Science and the Missing Energy

Does the first law of thermodynamics need revision? That was the question at the heart of a recent article in Scientific American.

I believe the author ends up answering "no," but it is an intriguingly tentative "no."

The first law is that "energy can be neither created nor destroyed." This law had to be modified back when scientists first realized that energy can be created with the loss of mass/matter (as at Hiroshima). But if we think of mass as stored energy, then the law holds.

Or does it? Here's the money quote from Tamara Davis' story. "Almost all of our information about outer space comes in the form of light, and one of light's key features is that it gets redshifted -- its electromagnetic waves get stretched -- as it travels from distant galaxies through our ever expanding universe....But the longer the wavelength, the lower the energy. Thus, inquisitive minds ask: When light is redshifted by the expansion of the universe, where does its energy go?" If the energy is simply lost, then the first law has been violated.

The author, Ms Davis, is a research fellow at the University of Queensland, in Australia, and an associate professor at the University of Copenhagen, in Denmark.

She seems to be saying that there are two ways to interpret the expansion and the resulting redshift, one involving the expansion of space itself, the other involving the movement of objects away from each other. In the later case, the redshift is a relatively straightforward matter of the workings of the Doppler effect, and doesn't imply any loss of energy. In the former case, if we think of space as an expanding balloon, it is more difficult to make the energy "accounting" work.

Indeed, Davis thinks it may be impossible to save the first law from that point of view, but she also seems to conclude that we simply shouldn't try. The loss of energy on the cosmic scale isn't so much a violation of the first law, in her view, as a category mistake.