Physicists are now foretelling the death of cosmology, or the study of our universe, as we know it. Thankfully, cosmologists won't be jobless for a couple trillion years.
The universe is rapidly expanding — perhaps not rapidly enough to rip to shreds, but enough that distant galaxies will eventually be moving away faster than the speed of light. This much has been known for decades.
Once all these galaxies blink out of existence, scientists ask in an upcoming issue of The Journal of Relativity and Gravitation, how will future intelligent beings study space if the human race's knowledge is long gone? Will they be able to figure out if the Big Bang happened? Or rediscover relativity?
Island universe
For the most part, said Lawrence Krauss, a theoretical physicist at Case Western Reserve University in Cleveland, Ohio, and co-author of the journal article, future observers will be out of luck.
"They'll be stuck in an endless black void," Krauss said, noting that any galaxies outside of our own cluster will disappear in about 100 billion years. "They'll feel very special after that happens, because our tiny cluster of galaxies will be the observable universe to them."
Without a cosmological frame of reference, Krauss explained, future observers will be clueless that their universe is still expanding. "It will be a sort of twisted situation, where thinking returns to what it was at the turn of the 20th century," he said.
In other words, observers will think the universe is just a static — or non-expanding — cluster of galaxies just as scientists thought until the 1920s. "The static universe," as the journal article states, "will have returned with a vengeance."
No background material
An additional issue for future observers will be the disappearance of cosmic microwave background radiation — the fingerprint of the Big Bang's occurrence — in about 250 billion years. Without it, Krauss said, observers can't be certain about how the universe was created, not to mention when.
The problem relates to the Doppler effect: When a speeding train approaches, the sound waves from its whistle are squished together to make a higher pitch. As it passes, the sound waves are stretched out like a slinky and become lower in pitch and fainter. Similarly, as the universe expands outward, the "pitch" of light will lengthen and fade away. "The wavelength of light will be so large it will eventually reach the size of our galaxy," Krauss said. "It will just be absorbed."
Krauss, however, is confident that someone (presumably human in form) will be the next Einstein and rediscover general relativity. He's also hopeful that future observers will be able to explain the creation of the solar system by studying stars within the galaxy.
And, said Krauss, there's a positive side to not knowing the universe's true history: "There'll be almost no static on their TV screens," Krauss said, explaining that if there are no distant galaxies around to emit cosmic rays, the airways will be a lot cleaner.