View Full Version : The Big Rip

08-21-2015, 07:56 PM
I was reading about asteroids when I found this:
Everything we know, and everything else besides, burst into existence at the Big Bang. Now scientists have concluded that we could be heading for an equally dramatic cosmic finale: the Big Rip.
A new theoretical model suggests that as the universe expands, everything, from galaxies, planets and atomic particles to space-time itself, will eventually be torn apart before vanishing from view.
There’s no need for immediate alarm, however: the extreme sequence of events is predicted for around 22 billion years from now.
Dr Marcelo Disconzi, the mathematician who led the work at Vanderbilt University in Tennessee, said: “The idea of the Big Rip is that eventually even the constituents of matter would start separating from each other. You’d be seeing all the atoms being ripped apart ... it’s fair to say that it’s a dramatic scenario.”
Scientists are now fairly convinced that the universe began with the Big Bang, around 13.8 billion years ago – starting at a pinpoint of incredibly high density and expanding to what we have today.
But our ultimate cosmic destiny is still the subject of intense debate.
“The only thing we definitely know is that the universe is expanding and that the rate is accelerating,” said Disconzi. “That’s about the only thing we know for sure.”
The latest work suggests that this acceleration may become faster and faster until every point in space itself is moving apart at an infinite rate – at which point the Big Rip occurs.
“Mathematically we know what this means,” said Disconzi. “But what it actually means in physical terms is hard to fathom.”
The evidence for an accelerating expansion comes from observations of distant supernovae. The further away they are the redder they appear, because the light has been stretched out as it travels through space to reach us.
To explain this increasing rate of expansion, scientists have come up with a cosmological placeholder, known as dark energy, which is believed to make up about 70% of the content of the universe.
“It’s the physicists’ way to hide their ignorance by giving it a mysterious name,” said Professor Carlos Frenk, a cosmologist at the University of Durham. “We don’t have any physically compelling way to explain it.”
Whether the universe’s expansion continues to speed up or gradually eases off comes down to a sort of gladiatorial battle between two opposing cosmic forces.
“You have this competition between dark energy, that tries to expand the universe, and gravity, that tends to make it collapse again,” said Disconzi. The question is who wins?”
Under the gravity wins scenario, known as the Big Crunch, the expansion eventually slows down and a kind of reverse of the Big Bang occurs.
But scientists have been shifting in favour of a situation called the Big Freeze where the universe continues to expand, eventually growing so vast that supplies of gas become too thin for new stars to form and a thin soup of radiation is left. Eventually this cools down to the point where time loses any meaning because nothing happens any more.
The latest work suggests that we could be heading for less a gentle finale, and predicts that dark energy wins out in the most dramatic possible fashion.
The paper, published in the journalPhysical Review D (http://journals.aps.org/prd/abstract/10.1103/PhysRevD.91.043532), refines current models by finding a more consistent way to account for a property called bulk viscosity, a measure of a fluid’s ability to expand or contract. In this case, the fluid is the universe itself.
Previously, according to Disconzi, viscosity had been included in the equations but in a way that predicted that under certain conditions fluids could travel faster than light.
“This is disastrously wrong, since it is well-proven that nothing can travel faster than the speed of light,” said Disconzi.
The latest formulation gets rid of this inconsistency, but also gives a revised prediction of where the Universe is heading, suggesting that eventually the expansion of the universe will accelerate at an infinite rate.
“A Big Rip scenario is a natural consequence of the equations,” said Disconzi.
One way to think of the lead-up to the event, is a speeding car that goes 10mph faster for every mile it travels. But the rate of acceleration gradually increases until it goes 10mph faster for every half mile, and then every quarter of a mile and eventually every foot. Ultimately, the front and the back bumpers tear apart from each other and then rip apart themselves.
Whether this occurs in the cosmic version depends on how dark energy behaves in the distant future - a question that Frenk describes as the realm of pure speculation.
“Under the rip scenario, dark energy gets stronger and you get this wild expansion that essentially rips space-time apart,” he added. “The universe would vanish in front of your eyes. Basically, you don’t want to be around for it.”
-Hannah Devlin (The Guardian)

Pretty interesting to me. Fluid universe. Ever-increasing acceleration. Could be argued that it backs up the theory that our universe exists inside a black hole.