Black holes in a Big Bang Universe?

[Rolando]

According to my understanding, a black hole is defined as an object whose mass is hidden behind an event horizon. According to its definition, an event horizon represents a boundary from which it takes an infinite time for light to reach a distant observer. Thus, in the observer's frame of reference, event horizons are at an infinite distance in time.

 

 

Now, current doctrine teaches us that there are black holes in the Universe while it also teaches us that the Universe has existed for only a finite time. To me, it is obvious that these teachings contradict each other, yet I have seen them repeated over and over again also in the most prestigious publications. How can this be?

 

 

[Arch2008]

Huge stars of several hundred solar masses rapidly convert their core supply of hydrogen into iron after only a few million years and collapse into a black hole. The universe is 13.72 billion years old, so this is more than enough time for clouds of hydrogen to collapse into huge stars that then form black holes.

[Rolando]

There is enough time for a star to collapse into a state in which its density perhaps even exceeds that of a neutron star, but this is not yet a black hole. As seen by a distant observer, it takes an eternity for the collapsing material to reach the event horizon.

 

Edited May 15, 2012 by Rolando

[imatfaal]

According to my understanding, a black hole is defined as an object whose mass is hidden behind an event horizon. According to its definition, an event horizon represents a boundary from which it takes an infinite time for light to reach a distant observer. Thus, in the observer's frame of reference, event horizons are at an infinite distance in time.

 

 

Now, current doctrine teaches us that there are black holes in the Universe while it also teaches us that the Universe has existed for only a finite time. To me, it is obvious that these teachings contradict each other, yet I have seen them repeated over and over again also in the most prestigious publications. How can this be?

Not sure about defines as that, but the mass is within an event horizon. Again not sure about your definition of event horizon - the event horizon is the boundary such that events within cannot affect any outside observer. Cannot agree with your final sentence about observers frame of reference. An observer in an accelerated frame of reference will see an object that approaches an Event Horizon being more and more time dilated - the signal will be increasingly red shifted; I don't know really what "at an infinite distance in time" means in this context.

 

THe contradiction arises because of the unusual way you have defined the event horizon

[Rolando]

... Cannot agree with your final sentence about observers frame of reference. ...

This sentence was: "Thus, in the observer's frame of reference, event horizons are at an infinite distance in time."

 

Let me paraphrase it: "Thus, in an astronomer's frame of reference, event horizons are infintly remote in time, i.e., due to time dilation, it would take an eternity for light or any kind of signal to reach us from a position at the event horizon."

[imatfaal]

But Rolando - objects falling into the BH do not, from the observations of an outside accelerated reference frame, actual reach the EH - they slow down and time dilates to such an extent that they seem to freeze. EMF Signals from just outside the EH propagate at the speed of light (but are very red shifted) It is definitely not a simple matter that at the EH time is infinitely dilated.

[Rolando]

But Rolando - objects falling into the BH do not, from the observations of an outside accelerated reference frame, actual reach the EH - they slow down and time dilates to such an extent that they seem to freeze. EMF Signals from just outside the EH propagate at the speed of light (but are very red shifted) It is definitely not a simple matter that at the EH time is infinitely dilated.

 

imatfal - I do not see any disagreement with what you are telling, but I do not understand why you choose to consider an outside accelerated reference frame. What you say holds also for an outside stationary frame. You said that time dilates to such an extent that objects falling into the black hole seem to freeze at the event horizon. This just agrees with what I expressed in other words. Compared with an observer's time, this frozen time is infinitely dilated.

[Bill Angel]

It was stated that the universe is 13.72 billion yearrs old. Some cosmological theories incorporating quantum loop gravity effects have speculated that the universe oscillates from big bang to collapse and then to another big bang. So one can only assert that the universe we inhabit is 13.72 billion years old, as measured from the last big bang occurance.

[Airbrush]

I think what the opening post suggests is that if we were to observe an asteroid get sucked into a black hole, we would never see it disappear into the black hole. I don't think so, and what about the sparks that would fly off the black hole? I think we would see the asteroid get eaten, or some of it getting eaten since black holes are messy eaters. Most of what falls into a black hole is blasted away from it.

 

From Wiki, we can detect x-rays coming from matter falling into a black hole:

 

"Due to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disc-like structure around the object. Friction within the disc causes angular momentum to be transported outward, allowing matter to fall further inward, releasing potential energy and increasing the temperature of the gas.[92] In the case of compact objects such as white dwarfs, neutron stars, and black holes, the gas in the inner regions becomes so hot that it will emit vast amounts of radiation (mainly X-rays), which may be detected by telescopes. This process of accretion is one of the most efficient energy-producing processes known; up to 40% of the rest mass of the accreted material can be emitted in radiation.[92] (In nuclear fusion only about 0.7% of the rest mass will be emitted as energy.)"

 

http://en.wikipedia.org/wiki/Black_holes#Accretion_of_matter

Edited May 15, 2012 by Airbrush

[Rolando]

Considering the answers by imatfaal as well as by Arch2008 and Airbrush, so far, my understanding is this:

 

A black hole is an object whose mass is hidden behind an event horizon. The event horizon represents a boundary at which time is "frozen", i.e., infinitely dilated, as seen by a distant observer. This implies that it will take light (or any signal) emitted at the event horizon an eternity (= infinite time) to reach a distant observer. It also implies that material that falls towards the event horizon needs an eternity in order to reach it (as seen by the distant observer). From this, I have to conclude that black holes cannot arise in a Universe that has only been in existence for a finite time (and it is questionable whether they could in an eternal Universe).

 

There is no doubt about the existence of objects such as collapsed stars and galactic nuclei with very deep gravitational wells, which cause a very substantial time dilation and redshift, and infall phenomena of various kinds, but these objects are not "black holes".

[zapatos]

This implies that it will take light (or any signal) emitted at the event horizon an eternity (= infinite time) to reach a distant observer.

AFAIK light travels at c. Light will either travel to us at c and reach us in the time it takes light to travel from near the black hole to us, or it will not travel to us at all.

 

 

It also implies that material that falls towards the event horizon needs an eternity in order to reach it (as seen by the distant observer).

I don't think so. We see their clocks slow down, we don't see them slow down. They will crash and burn in short order.

 

From this, I have to conclude that black holes cannot arise in a Universe that has only been in existence for a finite time (and it is questionable whether they could in an eternal Universe).

 

There is no doubt about the existence of objects such as collapsed stars and galactic nuclei with very deep gravitational wells, which cause a very substantial time dilation and redshift, and infall phenomena of various kinds, but these objects are not "black holes".

So those things we are calling black holes are really deep gravity wells that light can escape from? Then why do they appear 'black'?

[Rolando]

AFAIK light travels at c. Light will either travel to us at c and reach us in the time it takes light to travel from near the black hole to us, or it will not travel to us at all.

Right, I meant even here the observer's time.

 

I don't think so. We see their clocks slow down, we don't see them slow down. They will crash and burn in short order.

Anything slows down.

 

So those things we are calling black holes are really deep gravity wells that light can escape from? Then why do they appear 'black'?

Yes. To my knowledge, the compact objects that have actually been observed directly are all bright.

[zapatos]

Right, I meant even here the observer's time.

I'm sorry I did not understand that. You said light will take infinite time to reach an observer. Infinite time implies movement that is less than c. I am saying there is no movement less than c for light.

 

Anything slows down.

No. From our perspective we see them accelerating toward the black hole until they reach the event horizon and then we don't see them at all.

[Airbrush]

My question for Rolando is what would we see if we could see a large asteroid approaching a black hole? Would it never penetrate the event horizon?

 

Why do we see quasars?

 

Any light that passes the event horizon is gone inside, never to be seen again. Any light exactly at the event horizon will orbit the black hole forever. And any light outside the black hole will travel to us at light speed.

[Rolando]

No. From our perspective we see them accelerating toward the black hole until they reach the event horizon and then we don't see them at all.

Even here, I expressed myself unclearly. I just meant that time dilation affects everyting that is in the same state of motion in the same gravitational well to the same extent.

However, we will have to wait for an eternity until we cannot see "them" at all.

[zapatos]

Even here, I expressed myself unclearly. I just meant that time dilation affects everyting that is in the same state of motion in the same gravitational well to the same extent.

However, we will have to wait for an eternity until we cannot see "them" at all.

Are you saying that we will see them reach the event horizon and then appear to just set there unmoving for eternity? We will be able to see this?

[Rolando]

My question for Rolando is what would we see if we could see a large asteroid approaching a black hole? Would it never penetrate the event horizon?

We would not see it reach the event horizon since, from our perspective, this would take an eternity.

 

Why do we see quasars?

I have neither a clear understanding of quasars nor any problem with the fact that we can see them.

 

Any light that passes the event horizon is gone inside, never to be seen again. Any light exactly at the event horizon will orbit the black hole forever. And any light outside the black hole will travel to us at light speed.

The orbit at which light will circle the black hole forever is, in fact, outside the event horizon. Such orbits exist already for objects that are not quite as extreme as black holes and whose possible existence my reasoning does not deny.

 

Are you saying that we will see them reach the event horizon and then appear to just set there unmoving for eternity? We will be able to see this?

We actually won't see anything, because of the infinte time dilation (= infinite redshift).

Edited May 15, 2012 by Rolando

[zapatos]

We actually won't see anything, because of the infinte time dilation (= infinite redshift).

What does that mean?

 

Why won't we see something if it takes an eternity? If someone is counting for an eternity, won't I see them counting? If something is moving for an eternity, won't I see them moving?

 

Can you tell me what will happen to an object approaching a black hole before it gets to the event horizon, when it is at the event horizon, and after it passes the event horizon? Both from the perspective of someone on the object, and from our perspective as distant observers?

[Rolando]

What does that mean?

 

Why won't we see something if it takes an eternity? If someone is counting for an eternity, won't I see them counting? If something is moving for an eternity, won't I see them moving?

 

Can you tell me what will happen to an object approaching a black hole before it gets to the event horizon, when it is at the event horizon, and after it passes the event horizon? Both from the perspective of someone on the object, and from our perspective as distant observers?

Let's say the object is a clock. As it approaches the event horizon, we see it tick slower and slower. When it reaches the event horizon, it stops. Time is frozen, but we can no longer see the clock, because the light waves are also frozen. Light waves become longer and longer when the clock approaches the event horizon and ultimately they would become infinite in length. However, this cannot happen within a non-eternal Universe, in which nothing can pass an event horizon or even reach it.

Edited May 15, 2012 by Rolando

[zapatos]

Let's say the object is a clock. As it approaches the event horizon, we see it tick slower and slower. When it reaches the event horizon, it stops. Time is frozen, but we can no longer see the clock, because the light waves are also frozen. Light waves become longer and longer when the clock approaches the event horizon and ultimately they would become infinite in length. However, this cannot happen within a finite Universe, in which nothing can pass an event horizon or even reach it.

The clock stops ticking; it does not stop moving toward the black hole. What force would counteract gravity?

[Rolando]

The clock stops ticking; it does not stop moving toward the black hole. What force would counteract gravity?

The movement we see slows down to the same extent to which the ticks slow down. And this is due to gravity.

Edited May 15, 2012 by Rolando

[zapatos]

The movement we see slows down to the same extent to which the ticks slow down. And this is due to gravity.

How does gravity, which is causing an object to accelerate toward the black hole, cause it to slow down? The closer you get to the black hole the stronger the gravitational pull.

[Rolando]

How does gravity, which is causing an object to accelerate toward the black hole, cause it to slow down? The closer you get to the black hole the stronger the gravitational pull.

Gravity causes objects to accelerate, but it is also the cause of gravitational time dilation, which affects all processes to the same extent, but this becomes substantial only in extreme gravitational fields - in the perspective of a distant observer.

Edited May 15, 2012 by Rolando

[zapatos]

Gravity causes objects to accelerate, but it is also the cause of gravitational time dilation, which affects all processes to the same extent, but this becomes substantial only in extreme gravitational fields.

So it speeds up and slows down at the same time?

[space noob]

The time that we experience is not at the same speed as the black hole, it's relativity is no different than ours

if you could safely stand close enough to watch without being affected the universe surrounding would speed up and you would see objects entering the event horizon

if time is infinite without considering the big crunch then doesn't the black hole have as much time as it needs? It just seems that the laws of physics govern that the objects would inevitably "have" to be dragged into the event horizon