SEMCIÊNCIA

Quantum Time Machine Solves Grandfather Paradox Posted:  18 Jul 2010 09:10 PM PDT A new kind of time travel based on quantum teleportation gets around the paradoxes that have plagued other time machines, say physicists Of all the weird consequences of quantum mechanics, one of the strangest is the notion of postselection: the ability to trigger a computation that automatically disregards certain results. Here's an example: suppose you have a long, tortuous expression in which there are a frighteningly large number of variables. The question you want answering is which combination of variables makes the expression logically true. And the conventional way to solve it is by brute force: try every combination of variable until you find one that works. That's hard. Postselection, however, makes the solution easy to find. Simply allow the variables to take any value at random and then postselect on the condition that the answer must be true. This automatically disregards any wrong...

John Bell And The Nature Of Reality Posted:  13 Jul 2010 09:10 PM PDT Why have so few heard of one of the great heroes of modern physics? In 1935, Einstein and his colleagues Boris Podolsky and Nathan Rosen outlined an extraordinary paradox associated with the then emerging science of quantum mechanics. They pointed out that quantum mechanics allows two objects to be described by the same single wave function. In effect, these separate objects somehow share the same existence so that a measurement on one immediately influences the other, regardless of the distance between them. To Einstein, Podolsky and Rosen this clearly violated special relativity which prevents the transmission of signals at superluminal speed. Something had to give. Despite the seriousness of this situation, the EPR paradox, as it became known, was more or less ignored by physicists until relatively recently. Today, we call the relationship between objects that share the same existence entanglement. And it is the f...

For a Proton, a Little Off the Top (or Side) Could Be Big Trouble By  DENNIS OVERBYE Published: July 12, 2010 FACEBOOK TWITTER RECOMMEND SIGN IN TO E-MAIL PRINT REPRINTS SHARE For most of us, 4 percent off around the waist — a couple of belt notches — would be a great triumph. Enlarge This Image Chris Gash Not so for the proton, the subatomic particle that anchors atoms and is the building block of all ordinary matter, of stars, planets and people. Physicists announced last week that a new experiment had shown that the proton is about 4 percent smaller than they thought. Instead of celebration, however, the result has caused consternation. Such a big discrepancy, say the physicists, led by Randolf Pohl of the Max Planck Institute for Quantum Optics in Garching, Germany, could mean that the most accurate theory in the history of physics, quantum electrodynamics, which describes how light and matter interact, is in trouble. “What you have is a result that actually shocked us,” said Paul ...

Estudo reduz tamanho do próton e pode revolucionar a ciência 07 de julho de 2010 • 15h19 • atualizado às 16h16 comentários 6 Notícia Reduzir Normal Aumentar Imprimir Cientistas de um grupo internacional de pesquisas afirmara, nesta quarta-feira, que um constituinte fundamental do universo visível, o próton, é menor do que se pensava anteriormente, segundo estudo publicado na revista científica Nature . Medições revistas reduziram em 4% o raio da partícula que, embora não pareça muito - especialmente dado o tamanho infinitesimal do próton -, em experimentos futuros pode representar um desafio a preceitos fundamentais da eletrodinâmica quântica, a teoria de como a luz e a matéria interagem, disseram os autores. Inicialmente, a equipe internacional de 32 cientistas, chefiada por Randolf Pohl, do Instituto Max Planck em Garching, Alemanha, só queria confirmar o que já se sabia e não derrubar conceitos. Por décadas, os físicos de partículas usavam o átomo de hidrogênio como um parâmetro p...