Cosmological Constant and Future of The Universe
The cosmological constant is the simplest solution to the problem of cosmic acceleration with just one number successfully explaining a variety of observations and has become an essential feature in the current standard model of cosmology. It is called the lambda–cold dark matter model, as it incorporates both cold dark matter and the cosmological constant, and can be used to predict the future of the universe.
Expansion and Future of The Universe
The accelerating expansion of the universe that is now accepted has a very interesting consequence. It used to be thought that with a slowing rate of expansion, as the universe became older we would see an increasing number of galaxies (as the distance we could see becomes greater). In a universe whose expansion is accelerating the exact opposite will be true – yes, we will be able to see farther out into space, but there will be increasingly less and less for us to see as the expansion carries galaxies beyond our horizon.
On the large scale, the space between the galaxy clusters will be expanding – carrying them ever faster apart – but it is believed that clusters like our own Local Group will remain gravitationally bound and, in fact, its members will merge into one single galaxy largely made up from our own Milky Way Galaxy and the Andromeda Galaxy. If one looks forwards in time to ∼100 billion years, any observers in existence within this ‘galaxy’ would see a totally empty universe! The expansion of space will have carried all other galaxies beyond our horizon – the edge of the visible universe.
It would be virtually impossible for such observers to learn about the evolution of the universe for a number of reasons including the fact that the peak of the energy spectrum of the CMB will have redshifted down to ∼1 m. A uniform radio background at this wavelength could, in principle, be detected, but its intensity will have reduced by 12 orders of magnitude so that it would be virtually impossible to detect!
Effect of Dark Energy on Future of the Universe
From theoretical studies of stellar evolution and how the relative abundances of the elements change with time (for example, the amount of hydrogen is reducing and that of helium increasing as a result of nucleosynthesis in stars) it might well be possible to estimate the age of the galaxy, but it would not be possible to infer that its origin involved a Big Bang. It would be tough being an astronomer!
We happen to live at the only time in the history of the universe when the magnitude of dark energy and dark matter are comparable and also when the CMB is easily observable; this enables us to infer the existence of dark energy, the way in which the universe has evolved since the Big Bang and its future in a runaway expansion.
Any observers present when the universe was young would not have been able to infer the presence of dark energy as, at that time, it would have had virtually no effect on the expansion rate. Those in the far future will not be able to tell that they live in an expanding universe at all, and not be able to infer the existence of dark energy either! As the longest-lived stars come to the end of their lives, the evidence that lies at the heart of our current understanding of the origin and evolution of the universe will have disappeared.
It is interesting to note that we live in what is perhaps the very best time in which to explore the mysteries of the universe. As Lawrence M. Krauss and Robert J. Scherrer have stated: ‘We live in a very special time in the evolution of the Universe: the time when we can observationally verify that we live in a very special time in the evolution of the Universe!’