General Relativity, Still Making Waves

In a validation of Albert Einstein’s genius, the power of new technology, and the relevance of the scientific method (even if it takes a century), scientists working on a project called LIGO have witnessed ripples in the fabric of spacetime caused by gravitational waves. First predicted by Einstein in 1916 on the basis of general relativity, gravitational waves are cosmic shock waves that can result from the interactions of massive objects like black holes and neutron stars. Unlike electromagnetic waves, which pass through space, gravitational waves change the shape of space itself. Extremely perceptive observers would find themselves in a funhouse as gravitational waves passed through, watching objects and distances get bigger and smaller without actually moving a micron: seeing solid matter jiggle like jello.

LIGO’s results are the most sensational in physics since the observation of the Higgs boson in 2013. Ethan Siegel puts the discovery into perspective on Forbes, writing “we’ve just detected two merging black holes for the first time, tested their physics, found a tremendous agreement with Einstein, and seen evidence that this happens over a billion light years away across the Universe.” Meanwhile Greg Laden says “the gravity of this situation” deserves a newton of skepticism until scientists can repeat their result. And on Dynamics of Cats, Steinn Sigurðsson shares videos from the LIGO team to help everyone understand the project.

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Cold, Hard Facts

Coldness can manifest where you least expect it: on a planet rapidly warmed by the combustion of fossil fuel, or in the heart of a star 250 times as massive as our own. On Greg Laden’s Blog, Greg explains that an apparent “recovery” of Arctic sea ice from its historic low in 2012 does not invalidate the long-term trend. Greg also explains this year’s legacy of extreme weather, such as snow in Cairo, writing that when there is less difference in temperature between equatorial and polar regions, “the jet streams get all wiggly and cause northerly air to reach far to the south in some places and southerly air to reach farther north in other places.” Meanwhile, on Starts With a Bang, Ethan Siegel explores the different fates awaiting stars of different sizes. When a star like our own runs out of fuel and begins to collapse, it blows off its outer layers and leaves behind a neutron star or small black hole. Bigger stars, however, start producing antimatter, which lowers the pressure in the star and generates gamma rays that heat up the core even further. These stars end in a pair-instability supernova, which “not only destroys the outer layers of the star, but the core as well, leaving absolutely nothing behind!” But in the biggest stars in the universe, gamma rays cause photodisintegration, which cools down the interior of the star and allows all its mass to collapse into a black hole. The earliest of these massive black holes probably seeded the centers of galaxies, which now contain millions of solar masses.