Big Bang Secrets Swirling in a Fluid Universe


A new model that treats the matter in the universe as a fluid could enable researchers to retrace the flow of the cosmos back to the Big Bang. In this image, fluidlike wisps are created as ejected gas from a supernova collides with gas and dust in the surrounding interstellar medium. 

To a sound wave, the cosmos has the consistency of chocolate syrup.

That’s one discovery that scientists investigating the Big Bang have made using a new approach that treats the matter in the universe as a peculiar kind of fluid. They have calculated properties that characterize the universe’s behavior and evolution, including its viscosity, or resistance to deformation by sound waves and other disturbances.

“Twenty pascal-seconds is the viscosity of the universe,” said Leonardo Senatore, an assistant professor of physics at Stanford University — just as it is for the ice cream topping.

The viscosity calculation could help cosmologists sleuth out the details of the Big Bang, and possibly someday identify its trigger, by enabling them to track the fluidlike flow of the cosmos back 13.8 billion years to its initial state.

As other techniques for probing the Big Bang reach their limits of sensitivity, cosmologists are co-opting the fluid approach, called “effective field theory,” from particle physics and condensed matter physics, fields in which it has been used for decades. By modeling the matter swirling throughout space as a viscous fluid, the cosmologists say they can precisely calculate how the fluid has evolved under the force of gravity — and then rewind this cosmic evolution back to the beginning. “With this approach, you can really zoom in on the initial conditions of the universe and start asking more and more precise questions,” said Enrico Pajer, a postdoctoral research fellow at Princeton University with a recent paper on the technique that has been accepted by the Journal of Cosmology and Astroparticle Physics.

The more information that astronomers gather about the distribution of galaxies throughout space — known as the “large-scale structure” of the universe — the more accurate the fluid model becomes. And the data are pouring in. The sketchy scatter plot of several thousand nearby galaxies that existed in the 1980s has given way to a far richer map of millions of galaxies, and planned telescopes will soon push the count into the billions. Proponents believe that tuned with these data points, the fluid model may grow precise enough within 10 or 15 years to prove or refute a promising Big Bang theory called “slow-roll inflation” that says the universe ballooned into existence when an entity called an inflation field slowly slid from one state to another. “There has been a big community trying to do this type of calculation for a long time,” said Matias Zaldarriaga, a professor of cosmology at the Institute for Advanced Study in Princeton, N.J. Further in the future, the researchers say, applying effective field theory to even bigger datasets could reveal properties of the inflation field, which would help physicists build a theory to explain it.

“It’s obviously the right tool to be using,” said John Joseph Carrasco, a theoretical physicist at Stanford. “And it’s the right time.”

Senatore, Carrasco and their Stanford collaborator Mark Hertzberg first proposed the fluid approach to modeling the universe’s large-scale structure in a 2012 paper in the Journal of High Energy Physics, motivated by the Big Bang details it could help them glean from the increasingly enormous data sets. Other researchers have since jumped on board, helping to hone the method in a slew of papers, talks and an upcoming workshop. “We’re a small, plucky band of people who are convinced this is the way forward,” said Sean Carroll, a theoretical cosmologist at the California Institute of Technology.

A Fluid Cosmos

In water, chocolate syrup and other fluids, matter is smoothly distributed on large scales and partitioned into chunks, such as atoms or molecules, on small scales. To calculate the behavior of water on the human scale, where it is a fluid, it isn’t necessary to take into account every collision between H₂O molecules on the atomic scale. In fact, having to do so would render the calculation impossible. Instead, the collective effects of all the molecular interactions at the atomic scale can be averaged and represented in the fluid equations as “bulk” properties. (Viscosity, for example, is a measure of the friction between particles and depends on their size and shape as well as the forces between them.)

A similar trick works for modeling the evolution of the universe’s large-scale structure.

Just like water, the universe is smooth on large scales: The same amount of matter exists in one billion-light-year-wide region as the next. Slight variations in the matter distribution, such as more- and less-dense patches of galaxies, appear when you zoom in. At short distances, the variation becomes extreme: Individual galaxies are surrounded by voids, and within the galaxies, stars pinprick empty space. The matter distribution is constantly changing at every scale as gravity causes stars, galaxies and galaxy clusters alike to clump together and dark energy stretches the space between them. By modeling these changes, cosmologists can use the output — galaxy distribution data — to deduce the input — the initial conditions of the universe.

Written By: Natalie Wolchover
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  1. And here am I, thinking that the appearance of the Northern Lights in southern England is pretty remarkable ! But without the Earth’s magnetic field and its protective effect against the bombardment of solar radiation, there would be no life on Earth, no atmosphere as we know it and no known beings able to contemplate a “fluid” big bang.

    I am lucky to be around right now !

  2. Since I’m no physicist – I only visualise ideas……. If the universe is ‘fluid’ energy – then the big bang may have been an energy geyser ? implying that the pressurised energy came from the multiverse outside our universal membrane and inflated into our universe ?
    Viscosity must have everything to do with temperature cooling…
    It fascinated me about the early universe being cloudy until the temp dropped enough to clear the clouds and let star light shine for the first time….wow…..The temperature change was key to allowing life to begin…..

    Life force is in the light and I’m only Particular when someone is viewing me….otherwise I travel in waves on the surface of the fluid universe….

  3. I studied then taught Biology so a lot of this article hurts my head when I think about it, as does much of cosmology, particle & theoretic physics. However, I’m more than prepared to ‘have a go’ and think about this than swallow the idea that some old guy with a beard set up the whole thing because he was bored one day (or is that 7??). Now where’s the aspirin?

  4. The universe as fluid is not something new. Some spiritual systems have expounded this as such. Water is the source of life. It has always been a fact. The universe is a boundless big sea…

    • In reply to #6 by Omegatron:

      The universe as fluid is not something new. Some spiritual systems have expounded this as such. Water is the source of life. It has always been a fact. The universe is a boundless big sea…

      That does kind of demonstrate that they have no concept of “fluid” beyond liquid water!

  5. Sean Carroll

    Dang it, Sean M Carroll, not Sean B Carroll. Studious journalists would note the difference. Rant over.

    Shamelessly going OT – Noah, the movie, is set to open soon. It is admitted to be allegorical, not literal. So here we go again, debate over who’s “correct”.

    Purportedly, another “Jesus Entertainment” film, Son of God, is doing well at the box office. According to one source, the makers plan to upload this movie to internet, phones, etc.”Isn’t this great, even people living in secluded, far off places can watch !” Gag.

  6. The idea of fluid is water. That makes simple sense. But would a fish born into water be aware of the water it is born into? Similarly we are born into this seemingly empty Space that exist in both air and water. Are we like the fish that is born into the Space that we are unaware of. Spirituality speaks alot about the unseen and the sea they speak of is a sea of energies that too is found in fluid.

    In reply to #8 by Alan4discussion:

    In reply to #6 by Omegatron:

    The universe as fluid is not something new. Some spiritual systems have expounded this as such. Water is the source of life. It has always been a fact. The universe is a boundless big sea…

    That does kind of demonstrate that they have no concept of “fluid” beyond liqu…

  7. In reply to #11 by Omegatron:

    Spirituality speaks alot about the unseen and the sea they speak of is a sea of energies that too is found in fluid.

    Actually, no. Physics is clearly doing all the leg work here. Spirituality – after making complete guesses – just hops in after the fact and says “I knew that all along!” Making vague, bland, and imprecise metaphorical statements like “the universe is water”, which was a readily accessible metaphor in its day, and claiming that this part predicted the successful application of fluid dynamics in the physics of matter distribution (such as stars and galaxies) in the universe, is scraping the barrel of apologetics.

    By the same logic, you could argue that the originators of the constellations – who saw patterns in meaningless arrangements of stars from Earth’s POV – predicted the tendency to see shapes of nebulae like the crab and cat’s eye nebulae because both involve seeing matter form recognizable shapes in the night sky. The lack of connection between the two claims, coupled with the vagueness of what little connection there is, reveals the weakness in making the comparison in the first place.

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