What is the impact of the refutation of "quantum foam"?

[sshai45]

Hi.

I just saw this:

http://phys.org/news/2015-03-einstein-scientists-spacetime-foam.html

They are saying that they have found data showing that the "quantum foam" does not exist. What is the impact of the disproof of "quantum foam", anyways, on the search for a theory of quantum gravity?

 

[marcus]

No impact on covariant LQG (spin foam models) because the theory does not predict energy-dependent speed of light.

I don't know of an approach to QG which is currently being worked on which does predict energy-dependent speed of light.

I can't say what the article means by "quantum foam" but the scientists quoted were testing for energy-dependent speed of light, so "quantum foam"must be some theory they have in mind which has that feature.
Or maybe it is just a way they and the journalist thought up to interest the public.

 

[sbrothy]

Hi.

I just saw this:

http://phys.org/news/2015-03-einstein-scientists-spacetime-foam.html

They are saying that they have found data showing that the "quantum foam" does not exist. What is the impact of the disproof of "quantum foam", anyways, on the search for a theory of quantum gravity?

Sabine Hossenfelder discuss this paper at her blog I think. Or something similar at least.: http://backreaction.blogspot.dk/

 

[wabbit]

Sabine Hossenfelder discuss this paper at her blog I think. Or something similar at least.: http://backreaction.blogspot.dk/

...and a very nice and thorough, if perhaps unusually clement analysis of hers that is. Thanks for the link.

 

[sshai45]

No impact on covariant LQG (spin foam models) because the theory does not predict energy-dependent speed of light.

I don't know of an approach to QG which is currently being worked on which does predict energy-dependent speed of light.

I can't say what the article means by "quantum foam" but the scientists quoted were testing for energy-dependent speed of light, so "quantum foam"must be some theory they have in mind which has that feature.
Or maybe it is just a way they and the journalist thought up to interest the public.

The abstract for the paper is here:
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3270.html

They claim it challenges something called "Wheeler's 'space-time foam' picture of quantum gravity (QG)" and that "Our results set a benchmark constraint to be reckoned with by any QG model that features spacetime quantization.".

 

[wabbit]

Yes Sabine H. assigns the blame here more to the loose (to say the least) wording of these claims in the paper than to poor reporting by the journalists.

In short, none of the main proposed theories of QG is in the least impacted, the paper rules out a few somewhat exotic ones that were already considered unlikely.

 

[marcus]

The abstract for the paper is here:
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3270.html

They claim it challenges something called "Wheeler's 'space-time foam' picture of quantum gravity (QG)" and that "Our results set a benchmark constraint to be reckoned with by any QG model that features spacetime quantization.".

Their reference for that "picture" is to some pages in a 1964 book:

Wheeler, J. in Relativity, Groups and Topology (eds DeWitt, C. M. & DeWitt, B. S.) 467–500(Gordon and Breach, 1964).

As I said, I don't know any QG approach that is currently being worked on that fills the bill.

Brody and Wabbit have mentioned Bee Hossenfelder's blog commentary on this paper. You might find it informative. She is a recognized expert on QG testing and phenomenology---and has organized several international conferences on potential tests of QG theories/pictures/effects.

Wheeler (Feynman's PhD advisor) was a wonderfully creative man. Unfortunately he is not around these days to take up these authors' "challenge" to his 1964 foam notion.