What happens when the universe runs out of energy?

Good question! This state is called heat death, that is, the energy is equal everywhere in the entire universe, and no energy can be transmitted. At this time, the entropy value in the universe reaches its maximum, and there is no more tangible matter (including black holes, the existence of matter means that the energy is unequal), only the occasional energy fluctuations under the quantum tide.

Specifically, you can check out more specialized books (decay of elementary particles, evaporation of black holes, etc.).

There are two possible outcomes for the universe as currently understood

Great collapse. The entire universe went from an expanding state to a contractionary state, and finally back to the initial singularity.

Heat death. The entire universe expands infinitely, but all matter in the universe ceases to exist.

Energy follows the law of conservation of energy, and there is no such thing as energy being used up.

It's just that although energy is conserved, the way energy exists is not the same, some energy can be released more conveniently, and some cannot.

You can't live that long, not even a black hole can live that long

About five billion years later, the solar system will run out of energy.

In another 5 billion years, the Milky Way will run out of energy, and in the red dwarf era, all the stars will be less bright than the Sun is now, which means that the universe will be a little darker

In another 5 billion years, 5 billion times, the stars will lose their brightness and enter the era of black holes, which will be darker than if you can't reach your fingers, and the energy will be lower, and the universe will be colder, but not yet absolute zero

And then after much longer, much longer than we use now, the black hole runs out of energy, and even the energy that sustains elementary particles is used up, and we enter the proton epoch, where the atoms no longer exist, and the protons collapse

And then there's the heat death, and the gods don't exist, and even the elementary particles don't exist, and the time span is beyond imagination

The law of conservation of energy is one of the universal fundamental laws of nature.

It is generally stated that energy is neither created nor disappeared out of thin air, it only changes from one form to another, or from one object to another, while the total amount of energy remains the same.

It can also be expressed as follows: the change in the total energy of a system can only be equal to the amount of energy transferred into or out of the system. Total energy is the sum of mechanical energy, thermal energy, and any form of internal energy other than thermal energy of the system.

If a system is in isolation, it is unlikely that energy or mass can be transferred to or from the system. In this case, the law of conservation of energy is expressed as follows: "The total energy of an isolated system remains constant." ”

Energy is conserved, and the energy released since the birth of the universe has not decreased or increased, because energy is conserved and unchanged, will not increase or decrease, energy can be converted into matter, matter can also be converted into energy, the total amount of matter in the universe is unchanged, just transformed back and forth, and the law of conservation of energy can also be explained as: all things are born and die in cycles, and death is not completely over. Rather, it is transformed into energy to continue to exist, and then from energy to matter again, which illustrates:

Everything has a past life, an afterlife, a future life, a past life, not only people have an afterlife, but in fact, everything has an afterlife

There are still in the millions.