Tuesday, November 27, 2007

Observation shortens the universe's life?

A reader showed me a recent article in the Telegraph: Mankind 'shortening the universe's life'. As a resident "physicist" of the blogosphere, I feel obligated to comment. My warning is that the science here is quantum mechanics, and I have not yet received a full formal education about the theory. I may or may not know what I am talking about. For a real physicist's comment, I refer you to Rob Knop, Chad Orzel, or Pamela (Edit: also, John Baez). Another warning is that I usually try to "work my way up" to complicated science like this by explaining the background first, but there will be none of that this time. We're heading into deep waters!

The article is based on a paper in New Scientist. I haven't read the paper, and probably wouldn't understand it, so I can't say whether the Telegraph has over-sensationalized it or if it was New Scientist itself. But the article states that we may be shortening the universe's life expectancy (which is still many billions of years) simply by making astronomical observations of dark energy. Hmm, well... making wild claims might impress the Telegraph, but it just makes me more skeptical.

The first thing I thought was, "Life expectancy?" Last I checked, cosmologists think the universe extends infinitely into the future. The article explains that dark energy, which (allegedly) caused the Big Bang, and currently accelerates the expansion of the universe, may at any point in time cause another Big Bang of sorts. "Any point in time", of course, means that it has a very small chance to occur over any given billion-year period. That sounds pretty iffy to me, where "iffy" means "legitimate, but not well-established". Actually, I suspect this hypothesis is the main topic of the New Scientist paper.

The reason that observing dark matter might affect the age of the universe is because of something called the Quantum Zeno Effect. Perhaps I will fully explain this in the distant future (Cosmic Variance already has), but I'll just summarize for now. The Quantum Zeno Effect is a way of affecting quantum states by making multiple measurements. Each measurement "collapses the wavefunction", which means the quantum state has changed. With enough of these measurements, you can change the quantum state to something completely different from what it would have been otherwise. This is not to be confused with the "observer effect" in which the act of shooting photons at what you want to see changes it. This is a genuine, tested quantum effect that requires no physical contact of any sort. Yes, it is very strange.

I'm not sure of the details, but supposedly observing dark energy may "reset" its quantum state such that the universe's life expectancy shortens. But the problem with this is that it assumes a specific interpretation of quantum mechanics. That is, it assumes that wavefunctions collapse only when humans observe them. See, there are lots of interpretations of quantum mechanics, most of which are mathematically (if not philosophically) equivalent. So if you've got some theory, it should work under all interpretations or none of them. The fact that this theory relies on one specific interpretation makes it suspect in my admittedly uneducated eyes. All the interpretations must come out the same, or you're doing something wrong.

In the unlikely scenario that their idea is correct, I think they are mistaken if they think that quantum state should reset only when scientists try to measure dark energy. I think the wavefunctions collapse as soon as you look into the sky, regardless of whether you decide to do some mathematical calculations afterwards to find how much dark energy there is. For that matter, I think that there is not even any need to look at the sky. If the photons from the sky hit my desk, then merely looking at my desk is an indirect observation of dark energy. Does looking at my desk shorten the lifespan of the universe? I doubt it.

The second half of the article talks about an unrelated story in which a previous measurement of mass turned out to be wrong by a certain amount. I don't know much about that, but it sounds completely legitimate. However, there is a misleading segue between the two stories. This is not a case of measurements changing the universe, just a case of human errors changing measurements.