Idea for experimental test of LQG

In summary, the conversation revolved around the topic of experimental tests for quantum gravity, with various papers and ideas being discussed. Some of the proposed tests include using cosmic rays, the cosmic microwave background, and the primordial spectrum of cosmological tensor perturbations. There is a growing interest in observational tests for loop quantum gravity, and several physicists are working on developing new methods and conducting experiments. One of the ideas proposed was using satellite orbits to test for the effects of quantum gravity. The conversation also touched on the beauty and potential of quantum gravity as an emergent explanation for many phenomena.
  • #1
VCortex
24
0
Hello! Long time peeker, first time poster. I recently made a GR joke/brainteaser on a pop sci blog I frequent, and the tirade of nutty reactions it provoked drove me to an agitated contemplation of the matter, which gave rise to a few ideas.

I was thinking that maybe a Gallileo type orange/grape experiment in a decent sized vacuum chamber, shielded with a high powered electromagnetic armour (maybe with testing at different altitudes) might give results that could differ enough from the GR warped space-time model to support a quantum gravity based theory?

Does anyone know if such an experiment has been done already, and if not does anyone want to lend me a blowtorch, a few shipping containers, some jet engines, a power station, and a mountain? And an orange?
 
Physics news on Phys.org
  • #2
I guess you are suggesting a test of the equivalence principle? I don't think that is related to LQG specifically. A related proposal might be:

Breaking Diffeomorphism Invariance and Tests for the Emergence of Gravity
Mohamed M. Anber, Ufuk Aydemir, John F. Donoghue
http://arxiv.org/abs/0911.4123

Apparently, a failure of Lorentz invariance would lead to a failure of the equivalence principle, so one could also test for a failure of Lorentz invariance:

Modern tests of Lorentz invariance
David Mattingly
http://arxiv.org/abs/grqc/0502097 (section 2.5)

I think the Eot-Wash group has done a test very similar to what you propose.

Test of the Equivalence Principle Using a Rotating Torsion Balance
S. Schlamminger, K.-Y. Choi, T. A. Wagner, J. H. Gundlach, and E. G. Adelberger
http://www.npl.washington.edu/eotwash/publications/pdf/schlamminger08.pdf
 
Last edited by a moderator:
  • #3
Hi atyy,

Yeah, I suppose that is the kind of thing I was trying to propose (in a more break than make capacity!). What I envisaged was that if a differential could be obtained in the proposed "subatomic foam" that could form a mass-entropic conception of quantum gravity, via a high energy filter (such as an electromagnetic shield, or maybe a vacuum surrounded by a zero energy state BEC like a superconductor or superfluid?) then maybe you could filter out enough 'foam' to provide a result detectably different from one expected by equivalence/GR spacetime.

Thanks for the links (strange dreams for me tonight..), sorry if I'm just typing out loud!
 
  • #4
There are feasible observational tests being proposed, a physicist at Stockholm (S. Hossenfelder) has organized a couple of conferences/workshops on *Experimental Search for Quantum Gravity*. Here is a writeup on the one in Stockholm in 2010:
http://arxiv.org/abs/1010.3420

Hossenfelder and co-workers recently proposed a new trace of Loop qg to look for in cosmic ray spectrum. From Loop-type BH. Google "hossenfelder emission spectra" and get http://arxiv.org/abs/1202.0412

Loop leads to a simple explanation of what makes up dark matter, which if correct, would result in a signature in high energy radiation such as cosmic ray. This is new (2012) and not in the 2010 workshop report I mentioned.

Some other papers propose a LQG "footprint" to look for in the microwave background (left over light from early universe where LQG predicts a particular start to expansion).

Google "grain barrau footprint loop" and get http://arxiv.org/abs/0902.0145
Cosmological footprints of loop quantum gravity
J. Grain, A. Barrau
(Submitted on 2 Feb 2009 (v1), last revised 4 Mar 2009 (this version, v2))
The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated holonomy correction should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity.
Comments: Accepted by Phys. Rev. Lett., 7 pages, 2 figures

Most tests would require a new generation astrophysical instruments, or data that has not yet been reported from the Planck spacecraft , but this one by Wen Zhao uses already collected data:
Google "zhao constraints early universe models" and get http://arxiv.org/abs/1007.2396

Wen Zhao is already working with available CMB data from the WMAP spacecraft to limit the range of parameters for Loop and other models of early universe. He participated in Hossenfelder's 2010 workshop and the work is included in the report I mentioned.

More papers related to observational testing of LQG, these are all 2009 or later. The link is slow, Spires system will be replaced soon, but efficient. Some 49 papers including some I mentioned.
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29

Here's a less efficient search by the new tool which will replace Spires, but still pretty good:
http://inspirehep.net/search?ln=en&...earch=Search&sf=&so=d&rm=citation&rg=100&sc=0
Finds 48 papers from the period 2008-2011, mostly the same papers.
 
Last edited by a moderator:
  • #5
Good stuff. I'm just an interested observer, but I do find the whole quantum gravity concept a really beautiful, emergent way that could explain a whole raft of phenomena!

Had another idea today (maybe more of an engineering quandry than a theoretical issue?);

If several satellites of varying mass require orbit adjustment from time to time, assuming unperturbed trajectories & excluding lunar interference etc, is there a point (some kind of LEO lagrangian point) before which adjustment of trajectories is consistently away from from the gravity well, and beyond consistently towards it, to maintain stable orbits?
IE in warped spacetime, any idealised stable geostationary orbit will inevitably eventually decay into the gravity well, while with quantum gravity an idealised stable geostationary orbit has a quantum uncertainty, and will eventually decay either towards or away from the gravity well (or not exist?!). Gakk. Brain off.. :/
 
Last edited:
  • #6
We should check those links again, to see if more LQG and LQC phenomenology papers show up.
The DESY search that I linked in post#4 used to get 49 papers back in February. Now it finds 58.
It is slow but still works!
http://www-library.desy.de/cgi-bin/spiface/find/hep/www?rawcmd=FIND+%28DK+LOOP+SPACE+AND+%28QUANTUM+GRAVITY+OR+QUANTUM+COSMOLOGY%29+%29+AND+%28GRAVITATIONAL+RADIATION+OR+PRIMORDIAL+OR+inflation+or+POWER+SPECTRUM+OR+COSMIC+BACKGROUND+RADIATION%29+AND+DATE%3E2008&FORMAT=www&SEQUENCE=citecount%28d%29
 
Last edited by a moderator:
  • #7
I heard some rumours along the lines of "proton dissapearance at super low temperatures" & some purported support for astronomical observations with an inverse lambda value for the cosmological constant (which superficially sound like they may be conducive to analysis by some of the more leftfield physical theorems) a while ago, but I haven't seen any papers directly citing such. I suppose I've been to busy contemplating the immense philosophical, metaphysical & industrial ramifications of the discovery of the higgs bourbon to look into it right now.
 

FAQ: Idea for experimental test of LQG

What is LQG and how does it differ from other theories?

LQG (Loop Quantum Gravity) is a theoretical framework that attempts to reconcile Einstein's theory of General Relativity with quantum mechanics. It differs from other theories such as string theory in its approach to understanding the fundamental nature of space and time.

What is the proposed experimental test for LQG?

The proposed experimental test for LQG involves using precision measurements of the cosmic microwave background radiation to search for signatures of quantum gravitational effects.

Why is it important to test LQG experimentally?

Testing LQG experimentally is important because it will provide evidence for or against the validity of the theory. It will also help us understand the fundamental nature of space and time, and potentially lead to advancements in our understanding of the universe.

What challenges may arise in conducting an experimental test of LQG?

One of the main challenges in conducting an experimental test of LQG is the extremely small scale at which quantum gravitational effects are expected to occur. This requires highly sensitive instruments and precise measurements, which can be difficult to achieve.

What are the potential implications of a successful experimental test of LQG?

If a successful experimental test of LQG is achieved, it could provide a breakthrough in our understanding of the universe and potentially lead to the development of a unified theory of physics. It could also have practical applications, such as advancements in technologies like quantum computing.

Back
Top