Astronomers today can look at galaxies more than 13 billion years away that were formed only millions of years after the universe began. They can also study the so-called cosmic microwave background radiation — a pervasive light in the cosmos that was created by the Big Bang and still lingers on.
So, in the distant future intelligent beings will have no way of formulating the big bang theory due to the infinite expansion of the universe and the cosmic background radiation fading away.
The cosmic microwave background light will have faded away and been stretched to the point that its particles of light, called photons, will have wavelengths longer than the visible universe.
And because the universe is expanding, the ancient galaxies that are now just within our field of view will be too far away to see from future Earth. The sun and many other stars will have burned out, and our cosmic neighborhood will be much emptier than it is today.
However, all hope for future celestial sleuths is not lost, because future astronomers might be able to study the Big Bang through so-called hypervelocity stars that have been flung out of the Milkomeda galaxy.
The gravitational forces there can rip apart the binary, sucking one star into the black hole and flinging the other outside the galaxy at speeds greater than 1 million miles per hour (1.6 million kilometers per hour).
Having escaped the galaxy, hypervelocity stars will be accelerated by the expansion of the universe. By measuring the speeds of hypervelocity stars, future astronomers can deduce the expansion of the universe, which in turn can be traced back to the Big Bang.