Passage 1 is excerpted from tamara davis, if galaxies are all moving apart, how can they collide? reproduced with permission. © 2009 by scientific american, a division of nature america, inc. All rights reserved. Passage 2 is excerpted from david biello, more often than not, massive galaxies form by mergers. Reproduced with permission. Copyright © 2005 by scientific american, a division of nature america, inc. All rights reserved.