If the Hawking radiation temp of a black hole is less that CMB temp how can it net evaporate?

[repoman]

Will it not absorb all of the CMB radiation as well as the CNB neutrinos which is more gained than lost from Hawking radiation?

Won't it take a far distance future of insanely low CMB and CNB temperatures (below Hawking temp) for black holes to actually lose net mass-energy?

 

[skepticalbip]

I think that in Hawking's description of black holes evaporating, he was talking about micro black holes (the sort that some speculate may be created in the LHC) which would be quite hot. A Black hole with a mass of about 1% of the Earth would absorb about the same amount of radiation from the CBR as it emits. For massive black holes, we will have to wait many, many trillion years for the CBR to cool to a few micro or nano-Kelvin before they began to evaporate.

At least that is my understanding.

 

[bilby]

I think that in Hawking's description of black holes evaporating, he was talking about micro black holes (the sort that some speculate may be created in the LHC) which would be quite hot. A Black hole with a mass of about 1% of the Earth would absorb about the same amount of radiation from the CBR as it emits. For massive black holes, we will have to wait many, many trillion years for the CBR to cool to a few micro or nano-Kelvin before they began to evaporate.

At least that is my understanding.

So you're telling me that taking out evaporation insurance on Sagittarius A* is a poor investment?

Good to know. I had a sneaking suspicion that tbat black hole salesman was a scammer.

 

[steve_bank]

Adding to what I think skepticalbip is saying.

Objects at different temperature will go towards equilibrium.

If you look at a black hole as a black body, it wants to go to equilibrium with the CMBR.

- - - Updated - - -

Adding to what I think skepticalbip is saying.

Objects at different temperature will go towards equilibrium.

If you look at a black hole as a black body, it wants to go to equilibrium with the CMBR. Evaporation is giving up energy.

Lear something new everyday. How a BB exhibits a temperature.

https://phys.org/news/2016-09-cold-black-holes.html
https://en.wikipedia.org/wiki/Hawking_radiation#Large_extra_dimensions

 

[repoman]

Is there a reasonable chance that Hawking was wrong and Black Holes don't emit radiation through the effect he postulated and then calculated?

Also, assuming that he was correct and there were smallish primordial black holes made in the Big Bang that would have fully evaporated in the part couple billion years...

Is there an exact brightness/spectrum vs time that has been calculated for this final evaporation? If so, the only adjustment to detection would be accounting for z, redshift.

Obvioulsy, this is no joke the calculation. But someone must have done it.

 

[steve_bank]

Cosmology is out of my depth but I'd answer that by saying there is no such thing as a true black hole, meaning infinite density. A true singularity would require infinite energy. Once the black hole is formed and no longer acquiring mass I'd assume basic thermodynamics apply as a whole. The black hole will want to go to equilibrium with surroundings through radiation. From the links the black hole is so cold that it would take a long time to go to background.

Any science can be wrung. That is a given. From the links Hawking's Radiation is too small be detected so it is a theory.

 

[Loren Pechtel]

Stellar black holes do not currently have net evaporation as their temperature is far below the CMB temperature. However, as time passes the CMB temperature will fall, eventually going below the Hawking temperature. At that point you will have net evaporation and thus the eventual destruction of the black hole.

 

[Gun Nut]

No, Hawking was talking about all black holes... the context actually being super massive black holes of the type that will dominate the universe in the age of black holes, approximately 1 billion trillion trillion trillion trillion trillion trillion years from now. Trillions of years later, during the age of Black Hole Death, the notion of Black Hole radiation (and collision) dominates the universe. The idea (as I weakly understand) is that near the event horizon, temperatures are such that particles begin to annihilate each other, and when one of the pairs is trapped in the event horizon, and the other is not, that is the black hole evaporating.

 

[Loren Pechtel]

No, Hawking was talking about all black holes... the context actually being super massive black holes of the type that will dominate the universe in the age of black holes, approximately 1 billion trillion trillion trillion trillion trillion trillion years from now. Trillions of years later, during the age of Black Hole Death, the notion of Black Hole radiation (and collision) dominates the universe. The idea (as I weakly understand) is that near the event horizon, temperatures are such that particles begin to annihilate each other, and when one of the pairs is trapped in the event horizon, and the other is not, that is the black hole evaporating.

No. The issue isn't annihilation, but rather the spontaneous creation of matter. Crazy as it sounds it's very real--tunnel diodes wouldn't work without it. We don't see it at the macro level because of the tiny scale--you can borrow energy from the universe but you have to repay the loan very quickly. Particle conservation laws say you must always create pairs (a particle and an antiparticle) and when you're very near the event horizon of a black hole it's possible that one particle of the pair winds up beyond the event horizon. Oops, now you can't annihilate them, the debt has to be paid from elsewhere and the only source available is the black hole itself. Now, with a big black hole if one goes down the hole the other almost certainly does also and the leakage rate is tiny. When the black hole is tiny, however, the gradient is very steep and it's quite possible for one to escape--when they get really tiny they glow with furious energy.

 

[steve_bank]

Sorry Loren, tunnel diodes do not spontaneously create matter. The doping and materials creates a condition where current can 'tunnel' around the potential barrier.

https://en.wikipedia.org/wiki/Tunnel_diode
https://en.wikipedia.org/wiki/Quantum_tunnelling

I think it was in the 90s Hawking wrote that he could prove the universe could create itself from nothing. It caused an expected theist response. Perhaps that is what you are talking about?


https://evolutionnews.org/2018/03/spontaneous-creation-meyer-on-stephen-hawkings-category-error/
In his book The Grand Design, as you know, Hawking argues that “Because there is a law such as gravity, the universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist.” Thus, for Hawking, “It is not necessary to invoke God to light the blue touch paper and set the universe going.”

Meyer points out, though, that Hawking’s statement betrays a kind of category error — a philosophical misunderstanding of what the laws of nature do. Meyer notes that “the laws of nature describe how matter and energy in different states or configurations interact with other material entities. They do not tell us where matter and energy (or space and time) came from in the first place.” He goes on:

https://www.theguardian.com/science/2010/sep/02/stephen-hawking-big-bang-creator

 

[bilby]

The Casimir effect demonstrates that matter is spontaneously and continuously created and destroyed in 'empty' space.

 

[Gun Nut]

Here is the video that I recently watched that touches on Hawking Radiation, in the context of the end of the Universe.
It is fantastic... it is a CGI representation of the timeline between now and total entropy... time accelerating exponentially every 5 minutes throughout the duration of the video. It touches on global warming impact... massive meteor impact.. loss of Saturn's rings, gain of a ring around one of the outer planets (forget which), death of our sun... death of all stars.... age of black holes... proton degeneration... all the way to the end of time (when entropy is maximum and time loses all meaning. It was just amazing.
Just wait until you get to them part about the amount of time that life can possibly exist in our Universe as a percentage of its lifespan... Our Universe is not "designed" for life. It is "designed" for black holes. They express that if the universe was a human life, then by the time all of the stars in the universe die out, we are still in the womb. The perspective is incredible

[YOUTUBE]https://www.youtube.com/watch?v=uD4izuDMUQA[/YOUTUBE]

 

[steve_bank]

I do not an accept and absolute end of the universe scenario.

 

[bilby]

I do not an accept and absolute end of the universe scenario.

I am sure that reality will give your opinions the weight that they deserve.

 

[skepticalbip]

I do not an accept and absolute end of the universe scenario.

That video did not suggest an absolute end of the universe. It offered an eternal universe of maximum disorder after an unimaginable (for humans) length of time of increasing entropy. It was essentially an ultimate expression of the second law of thermodynamics.

 

[steve_bank]

I do not an accept and absolute end of the universe scenario.

That video did not suggest an absolute end of the universe. It offered an eternal universe of maximum disorder after an unimaginable (for humans) length of time of increasing entropy. It was essentially an ultimate expression of the second law of thermodynamics.

Back to cosmology. The Laws Of Thermodynamics apply only to a bounded system. A human body, car, refridgerator, planet, solar system, galaxy...

When you increase the thermodynamic boundary to infinity it breaks down. The universe in toto does not necessarily run down. Energy is never lost.

And what I always say we are basing cosmology on our limits of observation of EM.

We have no idea what things look like from the edge of our observation. And for me the most important, if the unversed runs down, who or what wound it up? Unanswerable questions.

Cosmology is science based speculation. The fact that the BB is constructed to predict what we see today from an event is not proof the theory is true.

 

[skepticalbip]

I do not an accept and absolute end of the universe scenario.

That video did not suggest an absolute end of the universe. It offered an eternal universe of maximum disorder after an unimaginable (for humans) length of time of increasing entropy. It was essentially an ultimate expression of the second law of thermodynamics.

Back to cosmology. The Laws Of Thermodynamics apply only to a bounded system. A human body, car, refridgerator, planet, solar system, galaxy...

When you increase the thermodynamic boundary to infinity it breaks down. The universe in toto does not necessarily run down. Energy is never lost.

It breaks down because energy can be introduced from outside. If it is assumed that there is an infinite but bounded universe then there is no outside and the universe can be treated as bounded. You are right that energy isn't lost and such a degenerate universe as described in the video would still contain the same amount of energy but it would be evenly and uniformly distributed. Work can only be done if there is a difference of energy or potential and with no difference in potential across a universe there is no usable energy. Example: any heat engine only works if there is a difference in heat between inside and outside the engine. And doing work increases entropy.

And what I always say we are basing cosmology on our limits of observation of EM.

We have no idea what things look like from the edge of our observation. And for me the most important, if the unversed runs down, who or what wound it up? Unanswerable questions.

Cosmology is science based speculation. The fact that the BB is constructed to predict what we see today from an event is not proof the theory is true.

You are right. We don't know but we can make assumptions based on what we can observe. What we assume the universe is may be wrong but an educated guess is better than shrugging, giving up, and "leaving it to god". New observations may show our assumptions were wrong but that is the way science works. We admit our error, make new assumptions based on the new data then make more observations to either belie or confirm those new assumptions.

 

[Loren Pechtel]

Sorry Loren, tunnel diodes do not spontaneously create matter. The doping and materials creates a condition where current can 'tunnel' around the potential barrier.

https://en.wikipedia.org/wiki/Tunnel_diode
https://en.wikipedia.org/wiki/Quantum_tunnelling

The tunnel diode doesn't create matter. It uses the already-existing creation of matter to do the tunneling.

I do not an accept and absolute end of the universe scenario.

What you accept or don't accept has nothing to do with reality.

 

[steve_bank]

I thought the idea of thermal death had fallen by the wayside.

Energy is tha abilioty to do work derived from relative staes of matter. Gravitaional potential enegy is an example.

At thermal death of the universe it does not seem there would be any energy.

The question remains of what set the initial conditions for the BB? Theory does not start at time zero and does not explain where the initial conditions came from.

Back in the 70s when I took astronomy the question was of the missing mass in the universe. The universe was one shot out expanding forever, oscillating out and back, or steady state depending on the amount of mass.

It is not testable. From Popper if it I not testable it is not science, more philosophy.

 

[skepticalbip]

I thought the idea of thermal death had fallen by the wayside.

Energy is tha abilioty to do work derived from relative staes of matter. Gravitaional potential enegy is an example.

Well kinda. It is the difference in energy density that is the ability to do work. Assume that you have an ideal dewar jar that is divided with hot water on one side and cold water on the other side separated by a thermoelectric device. The thermoelectric generator will generate electrical power that could turn a paddle wheel on either or both sides but it does so by absorbing calories from the hot side and delivering calories to the cold side. The hot side cools and the cold side warms until they are the same temperature then no more usable energy is available. The dewar will still contain the same amount of calories (energy) but there will be no caloric difference between the two sides so no longer able to do work. This would be the state of a universe at maximal entropy.

At thermal death of the universe it does not seem there would be any energy.

As above, there would be energy but no usable energy because there would only be equipotential areas of the universe.

The question remains of what set the initial conditions for the BB? Theory does not start at time zero and does not explain where the initial conditions came from.

Back in the 70s when I took astronomy the question was of the missing mass in the universe. The universe was one shot out expanding forever, oscillating out and back, or steady state depending on the amount of mass.

It is not testable. From Popper if it I not testable it is not science, more philosophy.

Some assumptions of cosmology can be tested but we don't have the ability to test many of them at present. Assumptions in cosmological proposals have been tested, many have been verified, many have been shown to be wrong so the model dropped (such as the steady state universe model).