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A11out
Post  Post subject: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 3:49 pm

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"The law of Conservation of Energy states that "Energy cannot be created or destroyed." In other words, the total amount of energy in the universe never changes, although it may change from one form to another. Energy never disappears, but it does change form."

It might be a dumb question, but I'm totally serious. How does the Earth lose energy to space so fast? Earth is getting warmed up with the sun, receiving energy. So, how comes if you remove the sun the Earth freezes and becomes a lifeless rock? How does it loose energy, if it pretty much floats in the vacuum of space? I know the vacuum is not completely empty, but it is mostly empty. Wouldn't it mean that Earth will be cooled off in millions of years?

Next question if more of a theory, a science fiction. So, let's say, we have a certain amount of energy on Earth and we manage completely trap all of that and lose nothing at all. I do not know, put a membrane that lets nothing in and nothing out. Would it be possible to create a self-supporting ecosystem? You know, energy is being transformed from plant to animal, animal to plant, no energy escapes or enters so it is going on forever?


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janus
Post  Post subject: Re: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 6:13 pm

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A11out wrote:
"The law of Conservation of Energy states that "Energy cannot be created or destroyed." In other words, the total amount of energy in the universe never changes, although it may change from one form to another. Energy never disappears, but it does change form."

It might be a dumb question, but I'm totally serious. How does the Earth lose energy to space so fast? Earth is getting warmed up with the sun, receiving energy. So, how comes if you remove the sun the Earth freezes and becomes a lifeless rock? How does it loose energy, if it pretty much floats in the vacuum of space? I know the vacuum is not completely empty, but it is mostly empty. Wouldn't it mean that Earth will be cooled off in millions of years?
Radiation. The earth loses heat in the form of infrared radiation just as fast as it receives it from the Sun. Otherwise the Earth wouldn't maintain a constant temperature but would get hotter and hotter. Remove the Sun and you just have a net energy loss. Just consider how cold it gets in Northern latitudes in the Winter, and this is just because the sun is lower in the sky and you have longer nights. And even this is mitigated by the fact that the sun is heating other parts of the globe fully and you get some air mixing. Now imagine the Sun going away completely; it would get very cold in a very short time.
Quote:

Next question if more of a theory, a science fiction. So, let's say, we have a certain amount of energy on Earth and we manage completely trap all of that and lose nothing at all. I do not know, put a membrane that lets nothing in and nothing out. Would it be possible to create a self-supporting ecosystem? You know, energy is being transformed from plant to animal, animal to plant, no energy escapes or enters so it is going on forever?

No. While the total amount of energy might remain the same, the total amount of usable energy would not. In order to use energy to do work (like running the metabolism of a living being), it has go from a higher state to a lower state. To give a simple example, a heat engine runs by having a hot reservoir and a cold reservoir, and work is done by energy moving from the hot to the cold. Once they reach the same temp, the system could contain exactly the same amount of energy but would not be capable of performing any additional work. To reset it to its original state, you would need to supply energy from some outside source. The same basic principle applies to all means of getting work from energy.

In this manner, the Earth is one giant heat engine. We receive energy from the Sun is the form of visible light, and through a complex series of interactions, convert that to infrared preforming the work needed to run our biosphere and then let that infrared escape into space. Remove the Sun's energy input, and the usable energy resources on the planet would be quickly used up.


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A11out
Post  Post subject: Re: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 6:44 pm

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janus wrote:
No. While the total amount of energy might remain the same, the total amount of usable energy would not. In order to use energy to do work (like running the metabolism of a living being), it has go from a higher state to a lower state. To give a simple example, a heat engine runs by having a hot reservoir and a cold reservoir, and work is done by energy moving from the hot to the cold. Once they reach the same temp, the system could contain exactly the same amount of energy but would not be capable of performing any additional work. To reset it to its original state, you would need to supply energy from some outside source. The same basic principle applies to all means of getting work from energy.


Higher state and lower state? Never heard about these concepts. For some reason, I cannot google it. Is there a different name, scientific, so I can look it up and do more reading?

Also, what does it take, hypothetically, to bring energy back from one state to another? How does it happen on the cosmic scale and is there a way, in theory, to create an enclosed system of such on the lower scale? I would assume that energy in the universe is going from one state to the other all the time. Or is it a one-way process and one day all the energy in the universe will go from one state to the other and this will be it for us?


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PhDemon
Post  Post subject: Re: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 6:54 pm

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The concept you are looking for is entropy and the second law of thermodynamics...

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A11out
Post  Post subject: Re: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 7:24 pm

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Also, I found a curious piece of info. Turns out that 1/3 to 1/2 of heat output from Earth is caused by gravitationally driven heat - a slow collapse of planetary material to a smaller size driven by gravity. Do you think, in theory, that you can create an enclosed ecosystem on Earth by tapping into Earth's core and use that for the transition of energy to the higher state? In theory, gravitational collapse can provide a source of energy that will last billions of years.

What do you guys think?


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A11out
Post  Post subject: Re: The law of Conservation of Energy  |  Posted: Thu Feb 23, 2017 7:26 pm

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PhDemon wrote:
The concept you are looking for is entropy and the second law of thermodynamics...

Thank you! I'll read more on that. Also, I have another question (stupid theory?) in a post above.


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Olinguito
Post  Post subject:   |  Posted: Sun Feb 26, 2017 12:07 am
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A11out wrote:
So, let's say, we have a certain amount of energy on Earth and we manage completely trap all of that and lose nothing at all. I do not know, put a membrane that lets nothing in and nothing out. Would it be possible to create a self-supporting ecosystem? You know, energy is being transformed from plant to animal, animal to plant, no energy escapes or enters so it is going on forever?

You're right in saying that the total energy will remain constant (ignoring relativistic mass–energy conversions). This is the first law of thermodynamics. However there is the second law of thermodynamics, which states that the entropy of a closed system never decreases. Entropy is a measure of the "disorderliness" of a physical system; the higher the entropy, the more "disorderly" it is. As an example, consider the melting of an ice cube. The ice consists of an orderly arrangement of $ \displaystyle \mathrm{H_2O}$ molecules whereas the water to which it melts contains a less orderly arrangement of the molecules. Thus, entropy increases when the ice melts. Energy can exist in various forms, but in a closed system useful work will only be done by energy being converted from an "orderly" form to an "disorderly" form (with an accompanying increase in entropy). The most "disorderly" form of energy is heat. When all the energy in a system is in the form of heat, maximum entropy is reached and nothing further will happen. (It is conjectured that this is eventually what will happen to the Universe, a phenomenon known as the heat death of the Universe.)

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