Comments on: Modifications to General Relativity?

By: Now That’s What I’m Talking About! | Cosmic Variance

Now That’s What I’m Talking About! | Cosmic Variance — Mon, 26 Sep 2005 22:09:52 +0000

[...] There’s a little article on science blogs, by the way (this was bookmarked with a post-it note: thanks, whoever, for sending it!). We’re mentioned, along with Pharyngula, Not Even Wrong, String Coffee Table and Quantum Diaries. Contributor Joshua Roebke talked about the aspects of the role of science blogs, quoting Peter Woit, and our very own Sean Carroll (who is apparently one of the “main contributors” to cosmicvariance, although I note that the discussion they quote from is in fact a post of JoAnne’s …..ahem!). [...]

By: Ivan Alexander

Ivan Alexander — Mon, 26 Sep 2005 21:26:21 +0000

What if Newton’s G ain’t a “universal” constant, but merely a “variable” constant?

I know it sounds strange, but think that we computed all astrophysics using a flat G, so if it is variable, we can’t see it. For example, why is Jupiter’s core only 2-3 Earth masses, but it can retain a giant atmosphere? Or the Pioneers Anomaly, at a constant rate of ~8E-8 cm/s^2, which is within range of delta G growing at the rate of 1 G per 1 AU? Or why outer fringe of galaxy acting as if “dark matter” gives it greater mass? Per Equivalence, greater G translates into greater inertial mass (per reference paper in the website linked) so rotation velocity is affected. Would this variable G not be a better explanation? Hypothetically, G would flatten out in space at about 10X-6 N kg^-2 s^-2, which coincides with calculations (per paper above) within range of the photoelectric effect e.m. wavelength. Strange coincidences?

I think GR will need modifications, likely after ESA tests for gravitational anomalies in the outer system. Stay tuned!

Ivan

By: Gordon Chalmers

Gordon Chalmers — Fri, 12 Aug 2005 21:14:56 +0000

With the new ideas in condensed matter theory that are arriving, a slab of some meters could it, even with time polyphasing, not your usual STAP.

By: Rumors of new forces | Cosmic Variance

Rumors of new forces | Cosmic Variance — Fri, 12 Aug 2005 20:52:18 +0000

[...] Eric Adelberger, leader of the experimental gravity group at the University of Washington, left a comment in the discussion about new forces, which is worth elevating to the front page here: Please donâ€™t get too excited yet about rumors concerning the Eot-Wash test of the 1/r^2 law. We can exclude gravitational strength (|alpha|=1) Yukawa violations of the 1/r^2 law for lambda>80 microns at 95% confidence. It is true that we are seeing an anomaly at shorter length scales but we have to show first that the anomaly is not some experimental artifact. Then, if it holds up, we have to check if the anomaly is due to new fundamental physics or to some subtle electromagnetic effect that penetrates our conducting shield. We are now checking for experimental artifacts by making a small change to our apparatus that causes a big change in the Newtonian signal but should have essentially no effect on a short-range anomaly. Then we will replace our molybdenum detector ring with an aluminum one. This will reduce any signal from interactions coupled to mass, but will have little effect on subtle electromagnetic backgrounds. These experiments are tricky and measure very small forces. It takes time to get them right. We will not be able to say anything definite about the anomaly for several months at least. [...]

By: Gordon Chalmers

Gordon Chalmers — Fri, 12 Aug 2005 20:33:37 +0000

Maybe Eric you need a SAR apparatus, with 10^30 detectors.

By: Mark

Mark — Fri, 12 Aug 2005 20:20:38 +0000

Thanks for taking time to give us an update Eric. It’s very valuable.

By: Eugene

Eugene — Fri, 12 Aug 2005 20:04:04 +0000

As a rational theorist, I will now calm myself down after reading Eric Adelberger’s post.

(Arrrghghghghgh arghganomalyhgh arrrrrghghghgh).

Okay, I feel better now.

By: Eric Adelberger

Eric Adelberger — Fri, 12 Aug 2005 19:37:23 +0000

Please don’t get too excited yet about rumors concerning the Eot-Wash test of the 1/r^2 law. We can exclude gravitational strength (|alpha|=1) Yukawa violations of the 1/r^2 law for lambda>80 microns at 95% confidence. It is true that we are seeing an anomaly at shorter length scales but we have to show first that the anomaly is not some experimental artifact. Then, if it holds up, we have to check if the anomaly is due to new fundamental physics or to some subtle electromagnetic effect that penetrates our conducting shield. We are now checking for experimental artifacts by making a small change to our apparatus that causes a big change in the Newtonian signal but should have essentially no effect on a short-range anomaly. Then we will replace our molybdenum detector ring with an aluminum one. This will reduce any signal from interactions coupled to mass, but will have little effect on subtle electromagnetic backgrounds. These experiments are tricky and measure very small forces. It takes time to get them right. We will not be able to say anything definite about the anomaly for several months at least.

By: Simon DeDeo

Simon DeDeo — Fri, 12 Aug 2005 14:35:46 +0000

“if the fat graviton starts to show itself at the same scale that neutrinos are”

It’s a grand conspiracy of scales!

By: Alejandro Rivero

Alejandro Rivero — Fri, 12 Aug 2005 09:49:30 +0000

Hmm yep Aaron, hep-th/0306106 does better lecture.

About strings and attachments, consider than in 1997 Sundrum had not yet scored his “home runs”; from his bibliography he could be seen mainly as a young technicolored guy.

Aside: it is an amusing coincidence if the fat graviton starts to show itself at the same scale that neutrinos are, isn’t it? Smolin did a listing of such coincidences some months ago in Lubos blog.

By: Robert

Robert — Fri, 12 Aug 2005 08:44:07 +0000

If you like you can count all dark matter as a modification of GR, at least until you’ve pinpointed the particle. As long as this is missing, all you are seeing is that galaxies (and other stuff) do not rotate according to Newton’s law (or the GR equivalent).

By: Quantoken

Quantoken — Fri, 12 Aug 2005 00:41:45 +0000

Shantanu:

I know about the DI Hercules data. Some Russian physicist proposed a model where there are three stars of about the same order of mass circling each other, although any one who received any decent training in classical mechanics knows any three star system (one all stars have similar masses) are unstable dynamic system.

My opinion is these kind of observational data is extremely unreliable and the systematic errors are greatly under-estimated. So it is really not very credible whether it is pro or anti GR, that includes the famous PSR 1913.16, which was awarded the Nobel Prize.

I have yet to find some one who is willing to express an opinion, whether positive one or negative one, regarding my assertion that the Eddington 1919 solar eclipse is simply too coarse in precision to say anything either way about GR. The predicted light bending of about 1 arcsecond or so is just too small to be observed by a 4 inch diameter telescope, not to meantion the atmospheric disturbance known as “seeing”. There is a deafening silence than no one eants to say anything about it.

Quantoken

By: Matt McIrvin

Matt McIrvin — Fri, 12 Aug 2005 00:28:39 +0000

I have my doubts that you could measure the Pioneer anomaly with Cassini, even if it’s new physics and even if Cassini stopped maneuvering. Cassini is orbiting Saturn, which would tend to obscure any anomalous acceleration toward the sun that doesn’t act on planets.

By: Shantanu

Shantanu — Fri, 12 Aug 2005 00:02:41 +0000

Sean and/or Joanne did anyone in the competition mention
about the anomolous precession of DI Hercules which if
I recall correctly does not agree with GR, (though it’s been a while
since I heard anything about this system and the discrepancy
may have gone away)

By: Vish Subramanian

Vish Subramanian — Thu, 11 Aug 2005 23:28:35 +0000

I think point (i) comes simply from my reading of the history of special relativity. Not too many people put much stock in one hard-to-perform, subtle experiment (Michelson Morley) until Einstein. Not that people disbelieved the experiment (and of course Lorentz et al came up with theories to explain it), but they just sort of cautiously waited around until someone told them what it meant.

By: Ben Lillie

Ben Lillie — Thu, 11 Aug 2005 18:37:11 +0000

It’s not so clear to me that point (i) is very important for whether I’d believe the sub-millimeter deviation. Even if we had a compelling theoretical framework the effect would still need independent confirmation.

By: Vish Subramanian

Vish Subramanian — Thu, 11 Aug 2005 18:28:13 +0000

I should say
i) A compelling theoretical framework appears which explains it.

ii) An unrelated experiment/observation confirms it.

Sorry - it seemed clear when I wrote it but not as I read it.

By: Mark

Mark — Thu, 11 Aug 2005 18:10:10 +0000

At least in the case of the cosmological constant, I would say that we don’t have a compelling theoretical framework that explains it.

By: Vish Subramanian

Vish Subramanian — Thu, 11 Aug 2005 17:46:11 +0000

“… chased down every imaginable systematic error”

What about unimaginable ones? I would think that people will (or at least, should) remain sceptical of sub-millimetre deviations until

i) A compelling theoretical framework appears which explains it.
ii) An unrelated experiment/observation confirms it.

As was the case with Michelson-Morley, or the cosmological constant.

By: Aaron Bergman

Aaron Bergman — Thu, 11 Aug 2005 17:33:31 +0000

I’m guessing that Raman doesn’t feel obligated to “attach” himself to anything. I was thinking of the follow-up paper hep-th/0306106.