Friday, August 12, 2005

What! Superficiality has extra dimensions to it?

Sometimes I like to play, "knock knock whose there" on my head. :)

Quantitative studies of future experiments to be carried out by LHC show that any signatures of missing energy can be used to probe the nature of gravity at small distances. The predicted effects could be accessible to the Tevatron Collider at Fermilab, but the higher energy LHC has the better chance.

These colliders are still under construction, but results also have consequences for "table-top" experiments, being carried out here at Stanford, as well as the University of Washington and the University of Colorado. Here’s the basic idea: imagine there are two extra dimensions on a scale of a millimeter. Next, take two massive particles separated by a meter, at which distance they obviously behave according to the well-known rules of 3-D space. But if you bring them very close, say closer than one millimeter, they become sensitive to the amount of extra space around. At close encounter the particles can exchange gravitons via the two extra dimensions, which changes the force law at very short distances. Instead of the Newtonian inverse square law you’ll have an inverse fourth power law. This signature is being looked for in the ongoing experiments.

Eöt-Wash Group

However, until evidence for new physics is found, it is clearly better to work on tests of the inverse-square law than on equivalence-principle tests: the 1/r2 tests are more general (probing all finite-range effects), and more sensitive (in particle-exchange scenarios the composition-dependence is expected to be a relatively small fractional effect). But testing the gravitational 1/r2 law for length scales less than 50 µm will probably require a somewhat different technology. In a planar geometry (optimum because one gets the maximum amount of mass in close proximity) the signal of a short-range Yukawa interaction drops as roughly the 4th power of the Yukawa range while extraneous disturbances stay roughly the same size. This will present an interesting challenge for future experimental work.

Imagine, if such assertions to extra-dimension were just superficial statements drawn from historical literature that people drummed up to create mysticism? Oh how safe I would feel drawing from such statements, that wonder of all wonders, there was a scientific basis assigned this perspective of Georgi's.

Georgi Dvali

Dvali posits that this leakage has a profound effect on the gravitational force between objects separated by more than the critical distance. Specifically, the theory of modified gravity has a characteristic length-scale r_c, or approximately 15 billion light years. This marks a crossover distance beyond which the cosmological expansion becomes accelerated, and thus, from cosmological observations r_c is fixed to be the size of the observable universe. Even though r_c scale is enormous, the imprints of modification are detectable at much shorter distances because of the additional gravitational force.

"This is the crucial difference between the dark energy and modified gravity hypothesis, since, by the former, no observable deviation is predicted at short distances," Dvali says. "Virtual gravitons exploit every possible route between the objects, and the leakage opens up a huge number of multidimensional detours, which bring about a change in the law of gravity."

Dvali adds that the impact of modified gravity is able to be tested by experiments other than the large distance cosmological observations. One example is the Lunar Laser Ranging experiment that monitors the lunar orbit with an extraordinary precision by shooting the lasers to the moon and detecting the reflected beam. The beam is reflected by retro-reflecting mirrors originally placed on the lunar surface by the astronauts of the Apollo 11 mission.

I think Eddington expeirment and methods used in LIGO speak directly to the range of sublte thinking that was necesary from a broad landscape of bulk gravitonic perception, that could be the effect of such things as lensing, dilation and gravtonic scattering effects?

So we understand here do we, that procedures to conceptual fabrication has some basic formulation to those short distances? Eöt-Wash Group was also asking something about these short distances were they not? The history her eis a short one from 2001 but it bascialy answer soem questions about what those extra dimensions mean.

So don't take my word for it or someone who just scoffs at the very notion. Apply yourself to see what is meant. Maybe you will tend to wonder what crazy ideas Brian Josephson had about the nature of civilzations living amidst our own?

Rumour of New Forces
Just had a look at Cosmic Variance and found this statement by Sean Carroll about the Eotwash group update. Here is what Eric Adelberger had to say.

Eric Adelberger on Aug 12th, 2005 at 2:37 pm
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.

As stated maybe this anomalie might be significant and for scientists it is necessary such a quirk of nature be seen and understood. I relayed Einstein's early youth and the compass for a more introspective feature that such anomalies present.

The Eotwash Group is a sign of relief, for the speculative signs attributed from other scientists, made this topic of extr-dimensions unbearable and unfit for the general outlaid of scientists who did not understand this themselves.

Deviations from Newton's law seen?

So what does Lubos have to say about this in his column?

Lubos Motl:
The most careful and respected experimental group in its field which resides at University of Washington - Eric Adelberger et al. - seems to have detected deviations from Newton's gravitational law at distances slightly below 100 microns at the "4 sigma" confidence level. Because they are so careful and the implied assertion would be revolutionary (or, alternatively, looking spectacularly dumb), they intend to increase the effect to "8 sigma" or so and construct different and complementary experiments to test the same effect which could take a year or two (or more...) before the paper is published. You know, there are many things such as the van der Waals forces and other, possibly unexpected, condensed-matter related effects that become important at the multi-micron scales and should be separated from the rest.


  • Inverse Fourth Power Law
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