Astronomy & Cosmology


The End of the Universe

The idea of the Universe ending in a Big Rip was first postulated in 2003.  If the ratio of the dark energy pressure to its energy density, its equation of state, has a value less than -1, the Universe ends in a Big Rip.  This scenario results in the Universe expanding not with a constant rate of acceleration, but at an increasing rate of acceleration.  The driving force is a variant of dark energy called Phantom Energy.  While uncomfortable with phantom energy, theoreticians have been unable to rule it out.  On of its consequences is that the microscopic worm holes, predicted by special relativity, normally close so fast they are undetectable.  The repulsive effect of phantom energy could not only hold worm holes open, but possibly expand them to macroscopic size.  This raises the specter of using them as "time machines" with all the theoretical baggage that produces. 

Leaving time travel aside, as the Universe expands in this scnario, the point at which the rate of the expansion exceeds the speed of light gets closer to us.  Thus, the size of the observable Universe shrinks.  Over time, this means that, for example, the other galaxies in the local group would be outside of the observable Universe as their recession speed exceeds the speed of light.  Extrapolating this, the rest of the solar system itself would become unobservable.  Eventually, individual atoms would be torn apart and possibly even individual particles.  This is the Big Rip, and essentially results in an enormous Universe in which there is no matter and no energy.  If Dark Energy is actually a cosmological constant, rather than something like quintessence that can vary over time, then this is the most likely scenario based on current observations as it would not be possible for the rate of acceleration of the expansion to slow.  The cosmologist Robert Caldwell calculated, in 2003, that by 19 to 21 billion years in the future, all the other galaxies will have receded so far from the Milky Way that they will cease to be visible.  One billion years after that, all the atoms and particles in the Universe would have flown apart, so the timescale is another 20 to 22 billion years. 

The Big Rip