Dark matter critics focus on details, ignore big picture

Ars Technica » Scientific Method 2012-11-14

Way back in the olden days, when the world was young and we were all much more innocent*, the Bullet Cluster was discovered. It was a revelation: two galaxy clusters had collided, leaving a mess of glowing ordinary matter and large clumps of invisible, gravity-rich material—in completely separate locations. Combined with some modeling, this was hailed as an unambiguous observation of dark matter.

Scientists, who were thinking of committing the sacrilege** of modifying the theory of gravity in a way that made dark matter superfluous, were saved. Our existing theory of gravity seemed to work, and they could return to reveling in the certainty of the known and simply reap the reward of... well, certainly there was some sort of reward.

Unfortunately, someone forgot to put the lens cap back on the Hubble telescope. Much to everyone's dismay, it snapped a picture of the Abell 520 cluster, which had dark matter where it shouldn't be. To make matters worse, it certainly didn't have visible matter where it should. Those few scientists who, disturbingly, enjoy thinking dark and sacrilegious thoughts were back in action. They might be allowed to modify gravity after all.

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