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One trillion years from now, alien astronomers in our galaxy will have a difficult time figuring out how the universe began. They won't have the evidence that we enjoy today.

Edwin Hubble made the first observations in support of the Big Bang model. He showed that galaxies are rushing away from each other due to the universe's expansion. More recently, astronomers discovered a pervasive afterglow from the Big Bang, known as the cosmic microwave background, left over from the universe's white-hot beginning.

In a trillion years, when the universe is 100 times older than it is now, alien astronomers will have a very different view. The Milky Way will have merged with the Andromeda Galaxy to form the Milkomeda Galaxy. Many of its stars, including our Sun, will have burned out. The universe's ever-accelerating expansion will send all other galaxies rushing beyond our "cosmic horizon," sending them forever out of view.

The same expansion will cause the cosmic microwave background to fade out, stretching the wavelength of CMB photons to become longer than the visible universe. Without the clues of the CMB and distant, receding galaxies, how will these far-future astronomers know the Big Bang happened?

According to Harvard theorist Avi Loeb, clever astronomers in 1 trillion C.E. could still infer the Big Bang and today's leading cosmological theory, known as "lambda-cold dark matter" or LCDM. They will have to use the most distant light source available to them -- hypervelocity stars flung from the center of Milkomeda.

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Category: Science