Will Cosmos end up in cold, or fiery blast?

Big Crunch and Big Rip. PHOTO Courtesy: Google Images

The Earth was born 4.6 billion years ago and the Universe about 13.7 billion years ago. Compared to these numbers the brief flicker of our existence seems inconsequential, and yet we cannot resist the temptation to ask the question: What's the future of the Universe? There is no definitive answer to this question because the fate depends on the shape of the Universe.
HE Earth was born 4.6 billion years ago and the Universe about 13.7 billion years ago. Compared to these numbers the brief flicker of our existence seems inconsequential, and yet we cannot resist the temptation to ask the question: What's the future of the Universe? There is no definitive answer to this question because the fate depends on the shape of the Universe.
A closed, spherical Universe contains enough mass for gravity to emerge victorious. Its expansion will ultimately stop because of the mutual gravitational pull of all its matter. It will pause momentarily at its maximum size, reverse direction, begin to contract and accelerate toward its point of origin for a "second appointment with singularity." As the space shrinks, galaxies will begin to approach each other and red shifts will be replaced by blue shifts - decrease in the observed wavelength of radiation when the source approaches the observer. Finally, all matter would coalesce into a giant black hole, mimicking its birth, but in reverse. If we believe in this model known as the Big Crunch, then our Universe was born out of the collapse of a previous Universe. In all likelihood, after the Big Crunch there will be a Big Bounce - reincarnation of a new Universe in an event similar to the Big Bang. Our Universe was born out of naught and will perish into naught. There will be no memory of its "glorious few zillion years of existence."
For an open, hyperbolic Universe, there are several possible scenarios. One of them is known as the Big Rip. In this model, the Universe lacking enough matter expands at an ever increasing rate, undoing the work of gravity. The expansion, accelerated by a mysterious force called Dark Energy, will cause the galaxies to be separated from each other, ripping them apart. The galaxies will be followed by stars, planets, and finally atoms. As matter is ripped apart, interaction between different parts of the Universe will cease to exist. The Universe that was born with a violent explosion will end with an even more violent explosion.
If the Universe is flat, it will have the right amount of matter for their collective gravitational attraction to balance the expansion. It will reach equilibrium after using up all of the energy from the Big Bang. This Universe will never collapse but will expand for an immeasurably long time. Eventually far out into the future, expansion will abate and it will coast to a halt but will never reverse direction and start to shrink. Nevertheless, it will be a dead Universe. The death will be slow and less painful.
The most widely accepted scenario for the fate of the Universe, consistent with observations and the laws of Thermodynamics, is known as the Heat Death. In this scenario, the Universe will cool as it expands and the temperature will asymptotically approach absolute zero (-273 degrees Centigrade). Consequently, there will be no "free energy" available to sustain motion or life and it will be a cold, stationary, dead Universe. A vast, empty, frozen Universe is compatible with either a flat or an open Universe.
We seem to have four and possibly more cosmic destinies. Which one awaits us is not yet clear. To date results have been a mixed bag, some favoring the fate of an open, while others of a closed Universe.
How long will it take for the ultimate fate? The time frame is incomprehensible, probably zillions of years from now. Will humankind be able to behold the death of the Universe? Will this be the doomsday? Humans or their descendents will not be around to witness this cataclysmic event. Before this happens, the Sun will admittedly bloat into a red giant and swallow everything in its neighborhood, including our planet. We won't be able to witness this apocalyptic event either. Our doomsday will occur much earlier. How soon? Stay tuned.
"It is a tough choice between ending up in the cold or ending up in a fiery blast." - Nobel physicist Saul Perlmutter.

The writer is Professor, Dept. of Physics and Engineering Physics, Fordham University, New York.