文档介绍：Why Does Time Only Move Forward?(page 48)Meteor Mystery What Really Happened 100 Years Ago in Siberia Trust Hormone Neurobiology Reveals What Makes Us Connect Photo Frauds Spot Digital Fakes June 2008$ ate ChangeEthics and Economics ofTherapies That Beat BREAST CANCERpage 58 Balancing Current Costsagainst Future Well-Being? 2008 SCIENTIFIC AMERICAN, ■ENTIFIC AMERICAN5SCIENTIFIC AMERICAN June 2008 ■ Volume 298 Number 6 96Ethics and economics inform every decision about whether to prevent gl obal warmi ng or l et future gen-erati ons deal wi th i t. Image by Jean-Francoi s Podevi THE COVER 4866COSMOLOGY48 ?The?Cosmic?Origins??of?Time’s?ArrowBy Sean M. CarrollMaybe time’s seemingly unvarying flow forward is a short-term fluke in a universe where the distant future and distant past look the ?Gaining?Ground?on??Breast?CancerBy Francisco J. Esteva and Gabriel N. HortobagyiThe newest targeted therapies help doctors to tailor effective treatments to individual Digital?Image?ForensicsBy Hany FaridModern software makes image tampering easier but also enables new methods of BIOLOGY72 What?Is?a?Species?By Carl ZimmerBiologists still struggle with that fundamental but scientifically pivotal ?Ethics?of?Climate?ChangeBy John BroomeWhen economists analyze how much to spend on global warming, they must weigh the value of our current prosperity against that of the diminished well-being of our grandchildren. 5872Image by Jean-Francois Podevin? 2008 SCIENTIFIC AMERICAN, FEATURES ■Sci ent i fi c A mer i can ( I SSN 0 036- 8733) , publ i s hed mont hl y by S ci ent i fi c A mer i can, I nc. , 415 Madi s on Avenue, New York, . 10017-1111. Copyr i ght ? 2008 by S ci ent i fi c American, Inc. All rights reserved. No part of t hi s i ssue may be reproduced or t ransmit ted i n any form or by any means, el ect roni c or mechani cal , i ncludi ng photocopyi ng an