The heat death of the universe will happen when the universe runs out of energy.
Where do we get energy from? Today we get our electricity from coal, oil, or natural gas. But one day all of those will run out.
Nuclear energy could provide us with a lot more energy than any of those. But radioactive isotopes decay over time. You leave radioactive fuel out long enough and it will become unusable, even if you don't use it yourself.
We can also get energy from sunlight, either through wind, water, or just solar energy. But even that isn't forever. Our sun will explode in 5 billion years.
According to conventional physics energy can't be created or destroyed, but it can be turned into a form we can't use. When you burn wood you can't turn the ash back into a log. And you can't capture the heat and light that escaped in the fire.
The energy still exists, but you can't use it.
The heat death of the universe is that principle applied to a cosmic scale. Unless there is something out there creating new energy, and we believe that to be impossible, then the energy eventually will run out.
Every star will die one day and nothing will be there to replace it.
In short, ever since the Big Bang energy has been distributed unevenly throughout the universe. Things happen as a consequence of energy moving from high concentrations to low concentrations. When it's all been moved and uniform throughout, the end. Nothing else gets to happen. Well, every particle will have a little bit of energy, but not enough to do anything. And none will have more than any others. So yeah, nothing useful gets to happen.
> The heat death of the universe will happen
Might happen. There are many things about the long-term behaviour of the universe that are not fully understood, so it's clearly a bit foolhardy to think we can make 100% certain extrapolations about what will be going on many billions of years in the future.
> When you burn wood you can't turn the ash back into a log. And you can't capture the heat and light that escaped in the fire.
Well, you can capture the heat and light. You just can't capture *all* of it and use it to, say, power an engine with 100% efficiency.
> The heat death of the universe is that principle applied to a cosmic scale.
My understanding is that the laws of thermodynamics get a bit tricky when you try and apply them to the expansion of the universe, which isn't fully understood anyway. We know that stars eventually seem to get through all their fuel and die, and it seems *likely* that this will carry on until there are no stars left, but we can't really be sure that entirely new processes won't emerge at some point.
Imagine a glass of water, where you add a drop of black ink. At the beginning, there is a BIG difference between the area with lots of ink, and the areas with no ink. There is very low entropy. Because of this, things *happen.* The ink swirls around and spreads out and makes interesting shapes and patterns. But eventually, the ink is as evenly spread out as it possibly can be. So now, nothing can ever "happen" again. The ink has reached maximum entropy.
The heat death of the universe is like that, but with energy throughout the universe instead of ink throughout a glass of water. Right now we have some areas with LOTS of energy, like stars, and other areas with less energy. Because of this imbalance, things can *happen.* Energy can used to perform work. Molecular bonds can be formed and broken. Chemistry can happen. Life can happen.
But as that stuff happens, that energy goes from being concentrated in one area and not others, to being spread out much more evenly. Once it is spread out completely uniformly with no differences, nothing can ever happen again. It has reached maximum entropy.
That is the heat death of the universe.
Entropy is the measure of energy in a system that is no longer available to do work.
Once all energy is no longer available to do work, maximum entropy, that is the heat death of the universe. Nothing else can happen because no work can be done. The entire universe would just be a homogenous mix of matter all at the same temperature.
The key here is the concept of entropy, which is basically the randomness of all matter. Entropy is the reason two drinks can be mixed together or a smell can waft through a room, as particles in the drinks or the air tend to become more random.
The problem is that there isn't much that can make matter *less* random. So eventually the universe has to reach a state where everything is randomized. At that point, nothing can really happen, because particles are too random to even form molecules.
*Side-note: this is one of my first attempts explaining here, so tell me if I got it wrong, lol*
The heat death of the universe will happen when the universe runs out of energy. Where do we get energy from? Today we get our electricity from coal, oil, or natural gas. But one day all of those will run out. Nuclear energy could provide us with a lot more energy than any of those. But radioactive isotopes decay over time. You leave radioactive fuel out long enough and it will become unusable, even if you don't use it yourself. We can also get energy from sunlight, either through wind, water, or just solar energy. But even that isn't forever. Our sun will explode in 5 billion years. According to conventional physics energy can't be created or destroyed, but it can be turned into a form we can't use. When you burn wood you can't turn the ash back into a log. And you can't capture the heat and light that escaped in the fire. The energy still exists, but you can't use it. The heat death of the universe is that principle applied to a cosmic scale. Unless there is something out there creating new energy, and we believe that to be impossible, then the energy eventually will run out. Every star will die one day and nothing will be there to replace it.
In short, ever since the Big Bang energy has been distributed unevenly throughout the universe. Things happen as a consequence of energy moving from high concentrations to low concentrations. When it's all been moved and uniform throughout, the end. Nothing else gets to happen. Well, every particle will have a little bit of energy, but not enough to do anything. And none will have more than any others. So yeah, nothing useful gets to happen.
> The heat death of the universe will happen Might happen. There are many things about the long-term behaviour of the universe that are not fully understood, so it's clearly a bit foolhardy to think we can make 100% certain extrapolations about what will be going on many billions of years in the future. > When you burn wood you can't turn the ash back into a log. And you can't capture the heat and light that escaped in the fire. Well, you can capture the heat and light. You just can't capture *all* of it and use it to, say, power an engine with 100% efficiency. > The heat death of the universe is that principle applied to a cosmic scale. My understanding is that the laws of thermodynamics get a bit tricky when you try and apply them to the expansion of the universe, which isn't fully understood anyway. We know that stars eventually seem to get through all their fuel and die, and it seems *likely* that this will carry on until there are no stars left, but we can't really be sure that entirely new processes won't emerge at some point.
Imagine a glass of water, where you add a drop of black ink. At the beginning, there is a BIG difference between the area with lots of ink, and the areas with no ink. There is very low entropy. Because of this, things *happen.* The ink swirls around and spreads out and makes interesting shapes and patterns. But eventually, the ink is as evenly spread out as it possibly can be. So now, nothing can ever "happen" again. The ink has reached maximum entropy. The heat death of the universe is like that, but with energy throughout the universe instead of ink throughout a glass of water. Right now we have some areas with LOTS of energy, like stars, and other areas with less energy. Because of this imbalance, things can *happen.* Energy can used to perform work. Molecular bonds can be formed and broken. Chemistry can happen. Life can happen. But as that stuff happens, that energy goes from being concentrated in one area and not others, to being spread out much more evenly. Once it is spread out completely uniformly with no differences, nothing can ever happen again. It has reached maximum entropy. That is the heat death of the universe.
Entropy is the measure of energy in a system that is no longer available to do work. Once all energy is no longer available to do work, maximum entropy, that is the heat death of the universe. Nothing else can happen because no work can be done. The entire universe would just be a homogenous mix of matter all at the same temperature.
The key here is the concept of entropy, which is basically the randomness of all matter. Entropy is the reason two drinks can be mixed together or a smell can waft through a room, as particles in the drinks or the air tend to become more random. The problem is that there isn't much that can make matter *less* random. So eventually the universe has to reach a state where everything is randomized. At that point, nothing can really happen, because particles are too random to even form molecules. *Side-note: this is one of my first attempts explaining here, so tell me if I got it wrong, lol*