Black Hole Question

[Obnoxious]

Okay, Hawking suggested that black holes disappear due to the fact that because the Uncertainty Principle states that the more accurately we know how fast something is, the less so we know where it is. Applying that to black holes, and empty space, Hawkings stated that the spaces right outside the event horizon was full of "+" and "-" stuff forming then being destroyed on each other. Occasionally, however, the "-" stuff that goes into the black hole causes it lose mass because - energy is essentially - mass.

Now, here's my question, wouldn't the + particle have just as great a chance of falling into the black hole as the - one? So why would a black hole decrease in size as it goes on in time?

[[Tycho?]]

I never got this either.

[Spyman]

The main idea of Hawking is that a rotating black hole with it's powerfully gravitionally rotating space-time somehow creates this "-" and "+" stuff and if they not destroys eatch other, eg: if one falls back into the black hole and one escapes, then the black hole loses the amount of energy used to create the particles.

 

So it doesn't matter if it's "-" stuff or "+" stuff that falls back, both have mass, and the one escaping is the one taking it's mass away from the black hole.

 

How this quantum mechanics makes it possible to transform matter inside the black hole to energy, which then escapes the event horizon and transforms back to matter outside the black hole is more than I can understand, it's way over my head.

[Obnoxious]

I thought Hawking said that all of empty space was full of tiny particles forming, parting, and then destroying each other, not just the area around the black hole...>_>

[Spyman]

I thought Hawking said that all of empty space was full of tiny particles forming, parting, and then destroying each other, not just the area around the black hole...>_>

Like I said, "I don't understand quantum mechanics", but I though like you before I found an simple article explaining this. (Sadly I don't remember where... )

 

Anyway somehow the particles are borrowing energy from space to be created and when they annihilate they return the energy. If the Black Hole takes one of the particles, the energy still has to be returned, so the Black Hole has to pay for the energy. According to Hawking it pays by loosing the same amount of mass.

[Severian]

The e+ and e- both have positive mass. It is not the mass which is important, but the energy. In the vacuum just outside the black hole the e+ and e- are created by 'borrowing' energy from the Heisenberrg Uncertainty Principle. Normally, they would have to annihilate again to give back the energy before the loan time is up. If one of them goes into the black hole, it cannot get back to the other (which has in the meantime absconded) then the black hole will have to pay the debt by giving up some of its energy. Since the energy it has to pay back is the mass of the positron and the electron, but it has only gained the mass of one of them back (by absorbing it) it loses energy (and thus mass).

[Martin]

an interesting side aspect to this is the hawking (or bekenstein-hawking) temperature of the black hole.

 

because of this radiation that Severian just described, the BH is radiating like a black body at a certain temperature which Hawking showed how to calculate from the mass. Little holes glow hotter.

 

an easy way to calculate the temperature is with QG units (with c=hbar=8piG=1) in which case the temp is just the reciprocal of the mass.

 

For example earth mass is around E33, a hole with mass E33 would be extremely cold (temperature E-33)

 

but a less massive hole like one with mass E29 would have temperature E-29 which is is room temperature. That one's mass would be a tenthousandth of the mass of the earth

 

and one with mass E28 would have temperature about like the tungsten filament of a conventional 100-watt lightbulb. The mass of such a hot hole, with temp E-28, would be about one hundredthousandth of the mass of the earth.

[Obnoxious]

So in a black hole, temperature has a direct link to the size of the black hole?

So...is there a limit to how big a black hole can be before it breaks the -273 Kelvin law dealie?

[Kygron]

QG units (with c=hbar=8piG=1)

 

This is the first time I've heard of these units in my (non-) experience. I had questioned myself why people didn't just set c=1 to ease calculations! Please elaborate a bit for me if you don't mind, if there's anything to say that is, lol.

[[Tycho?]]

So in a black hole' date=' temperature has a direct link to the size of the black hole?

So...is there a limit to how big a black hole can be before it breaks the -273 Kelvin law dealie?[/quote']

 

Kelvin goes down to 0. No lower.

[ed84c]

Kelvin=Heat=Sum of all the energies. Technically as in an evaporating black hole when negative energy photon falls into the hole, i guess you could thionk of it as below 0 Kelvin, although it is somewhat of a paradox.........

[Martin]

So in a black hole' date=' temperature has a direct link to the size of the black hole?

So...is there a limit to how big a black hole can be before it breaks the -273 Kelvin law dealie?[/quote']

 

the Hawking temperature goes as the RECIPROCAL

 

if mass is 10 then temp is 1/10 (if you use correct units)

 

if mass is 100 then temp is 1/100

 

if mass is 1,000,000 then temp is 1/1,000,000

 

but hawking temp can never get down to zero no matter how big mass is.

the temp can only get smaller and smaller, but never zero

 

so it never breaks the dealie.

 

====================

 

another thing to remember, past a certain point you would have to protect the hole from being warmed by its surroundings

 

even if it wanted to be, say, 1 kelvin

because it was very massive and its hawking temperature was that low,

even then the space around it has some heat

and the like background radiation of empty space would tend to warm it

 

but that is just a practical problem. let us assume we protect it from being warmed by surrounding stuff, we shelter it from starlight and sunlight and microwave background etc.

 

======================

 

the sun is on the order of E38 on the natural mass scale

 

therefore a black hole with roughly same mass as the sun

would have hawking temperature of E-38 on the nat. temp. scale.

 

the cosmic microwave background (approx 3 kelvin) is E-31 natural

so the solarmass black hole would be tenmillion times colder than that

(approx 0.0000003 kelvin)

but still not zero!

[Kygron]

let us assume we protect it from being warmed by surrounding stuff' date=' we shelter it from starlight and sunlight and microwave background etc.

...

the cosmic microwave background (approx 3 kelvin) is E-31 natural

[/quote']

 

does this mean that a black hole with mass > E31 will actually NEVER evaporate because it is constantly absorbing energy from the microwave background, while those with mass < E31 ARE capable of evaporating?

[Obnoxious]

Blast it! Entropy has won again! Not even the powers of gravity can overcome this nusiance! Curse you Entropy!!

[Martin]

does this mean that a black hole with mass > E31 will actually NEVER evaporate because it is constantly absorbing energy from the microwave background, while those with mass < E31 ARE capable of evaporating?

 

Kygron that's a smart question. I cannot speak with authority but here is my understanding of it.

 

as the universe expands the CMB gets colder and colder, indeed the present Lambda CDM model (about which there is rough consensus) is expected to keep on expanding indefinitely. So the CMB is no obstacle to holes eventually evaporating.

 

However if the CMB for some odd reason were to stay at the present temperature (2.7 kelvin, or E-31 in quantum gravity units with c,hbar,8piG having unit value) then I believe that holes of mass E31 could not evaporate because they would be in equilibrium with the CMB.

 

 

BTW as you may know the energy per unit volume of the CMB goes down as the fourthpower of the universe scale factor so when space expands by a factor of 2 the energy per unit volume of CMB goes down by factor of 16 and its temperature goes down by factor of 2. so the temperature of the CMB is like a record of how much expansion there has been since the moment (about 300,000 years after bang) when space became transparent and stopped scattering. the original temp was 1100 times 2.7 kelvin, because expansion by a factor of 1100 since last scattering (also called "recombination" tho that is not such an accurate description)

 

so if you are an overweight black hole all you need to do is bide your time till space is cold enough and you too will be able to evaporate

[Martin]

 

QG units (with c=hbar=8piG=1)

 

This is the first time I've heard of these units in my (non-) experience. I had questioned myself why people didn't just set c=1 to ease calculations! Please elaborate a bit for me if you don't mind' date=' if there's anything to say that is, lol.

 

__________________

Some people have gone beyond correct, even becoming helpfull;

I'd love to be helpfull, but sometimes can't make it to correct;

Is there a way to be helpfull, while at the same time asking for help?[/quote']

 

Hi Kygron, you are being helpful to me by expressing interest in QG units because I can get to understand the situation better by explaining it to someone who's interested.

 

I will start a QG units thread in this forum so as not to introduce too much offtopic stuff here.

 

the gist of it is that socalled "Planck units" (based on |c|=|hbar|=|G|=1) have been known for about 100 years and the are used a significant amount in some technical writing. the NIST.gov website that lists the fundamental physics constants has values in metric for the planck mass, time, length, and temperature.

 

But for the past 3 years or so I have been reading a lot of Quantum Gravity articles (it is an interesting area of theoretical physics research to watch) and a lot of the time I see a variation of Planck units being used where you dont make G have value one, you make |8piG| = 1 instead.

In the Einstein equation of gen rel it is actually 8piG that appears as a key constant and if you do gen rel (or the quantized version LQG) then it is actually more convenient to have 8piG take unit value. Then the equations are the cleanest possible and easiest to work with.

 

So the QG people are using these units which are LIKE conventional Planck units but some of them differ by a factor of 8pi, which is about 25, or they differ from conventional by a factor of sqrt(8pi) which is about 5. But nobody cares because traditionally physicists use whatever units are easiest.

 

If you are in school it is possible that your teacher knows the conventional Planck units ( |c|=|hbar|=|G|=1) but very unlikely that he or she knows\

this variant on them QG units ( |c|=|hbar|=|8piG|=1) so be careful.

These are actually better than conventional Planck! But being slightly different can get you into trouble with a teacher who doesnt realize this and thinks you are making a mistake by a factor of 5 or 25.

 

I will try to do a new improved brief discussion of QG units in a thread of that name. It will have simple problems to work as exercises to get used to the units. Any reading and commenting you do will be very helpful and that goes for other SFN people too.

[quantump4577]

;140465'']Kelvin goes down to 0. No lower.

 

but couldn't zero become a lower degree celcius than it was before?

[Klaynos]

but couldn't zero become a lower degree celcius than it was before?

 

urmmm no, 0K is -273.15degC, this is the lowest possible theoretical equilibrium temperature, although in practise you can't actually get to 0K for a system in equilibrium.

 

Unless I've misunderstood you?

[foodchain]

but couldn't zero become a lower degree celcius than it was before?

 

 

There is a debate on if physical constants could change without our senses or understanding being able to see or understand such. So in reality the current answer to that question I think is that it cant be answered yet by anything. Such as if the speed of light has changed, but really gives no noticeable way in the context of other physical constants or effects to determine such, its an actual debate(scientific) with a name I just don’t know it.

 

As far as I know about BEC’S its opening up a new area for like solid state physicists and related. I am sure it would be used in a broad range of applications, like chemistry for instance, or heck maybe medicine and computing. When the stage of matter actually occurs you get its own phenomena overall I would think, thus the title, but it has effects similar to those experienced in other physical phenomena. One experiment that I have read about basically had a BEC explode or implode or both, in which half of the material had "disappeared" in regards to the measurement apparatus. The thing that is weird to me is if BEC really could be viewed as some kind of a reverse process or engineering of the current state. I also wonder that if when a BEC is reached that physical measurement does simply not detect "particles" that evolved from such rather then exploded material. In that context I think of conservation of energy, but why then the barrier to absolute zero? The only thing I can think of is the degree of entanglement that exists is currently beyond measurement. Such as why the universe itself is not in absolute zero. From this I would think conservation of energy and entanglement might need a BEC to reach absolute zero would require maybe the freezing of the universe:D Beyond that I think the professional view is its just uncertainty that is accepted currently as to why absolute zero has not been reached yet, besides that I don’t really know.

[iNow]

Isn't this all a bit like asking if the number of quarts in a gallon has changed? Come on... It's arbitrary by scale, by the concept remains. No motion. Pretty simple really.

[foodchain]

Isn't this all a bit like asking if the number of quarts in a gallon has changed? Come on... It's arbitrary by scale, by the concept remains. No motion. Pretty simple really.

 

I am not exactly sure but I don’t think you can give anything quantum a zero probability, such as with a barrier or well. I am not sure of course but I think this ties into uncertainty. That even in light of a barrier or a well, that you still deal with a non zero probability overall for some quantum phenomena to occur, example being quantum tunneling.

[iNow]

I don't follow your meaning.

 

Also, in my quote, I mistyped. I meant:

 

It's arbitrary by scale, but the concept remains. No motion.

 

 

If we hit it, I suppose existence would stop. But... I'm not sure how this relates to black holes either. I should probably bow out. There are several pieces of this thread I'm not following.

[foodchain]

I don't follow your meaning.

 

Also, in my quote, I mistyped. I meant:

 

 

 

 

If we hit it, I suppose existence would stop. But... I'm not sure how this relates to black holes either. I should probably bow out. There are several pieces of this thread I'm not following.

 

I think I am in the same boat, sorry about the confusion.

[swansont]

The barrier of absolute zero is purely classical in nature. QM doesn't get you around it, though.

 

As far as a BEC supposedly exploding/imploding and disappearing: if you can find a reference I'll try and translate.