https://phys.org/news/2018-09-gravitational-dose-reality-extra-dimensions.html

Gravitational waves provide dose of reality about extra dimensions:

September 14, 2018 by Louise Lerner, University of Chicago:

While last year's discovery of gravitational waves from colliding neutron stars was earth-shaking, it won't add extra dimensions to our understanding of the universe—not literal ones, at least.
 

University of Chicago astronomers found no evidence for extra spatial dimensions to the universe based on the gravitational wave data. Their research, published in the Journal of Cosmology and Astroparticle Physics, is one of many papers in the wake of the extraordinary announcement last year that LIGO had detected a neutron star collision.

The first-ever detection of gravitational waves in 2015, for which three physicists won the Nobel Prize last year, was the result of two black holes crashing together. Last year, scientists observed two neutron stars collide. The major difference between the two is that astronomers could see the aftermath of the neutron star collision with a conventional telescope, producing two readings that can be compared: one in gravity, and one in electromagnetic (light) waves.

Read more at: https://phys.org/news/2018-09-gravitational-dose-reality-extra-dimensions.html#jCp

 

the paper:

http://iopscience.iop.org/article/10.1088/1475-7516/2018/07/048/meta

Limits on the number of spacetime dimensions from GW170817:

Abstract:

The observation of GW170817 in both gravitational and electromagnetic waves provides a number of unique tests of general relativity. One question we can answer with this event is: do large-wavelength gravitational waves and short-frequency photons experience the same number of spacetime dimensions? In models that include additional non-compact spacetime dimensions, as the gravitational waves propagate, they "leak" into the extra dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and a commensurate systematic error in the inferred distance to the gravitational wave source. Electromagnetic waves would remain unaffected. We compare the inferred distance to GW170817 from the observation of gravitational waves, dLGW, with the inferred distance to the electromagnetic counterpart NGC 4993, dLEM. We constrain dLGW = (dLEM/Mpc)γ with γ = 1.01+0.04−0.05 (for the SHoES value of H0) or γ = 0.99+0.03−0.05 (for the Planck value of H0), where all values are MAP and minimal 68% credible intervals. These constraints imply that gravitational waves propagate in D=3+1spacetime dimensions, as expected in general relativity. In particular, we find that D = 4.02+0.07−0.10 (SHoES) and D = 3.98+0.07−0.09 (Planck). Furthermore, we place limits on the screening scale for theories with D>4 spacetime dimensions, finding that the screening scale must be greater than ~ 20 Mpc. We also place a lower limit on the lifetime of the graviton of t > 4.50 × 108 yr.

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Related: http://astrokatie.blogspot.com/2018/09/extra-dimensions-black-holes-and-vacuum.html

Extra dimensions, black holes, and vacuum decay, oh my

Sometimes you get an idea. And it's a fun idea, and it brings together a lot of cool weird things, and you think, "maybe this could actually work out." This post is the story of one such idea. It's also the story of a paper, "Bounds on extra dimensions from micro black holes in the context of the metastable Higgs vacuum," by me and Professor Robert McNees, just posted on the arxiv.

33 minutes ago, beecee said:

Is this the final death knell for string theory and its derivatives?

My understanding is that this only rules out large-scale extra dimensions, not the compact ("curled up") ones of string theory. 

Edited September 14, 20187 yr by Strange

On 9/15/2018 at 7:26 AM, Strange said:

My understanding is that this only rules out large-scale extra dimensions, not the compact ("curled up") ones of string theory. 

 

If any extra dimensions exist, other then the four we are familiar with, are they not necessarily all "curled up" as we are unable to see them? 

I certainly do not know enough about string and/or its derivatives to criticise them too much, other then repeat what criticism I have heard of them from other quarters...namely that after 3 or so decades, they still are not evidenced despite the apparent mathematic beauty that they contain.

Edited September 17, 20187 yr by beecee

1 hour ago, beecee said:

 

If any extra dimensions exist, other then the four we are familiar with, are they not necessarily all "curled up" as we are unable to see them? 

I certainly do not know enough about string and/or its derivatives to criticise them too much, other then repeat what criticism I have heard of them from other quarters...namely that after 3 or so decades, they still are not evidenced despite the apparent mathematic beauty that they contain.

They'll make it work.

That was my understanding also, Strange.

Large scale 'extra' dimensions are pretty well ruled out by the fact that gravity falls off with the inverse of the distance squared.
( exactly the same as EM radiation, as the neutron star collision observations re-affirmed )

Curled up, Planck scale dimensions would predict a 'leakage', and much steeper fall-off for gravity ( as the inverse of the distance to the power D-1, where D is the number of spatial dimensions ), but only at extremely small separations. We would need a collider the size of the galaxy to generate the energies that would allow us to probe such small separations.

On 9/16/2018 at 9:21 PM, beecee said:

 

If any extra dimensions exist, other then the four we are familiar with, are they not necessarily all "curled up" as we are unable to see them? 

I certainly do not know enough about string and/or its derivatives to criticise them too much, other then repeat what criticism I have heard of them from other quarters...namely that after 3 or so decades, they still are not evidenced despite the apparent mathematic beauty that they contain.

If there was an extra large dimension, and everything we knew was traveling at lightspeed in the same direction wrt it, how would we be able to see it?

Edited September 18, 20187 yr by J.C.MacSwell