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View Full Version : General question about Black Holes (BH) and fate of the Universe



JGHeyen
2010-Aug-04, 03:00 PM
Since it seems that BH are at the center of all gallaxies and are a central part of the dynamics of the Universe, I'm wondering if the Universe could/will become one large BH ?

WayneFrancis
2010-Aug-05, 12:37 AM
If the universe did collapse back down to a singularity there would be no "out side" to refer to it as a black hole. In addition to that the universe's expansion may continue accelerating in which case the answer is again no.

I guess you could end up with a situation where most matter in any part of an observable universe could all be in a black hole but there would, most likely , still be photons, virtual particles, etc., that out there.

Basic answer is "no".

AriAstronomer
2010-Aug-05, 10:53 AM
I think there's a misconception that when a star turns into a black hole, it automatically turns into this blood thirsty (and by blood I mean matter) tyrant trying as hard as it can to gobble anything and everything to the far reaches of the universe...

In reality, if the sun suddenly turned into a black hole, the orbit of earth would not change (assuming no cataclysmic supernova occurred to wipe out earth in the first place). The amount of mass has not changed, and gravity is a function of mass. This being said, the supermassive black holes are much larger, but the principle is the same. Their pull only extends so far. For a supermassive black hole to be able to reach out to the far edges of our galaxy, it must acquire ALOT of material, possibly too much than what is in the local vicinity. If everything steers clear of the black hole in the billions of years to come, the galaxy will remain in equilibrium. If it continues to acquire more material over time, there will be a slow decay of the stars into the center, and I suppose yes one day it could engulf the entire galaxy (assuming there are no upper limits to the size of a black hole), but this would probably be billions if not trillions of years away.

JGHeyen
2010-Aug-05, 11:46 AM
If the universe did collapse back down to a singularity there would be no "out side" to refer to it as a black hole. In addition to that the universe's expansion may continue accelerating in which case the answer is again no.

I guess you could end up with a situation where most matter in any part of an observable universe could all be in a black hole but there would, most likely , still be photons, virtual particles, etc., that out there.

Basic answer is "no".

I thought that the "Big Bang" supposedly resulted from a singularity. Was that singularity possibly a black hole? What was "out side" of it?

clop
2010-Aug-05, 12:48 PM
I seem to remember being told that all the matter in the universe will eventually consist of numerous black holes of various sizes, which will slowly evaporate via Hawking radiation until there are no black holes left and the entire universe is composed of a sea of whatever the particles are that get produced by Hawking radiation, and then it'll stay like that forever.

clop

Cougar
2010-Aug-05, 01:22 PM
I seem to remember being told that all the matter in the universe will eventually consist of numerous black holes of various sizes....

I would be very surprised if you could find a reliable source for such a claim. Offhand, this sounds highly unlikely, if not nonsense.

Cougar
2010-Aug-05, 01:32 PM
In reality, if the sun suddenly turned into a black hole, the orbit of earth would not change...

Correct.


For a supermassive black hole to be able to reach out to the far edges of our galaxy, it must acquire ALOT of material, possibly too much than what is in the local vicinity. If everything steers clear of the black hole in the billions of years to come, the galaxy will remain in equilibrium. If it continues to acquire more material over time, there will be a slow decay of the stars into the center...

(1) The effect of gravity decreases in relation to the square of the distance, but it never goes to zero. (2) Any mass that a supermassive galactic black hole acquires would have already been interior to the orbits of most disk stars. The fact that the black hole gains that mass will not cause any decay to the orbits of those outer stars.

Peter B
2010-Aug-05, 01:39 PM
I would be very surprised if you could find a reliable source for such a claim. Offhand, this sounds highly unlikely, if not nonsense.

Out of interest, what IS the current consensus on the fate of the universe?

Cougar
2010-Aug-05, 02:17 PM
Out of interest, what IS the current consensus on the fate of the universe?

Expand forever. Star formation continues to decrease. Most stars become white dwarfs, which cool very slowly. Paul Davies wrote a book on the topic: The Last Three Minutes, Conjectures About the Ultimate Fate of the Universe [1994]. Dark energy is currently a wild card....

JGHeyen
2010-Aug-05, 04:01 PM
I have a hard time believeing the universe is going to reach a particular state and remain that way forever. Systems just don't work that way. Change/evolution are a part of the basic nature of systems including the Universe (the biggest system we know about). If nothing else I think the Universe will reach a state where it will start over or just keep evolving.

caveman1917
2010-Aug-05, 05:22 PM
I would be very surprised if you could find a reliable source for such a claim. Offhand, this sounds highly unlikely, if not nonsense.

Considering a couple of effects, that claim wouldn't seem so surprising to me.

First we have that Hawking radiation behaves inversely to the mass of a black hole, SMBH's could remain in existence for trillions of trillions of years. To put things in perspective, at this moment even the photons from the CMBR are enough to counteract Hawking radiation for even stellar sized black holes.
Second we have that by GR every orbit should be constantly shedding some energy by gravitational waves. This would seem to suggest any galaxy, given enough time, will collapse on itself.

It would depend on the relative speed of both processes wether this happens or not, i wouldn't know really.
Since black holes are really 'messy' eaters, shooting away a high percentage of the infalling matter through jets (at >escape velocity), it might be that most matter would actually end up doing that. I suppose this also depends on how big the flow of incoming matter is. But this might not apply to dark matter if that process ('messy' eating) relies fundamentally on EM interaction. Then you'd get in the funny situation that you'll have most dark matter tied up in huge black holes, and most normal matter shooting away between them.

Either way, making that claim doesn't seem that unlikely to me, i wouldn't call it nonsense. Even though it may very well be untrue.

astromark
2010-Aug-06, 12:17 AM
The thing with this question is the extended time scale... We at a young four and a half billion years down a nine to twelve billion year track.

As parts of a galactic time frame that could be thirteen point seven billion years old.

We look out into a receding universe and wonder about us having bad breath...:eh:

What of the eventual fate of the whole Universe. Expansion and, cooling.,

but still on a local scale some ongoing star formation for many more billion years yet...

We are not looking at ending our stable galactic gravity driven program any billinia soon... ( hay look a new word.)

JGHeyen
2010-Aug-06, 02:11 AM
It's great fun to think about these questions and the various answers that are provided. As knowledge grows we will continue to have better and better answers.

WaxRubiks
2010-Aug-06, 02:58 AM
Fate of the Universe: proton decay>all matter turns to EM radiation>time stops>matter reforms(condenses)>another big bang.

or so I gather Roger Penrose has speculated..

I think it may be right.


There maybe a few black holes along the way.

caveman1917
2010-Aug-06, 08:28 AM
Fate of the Universe: proton decay>all matter turns to EM radiation>time stops>matter reforms(condenses)>another big bang.

or so I gather Roger Penrose has speculated..

I think it may be right.


There maybe a few black holes along the way.

With enough black holes along the way, we might not even need proton decay. Proton goes in - hawking radiation comes out.

clop
2010-Aug-06, 09:31 AM
Considering a couple of effects, that claim wouldn't seem so surprising to me.

Well it was explained to me by a significant scientific authority at an ASSA lecture I attended. I can't remember exactly who it was, but they seemed to know what they were talking about.

These lectures are not small town affairs, we have guys like Ian Plimer and David Malin talk.

clop

Cougar
2010-Aug-06, 02:08 PM
I have a hard time believeing the universe is going to reach a particular state and remain that way forever. Systems just don't work that way.

I'm afraid you're in for a shock, because that's exactly how isolated systems work. Pour a little milk into your coffee. The mixture is going to reach a state of milk-coffee equilibrium that is vanishingly unlikely to spontaneously unmix... well until the milk goes bad - not the greatest example, but I trust you get the idea. Check out Ludwig Boltzmann (http://en.wikipedia.org/wiki/Ludwig_Boltzmann#The_Second_Law_as_a_law_of_disord er) and the Second Law of Thermodynamics.

caveman1917
2010-Aug-06, 10:58 PM
I'm afraid you're in for a shock, because that's exactly how isolated systems work. Pour a little milk into your coffee. The mixture is going to reach a state of milk-coffee equilibrium that is vanishingly unlikely to spontaneously unmix... well until the milk goes bad - not the greatest example, but I trust you get the idea. Check out Ludwig Boltzmann (http://en.wikipedia.org/wiki/Ludwig_Boltzmann#The_Second_Law_as_a_law_of_disord er) and the Second Law of Thermodynamics.

But as you probably know, thermodynamics is the study only of the evolution of the macroscopic parameters of a system. The milk and coffee would at some point reach thermal equilibrium, and maximum entropy, and this wouldn't change anymore (barring small-time statistical deviations). But if we zoom in on the system to the molecular level, we find that both the milk and coffee molecules are still zipping around as much as they always have. The system continues to change states, thermodynamics only puts in some constraints as to what are 'acceptable' state changes.

If we consider this to the universe as a whole (i don't know if we even can apply those laws to that scale, but let's do so anyway), the universe would continue to change states - albeit restricted in what changes are allowed. It is not so that upon reaching thermal equilibrium (and maximum entropy) the system suddenly goes sterile.

Cougar
2010-Aug-07, 02:04 AM
But if we zoom in on the system to the molecular level, we find that both the milk and coffee molecules are still zipping around as much as they always have.

Right. But thermodynamics is one thing, then you throw in gravity...


The system continues to change states, thermodynamics only puts in some constraints as to what are 'acceptable' state changes.

Yeah - the microstates keep humming, but there are so ridiculously many more high entropy states than low states, we perceive a general trend.


It is not so that upon reaching thermal equilibrium (and maximum entropy) the system suddenly goes sterile.

I don't know. There'd be no "work" possible. All macrostates look indistinguishable, even though the microstates are jumbling around... I must say, I'm appreciative of living at this time in the universe, when the entropy level ain't so bad. :razz:

mugaliens
2010-Aug-08, 05:43 AM
I think I'd like some milk with my black hole after all...

cosmocrazy
2010-Aug-08, 08:06 PM
Since it seems that BH are at the center of all gallaxies and are a central part of the dynamics of the Universe, I'm wondering if the Universe could/will become one large BH ?

There is a difference between black holes and the singularity at the big bang. Black holes exist in space, the singularity at the centre warps space to an extent that even light cannot escape beyond the event horizon. The BB singularity (if there was one as such) existed in "nothing", there was no event horizon, all space & time came from this point. How and why this point started and continues to expand is still a mystery. Unless the space that is still expanding stops and begins to contract then no, the matter contained within it is not close enough together to become one singularity.

neilzero
2010-Aug-08, 08:55 PM
As long as the Universe is expanding, at about the present rate, less than 10% of the matter in the Universe will be in one black hole in a million times a million times a million = 10E18 years, and black hole mergers will be extremely rare. If the universe starts contracting, then the merging of black holes will accelerate. Even if the Universe shrinks to the size of our galaxy, at least 1% of the mass will be outside the big blackhole. The universe does not necessarily shrink just because nearly all the mass is in one giant black hole. Neil

forrest noble
2010-Aug-08, 09:11 PM
JGHeyen,


General question about Black Holes (BH) and fate of the Universe
Since it seems that BH are at the center of all gallaxies and are a central part of the dynamics of the Universe, I'm wondering if the Universe could/will become one large BH ?


According to present beliefs, the universe is expanding at an accelerated rate. This idea projected forward would lead to the heat-death of the universe. The same dark energy idea, however, asserts that expansion rates have changed over time. Following this idea you could seemingly have a universe with no expansion that eventually could contract under the influences of gravity, hence a big crunch with a possible black hole as its consequence. Since no one really knows what dark energy really is or whether it really exists at all, instead the universe could be a far simpler place than present theory asserts.

mugaliens
2010-Aug-09, 09:51 AM
Even if the Universe shrinks to the size of our galaxy, at least 1% of the mass will be outside the big blackhole. The universe does not necessarily shrink just because nearly all the mass is in one giant black hole. Neil

I think the measurements very contrary to this have been very widely substantiated and published.