The BB and energy

[steve_bank]

A question came up that I did not have a ready answer for. The assertion place a hot object in deep space and the cooling to equilibrium with the cosmic background does not take energy, an implied perpetual motion of sorts.

I worked black body and radiation heat transfer in the past for local Erath bound situations. A hot object in space radiates in proportion to temperature and at the same time receives photons from the background, which appears as a black body. When equilibrium is reached the recieved and sent radiation are equal.

The source of the forms of energy we define would seem to be the initial conditions of the BB. As such the equilibrium process in space is driven by heat which originated with the BB. Photons are energy carriers as such require energy to create, that energy being heat originating in the BB.
I do not know enough QM and cosmology to see where entropy would apply to cooling by radiation in space. In Earthbound situations there always identifiable sources of heat and LOT applies.

If entropy applies then the process of keeping the object at the background temperature will result in a loss and then cosmic 'thermal death' comes to mind. That is as far as my thinking goes.

 

[Jokodo]

A question came up that I did not have a ready answer for. The assertion place a hot object in deep space and the cooling to equilibrium with the cosmic background does not take energy, an implied perpetual motion of sorts.

I worked black body and radiation heat transfer in the past for local Erath bound situations. A hot object in space radiates in proportion to temperature and at the same time receives photons from the background, which appears as a black body. When equilibrium is reached the recieved and sent radiation are equal.

The source of the forms of energy we define would seem to be the initial conditions of the BB. As such the equilibrium process in space is driven by heat which originated with the BB. Photons are energy carriers as such require energy to create, that energy being heat originating in the BB.
I do not know enough QM and cosmology to see where entropy would apply to cooling by radiation in space. In Earthbound situations there always identifiable sources of heat and LOT applies.

If entropy applies then the process of keeping the object at the background temperature will result in a loss and then cosmic 'thermal death' comes to mind. That is as far as my thinking goes.

I think you're making this way more complicated than it has to be.

The rate at which an object looses energy depends on surface area and temperature.

The rate at which it gains energy is (almost) independent of the object's property (except to some extent how reflective its exterior) and almost entirely depends on its surroundings.

Given that the two processes are independent, they don't have to agree. When they don't, the temperature changes, and therefore emissions (but not immissions) also change. Until such time as the two figures become identical. That is, when the object has reached the same temperature other objects (without an internal heat source) in its region of space tend to have.

No cosmology or QM is even required.

 

[barbos]

What is the question?

 

[repoman]

This is not related to the question, but BB radiation and global warming is pretty interesting. Humans (or the slower process of volcanos and weathering) changes the amount of absorbtion/transmission of specific wavelengths due to the methane, carbon dioxide in the atmosphere. With a constant solar output it will be something like this simplified model:

http://claesjohnson.blogspot.com/2013/02/modtran-high-emissivity-of-1-ppm-co2.html

There are a lot of other things to be found by searching for Blackbody and carbon dioxide and methane.

So eventually the temp has to increase to keep the energy balance. Then global warming will stop - with maybe no icecaps anywhere. Mission accomplished

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The second one is that there apparently is a place in space colder than the CMB temperature, the Boomerang Nebula. So it will warming up from the CMB, but how fast will that happen? Do CMB microwaves (coming in a BB distribution itself?) interact well with the material in the Boomerang nebula? Perhaps other factors will warm it up after that.

https://www.universetoday.com/135920/finally-know-boomerang-nebula-colder-space/

 

[steve_bank]

Heat transfer is often modeled as an electric circuit. Rate of transfer is proportional to area and difference in the temperature.
Analogous to voltage, current, and resistance.

Restating the question.

All objects above 0k radiate. Put two objects at different temperature in a theoretical isolated bubble vacuum. They exchange radiation until the temperatures are equal, what happens next? If they continue to exchange energy that takes energy, implying that the temperature of the objects must drop if entropy applies. If the two objects stay at a constant equilibrium temperature that seems to imply perpetual motion with radiation and absorption are lossless processes.

If an object in deep space cools to the background temperature the thermal energy powering the process must come from the BB initial conditions. I do not see where entropy might apply on cooling in deep space.

 

[skepticalbip]

I still don't really understand your question. Maybe you are assuming but not describing something that just ain't so that is causing the problem.

Put a BB in an oven at a few hundred degrees and it will reach thermal equilibrium at the oven's temperature. Turn the oven off and it and the BB will cool and thermal equilibrium will be reached at a lower temperature.

The CMB is cooling as the universe expands. Thirteen billion years ago the universe was much hotter and much denser. A BB adrift in the universe thirteen billion years ago would have reached thermal equilibrium with the background temperature at that time. The universe is now cooler than then so the hot BB would radiate more energy now than it absorbs from the background temperature until equilibrium is reached.

ETA:
After re-reading, I notice that you are concerned over the idea of perpetual motion. I don't see how that applies. What should be focused on is what is pretty much the basis of such physics, conservation of energy.

 

[Jokodo]

Heat transfer is often modeled as an electric circuit. Rate of transfer is proportional to area and difference in the temperature.
Analogous to voltage, current, and resistance.

Restating the question.

All objects above 0k radiate. Put two objects at different temperature in a theoretical isolated bubble vacuum.

In order for your thought experiment to work, you need a "bubble vacuum" that's perfectly guarded against energy losses to guarantee that all radiation emitted by the objects will eventually be absorbed again by one or the other: either a 100% reflective hull, or a strongly curved space.

They exchange radiation until the temperatures are equal, what happens next?

From the perspective of thermodynamics: Nothing. Unless the system is leaking energy into empty space (as per my above comment), both objects will stay at the same, and equal, temperature for ever after. Even if they do heat up or cool because the bubble universe they sit in is moving towards a Big Crunch or Big Freeze end, they'll do so at the same rate and thus maintain an equal temperature.

If they continue to exchange energy that takes energy

,

Why would that be so?

implying that the temperature of the objects must drop if entropy applies.

A dropping system-wide temperature in a closed system that neither expands nor contracts would violate the law of the conservation of energy. LoT does not beat conservation of energy. Indeed, they don't contradict each other.

If the two objects stay at a constant equilibrium temperature that seems to imply perpetual motion with radiation and absorption are lossless processes.

How is "nothing ever changes thereafter into infinity, or at least as long as the universe exists" even close to perpetual motion?

And yes, conservation of energy tells us that in a closed system with no leaks into empty space, all energy that is radiated will eventually be absorbed. It's lossless alright because uniform heat is the most entropic form of energy.

If an object in deep space cools to the background temperature the thermal energy powering the process must come from the BB initial conditions. I do not see where entropy might apply on cooling in deep space.

There's no "thermal energy" needed to power the process of an object cooling until it becomes cold enough for the radiation it absorbs to cancel out the black body radiation it emits.

 

[Jokodo]

Heat transfer is often modeled as an electric circuit.

I think here's where you went wrong. You're taking this analogy too far, thinking that as electric circuits are less than 100% efficient, so must heat transfer be.

There's one important aspect in which heat transfer is nothing like an electric circuit or any other kind of energy transfer or transform, and the hot keyphrase that should alarm us is the word heat.

Heat is what happens as the side product of any less-than-100% efficient energy transfer. If storing energy in pumped hydro is only about 90% percent efficient, it's because 10% of the energy is "used" to heat up the turbines and the pipes due to friction. If synthesising fuels to burn them at peak times is only about 35% efficient, it's because 65% is "used" to heat up the facilities at both stages, though mostly at the burning stage (ever wondered why thermoelectric plants require coolant water?). So worrying about efficiency when what's transferred is heat and we don't care where it's transferred to makes no sense. We can define it as anything between 0% and 100% efficient, and all those values yield the correct result: 100% of the energy transferred comes out as heat.

 

[steve_bank]

I still don't really understand your question. Maybe you are assuming but not describing something that just ain't so that is causing the problem.

Put a BB in an oven at a few hundred degrees and it will reach thermal equilibrium at the oven's temperature. Turn the oven off and it and the BB will cool and thermal equilibrium will be reached at a lower temperature.

The CMB is cooling as the universe expands. Thirteen billion years ago the universe was much hotter and much denser. A BB adrift in the universe thirteen billion years ago would have reached thermal equilibrium with the background temperature at that time. The universe is now cooler than then so the hot BB would radiate more energy now than it absorbs from the background temperature until equilibrium is reached.

ETA:
After re-reading, I notice that you are concerned over the idea of perpetual motion. I don't see how that applies. What should be focused on is what is pretty much the basis of such physics, conservation of energy.

Not concerned. Somebody posed something on another thread I did not have an answer for. That is radiative cooling to equilibrium with the background does not consume energy. It inevitably comes back to cosmology and if entropy applies to the totality of the universe. Drawing a thermodynamic boundary around the object in space and the background does not seem possible so LOT does not apply. Drawing a bubble around the object with the background as an energy source and sink for energy though the bubble and LOT applies in the boundary around the object. . The BB can not answer the question because what led to the initial conditions is not known. So my question appears unanswerable.

If the total energy of the universe remains constant then entropy does not apply.

 

[steve_bank]

Heat transfer is often modeled as an electric circuit.

I think here's where you went wrong. You're taking this analogy too far, thinking that as electric circuits are less than 100% efficient, so must heat transfer be.

There's one important aspect in which heat transfer is nothing like an electric circuit or any other kind of energy transfer or transform, and the hot keyphrase that should alarm us is the word heat.

Heat is what happens as the side product of any less-than-100% efficient energy transfer. If storing energy in pumped hydro is only about 90% percent efficient, it's because 10% of the energy is "used" to heat up the turbines and the pipes due to friction. If synthesising fuels to burn them at peak times is only about 35% efficient, it's because 65% is "used" to heat up the facilities at both stages, though mostly at the burning stage (ever wondered why thermoelectric plants require coolant water?). So worrying about efficiency when what's transferred is heat and we don't care where it's transferred to makes no sense. We can define it as anything between 0% and 100% efficient, and all those values yield the correct result: 100% of the energy transferred comes out as heat.

I think you are making my point, is radiative cooling to cosmic background equilibrium a lossless process?

 

[skepticalbip]

If the total energy of the universe remains constant then entropy does not apply.

I don't know of any cosmological model that doesn't assume that the total energy of the universe is a constant. However, energy density (so background temperature) decreases as the universe continues to expand (at least for the current expansion phase).

... is radiative cooling to cosmic background equilibrium a lossless process?

Energy in any process is not lost. Energy may be converted to an undesired form during a process though such as heat in electrical circuits due to resistance.

 

[Jokodo]

Heat transfer is often modeled as an electric circuit.

I think here's where you went wrong. You're taking this analogy too far, thinking that as electric circuits are less than 100% efficient, so must heat transfer be.

There's one important aspect in which heat transfer is nothing like an electric circuit or any other kind of energy transfer or transform, and the hot keyphrase that should alarm us is the word heat.

Heat is what happens as the side product of any less-than-100% efficient energy transfer. If storing energy in pumped hydro is only about 90% percent efficient, it's because 10% of the energy is "used" to heat up the turbines and the pipes due to friction. If synthesising fuels to burn them at peak times is only about 35% efficient, it's because 65% is "used" to heat up the facilities at both stages, though mostly at the burning stage (ever wondered why thermoelectric plants require coolant water?). So worrying about efficiency when what's transferred is heat and we don't care where it's transferred to makes no sense. We can define it as anything between 0% and 100% efficient, and all those values yield the correct result: 100% of the energy transferred comes out as heat.

I think you are making my point, is radiative cooling to cosmic background equilibrium a lossless process?

The question whether or not an energy transfer is lossless is meaningless when talking about heat transfers. It's lossless and at the same time associated with a 100% loss -- to heat.

The things you know as energy losses aren't actual losses of energy, and cannot be due to the law of conservation of energy. They are conversion of energy to a less readily usable form -- namely heat!

 

[steve_bank]

Thanks for the responses. I do not have the energy or eyes to jump into cosmology where the answer for me would be. I'll leave it here.

 

[Jokodo]

Thanks for the responses. I do not have the energy or eyes to jump into cosmology where the answer for me would be. I'll leave it here.

No cosmology is required.

 

[Jokodo]

If the total energy of the universe remains constant then entropy does not apply.

Of course it does. Entropy is a decrease in usable energy, energy able to perform work.
The total energy of the universe remains constant while a growing portion of it is present in the form of diffuse, uniform heat - exactly what the Laws of Thermodynamics describe.

 

[steve_bank]

If the total energy of the universe remains constant then entropy does not apply.

Of course it does. Entropy is a decrease in usable energy, energy able to perform work.
The total energy of the universe remains constant while a growing portion of it is present in the form of diffuse, uniform heat - exactly what the Laws of Thermodynamics describe.

I am well versed in applying thermodynamics. LOT applies to a bounded system. Consider an audio amp. It is delivering 100 watts to the air through a speaker. The power at the mains input will be 100 watts plus loses in the system. Within the amp there will be energy that can not be used or recovered to do useful work in the system. Waste heat goes to the mass surrounding the amp via conduction, convection, and radiation.

A thermodynamic boundary or system can be Earth-sun or solar system-galaxy. The problem with entropy is when the boundary is the universe. If entropy applies to the universe then processes inevitably run down due to increasing entropy. Applying LOT is about where the system boundary is set. A system defined as an object in space radiates and receives energy proportional to temperature difference to the background. Simple analysis. There is no possible system boundary to encompass background as an isolated source of heat. LOT can not be applied.

My view is that in an infinite universe total energy can not decrease or increase, only form changes. It is what makes sense to me.

 

[Jokodo]

If the total energy of the universe remains constant then entropy does not apply.

Of course it does. Entropy is a decrease in usable energy, energy able to perform work.
The total energy of the universe remains constant while a growing portion of it is present in the form of diffuse, uniform heat - exactly what the Laws of Thermodynamics describe.

I am well versed in applying thermodynamics. LOT applies to a bounded system. Consider an audio amp. It is delivering 100 watts to the air through a speaker. The power at the mains input will be 100 watts plus loses in the system. Within the amp there will be energy that can not be used or recovered to do useful work in the system. Waste heat goes to the mass surrounding the amp via conduction, convection, and radiation.

You said it yourself: waste heat. If total energy in any transfer or transform is preserved, even is some is lost as heat, how do you think you can meaningfully even ask whether heat transfer is lossless?

A thermodynamic boundary or system can be Earth-sun or solar system-galaxy. The problem with entropy is when the boundary is the universe. If entropy applies to the universe then processes inevitably run down due to increasing entropy.

How is that a problem?

Applying LOT is about where the system boundary is set. A system defined as an object in space radiates and receives energy proportional to temperature difference to the background. Simple analysis. There is no possible system boundary to encompass background as an isolated source of heat. LOT can not be applied.

How does that follow?

My view is that in an infinite universe total energy can not decrease or increase, only form changes. It is what makes sense to me.

It didn't make sense to you yesterday. Also, you're about 200 years late to figuring this out.

 

[barbos]

Heat transfer is often modeled as an electric circuit. Rate of transfer is proportional to area and difference in the temperature.
Analogous to voltage, current, and resistance.

Restating the question.

All objects above 0k radiate. Put two objects at different temperature in a theoretical isolated bubble vacuum. They exchange radiation until the temperatures are equal, what happens next? If they continue to exchange energy that takes energy,

No, it does not.

implying that the temperature of the objects must drop if entropy applies.

Absolutely not.

If the two objects stay at a constant equilibrium temperature that seems to imply perpetual motion with radiation and absorption are lossless processes.

Yes, they will reach thermodynamic equilibrium and stay that way until some external influence change that.

If an object in deep space cools to the background temperature the thermal energy powering the process must come from the BB initial conditions. I do not see where entropy might apply on cooling in deep space.

You clearly misunderstand thermodynamics.

 

[barbos]

I think you are making my point, is radiative cooling to cosmic background equilibrium a lossless process?

The question whether or not an energy transfer is lossless is meaningless when talking about heat transfers. It's lossless and at the same time associated with a 100% loss -- to heat.

The things you know as energy losses aren't actual losses of energy, and cannot be due to the law of conservation of energy. They are conversion of energy to a less readily usable form -- namely heat!

Exactly, energy conserves. what is not conserved is entropy, it can only increase or stay the same when it can no longer increase, this is called thermodynamic equilibrium.

 

[skepticalbip]

Thanks for the responses. I do not have the energy or eyes to jump into cosmology where the answer for me would be. I'll leave it here.

I don't think cosmology is the problem. It seems to be more the difference in how problems are approached in engineering and in physics. You seem to be making more of the problem than it merits.

Engineering assumes that there are always energy losses in any system. The loss being defined as the difference between the energy applied and the desired work done by the system. For example: in using an electric motor to lift a heavy weight, the potential energy of the lifted weight will always be less than the electrical energy applied to the motor. The difference is "lost energy" for engineers.

In Physics energy can not be created or destroyed, only converted to different forms. Using the same example: The electrical energy converted to the potential energy of the lifted weight is only part of the energy budget to be accounted for. Some of the applied electrical energy was converted to heat in the motor and wiring due to resistance, some to heat in the pulley due to friction, etc. No energy is "lost"... some was converted to potential energy in the lifted the weight and some converted to heat.

In the black body radiation of a hot body in space, the heat energy is radiated away as photons with "100% efficiency". The photons absorbed are done so with "100% efficiency". There will be a difference in the amount radiated and absorbed until equilibrium is reached.