Don’t blame me for the clickbait heading. Capitalizing on Dubya Bush’s 2002 State of the Union address in which he singled out Iraq, Iran and North Korea as Earth’s baddies, cosmologists Kate Land and João Magueijo employed the same phrase three years later for the title of their scientificxpaper. In it, they described a spooky coincidence linking a 14-billion-year-old pattern in the universe with the plane of our planet’s orbit around the sun. This link gives me a chance to discuss the Cosmological Principle.
One of the foundations of astrophysics — make that the foundation — is the assumption that we’re not in a privileged location in the Universe. Nowhere is. The Universe is homogenous, meaning that no matter where you are, the Universe will look much the same. Clearly this doesn’t apply on small scales — the solar system looks different from interstellar space, for instance. But at really large distances (on the order of half a billion light years), any one patch of the Universe is indistinguishable from another. Another foundation is that it’s isotropic: There’s no preferred direction in the Universe. Together, these two assumptions form the Cosmological Principle.
We usually date the first glimmerings of the principle to the renaissance polymath Nicolaus Copernicus (1473-1543), whose magnum opus is called (in English) On the Revolutions of the Celestial Spheres. Copernicus challenged the (then) accepted “Ptolemaic” model of the Universe by displacing a stationary Earth from the very center of everything. Others had preceded him (notably Aristarchus of Samos, some 18 centuries previously), but it was Copernicus’ book that pioneered a series of demotions, moving Earth’s place in the Universe from “center” to “nowhere in particular.” This culminated with Edwin Hubble’s discovery in the 1920s that the Milky Way is just one of billions of galaxies. Hence the Cosmological Principle, no place and no direction being more special than any other …
… which went unchallenged until about 20 years ago, when cosmologists found an odd coincidence when examining a detailed map of the cosmic background radiation (CBR) that fills all of space with faint microwaves. The CBR, energy released soon after the Big Bang, was only detected in 1965. Two space-based telescopes, the Wilkinson Microwave Anisotropy Probe and, later, the Plank satellite, precisely mapped the radiation (see illustration). This map of relic radiation from the very early Universe found that the CBR was uniform across the entire sky, to one part in 10,000. Finer than that, though, the telescopes found that some areas were slightly warmer and some slightly colder than the average. Using a statistical technique known as “multipole expansion,” in which the map is sampled in one, two, four, eight … 40,000 parts, cosmologists expected that the axes linking the hotter spots with the colder spots at different sample rates would point in purely random directions.
While most of the multipole samples did indeed show the anticipated randomness, the axes of two of the sampled poles (the divisions into four and eight) were oddly aligned, hence the tongue-in-cheek “Axis of Evil” moniker. This result flies in the face of the “homogenous and isotropic” Cosmological Principle; if correct, the alignment would upset everything previously assumed about the cosmos. Even weirder, when viewed from the plane of the solar system, the CMB is slightly cooler in the “up” direction than the “down.” That is, the odd alignment of those two similar CMB samplings is matched by the plane of Earth’s and the other planets’ orbits around the sun. Which, if not another coincidence, is really weird (cue Twilight Zone music), given that the CMB is about 9 billion years older than the Solar System.
So: A quirk of randomness (like twins separated at birth winning consecutive Powerball lotteries) or simply a screw-up in the data analysis? Or a real and spooky phenomenon, challenging our basic assumptions about the Universe? If you’re a student wondering which career path to embark upon, you might want to consider becoming a cosmologist and going on to solve the Axis of Evil problem.
Barry Evans (he/him, barryevans9@yahoo.com) doesn’t believe in spooky coincidences. He just writes about them.
This article appears in Taco Week 25.