Search FQXi


RECENT FORUM POSTS

Steve Dufourny: "happy to see you, but where were you Tom ? :)" in Manipulating the Quantum...

Thomas Ray: "Peter, Bravo!" in Manipulating the Quantum...

Joe Fisher: "Dearn Steve, There am no such a thing as a humanly contrived abstract..." in Watching the Observers

Steve Agnew: "Please understand that an infinite anything is unknowable and unmeasurable..." in Watching the Observers

kurt stocklmeir: "spring constant of time and space is not linear - this influences a lot of..." in Alternative Models of...

Kevin Adams: "Very interesting theme! Thanks a lot for this information. I just going to..." in Multiversal Journeys —...

Lorraine Ford: "Dear Rajiv, I have already addressed your 3 points, but I will put it to..." in FQXi Essay Contest 2016:...

munized ward: "Variety exists inside all populaces of life forms. This happens somewhat in..." in Natural Selection in...


RECENT ARTICLES
click titles to read articles

Watching the Observers
Accounting for quantum fuzziness could help us measure space and time—and the cosmos—more accurately.

Bohemian Reality: Searching for a Quantum Connection to Consciousness
Is there are sweet spot where artificial intelligence systems could have the maximum amount of consciousness while retaining powerful quantum properties?

Quantum Replicants: Should future androids dream of quantum sheep?
To build the ultimate artificial mimics of real life systems, we may need to use quantum memory.

Painting a QBist Picture of Reality
A radical interpretation of physics makes quantum theory more personal.

The Spacetime Revolutionary
Carlo Rovelli describes how black holes may transition to "white holes," according to loop quantum gravity, a radical rewrite of fundamental physics.


FQXI ARTICLE
June 26, 2017

Face Off: Building a Toy Universe to Pit Quantum Theory Against Gravity
Using superconducting circuits to create a curved-spacetime analog with stronger gravity than our cosmos.
by Nicola Jones
FQXi Awardees: Sorin Paraoanu
April 23, 2015
Bookmark and Share


Sorin Paraoanu
In his lab at Aalto University, Paraoanu plans to build an analog of
spacetime.

Credit: Sorin Paraonau
You’d have to go to extremes to carry out an experiment on a black hole: the nearest is thousands of light years away, and it’s not clear if you could ever get much information out of one. That’s a shame for physicists who would love to get their hands on one because it’s an arena in which gravity and quantum physics face off. But Sorin Paraoanu, a quantum physicist at the Aalto University School of Science in Finland, has come up with a way to custom-build a toy environment in his lab to test what happens when these two fundamental descriptions of reality collide.

If Paraoanu succeeds, the result will be like "a lego game for theorists working on unifying gravity and quantum physics," he says.

Physicists would love to learn more about this clash in order to reconcile the two titanic theories into a single theory of quantum gravity. The classical, gravitational theory of general relativity is hugely successful at describing the behaviour of large-scale objects by thinking in terms of their warping of spacetime. And quantum theory is wonderful for describing behaviour in the world of atoms. But these two can come into conflict when trying to describe situations with high energy packed into a small space—like black holes.

Doing any experiments in this regime is very difficult, however. One solution is to create an analog for gravity that is more powerful, and bends space-time more, than gravity itself. This ensures that the gravity analog will come into conflict with quantum rules in situations far less extreme than a black hole—involving less energy and a larger space. Paraoanu plans to do this using a "metamaterial" made from a chain of superconducting quantum interference devices (SQUIDs), each of which can be fine-tuned to precisely control how the material’s refractive index changes along its length. This is mathematically equivalent to changing the speed of light through the material or, in the context of building a gravity analog, changing the curvature of spacetime that light moves through. "In these analog systems we can be more efficient than real gravity," says Paraoanu. "We can bend spacetime as if we were near a black hole."

Spacetime SQUIDs

Sorin Paraoanu talks about testing quantum gravity and inflation using an artificial spacetime.

LISTEN:

Go to full podcast

Some popular models of quantum gravity propose that spacetime itself isn’t one classical continuum, but instead made up of quantized bits and pieces—and Paraoanu’s setup should be able to explore this notion. In the real world, one would have to examine impossibly small scales of space to see such a situation, zeroing down to 1.6×10−35 m (for comparison today’s most powerful accelerator, the Large Hadron Collider, can only probe down to 10-20 m). In Paraoanu’s toy world, he reckons such effects should be apparent on the perfectly-reasonable scale of about a micron (10-6m).

Originally from Romania, Paraoanu did his PhD under physics Nobelist Anthony Leggett at the University of Illinois at Urbana-Champaign. Family life then took Paraoanu to Finland, where his post-doc helped to shift his career towards practical experiments that test the boundaries of quantum mechanics. That remains his focus today, in his position at Aalto.

Progress will take time. "We can’t say we have created this curvature in spacetime yet. We have ideas of how to do that. But for now we’re still on a flat spacetime," he says. For now, his group is using an FQXi grant of over $75,000 to help to better understand their metamaterial’s properties. In 2013, for example, Paraoanu and colleagues demonstrated that a tiny amount of radiation could be created by fluctuating the refraction index in an array of SQUIDs, as predicted by the dynamic Casimir effect (PNAS, 110, 4234-4238 (2013)). (Paraoanu spoke about this paper on the FQXi podcast.) The fluctuations created a difference in the number of virtual particles popping in and out of existence between two parallel plates and outside those plates, which in turn produced a detectable flash of energy in the form of microwaves.


Curving Spacetime
This artist’s rendering shows a pair of white dwarfs, generating ripples in
spacetime as they spiral together. Can such effects be recreated in the lab?

Credit: NASA
The difficulty, Paraoanu adds, is in the technical details: his SQUIDs need to be made with greater precision than provided by commercial producers, and the signals they hope to detect are so tiny that they need to be very much amplified. "We have to fight with the background noise and be fast—measure before decoherence sets in," when quantum effects dissipate, he says. But, he adds, "It’s not so frustrating if you make progress one step at a time."

Other researchers are taking different approaches to creating toy environments where quantum theory and gravitational theory can collide, including looking at the propagation of sound in the weird, cold world of Bose Einstein condensates or at the propagation of tightly-focused lasers. FQXi member William Unruh of the University of British Columbia is attempting something similar with water waves.

We can bend spacetime
as if we were near
a black hole.
- Sorin Paraoanu
Broadly, "artificial systems for quantum simulation are really useful," says Christopher Wilson at the University of Waterloo, who has also worked with SQUIDs to show a dynamic Casimir effect. The general principle of any such simulation is to mimic quantum effects in a way that can be more easily measured. Paraoanu’s focus specifically on quantum gravity is interesting, Wilson says. Other analog systems could be used to study chemistry, or any other quantum-scale phenomena.

Paraoanu hopes his work will give birth to a new field: "solid-state quantum gravitation." In the meantime, he says, getting funding for such fundamental, non-applied research is tough work. "The aim is to acquire deep knowledge of the fundamental laws of physics, which I believe is necessary if we want, in the long run, to provide solutions for the more practical problems of our civilization," he says. Paraoanu himself is driven by more philosophical questions about why the Universe is the way it is: besides physics, he also has a degree in philosophy. "It doesn’t quite help fix a vacuum pump in the lab," Paraoanu admits. "But it gives an interesting motivation."

Comment on this Article

Please read the important Introduction that governs your participation in this community. Inappropriate language will not be tolerated and posts containing such language will be deleted. Otherwise, this is a free speech Forum and all are welcome!
  • Please enter the text of your post, then click the "Submit New Post" button below. You may also optionally add file attachments below before submitting your edits.

  • HTML tags are not permitted in posts, and will automatically be stripped out. Links to other web sites are permitted. For instructions on how to add links, please read the link help page.

  • You may use superscript (10100) and subscript (A2) using [sup]...[/sup] and [sub]...[/sub] tags.

  • You may use bold (important) and italics (emphasize) using [b]...[/b] and [i]...[/i] tags.

  • You may also include LateX equations into your post.

Insert LaTeX Equation [hide]

LaTeX equations may be displayed in FQXi Forum posts by including them within [equation]...[/equation] tags. You may type your equation directly into your post, or use the LaTeX Equation Preview feature below to see how your equation will render (this is recommended).

For more help on LaTeX, please see the LaTeX Project Home Page.

LaTeX Equation Preview



preview equation
clear equation
insert equation into post at cursor


Your name: (optional)



Important: In order to combat spam, please select the letter in this menu between 'I' and 'K':




Recent Comments


The search for gravity waves is not futile, just misdirected by the lack of a principle of unification. I like to call them matter waves since gravity and quantum forces are really just versions of each other. Matter is the constant and gravity is simply a scaling of charge force.

The CMB is not a remnant of the big bang, but rather simply a manifestation of a shrinking and not expanding universe. It is not clear to me why this is not clear to everyone else, but that is life.

The...


If LIGO keeps on getting null results then will that falsify gravity's space-time just like the Michelson-Morley experiment falsified the EM aether? What will happen to theories like: the Big Bang, inflation, string theory, loop quantum gravity, and the metric-expansion of space-time?

The steady state theory is out because the CMB is the echo of the Big Bang. There is no way the cosmic microwave background is a thermal reservoir for the slow and continuous creation of matter and...


gravitational constant is essential by gravity. We discover why G has such a different values beeing measured in last 30 years....

https://www.researchgate.net/publication/281079741_Motion_of_stellar_objects_and_variability_of_gravitational_constant_G

read all article comments

Please enter your e-mail address:
Note: Joining the FQXi mailing list does not give you a login account or constitute membership in the organization.