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19 October 2004

As usual we may have the cat by the Tail!

Scientists ponder the problem with gravity
By Robert Roy Britt

Imagine the weight of a nagging suspicion that what held your world together, a constant and consistent presence you had come to understand and rely on, wasn't what it seemed. That's how scientists feel when they ponder gravity these days. For more than three centuries, the basics of gravity were pretty well understood. Newton described the force as depending on an object's mass. Though it extends infinitely, gravity weakens with distance (specifically, by the inverse square of the distance). Einstein built on these givens in developing his theory of relativity. Then more than a decade ago a researcher noticed something funny about two Pioneer spacecraft that were streaming toward the edge of the solar system. They weren't where they should have been. Something was holding the probes back, according to calculations of their paths, speed and how the gravity of all the objects in the solar system — and even a tiny push provided by sunlight — ought to act on them. Now scientists have proposed a new mission to figure out what's up with gravity.

Staggering possibilities

Pioneer 10 and 11 launched in 1972 and 1973. Today each is several billion miles away, heading in opposite directions out of the solar system. The discrepancy caused by the anomaly amounts to about 248,500 miles (400,000 kilometers), or roughly the distance between Earth and the moon. That's how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct. (The distance figure is an oversimplification of the actual measurements, but more on that in a moment.) Scientists are quick to suggest the Pioneer anomaly, as they call it, is probably caused by the space probes themselves, perhaps emitting heat or gas. But the possibilities have been tested and modeled and penciled out, and so far
they don't add up. Which leaves open staggering possibilities that would force wholesale reprinting of all physics books:

- Invisible dark matter is tugging at the probes
- Other dimensions create small forces we don't understand
- Gravity works differently than we think

Reminds of one of my favorite quotes " There is more in heven and hell, Horatio, than is dream't of in your philosophies"

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