Some physicists are pushing back against ideas like string theory and the multiverse. Here, we see a computer-generated image of a black hole, which might, ultimately, be explained by ideas like string theory. Alain Riazuelo/IAP/UPMC/CNRS hide caption

toggle caption Alain Riazuelo/IAP/UPMC/CNRS

Observing the multitude of galaxies in our own universe is a piece of cake. Observing the multiverse, if such a thing exists, seems impossible. Above, the Milky Way rises above the ESO's ALMA observatory in Chile. Y.Beletsky/ESO hide caption

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Don't panic! The end of the Universe (as we know it) isn't likely to hit us for billions of years, if it comes at all. Pictured: the Milky Way rises above the ESO's ALMA facility in Chile. José Francisco Salgado/ESO hide caption

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An illustration shows the Earth's night sky 3.75 billion years from now, with the Andromeda galaxy (left) beginning to distort our own Milky Way as the two collide. While galactic collisions are eye catching, could something bigger be just over the horizon? Z. Levay/R. van der Marel/T. Hallas/A. Mellinger/NASA/ESA hide caption

toggle caption Z. Levay/R. van der Marel/T. Hallas/A. Mellinger/NASA/ESA

Just the tiniest slice of what's out there: the Pencil Nebula is pictured in an image from the European Southern Observatory's La Silla facility in Chile. This peculiar cloud of glowing gas is part of a huge ring of wreckage left over after a supernova explosion that took place about 11,000 years ago. ESO hide caption

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