We Are Not Special

Sorry kids. Contrary to what your parents told you when you were young, you and I and everyone else are not special. Well, we are not special in terms of our place in the universe.

Y'see, once upon a time, we thought that we are at the center of the universe, and everything revolves around us. We believed that we are in a privileged location in the universe. Well, someone by the name of Copernicus, and later on, Galileo, practically destroyed that delusion.

Yet, there are still ideas (some call them theories) even today that still want to place us at this special location in the universe, and if they do that, they said that they can explain the universe accelerating expansion without any need to invoke dark energy. As always, Mother Universe can throw a wrench into the best-laid theory. This latest wrench comes in the form of the latest observational data that basically conclude that the universe is homogeneous at a length scale up to a gigaparsec.

In a paper appearing in Physical Review Letters, Pengjie Zhang at the Shanghai Astronomical Observatory and Albert Stebbins at Fermilab show that a popular void model, and many others aiming to replace dark energy, don’t stand up against telescope observation.

Galaxy surveys show the universe is homogeneous, at least on length scales up to a gigaparsec. Zhang and Stebbins argue that if larger scale inhomogeneities exist, they should be detectable as a temperature shift in the cosmic microwave background—relic photons from about 400,000 years after the big bang—that occurs because of electron-photon (inverse Compton) scattering. Focusing on the “Hubble bubble” void model, they show that in such a scenario, some regions of the universe would expand faster than others, causing this temperature shift to be greater than what is expected. But telescopes that study the microwave background, such as the Atacama telescope in Chile or the South Pole telescope, don’t see such a large shift.

 So for now, we are nothing special in our place in the Universe. But that's OK. I still like myself, and I still like you!

Edit: read another review of this work here.

Zz.