57700957
submission
b30w0lf writes:
Gravitational wave detection—i.e. the detection of propagating ripples in spacetime—is a hot subject these days with ground-based interferometer experiments like LIGO active, and hopes for a space interferometer like LISA. But, physicist Freeman Dyson proposed back in 1969 that the earth itself could be used as a gravitational wave detector. The idea is behind the approach is that gravitational waves impact the earth’s crust, causing potentially detectable seismic waves. Using Dyson’s approach, Physicists at Harvard and NINP, Florence were able to put an upper limit on the intensity of gravitational background radiation based on a year of observational seismic data. The upper limit they found improved currently laboratory upper limits by 9 orders of magnitude.
38839079
submission
b30w0lf writes:
It is commonly understood that crystals exist in a state of matter that is periodic in space. Meanwhile, relativistic physics tells us that we should think of time as being a physical dimension, given similar status to the other spacial dimensions. The combination of these two ideas has lead researchers at the University of Kentucky and MIT to propose special manifestations of matter which would be periodic in both space and time, dubbed “time crystals.” Time crystals would continually transition between a set of physical states in a kind of perpetual motion. Note: the articles stress that this kind of perpetual motion in no way violates the established laws of thermodynamics.
While time crystals remain theoretical, methods have been proposed for creating them. The most obvious application of time crystals is the creation of very precise clocks; however, other applications to time crystals have been proposed, ranging from quantum computing to helping us understand certain cosmological models.
A technical summary with links to the original publications can be found at: http://physics.aps.org/articles/v5/116
For a less technical summary: http://www.scientificamerican.com/article.cfm?id=time-crystals-could-be-legitimate-form-perpetual-motion
