Black holes emitting radiation

[Mr. Healy]

This may be a dumb question. Theory tells us that black holes emit radiation as they lose mass. If a black hole swallows all that comes near, how does it lose mass?

[Implicate Order]

This may be a dumb question. Theory tells us that black holes emit radiation as they lose mass. If a black hole swallows all that comes near, how does it lose mass?

 

Ultimately a black hole will stop consuming matter when there is no remaining matter to collect from its accretion disc. At this state a black hole temporarily stops growing in size as it's mass does not increase further.

 

To understand why a black hole is proposed to lose mass you need to step into the domain of quantum mechanics.

 

Stephen Hawking surmised that a black hole will continue to very slowly lose mass attributed to vacuum fluctuations close to the event horizon (just outside) of the black hole. His reasoning is as follows. It is likely that particle-antiparticle pairs from the vacuum are produced close to the event horizon due to the energy boost attributed to the intense gravitational field in this locale. One of these partners cross the event horizon and is forever lost while the other partner is forced to materialse as a real (as opposed to virtual partner) and radiate away from the event horizon as thermal radiation (a black hole therefore emits black body radiation) . The particle that fell into the black hole has negative energy while it's partner that radiates has positive energy. (together this virtual partnership has zero net energy but it can exist as a virtual particle pair within the time-energy constraints imposed by the Heisenberg Uncertainty Principle). The negative energy contribution to the black hole means that it loses mass ( black hole evaporation) reflected by the positive energy increase of the region outside the black hole.

 

Now just remember the verdict on black holes as physical reality is still under dispute. Hawking only very recently is questioning his own powerful ideas so stay tuned to science news.

Edited February 6, 2014 by Implicate Order

[Sensei]

 

The particle that fell into the black hole has negative energy while it's partner that radiates has positive energy. (together this virtual partnership has zero net energy but it can exist as a virtual particle pair within the time-energy constraints imposed by the Heisenberg Uncertainty Principle). The negative energy contribution to the black hole means that it loses mass ( black hole evaporation) reflected by the positive energy increase of the region outside the black hole.

 

Negative mass, thus negative energy, is (or rather was) just hypothetical concept, not confirmed by evidence.

http://en.wikipedia.org/wiki/Negative_mass

 

Black hole radiation is also not experimentally confirmed. Which is stated on bottom of page

http://en.wikipedia.org/wiki/Hawking_radiation

[Implicate Order]

 

Negative mass, thus negative energy, is (or rather was) just hypothetical concept, not confirmed by evidence.

http://en.wikipedia.org/wiki/Negative_mass

 

 

 

Hi Sensei

 

Thanks for the valid comments.

 

Probably the use of the word negative mass in this context is misleading. What I think Hawking was referring to was the notion of the energy lost from the context immediately outside the event horizon from the point of view of an external observer (the external system). The energy contribution of the lost particle (added to the black holes confined system) is substracted from the perspective of the external observer. I should have spelt this out. I am not necessarily referring to negative mass as a property of the lost particle itself.

 

As you have mentioned, it is a still a very subjective 'hand waving' hypothesis and there are many different takes on what may be happenning. For example some view that energy is taken from the gravitational field at the event horizon itself to turn a virtual particle pair into a real particle pair and then via quantum tunnelling a real particle is emitted (escapes the event horizon) as thermal radiation.

 

Not only that, but the very notion of black holes themselves (as simpified GR constructs) is problematic in itself as quantum mechanics may forbid these classical simplifications occurring. As we cannot probe observationally beyond the the mathematical notion of an event horizon itself from the frame of reference of an external observer, there may be a profound reason in nature, why we can't. Hawking seems to be wrestling with this at the moment.

Edited February 6, 2014 by Implicate Order

[Airbrush]

so how long does it take a stellar mass black hole (of say about 10 solar masses) to evaporate?

[Implicate Order]

so how long does it take a stellar mass black hole (of say about 10 solar masses) to evaporate?

 

At this hypothetical stage, I think a question such as this cannot be answered. However it would hinge on the energy excitations of the vacuum that could be reached from virtual pair production within the energy and time constraints allowed by HUP. Not ony this, but the locale of the event horizon itself would have a significant source of energy made available to it from the gravitational field. These are just some of the factors to consider. Someone with good knowledge of vacuum excitation fields and gauge theory may be able to offer more insight.

 

It is worthwhile to comment at this stage on the thermodynamics and particle production associated with the notion of 'hidden regions' emerging from spacetime such as Rindler Horizons, Black Hole Event Horizons and Cosmological event horizons (eg.De Sitter boundaries). It gives a clue that spacetime and particle properties appear to emerge from these boundaries in the vacuum. Your question really can only be addressed once we have a firm understanding of quantum gravity. We obviously are a long way off.

 

Interestingly I have just been reading Amanda Geftner's "Trespassing on Einstein's Lawn' which is an account from a science journalist who has been asking the big questions of the heavyweights who are experts in this arena. One of the significant things that needs to be taken into account is the impact of seperated regions of the vacuum through the insertion of boundaries into the vacuum. The boundary we are talking about here is the event horizon itself. We see the effect of boundary insertion with the vacuum in the Casimir effect where a fictitious force is created to attract two metal plates that are microscopically seperated. The fictitious force arises from the insertion of boundaries into the vacuum that constrain possible energy states arising in the system of vacuum energy between these plates. The vacuum outside these plates is unconstrained allowing freedom of energy states. The boundary itself creates different energy profiles in each system hence the energy gradient and ultimate attraction of plates.

 

Now as you may be aware, an event horizon in GR is invariant and all observers external to the event horizon would agree this to be the case. However from the quantum gravity camp, they say that this is not so. The event horizon of a black hole is only identifable from an accelerating observer (external to the black hole) who is escaping it's curvature. The accelerating observer observes this hidden region and associated thermal energy and particles emerging from this boundary. An inertial observer however sees no event horizon, no hidden region and no particles or thermal energy. There is nothing for the inertial observer to distinguish this locale as different to bog standard spacetime. General covariance from this inertial frame of reference insists that the inertial observer simply assumes he is free falling in curved spacetime (under no forces).

 

The observer-dependent viewpoint of event horizons stressed by the QG camp is also shared by Rindler Horizons from constantly accelerating observers and the associated thermal radiation and particles associated with the Unruh effect and is assumed to be the case with cosmological event horizons from a De-Sitter universe.

 

Anyway recent doubts raised on black hole cosmology is raising more questions than answers at the moment. I think it is wiser to stay out of the debate until we get a better grip on Quantum Gravity.

Edited February 7, 2014 by Implicate Order

[davidivad]

a black hole, in theory, would not immediately start evaporating until background radiation levels fall below that of black body or hawkings radiation. consider when all the materials close enough to black holes has been consumed and the amount of time it takes the last stars to burn out. in these dark ages, according to current theory, even the cmb will no longer be noticeable. but the point is that you can put a definite age on this. anyone for a guess?

Edited February 7, 2014 by davidivad

[Airbrush]

.....you can put a definite age on this. anyone for a guess?

A very long time, certainly after all the red dwarfs have burned out. For a 10 stellar mass black hole to evaporate to nothing will take googols of years, or more. Will that happen before or after matter itself decays to nothing?

[hoola]

Implicate Order.....if the infalling particles are negative energy and the escaping particles near the event horizon are positive energy, leading to hawking radiation, what determines this ability for the negative energies and the positive energies to "know" which way to go? There must be some underlying reason for this classification to cause this case to be real. And, why would the high gravity of the black hole cause the particles to appear, which is inferred in the original dialogue with the "energy boost" of the hole? Seems to me they are everywhere and their appearances are not dependent on being next to a black hole horizon. This "energy boost", I would presume, is the work required to separate the two particles, and therefore a more likely candidate to explain hawking radiation. Statistically, a 50% probability of a matter or antimatter particle should be falling into the hole, leading to a zero sum of energies to both the black hole and the surrounding region. Regardless of which particle falls in or out, a fundamental and equal amount of work must be done to accomplish the task of separation......and that work can only come as a net loss of energy each time the process occurs from the black hole itself, using up a tiny bit of it's mass each separation in gravitational energy....I wonder if there is any work being done that would propose the amount of work required to separate the "conjoined twins" of casimir particles? If that could be determined, then a realistic prediction of how long a black hole of a particular mass will last, once it runs out of fuel, if indeed the underlying process is as I propose.....edd

Edited February 9, 2014 by hoola

[Implicate Order]

Hi Hoola

 

This is only my interpretation and needs the qualifications of experts in this area.

 

I am seeing two different perspectives about the reality of a black hole that are associated with the frame of reference of the observer external to the gravitationally compressed area. These two different frames of references create two different realities but a symmetry exists between their respective viewpoints. Namely that each viewpoint is equivalent to the other (they sum out to a big fat zero).

 

For example from the frame of reference of an inertial observer who simply follows the curvature of no escape they are actually not aware they are passing through any defined structure such as an event horizon. Their fate is sealed following the curvature. Their system therefore extends to include the external area and the internal area of curvature leading to the singularity.

 

However from the frame of reference of an accelerating observer who is escaping the curvature in this frame of reference their is a hidden region to that frame of reference which is defined by an event horizon. All observers who are not following the curvature of entry reach the same conclusion that there is an event horizon. Their system therefore does not include the hidden information applicable to the inertial observer. The missing information of this region is reflected by the information created through the 'apparrent' event horizon boundary. This is necessary to allow for a central tent of this assumption which is 'the conservation of information'.

 

The exclusion of this hidden region requires that the total state expression of the hidden region is expressed at this boundary. Structure therefore emerges from the frame of reference of the external accelerating observer. The mass-energy content of the hidden region is reflected by the boundary and particles are seen to emerge from the vacuum. This is where in my opinion the energy comes from from to create the reality for particles popping out of vacuum space.

 

In determining the energy content between frames of reference they are equivalent (Law of conservation of energy) but the boundary exclusion of the hidden region is supplemented with energy arising from the hidden region hence structure being created from the vacuum.

 

So if we assume that virtual particles are boosted by the energy contribution associated with the apparrent horizon, this is where the work is drawn from this boost from the perspective of an accelerated observer.

 

Regarding why I discussed the Casimir effect, the reason was to show how the discrepancy arising from a seperation of system (the vacuum) with a boundary displays how each seperated system possesses a different state from the previous state arising before seperation. The different states created through boundary conditions allows for dissipative force rules to emerge from this prior equilbrium state.

 

I am hoping from this description of the frames of reference between two perspectives you can see that from either perspective the net energy or information content of both systems are equivalent. For the inertial observer, include the state of the entire system which comprises the external and internal region of the black hole. For the accelerated observer include the state of the system comprising the external region plus the energy contribution of the boundary of the event horizon itself.

 

It is critical to note however that just like wave-particle duality you cannot take a perspective considering the frame of reference of both observers at once. It is either one OR the other. Not one AND the other. In this way there is no confusion arising from the mismatch of both observers viewpoints. There is a complemenarity principle being applied here to allow for both viewpoints.

 

This interpretation seems to be what Susskind is suggesting and according to many, he won the black hole war with Hawking. I could be wrong however as this is just how I am putting all the pieces together of readings on Quantum Gravity.

Edited February 9, 2014 by Implicate Order

[hoola]

You talk about the energy popping out of vacuum space in the 4th paragraph....I agree with this, and the question I raise is to how this happens. One idea is that somehow only matter flies out and antimatter flies in....at the event horizon. The other idea seems more likely to me, in that an equal amount of + and - matter goes in both directions, and the energy loss to the hole is strictly due to the energy required to separate the pair. Which idea do you see as more promising? Another problem I have with the idea of antimatter only entering the hole, is that the antimatter would be interacting with normal matter within the interior of the black hole. Wouldn't that in itself create a huge amount of energy? I have always heard that the most energetic energy source possible would be a matter/antimatter one......if I am thinking correctly, the interaction would not lower total energy, therefore mass.....it seems to me that either + or - matter falling in would be adding to mass, with the evaporation (hawking radiation) balanced against this..... this balance will determine if the black hole will evaporate or not. Perhaps the black hole obeys the conservation of energy law, and a stasis is reached, and an equivalent amount of energy is added to hole from infalling particles, that is subtracted from the hole to separate said particles. If true, wouldn't that weaken the idea of black hole evaporation?...edd

[Implicate Order]

Hi Hoola

 

In your interpretation I can see that possibly you may be dealing with 'the Dirac Sea' which is a very interesting viewpoint to consider the vacuum. I am really not sure about anything connected to the topic of black holes. It really is a moving feast. I am probably doing nothing constructive in giving my lay persons interpretation.

 

In the best interpretation I could muster above I was stipulating that you must use seperate the frames of reference when dealing with the topic of black holes. In one frame of reference the event horizon does not exist so Hawking Radiation does not apply. In the other relating to accelerated observers the event horizon exists and there is no interior to that boundary. In this instance 'real particles' emanate from that boundary and the notion of anything getting through that boundary into a hidden region does not exist. There are strong parrallells I am drawing in this interpretation to Susskind's viewpoints and he disagreed with Hawking on the subject of event horizons and black holes. I also assume from Susskind's viewpoint that it is irrelevent what goes on inside the hidden region son Hawking Radiation is once again not applicable in that interpretation.

 

In the interpretation I am using you can see two different system viewpoints that both obey conservation and information laws. Where trouble arises is when you try and pick both viewpoints. Things such as Laws of Conservation apply differently to these two viewpoints. In you interpretation it gets tricky as you need a balancing action when you are dealing with both sides of the event horizon.

 

I note that Hawking is also questioning his own viewpoints on the matter.

 

Perhaps however from your interpretation you could look at Dirac's interpretation of the vacuum. That may lead you on the way to working out the negatives and positives of energy and conservation laws that apply. It is a very interesting and exciting interpretation by the way. Sorry I can't be of more help in the matter.

Edited February 9, 2014 by Implicate Order

[hoola]

Implicate Order.......as far as I can understand the two frames of reference, the differences are in perceptions of what is happening in black hole physics. So, to a remote observer, the shell of particles is detected coming from the event horizon. To an observer who has fallen into the hole, as the horizon is passed, the particles disappear, along with the outside world. That seems pretty understandable to me, but the event horizon still exists, and still is spitting out particles into the outside universe even though the observer is no longer in a position to verify it. I don't see any conflict here. As far as the outside observer, stationed at a safe orbit near the hole, the interior cannot be directly seen, but doesn't hawking say (after losing the bet) that the information of what fell inside would be conserved? If the information is conserved, then the particles coming out of the horizon should have some informational bearing on what fell into the hole that exists within the central mass. This seems to indicate that the interior can be observed from the outside universe, given the proper tools...if this is true, wouldn't the hole act as a recording device of sorts? It seems a sort of holographically encoded "picture" of the hole contents could be read from a distance to determine not only what had happened surrounding the hole since formation, but all the way up to the approach of the vehicle that does the probe....by reading the details of the hawking radiation. One possible issue is the factor of time stopping at the event horizon due to gravitational effects.... I don't think that is the case. I see time as slowed down and observed as a red shifting of the information's spectrum...this being due to the escaping particles being slightly outside the event horizon, and therefore time hasn't stopped completely, if it ever did at all, at any point in black hole physics. I see time as any change in the information content of a given region of space, and therefore, can be slowed, but not to zero. Even if one were to imagine the event horizon itself having the slowest rate of time in black hole dynamics, it wouldn't be zero, as the gravity forces acting through it would offer the required changes that would indicate a default minimum increment of time passage.....another odd issue to me is the singularity itself. Isn't is supposed to be a dimensionless point? And the diameter of the event horizon indicates the mass of the dimensionless point? If the point is "dimensionless" under what conditions must the information exist? In the strings of string theory that describe matter and energy? edd

[Implicate Order]

Hi Hoola

 

For the inertial observer who is committed to travelling along the curvature, as they are unaware they are passing through the point of no return, they are therefore still able to access information from the exterior region as they are not aware of any system seperation. In GR the event horizon is a limit to things coming back out from the interior region into the external region. In this discussion we are talking about things that fall into the interior region.It is a one way limit only for things getting out. For an inertial observer falling in, they are unaware of this point of passage past any boundary. From the perspective of this inertial observer travelling into this gravitationally compressed area, they are simply travelling through space (as per normal) in free fall, and the frame of reference their system occupies includes the entire path of travel (from the past and into the future towards the singularity). There is nothing to distinguish anything different. It is only from the perspective of an accelerated observer that this observer actually sees or registers something different to simply travelling through spacetime. For the inertial observer their system includes the exterior region they have come from and the interior region they are now travelling through. This is unlike the accelerated observer who is safe outside the black hole. They do not see any interior region as their system is confined by the boundary of the event horizon. Note that therefore the different observers have a different system of reference to do their experiments in. This difference is what destroys any invariance between the two frames of reference. It is therefore observer dependant from this viewpoint. The physics applied to each viewpoint in this interpretation depends on the frame of reference as it is implied that the reality differs from these two frames of reference. This is the conclusion that is hitting me on the head at the moment. Furthermore what this is saying is that spacetime is emergent dependent on frame of reference. From one frame of reference there is no boundary and there is a additional region of spacetime to consider. From the other perspective there is a boundary and no additional region of spacetime. So what happens to the mass-energy of this discrepency in viewpoint if we abide by the Law of Conservatiion of Energy (let alone the Conservation of Information). We conclude that this missing energy between the frames of reference must be present in the boundary. Can you see how structure is being created simply from a change of reference frame in this thought bubble.

 

Hawking initially did not concede to this viewpoint. When Hawking radiation was derived by Hawking, this was in response to explaining gravitation that demonstrated that some very important conservation laws were being exposed and possibly incorrect. This is what through the physics community into a flap and why the Black hole war between Sussking and Hawking resulted.

 

Susskinds complementarity response was what ultimately won the debate. There was a recent worry about firewalls to consider but fortunately complementarity seems to have stood up to the test provided we strictly abide by the principle of insiting that we treat the problem from the perspective of two seperate reference frames. This centred on the notion that you cannot simultaneously treat both viewpoints as valid. It is like any complementary pair of variables. It is one viewpoint OR the other. Not one viewpoint AND the other. This therefore throws a possible spanner in the notion of Hawking radiation itself. The notion of information encoded on the boundary of an event horizon is from the frame of reference of an observer who is safe and accelerating away from the curvature. There is no information paradox as they say that instead of passing through the event horizon, infalling matter is splatterred across the event horizon and frozen in time from that reference point. Form arises and structure arises from this viewpoint. Information to the accelerated observer does not lie in the interior as this does not exist for them. It lies on the event horizon from this perspective. For the infalling inertial observer that information is still available to them in the interior of the black hole. Consequently from Susskinds perspective the Law of Conservation of Energy and Information is satisfed provided you look at it from the frame of reference of each individual observer.

 

Now when you look at manifolds in GR, you realise that curvature and mass-energy distribution are two sides of the one coin. They are equivalent. In GR with the Einstein equation. This equation however adopts a gods-eye view to the system which we know is not seen from the frame of reference of an internal observer. Their frame of reference will see one side of the coin OR the other but not both.

 

Susskinds approach to this complementarity has been significant for string theory. Initially the theory was dealing with strings, then structure was formed when dealing with D-branes and then M-branes but now string theory seems to be concluding that it is all about holography. They appear to be inexorably drawing closer guided by the process of enquiry they have taken and as they address string theories previous weakness of background dependence, we are now seeing suggestions that almost everything previously treated as invariant such as particles, fields, and spacetime itself, seems to be becoming observer-dependent. It recognises that dealing with 'things' in a fixed background was perhaps an inappropriate starting assumption and through a revised notion of relativism within string theory, theorists are starting to get a bit of headway. Holography appears to be the 3rd major revolution in string theory.

 

So how does this new approach treat the results of the double slit experiment say with an electron moving through the apparatus. From a God's eye view of this perspective, a component of the electron passes through both slits resulting in an interference pattern. When being observed however from the frame of reference of a particular observer it moves through one or the other but never both. When under the frame of reference of observation there is no interference. You need to treat frames seperately under observation. It certainly seems to be providing a very powerful way of dealing with some of the counterintuive notions of physics when viewed this way.

Edited February 10, 2014 by Implicate Order