Word: positrons
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Dates: during 2000-2000
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...time, eight years ago, PET (positron emission tomography) machines, which can reveal subtle metabolic processes such as tumor growth, and CT (computerized tomography) scanners, which show precise anatomical details, were already in widespread medical use. But doctors, especially cancer surgeons, were often frustrated in their attempts to match the two different scans to determine, for example, the precise location of a tumor in relation to an organ or to the spinal column. There seemed to be no better way than simply "eyeballing" the two separate images...
...laws of physics permit time travel, even in principle? They may in the subatomic world. A positron (the antiparticle associated with the electron) can be considered to be an electron going backward in time. Thus, if we create an electron-positron pair and the positron later annihilates in a collision with another, different electron, we could view this as a single electron executing a zigzag, N-shaped path through time: forward in time as an electron, then backward in time as a positron, then forward in time again as an electron...