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In any given energy transfer, from one form of energy to another, much of the energy is wasted. Turned into heat via friction or sound, or even radiated away as light.

In the case of an old filament lamp, much of the energy is converted to heat and that heat dissipates into the environment. Our most efficient lamps still lose a portion of their energy to heat, a wire itself will heat up over time as electrons come across atoms that resist the current and instead absorb them as heat, and electrons are lost this way as well, but what does it really mean to lose energy? What do scientists mean that some of this heat energy will be gone forever? Isn't that energy still there, in the room, as heat? Couldn't it be used again later down the line with a wind turbine or something? Doesn't the energy stay in the system?

Most of this energy does in fact stay on the Earth, for some time, but Earth is not an enclosed system. In fact, no thermodynamic system can be totally enclosed. All thermodynamic systems exist within the universe, and the universe is an open system.

Let me explain, some of that heat, is being lost to space. It's not conducting its heat energy to particles that I'm calling space either, it's lost via radiation.

All objects, depending on their temperature, radiate photons in the infrared spectrum or lower, that can be said to be a form of radiated heat. Infrared photons in this way are a method for heat to be transferred across empty space. Some of that radiation will radiate randomly and that direction will be towards the sky, and it will likely be absorbed and re-emitted by quite a few particles of greenhouse gas on the way up, losing more and more energy by transferring it to the heat of the air every time, but some of them will shoot off into space.

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This is a photograph of Earth taken in the infrared spectrum, as you can see, the atmosphere is generally opaque to infrared radiation. Greenhouse gasses form a blanket around the Earth, and tend to play hot-potato with infrared photons until they eventually hit an object or radiate off into space. The only reason we can see the Earth in this photograph is because Earth, evidently, is radiating heat via infrared radiation, into space.

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Some of that radiation, will never hit anything. It will fly off into intergalactic space, and the expansion of the universe will speed up such that it will never, ever reach a star or planet in its path. It will continue to fly out into the void at light speed for literally the rest of time, and as it does so, it will be stretched out in wavelength by the expansion of space time, slowly, slowly, creeping its way down the electromagnetic spectrum, becoming microwaves, radio, and eventually tending towards absolute zero.

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This energy is lost. Literally, lost in space. Unable to be found or interacted with ever again. This is, paraphrased, what astrophysicists mean that the universe loses its energy via heat. Engineers talk about waste heat because waste heat isn't useful to the machine at hand, but the energy still GOES somewhere, and even when astrophysicists talk about energy being lost, it isn't ever really destroyed... it's lost... lost. Like you might lose a shoe. It's unable to be found. Ever again.

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Here's some other cool things about blackbody radiation: black holes ALSO emit radiation along the blackbody curve.

Hawking radiation is emitted via electromagenetic radiation produced with a temperature inversely proportional to the mass of the black hole, the larger the black hole, the "colder" it appears to be. A small enough black hole would eventually start to become visible. Like a toaster coil heating up from black to a dull orange-red, to white, to eventually blue.

A black hole at human body temperature would be 6 meters across, have the mass of about 2 Earth masses, and it would have about 5 seconds left in its lifetime before exploding.

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Eventually, all black holes will do this. The most massive ones will last longer than smaller ones, and smaller ones will slowly and exponentially release more radiation and appear to heat up before getting to the end of the line and exploding, evaporating all of its mass into a burst of gamma rays, which will also go flying randomly off into the void, which will also slowly and slowly find their way to absolute zero.

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At the end of time, bursts of light from exploding black holes will be the last things illuminating the cosmos.

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@starwall The energy does stay in the system but typically heat energy is less readily useful

If you have a temperature gradient, you *can* make use of it to power whatever you want. But once the whole room is exactly the same temperature, you can't get anything out of it

en.m.wikipedia.org/wiki/Thermo

(Caveat: I may be misunderstanding)

@starwall single socks are are just entropy manifesting itself.

@starwall great thread also superconducting light bulbs when

@starwall Lost, but not gone. In other words, theoretically speaking, if another civilization stumbled across it and had the capability to harness it, they could still use it.

@KitsuneAlicia Well, it doesn't contain much energy to begin with, and the amount of energy it contains does eventually become functionally zero due to the expansion of spacetime. As we get out into deep time, you eventually get to a point where none of these strays can reach you even if they're travelling at the speed of light. So no, future civilizations would never be able to use that photon ever again, because it physically cannot reach them because at the speed of light (which it is travelling) it is running on a treadmill which is faster than it can run.

@KitsuneAlicia The real shot in the foot here is that any form of energy conversion will lose some of its energy to heat. There's no such thing as a 100% efficient machine, no such thing as a perpetual motion machine.

@starwall So what you're saying is, the universe would have to stop growing in order to avoid heat death?

@starwall Like, we obviously have no proof of this, so take our words with the appropriate grains/pile of salt, but there are elements that are inert, stable. There's also relative stability in life itself, i.e. the "adult" stage. But both can still be manipulated.

So, wouldn't it be reasonable to assume that the universe may act as a sort of balloon, expanding based on heat until it achieves stability, but not quite *complete* stability?

@starwall Hell, we can also assume that due to the way evolution works, in that "good enough" is acceptable, there could be a similar mechanic in physics itself so that the universe will slow/stop expanding when there's just enough heat to prevent it from "pushing" anymore, creating a stable bubble with a relatively constant temperature/energy level.

@starwall Obviously this theory assumes that there are boundaries to the universe and that there isn't just an endless void out past the last galaxy, but given how things *inside* the universe work, it's not an unreasonable assumption in our opinion.

@KitsuneAlicia Our best science suggests that dark energy is causing the expansion of the universe to accelerate. That acceleration, caused by this phenomenon that we still don't understand, is what we are using to predict the heat death of the universe. Ever since Hubble (the guy, not the telescope) found out that there were distant galaxies at all, we knew that they were getting further away from us at an accelerating rate.

@KitsuneAlicia Yes, you are exactly correct! If the universe wasn't expanding, then heat death wouldn't happen.

@starwall @KitsuneAlicia so what you have then is a Jevons issue? Where the cost of capturing the energy is greater than the profit in the energy itself, where cost and profit are in terms of joules?

@starwall And I think that's beautiful.

A shame no life we currently comprehend would exist to see it.

@LexYeen I still think it's pretty cool that we can see the cosmic microwave background, the leftover afterglow of the big bang itself. that's a special privilege that most life will not probably get.

@starwall @LexYeen distant galaxies too. most are moving away faster than the speed of light. one day the sky will be so much darker, even within the conditions for life

@CornishRepublicanArmy @LexYeen 98.6% of the galaxies we can observe today are already outside of the range where any light they emit today, will never reach us. That leaves roughly 66 billion galaxies that are emitting light at this moment that will eventually be able to reach Earth

@starwall @CornishRepublicanArmy @LexYeen and the earth is likely among the first 2% of planets that will ever be able to support liquid water and life... even if we aren't the only thinking beings out there, will we be the only cosmologists?

@luna it's truly awe inspiring that we, as lowly as we are, can predict this to be the likely fate of the universe

@starwall I really enjoyed reading this thread. Thank you.

@starwall this is a really good explanation of heat death

@starwall dude,,,, we live on one of those marbles with the swirly sand inside that you can see

@starwall lmao, imagine thinking the law of conservation of energy is real in 2020. it just gets used up Zach, duh

@starwall isn't the problem recapturing the energy in a usable form? Heat especially gets dispersed into the surrounding environment, making recapture problematic.

@WanderingBeekeeper generally, in engineering terms, yes. On cosmic terms, astrophysicists mean something else entirely in terms of heat lost. That heat is still energy, energy that isn't destroyed, and indeed if the Earth were surrounded by a perfectly energy-impermeable barrier, and the amount of space within that region never changed, then the amount of energy in the closed system would never go down because energy cannot be destroyed, only converted. See the rest of the tread for why I mean to make this distinction

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