The universe in a trillion years
The last blog post, Why Astronomy Matters, listed key astronomical observations that have fundamentally changed our understanding of the universe, and more importantly, our understanding of our place in the universe. We went from a scenario in which the Earth was at the centre to a sun-centred solar system, to an expanding universe that began in a big bang. The most recent set of observations in the late 1990s led to the discovery of dark energy, the energy that permeates the very fabric of spacetime and is causing the expansion of the universe to accelerate.
In a recent paper, Lawrence Krauss analyses the consequences of a universe dominated by dark energy whose density does not change with time (often referred to as the cosmological constant). One of the staggering implications of the cosmological constant is that in about 1-10 trillion years (which is comparable to the lifetimes of the longest-lived stars), all the astronomical evidence that led to the theory of the big bang will have vanished. Dark energy would have caused the expansion of spacetime to accelerate so much that all but the gravitationally-bound local cluster of galaxies (of which the Milky Way is a member) would have disappeared from sight. Given that we inferred the expansion of the universe by studying how distant galaxies are racing away from us, such a scenario would leave astronomers with little evidence of an expanding universe.
Krauss also points out that the cosmic microwave background (CMB) – the radiation leftover from the big bang, and another key piece of evidence for the big bang theory – would have been redshifted to such an extent as to make it practically unobservable. The wavelength of the CMB that would have the peak intensity would be larger than the universe’s light horizon.
So what would the universe look like to astronomers in such a universe? Krauss harkens back to a time when even Einstein thought that the universe was static, unchanging and eternal, a time before we knew of an expanding universe and a big bang. “Poetically their picture of the universe will not be significantly different than that which Einstein had when he developed general relativity: A static universe in which our galaxy was surrounded by eternal empty space, with which cosmology at the turn of the last century began, will have returned with a vengeance,” writes Krauss.
I don’t know about you, but that sends a chill up my spine.