A shove from Cosmos magazine

01Oct10

Between spraining my finger in a particularly aggressive game of netball, getting sick, getting back-to-back infections, having an exam, diving with sharks, attending Hen’s day/nights, and suddenly having a wave of scrapbooking inspiration (you just can’t ignore creativity when it strikes!), I haven’t had a lot of time to think about much, let alone cosmology controversies.

But, today, I got the latest Cosmos magazine in the mail. And what was one of its main features? An article on dark energy!

While half was about the South Pole Telescope and history behind dark matter and dark energy discovery, the other half briefly covered methods of detecting dark energy before discussing a caveat. This caveat is related to my thoughts in this post about the observational nature of cosmology contributing to any related controversy.

When I was writing that previous post, I avoided bringing this caveat up, partially because I read about it first in Leggett’s The Problems of Physics, written in 1987. Seeing it written in this most recent issue of Cosmos makes me feel a tad better about bringing it into the discussion.

From Cosmos (article written by Richard Panek):

All these methods come with a caveat. They assume we understand gravity, which is not only the force opposing dark energy but the foundation of physics.

My alarm bells went off when I read this, as Leggett talks about this in The Problems of Physics:

It is impossible to stress too much the fact that, in applying physics to the universe as a whole, we very often have to extrapolate laws which have been tested firmly and directly over only a very small range of density, temperature, and so on to conditions which are different by many orders of magnitude. Indeed, in many cases we have to invoke ideas which have not been tested directly at all, but are themselves inferred from a complex series of indirect experiments.

He expands this throughout the chapter; for example, he notes that the ‘celestial mechanics’ of Newton, inferred from observation of gravity on Earth, was only directly tested when rocket technology was developed and probes such as Voyager II were released into the solar system. An anomaly in Newtonian theory—the observed precession of the perihelion of Mercury did not match theory—should have signalled that, overall, the theory was unsound or incomplete. I wager that cosmology today is similar; little discrepancies in the current theory/observation, so that future scientists will look back on us as we look back on Newtonian-era scientists.

But, of course, we can only make progress in cosmology by making the assumption that the laws of physics observed on Earth hold in the rest of the Universe… so will any cosmological ‘discovery’ be wrapped in controversy?

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