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The Sciences

Rumors of new forces

Cosmic VarianceBy Sean CarrollAugust 13, 2005 12:52 AM

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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 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.

I suppose we have to go along, although it's hard to enforce levels of excitement. More importantly, it's precisely because these experimenters are so careful that we'll have every right to be very excited if they ultimately announce that they've really discovered a deviation from Newton's force law! While we're waiting, here's a great review article about tests of gravity at short scales. If you read it now, you'll be all ready to understand new results as they come in.

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