Pity the politicians as they struggle to a hammer out a deal on the US debt: the endless negotiations, the late agreements that collapse by the morning news cycle. Everywhere they turn they seem to constrained - hemmed in - by forces pulling in every direction.
But their real problem is not that they have too little freedom in choosing a direction but too much. Nature, it turns out, knows the meaning of ceilings - the hard kind you can't escape from. There are lessons in those ceilings, which, perhaps, we could all learn from.
Much of modern physics is built on principles called Conservation Laws. Conservation of charge holds for electromagnetic systems like radio broadcast towers. Conservation of angular momentum rules rotating systems like an Olympic skater executing a spin. And then there is the holy of holies: the conservation of energy. Energy can be neither created nor destroyed. It can only transformed from one form into another.
The principle of energy conservation is absolutely, positively, no-you-can't-break-it-even-this-once central to our understanding of the Universe. Many times physicists have been stuck in a corner facing an experimental result they did not understand. Many times someone, in response, suggested a breakdown of energy conservation. Always they have been proven wrong.
Sometimes the solution came when physicists recognized some new form of energy that needed to be added to the balance sheet. This is what happened when Albert Einstein demonstrated that matter itself was a kind of energy (or at least equivalent to energy via E=mc2). That addition happens rarely, however. Usually scientists simply recognize new pathways of transformation from one form of energy to another (magnetic to thermal for example) that had eluded them before.
Ironically the constraint of energy conservation (or any form of conservation law) can be blessing and not a curse for physicists. The world is both subtle and wild in its changes.
Tracking how vast spinning clouds of interstellar gas collapse to become stars is not easy but the conservation of angular momentum gives you at least one measure of the system that has to stay the same even as everything else changes. Following the dance of subatomic shape shifting as particles collide in the LHC would be impossible without the conservation of energy providing a sheltered place of constancy during the chaos.
When formulated in the language of mathematics, conservation laws can be unpacked to become the poetry on which all physics is built. While Newton's laws of forces were a triumph for science they could be very difficult to work with (like woodworking tools with ill shaped handles). In the early 19th century physicists like Sir William Rowan Hamilton re-expressed Isaac Newton's force-centered view in terms of energy conservation producing simple, elegant expressions that became the foundation for modern physics. The development of quantum mechanics, for all its weirdness, relied heavily on these energy conservation formulations. (Quantum mechanics, it should be noted, does allow a kind of "borrowing" violation of conservation but only for the briefest of instants).
So what do these conservation laws tell us about the imaginary human world of debt ceilings? Exactly that - they are imaginary. Our economic systems are the creation of human activity and human imagination.
And while conservatives appear to demand a kind of conservation by demanding a hard debt ceiling, they — like all the rest of us — want to dine on our cake while still leaving it on the table. We want our ever-growing economies to be free of real conservation. We want to ignore that we live on a finite planet that has it own very finite resources - water, oil, viable habitats.
Physics has known for a long time that there are real physical ceilings in the physical world. We appear to be living in the first human era that will be forced to watch that fact move from abstraction to global reality. Perhaps when our imaginary worlds of economics take those real constraints seriously it will give our beleaguered politicians firmer ground to stand on.