The late, great Carl Sagan was fond of including this line in his essays: "But I could be wrong." The idea is not merely humble, it is profound: we do not progress in our knowledge of the universe by making dogmatic assertions; we progress by guessing (Richard Feynman's word) and then testing. I *think* that nature works this way, Sagan is saying. Here's *why* I think so. And I remain open to other possibilities.
It's that "other possibilities" clause that makes Foundational questions so interesting. And exactly because they are Foundational, they don't necessarily come up where we are expecting them. Foundational insights can emerge from time to time from places where no one is looking, perhaps because we think we pretty much already understand how things go there. (Lord Kelvin famously got egg on his face by announcing that physics was over, save for one or two smallish clouds on the horizon -- in 1900.)
image: Shiny Things
There may be one such smallish cloud brewing right now in the edges of our solar system. There, two of humanity's most notable achievements -- Pioneer 10 and Pioneer 11 -- are continuing their potentially endless voyage among the stars. The problem -- as the people at the Pioneer Anomaly Project put it – is that the spacecraft aren't where they should be. And no one knows why:
"Something strange is happening in the outer reaches of our solar system. The Pioneer 10 and 11 spacecraft are not where they are supposed to be. These missions, launched in 1972 and 1973, have covered hundreds of millions of kilometers, heading toward the edge of our solar system. But something is holding them back. Each year, they fall behind in their projected travel by about 5,000 kilometers (3,000 miles).
Jet Propulsion Laboratory scientist John Anderson and his colleagues have been searching for an explanation since 1980. But as of yet, they have found nothing conclusive; no spacecraft behavior or previously unknown property of the outer solar system can explain the deceleration of the Pioneer spacecraft. Scientists are being forced to consider the unthinkable: something may be wrong with our understanding of the laws of physics."
That last line bristles with Foundational possibilities. Have we made a radical mistake in our understanding of spacetime, gravitation, or even the laws of motion, simply because from the days of Galileo until now we've never been able to toss an object far enough away to see what happens? Granted, it isn't likely -- as Executive Director and JPL alumn Louis Friedman says,
"That prospect is tantalizing, but it is more likely there isn't a "new physics" involved, and instead something is happening within physics-as-we-know-it that hasn't been properly accounted for. There are many options: The spacecraft could be falling apart in a way we didn't account for, or we incompletely understand spacecraft behavior, or there is an error in the tracking data. Or maybe they are directing us to discover some bizarre effects of physical objects -- planets or Kuiper Belt Objects or other bodies doing strange things. Or we've incorrectly predicted the effects of the interstellar wind, or we need to change a variable in the supposed constants of mass and gravitation in the solar system."
Or maybe not. From a certain perspective -- and with all deference to the people who actually build, launch, and remotely operate the things -- a hurling craft in deep space, executing no maneuvers, should be a fairly straightforward problem in mechanics. It isn't likely, but it is just conceivable that there isn't anything untoward going on way out there at all; that the problem lies not in our stars, dear Brutus, but in our science. This is a possibility on the periphery of our understanding in more ways than one.
(Full Disclosure: I happen to be an enthusiastic member of the Planetary Society myself, and would encourage anyone interested in FQX to check them out as well.)
image: East Lothian Museums
Also from the seems-small-be-might-be-huge file this month, the kilogram is disappearing.
As the AP tells it:
"The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight -- if ever so slightly.
Physicist Richard Davis of the International Bureau of Weights and Measures in Sevres, southwest of Paris, says the reference kilo appears to have lost 50 micrograms compared with the average of dozens of copies.
'The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart,' he said. 'We don't really have a good hypothesis for it.'"
What on Earth is going on? 50 micrograms -- about the mass of a fingerprint, we are told -- is no artifact. Ironically, the cylinder is kept in carefully controlled conditions specifically because it is meant to define "kilogram," an unchanging reference point in our ever-fluctuating world.
Which raises the rather Twilight Zone possibility that the official kilogram *has* remained the same, while all the *other* kilograms have gained:
"Of all the world's kilograms, only the one in Sevres really counts. It is kept in a triple-locked safe at a chateau and rarely sees the light of day -- mostly for comparison with other cylinders shipped in periodically from around the world.
'It's not clear whether the original has become lighter, or the national prototypes have become heavier,' said Michael Borys, a senior researcher with Germany's national measures institute in Braunschweig. 'But by definition, only the original represents exactly a kilogram.'"
Shades of early Einstein? My clock looks all right to me -- perhaps everyone else's clock is running slow. Which yardstick is really a yard -- yours or mine? What if mass itself changes as a result of an observer's relative motion? (Or shades of Heisenberg: What if the very attempt to make, and maintain, an absolute measurement system is inherently unachievable?)
Of course, the shrinking kilogram probably isn't telling us anything about fundamental physics. It's a glitch. The Pioneer Anomaly probably isn't telling us anything about the existence of a new fundamental force, or the structure of spacetime. These are most likely pseudo-effects, little mistakes that will be cleared up by some mathematical housekeeping, and won't require any major rethinking of physical or cosmological properties.
Of course, I could be wrong.