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The Possibility of Paradox-Free Time Travel 421

relliker writes in with word of a paper up on the ArXiv by Seth Lloyd and co-workers, exploring the possibility that "postselection" effects in non-linear quantum mechanics might allow paradox-free time travel. "Lloyd's time machine gets around [the grandfather paradox] because of the probabilistic nature of quantum mechanics: anything that this time machine allows can also happen with finite probability anyway... Another interesting feature of this machine is that it does not require any of the distortions of spacetime that traditional time machines rely on. In these, the fabric of spacetime has to be ruthlessly twisted in a way that allows the time travel to occur. ... Postselection can only occur if quantum mechanics is nonlinear, something that seems possible in theory but has never been observed in practice. All the evidence so far is that quantum mechanics is linear. In fact some theorists propose that the seemingly impossible things that postselection allows is a kind of proof that quantum mechanics must be linear."

Climate Change and the Integrity of Science 1046

blau tips news of an open letter from 255 members of the US National Academy of Sciences, including 11 Nobel laureates, decrying the "recent escalation of political assaults on scientists in general and on climate scientists in particular." The letter lays out the basics of the scientific method, and explains how certainly highly-regarded theories — such as the big bang, evolution, and Earth's origin — are commonly accepted due to the strength of the evidence supporting them, though "fame still awaits anyone who could show these theories to be wrong." It goes on to "call for an end to McCarthy-like threats of criminal prosecution against our colleagues based on innuendo and guilt by association, the harassment of scientists by politicians seeking distractions to avoid taking action, and the outright lies being spread about them." According to the Guardian, the letter "originated with a number of NAS members who were frustrated at the misinformation being spread by climate deniers and the assaults on scientists by some policy-makers who hope to delay or avoid making policy decisions and are hiding behind the recent controversy around emails and minor errors in the IPCC."

New Evidence Presented For Ancient Fossils In Mars Rocks 91

azoblue passes along a story in the Washington Post, which begins: "NASA's Mars Meteorite Research Team reopened a 14-year-old controversy on extraterrestrial life last week, reaffirming and offering support for its widely challenged assertion that a 4-billion-year-old meteorite that landed thousands of years ago on Antarctica shows evidence of microscopic life on Mars. In addition to presenting research that they said disproved some of their critics, the scientists reported that additional Martian meteorites appear to house distinct and identifiable microbial fossils that point even more strongly to the existence of life. 'We feel more confident than ever that Mars probably once was, and maybe still is, home to life,' team leader David McKay said at a NASA-sponsored conference on astrobiology."

We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise. -- Larry Wall