View Full Version : The big rip vs. black holes

Professor Tanhauser
2007-Sep-23, 06:49 AM

The bout you've all been waiting for!

In this corner, weighing in at an estimated 10^15 megatons, Black hole NGC 2193012048.

And in this corner, weighing in at exactly nothing, the big rip!

Ok, seriously, having heard about the big rip and how it's supposedly going to destroy the universe in some dozens of billions of years, I couldn't help thinking to myselves "What happens to Black Holes when the big rip gets going?"

I was curious to see if scientists had determined if the big rip could tear apaet a black hole or not. Anyone know?

2007-Sep-23, 12:53 PM
Following is the wikipedia article. I think it is technabable and so did some who posted in the dicussion of the big rip: The Big Rip is a cosmological hypothesis about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. Theoretically, the scale factor of the universe becomes infinite at a finite time in the future.

The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state w, the ratio between the dark energy pressure and its energy density. At w < − 1, the universe will eventually be pulled apart. Such energy is called phantom energy, a more extreme form of quintessence.

In a phantom energy man dominated universe the "fabric" of the universe expands at an ever increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point gets ever closer. When the size of the observable universe is smaller than any particular structure, then no interaction between the furthest parts of the structure can occur, neither gravitational nor electromagnetic (nor weak or strong), and they will be ripped apart.

First, the galaxies would be separated from each other. Arguably, this is what is happening right now, with galaxies that move outside the observable universe (approximately 46.5 billion light years away). About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the Solar system will be gravitationally unbound. In the last minutes, stars and planets will be torn apart, and an instant before the end, atoms will be destroyed.

The authors of this hypothesis calculate that the end of the universe as we now know it would be in approximately 50 billion years

2007-Sep-24, 08:06 PM
I wonder if vacuum fluctuations can continue to happen after that point in time? Once the Big Rip has progressed to the point where it can rip apart particles, is it possible for particle/anti-particle pairs to pop into existence out of the vacuum?

2007-Sep-24, 08:29 PM
We discussed the Big Rip scenario and this question a while a back in some thread I'm too lazy to hunt down. There was the question of quark confinement vs the Big Rip that was argued about. This is well beyond me and I can't speak with any authority, but from what I gather, the Big Rip overwhelms that. It is essentially a type of singularity, infinite scale factor, that occurs in finite time for co-moving observers.

Now, what about black holes. That is a pretty good question, and the high priests of GR and gravitation haven't gotten that one down pat either. This is far from romper room math here. No exact solutions exist (according to my understanding), and there are questions about various approximate solutions that have been explored.

Understand the following is my (limited) understanding, and don't take this with too much authority:

In a regular cosmological constant background, a type of deSitter space I believe, a black hole "holds together" always. No problem there. This problem is just plopping a point mass down against a "lamba background", or roughly "Schwarzschild" against a deSitter, rather than Minkowski, background.

When you do that, you get something slightly different from Schwarzschild, but it's very close, well, close to the mass. At some radius, the expansion becomes stronger and free-fallers would fly away from the source mass, rather than toward it. That radius depends on lamba and the mass. The event horizon remains undisturbed.

However, that applies on to a normal Lamba behavior. In a Big Rip universe, it's different, and this solution does not apply. I smoked over a paper on this, and for some types of dark energy behavior, you can indeed get a "black hole ripped apart". However, exactly what that would "mean", what it would "look like", the authors themselves weren't sure. Their approximate solution had some problems, and I rememeber a real singularity developed at the event horizon, not just a coordinate one. There were other mathematical problems as well.

At any rate, this is basically just highly theoretical explorations of solutions to the EFE under various "dark energy" and Big Rip conditions and very much a work in progress, just getting started.

If the Big Rip is going to happen, well, it all goes to infinity anyway, so having a black hole "baring its nakedness" in the final millisecond or so will be moot anyway.