swans on tea

Via Shores of the Dirac Sea I find The FQXi Inaugural Essay Contest (Summer 2008): THE NATURE OF TIME

Each essay contest will focus on a particular theme, question, or subject that the submitted work must directly address. For the current contest, this is “The Nature of Time,” including, but not limited to, the arrow of time; the emergence of time in quantum gravity; time, free will and determinism; time travel; the beginning or ending of time; and timelessness. Additionally, to be consonant with FQXi’s scope and goals, essays should be primarily concerned with physics (mainly quantum physics, high energy ‘fundamental’ physics, and gravity), cosmology (mainly of the early universe), or closely related fields (such as astrophysics, astrobiology, biophysics, mathematics, complexity and emergence, and philosophy of physics), insofar as they bear directly on questions in physics or cosmology.

Here’s the problem as I see it: the nature of time isn’t a science problem, it’s a philosophy problem. Many of the suggestions for essays aren’t really tied to physics all that strongly. Asking “how does time behave?” is a physics question, as is “how does this influence other phenomena?” But asking, “What is time, really?” is metaphysics.

That’s not to say the question has no value. If it can get someone to look at the problem from a different angle and it leads to a different description of nature, that’s great. But science is an investigation into how nature behaves, and not, fundamentally, into why it behaves that way. You reach the level of the four-year-old asking a question, and responding to each one with, “But why?” You can only give justification so many times before you run out of answers and have to say, “Go ask your mother.” Or, in the case of science, “We don’t know. It’s not the question we’re trying to answer.”

Science explains the operation of nature with models — mathematical descriptions that allow one to predict and explain what’s going on. But there’s nothing that guarantees that nature actually is this way, that the convenient terms we use are actually real. In many ways it’s bookkeeping. We notice that we can quantify certain things, like energy and work. Physics defines energy as the capacity to do work. That doesn’t tell you what energy is, it tells you why it’s useful. We have this quantity of something that doesn’t change — we can convert it from one form to another, and it allows us to predict things, like how far something will move, or whether an event will occur spontaneously. That’s useful to know! But it says nothing about what energy is. These are entries in a ledger that let us come up with an answer. Bookkeeping. This is one thing that can make thermodynamics difficult — all of those thermodynamic potentials make it advanced bookkeeping.

I recall being asked whether photons were real. I study atomic physics, so my reaction was, “Sure, photons are real.” Then I was asked about phonons. Nah — phonons are just a convenient way of describing vibrational modes of a lattice. Which is when it hit me that photons could just be a convenient way of describing the vibrational modes of an electromagnetic field. To a condensed matter physicist, I’m sure that phonons seem real. But we don’t do experiments that tell us that they are real, we do experiments that tell us how nature behaves. Nature may behave as if they are real, because we have accurately determined the properties, but that’s not the same thing. Physicists do this a lot, and some are easier to spot than others. We have electrons and holes in semiconductors. Are holes real, or are they just a convenient description of the lack of an electron? What is mass, anyway? What is charge? Is the Copenhagen interpretation of quantum mechanics the right one?