Atoms may hum a tune from grand cosmic symphony

April 19, 2018, Joint Quantum Institute
An expanding, ring-shaped cloud of atoms shares several striking features with the early universe. Credit: E. Edwards/JQI

Researchers playing with a cloud of ultracold atoms uncovered behavior that bears a striking resemblance to the universe in microcosm. Their work, which forges new connections between atomic physics and the sudden expansion of the early universe, was published April 19 in Physical Review X and featured in Physics.

"From the atomic physics perspective, the experiment is beautifully described by existing theory," says Stephen Eckel, an atomic physicist at the National Institute of Standards and Technology (NIST) and the lead author of the new paper. "But even more striking is how that theory connects with cosmology."

In several sets of experiments, Eckel and his colleagues rapidly expanded the size of a doughnut-shaped cloud of , taking snapshots during the process. The growth happens so fast that the cloud is left humming, and a related hum may have appeared on cosmic scales during the rapid expansion of the early universe—an epoch that cosmologists refer to as the period of inflation.

The work brought together experts in and gravity, and the authors say it is a testament to the versatility of the Bose-Einstein condensate (BEC)—an ultracold cloud of atoms that can be described as a single quantum object—as a platform for testing ideas from other areas of physics.

"Maybe this will one day inform future models of cosmology," Eckel says. "Or vice versa. Maybe there will be a model of cosmology that's difficult to solve but that you could simulate using a cold atomic gas."

It's not the first time that researchers have connected BECs and cosmology. Prior studies mimicked and searched for analogs of the radiation predicted to pour forth from their shadowy boundaries. The new experiments focus instead on the BEC's response to a rapid expansion, a process that suggests several analogies to what may have happened during the period of inflation.

The first and most direct analogy involves the way that waves travel through an expanding medium. Such a situation doesn't arise often in physics, but it happened during inflation on a grand scale. During that expansion, space itself stretched any waves to much larger sizes and stole energy from them through a process known as Hubble friction.

In one set of experiments, researchers spotted analogous features in their cloud of atoms. They imprinted a sound wave onto their cloud—alternating regions of more atoms and fewer atoms around the ring, like a wave in the early universe—and watched it disperse during expansion. Unsurprisingly, the sound wave stretched out, but its amplitude also decreased. The math revealed that this damping looked just like Hubble friction, and the behavior was captured well by calculations and numerical simulations.

"It's like we're hitting the BEC with a hammer," says Gretchen Campbell, the NIST co-director of the Joint Quantum Institute (JQI) and a coauthor of the paper, "and it's sort of shocking to me that these simulations so nicely replicate what's going on."

In a second set of experiments, the team uncovered another, more speculative analogy. For these tests they left the BEC free of any but provoked the same expansion, watching the BEC slosh back and forth until it relaxed.

In a way, that relaxation also resembled inflation. Some of the energy that drove the expansion of the universe ultimately ended up creating all of the matter and light around us. And although there are many theories for how this happened, cosmologists aren't exactly sure how that leftover energy got converted into all the stuff we see today.

In the BEC, the energy of the expansion was quickly transferred to things like sound waves traveling around the ring. Some early guesses for why this was happening looked promising, but they fell short of predicting the energy transfer accurately. So the team turned to that could capture a more complete picture of the physics.

What emerged was a complicated account of the energy conversion: After the expansion stopped, atoms at the outer edge of the ring hit their new, expanded boundary and got reflected back toward the center of the cloud. There, they interfered with atoms still traveling outward, creating a zone in the middle where almost no atoms could live. Atoms on either side of this inhospitable area had mismatched quantum properties, like two neighboring clocks that are out of sync.

The situation was highly unstable and eventually collapsed, leading to the creation of vortices throughout the cloud. These vortices, or little quantum whirlpools, would break apart and generate sound waves that ran around the ring, like the particles and radiation left over after inflation. Some vortices even escaped from the edge of the BEC, creating an imbalance that left the cloud rotating.

Unlike the analogy to Hubble friction, the complicated story of how sloshing atoms can create dozens of quantum whirlpools may bear no resemblance to what goes on during and after inflation. But Ted Jacobson, a coauthor of the new paper and a physics professor at the University of Maryland specializing in black holes, says that his interaction with atomic physicists yielded benefits outside these technical results.

"What I learned from them, and from thinking so much about an experiment like that, are new ways to think about the cosmology problem," Jacobson says. "And they learned to think about aspects of the BEC that they would never have thought about before. Whether those are useful or important remains to be seen, but it was certainly stimulating."

Eckel echoes the same thought. "Ted got me to think about the processes in BECs differently," he says, "and any time you approach a problem and you can see it from a different perspective, it gives you a better chance of actually solving that problem."

Future experiments may study the complicated transfer of energy during more closely, or even search for further cosmological analogies. "The nice thing is that from these results, we now know how to design experiments in the future to target the different effects that we hope to see," Campbell says. "And as theorists come up with models, it does give us a testbed where we could actually study those models and see what happens."

Explore further: Cosmologists a step closer to understanding quantum gravity

More information: A Rapidly Expanding Bose-Einstein Condensate: An Expanding Universe in the Lab. Phys. Rev. X. DOI: 10.1103/PhysRevX.8.021021

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Whydening Gyre
not rated yet Apr 19, 2018
An explanation for Brownian motion...?
BendBob
3 / 5 (2) Apr 19, 2018
Hmmm, a hum? Can sound travel through space? I thought not.
b_man
1 / 5 (7) Apr 19, 2018
The problem with this, they match their science to their religion. There was no big bang. The universe had no beginning. Start again...
Da Schneib
5 / 5 (3) Apr 19, 2018
@Bend, if the space has matter in it, what then? Ever heard of the intergalactic medium or the intra-cluster medium?
BendBob
3 / 5 (2) Apr 19, 2018
No, but I have heard sound here, in the air. But, science says not in space. Perhaps, general science is only telling me part of the story!?! Maybe next term (not! I'm 70 :)

Thanks
Da Schneib
5 / 5 (2) Apr 19, 2018
Well, as it turns out, in a plasma, because the electromagnetic force can act across empty space, sound can propagate (though it is far below our ability to hear, it is still technically sound). And such acoustic waves have been detected in various contexts in astrophysics.

Now, in this particular case, either in the context of the BEC, or the nascent universe undergoing inflation, the matter is thick enough to support sound waves even by close contact much as we know it here on Earth. So there's that to consider as well.

Sound as we know it, however, occurs in uncharged gas, and you're correct for that kind of sound; it doesn't propagate in space. But that's not the only kind of sound!
Whydening Gyre
not rated yet Apr 19, 2018
And I'm wonderin'...
could this be related to gravity somehow...?
Da Schneib
5 / 5 (1) Apr 19, 2018
@Whyde, they got some gravity physicists to look things over and they found them interesting. But in the BEC context there's no gravity involved. So it's kinda hard to say without knowing more about what you have in mind when you say "related to gravity somehow."
humy
5 / 5 (6) Apr 20, 2018
The problem with this, they match their science to their religion. There was no big bang.

Here is the evidence that tells us there was a big bang;

https://en.wikipe...evidence

No religion there! Just good science. There clearly was a big bang (albeit that term "big bang" is misnomer because it wasn't an explosion but space itself that expanded).

Besides, why cannot there be both a god/gods and a big bang? There wouldn't be any logical contradiction with having both (although god/gods/tooth-fairy would be an unnecessary hypothesis either way and should be assumed false via application of Occam's razor until if or when we have adequately empirical evidence for god/gods/tooth-fairy). There being no big bang wouldn't be evidence for a god/gods/tooth-fairy just as there being a big bang wouldn't be evidence for no god/gods/tooth-fairy; its pretty much irrelevant actually.
mackita
1 / 5 (1) Apr 20, 2018
Here is the evidence that tells us there was a big bang..
LOL, nothing is more volatile than the "scientific evidence". Most of evidence linked by you actually deals with expansion of space time and the inflation concept is already doubted (1, 2, 3...) in similar way, like the string theory, WIMPs dark matter and similar speculative stuffs.
No religion there! Just good science

"Good science" is based on falsification of theories - not their parroting at nauseam. In particular the Big Bang theory doesn't fit Occam's razor at all, as it's all based of assumptions deeply violating established physics (formation of Universe from nothing, fast expansion from no reason).
mackita
1 / 5 (1) Apr 20, 2018
so the team turned to numerical simulations that could capture a more complete picture of the physics
This is typical postmodern BS: a speculation (no link to cosmic phenomena has been actually given or even studied) based on numerical simulation (no actual experimental results were made). With such an attitude you could prove everything about everything and still take money for it - this is what the embezzling of tax payers money is called in its pure crystalline form.
Whydening Gyre
5 / 5 (2) Apr 20, 2018
@Whyde, they got some gravity physicists to look things over and they found them interesting. But in the BEC context there's no gravity involved. So it's kinda hard to say without knowing more about what you have in mind when you say "related to gravity somehow."

I kinda got thinking bout it, when we consider gravity waves...
Gravity only affects mass - matter. Same with sound waves.
And, (as Benni has stated) since gravity is mass dependent, any/all mass in motion (and you'll notice - ALL of it is) is going to create waves, regardless of how significant. Enough waves of all sizes and shapes bouncing around and...
Anyway... WIP.
IwinUlose
5 / 5 (2) Apr 20, 2018
@Whyde, they got some gravity physicists to look things over and they found them interesting. But in the BEC context there's no gravity involved. So it's kinda hard to say without knowing more about what you have in mind when you say "related to gravity somehow."

I kinda got thinking bout it, when we consider gravity waves...
Gravity only affects mass - matter. Same with sound waves.
And, (as Benni has stated) since gravity is mass dependent, any/all mass in motion (and you'll notice - ALL of it is) is going to create waves, regardless of how significant. Enough waves of all sizes and shapes bouncing around and...
Anyway... WIP.


Gravity is the effect of mass on spacetime, the medium in which the waves propagate, which in turn acts on other local mass.

That might help with what's got you thinking?
Da Schneib
3.7 / 5 (3) Apr 20, 2018
@Whyde, more food for thought: most gravity waves are incredibly weak. That's because gravity itself is pretty weak. It just looks strong because it has no negative and therefore builds up without anything to limit it.

Also, it's incorrect to state that gravity doesn't affect things other than matter. For example, it affects light (if you think of it as a force; from the relativistic point of view it affects spacetime and the light just naturally follows geodesics. On the other hand, the same may be said of matter...).
rrwillsj
3 / 5 (2) Apr 20, 2018
DS, {KISS} the problem you are having with explaining things to BendBob is that you did not use the word vacuum.

Which is what Bb (and myself also) are educated to imagine when we think of space. No material, nothing to vibrate to make any sound.

Of course space is not empty and over giga-parsecs of distance, with modern instrumentation, there is a whole lot of interaction and reactions going on across that scale of the cosmos.

Holy Cow, Brahmin. Should we be measuring in Lakh Crore?

If Space/Time has any sort of reality? There remains explaining it's existence.

Αρμονία των σφαιρών. Which came first the music or the instrument? And was a composer actually necessary? Than why do we need editors?
tallenglish
not rated yet Apr 21, 2018
This is a good way to explain both how galaxies form and also planets around stars as both are large versions of wirlpools.
Whydening Gyre
not rated yet Apr 21, 2018
This is a good way to explain both how galaxies form and also planets around stars as both are large versions of wirlpools.

indeed...
Do galactic clusters also arrange in the "whirlpool" manner?
(I believe they do...)
Is gravity a "hum" derived from all those whirlpools?

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