El Gordo to the carbon in your bones, come from this Superman-vs.-Godzilla struggle between gravity and dark energy. But it is not a fair fight. As the Universe grows, dark energy grows with it and the Universe expands forever until it reaches what is known as a state of thermal equilibrium, in which nothing can happen.
To better understand the accelerated expansion of the Universe, scientists will continue to make and use the tools we call technology. But to think that the point of science is to make these bigger and better technologies instead of answering these huge questions--how did we get here? What is this place? Is anyone else out there?--is to confuse the finger for the moon.
“This work doesn’t save anyone’s life.” Menanteau says.
“Instead, it helps us understand what life is.”
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