How come there isn’t a conflict between the first law of thermodynamics and the theoretical scenario of the Heath Death theory?
In: 30
The energy is still everywhere. It is neither created or destroyed. It can just no longer be used to do useful work, as per the second law of thermodynamics.
Is this a popular question in school right now? It keeps coming up a couple times a day suddenly.
No.
The heat death is about no thermodynamic free energy not about no energy. That is energy that is available to do work.
There is a lot of energy because of the temperature of the air in your room. But you can extract it to do work if the air is all you have access to. You can extract energy if you have air with less energy than it cool air outside the house. To do work you need temperature differences you can exploit. The heat death is when there is no temperature difference or other way to do work.
Look at the second law of thermodynamics that can be stated as
>”Not all heat energy can be converted into work in a cyclic process”
You can also formulate it with entropy as
>the state of entropy of the entire universe, as an isolated system, will always increase over time
The problem at the head death is if everything has the same temperature you can increase entropy and that is needed to do work
ELI5 Version –
People need food, obviously. If I take a sandwich and feed it to someone, they’ll live. Now I have a million people and still only the 1 sandwich. If cut up that sandwich into a million pieces and give them out, no one gets enough energy to live and they all die.
The first law says that energy can’t be created or destroyed, that’s the 1 sandwich, I start with 1 sandwich and only have 1 sandwich. The Heat Death scenario is spreading that 1 sandwich among the million people. It’s not enough to satisfy anyone, and they all die.
The certainty of the heat death of the universe if the universe is proven to be ever-expanding is in fact dictated by the laws of thermodynamics themselves
If the universe is ever-expanding, the volume of the universe is therefore always increasing. If energy cannot be created, then as the volume increases, the average amount of energy in any given place is constantly falling, and approaching the limit of zero energy per unit of volume. The next assumption is that life requires a given amount of energy to survive, and we have no evidence to really disprove that assumption at this point.
The expansion of the universe is generally confirmed by observation and there is little if any evidence to the contrary. It’s possible that the expansion is slowing down though, and that it eventually might contract back into a singularity and followed by another big bang.
It is much the same as why your car can get hot when parked in the sun, but if you open the doors it cools down. The energy existed in the universe before it heated up your car, primary in the form of light, and still exists after it cools down, but is now spread out over a much larger volume.
The heat death theory basically says that eventually the energy in the universe will be completely uniformly distributed. The total amount of energy in the universe will remain constant, however, and, according to all current theories, has always been the same: only how it is distributed has changed.
Per the second law of thermodynamics, if the energy is evenly spread out, nothing useful can be done with it, thereby “killing” the universe.
You don’t just need energy to do work. You actually need an energy *difference* between two points to do work. When you do the work, it brings the energy levels of those two locations closer together by transferring some from the higher energy point to the lower point.
Heat death is occurs once the energy is spread pretty much equally everywhere. Since there’s no longer any energy difference between different points in the universe, no more work can be done. The energy is still there though.
There was an interesting idea I read recently where heat death doesn’t happen because black holes absorb more dark energy after a certain size than they lose to black body radiation keep growing. So there would eventually be ever growing lonely black holes that are the remnants of galaxies for the rest of time.
When we care about energy, we really care about useful energy. This means energy that can do *work*, i.e. move something from A to B. If you’ve got a hot thing and a cool thing, you can make a heat engine where you transfer some energy from the hot thing to the cooler thing. This makes the hot thing a bit cooler and the cool thing a bit hotter, and in the process we get the chance to move something a bit.
The trick is that we can only ever make it so that the two sources get *closer* in temperature, not further away. This is (a very simplified version of) the second law of thermodynamics. So once the hot and cool things have reached the same temperature, we’re stuffed! We’ve got nothing else to work with. The total amount of energy is the same (the first law), but we can’t use it anymore. This is the heat death state.
No one else has actually answered this correctly. The reason there’s no conflict is that in the universe, energy is not conserved and it doesn’t need to be. The law of conservation of energy comes from [Noether’s theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem), but Noether’s theorem only applies to a time translation invariant universe. What that time translation invariance means is beyond the scope of this question – all you need to know is that the universe is *not* time translation invariant, which means Noether’s theorem, and thus the conservation of energy, does not apply.
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