# Is most of the energy in the universe potential energy?

So I asked a question about what would happen in regards to gravitational potential if I left earth and then vaporized it. The answer I got was that the Mass would still remain the same and even if something is split the total amount of gravity it generates is linearly proportional to mass. So if no matter what, everything has gravitational potential in relatively to everything else, does that mean that the majority of energy in the universe is potential?

• You might want to look into the virial theorem. Feb 23 at 17:44

The energy of the whole universe is not well defined. However, if you are dealing with some smaller system where the energy is well defined, then you can always choose a reference frame where the kinetic energy is greater than the potential energy.

Most energy in the universe is potential. Only when all mass has turned into photons, by evaporation of black holes, the universe will be energy dominated.

If you talk about the kinetic and potential energy of massive particles, the situation is tricky. Galaxies have velocity and rotate, like atars and planets. But all their mass contains potential gravitational energy too. The three basic forces of nature keep it from collapsing and gain kinetic energy. The Earth got kinetic energy by gravity. The Earth has a lot of potential energy as well as kinetic energy. The potential energy would be released if the EM forces wouldn't keep the parts from collapsing. How big is the potential energy of the Earth?

Now the total kinetic energy of all masses in the universe is the negative of all gravitational potential energy. But there is still a lot of potential energy that is stored in all massive gravitationally bound objects. To know how big this stored energy is in comparison to the kinetic energy prsent, you need to calculate all potential gravitational energies and all kinetic energies. I'm not sure if you can reason what their ratio is. But both are much smaller than the energy equivalent of all mass present, i.e, $$10^{53} (kg)$$.

• In general relativity, there is no such thing as gravitational potential energy, those are just fraction of kinetic energy of objects due to free falling motion. So it's misleading to say all masses carry gravitational potential energy. Also, how can you say that total kinetic energy of all masses is negative of all gravitational potential energy? It's not true in the context of general relativity
– KP99
Feb 23 at 20:35
• But there is no such thing as absolute kinetic energy. The kinetic energy of an object can take any non-negative value, dependent solely on your choice of reference frame. Gravitational potential energy does not depend on velocity and is independent of frame-relative velocity. No matter how much potential energy a system has, I can pick a reference frame where it has even more kinetic energy. Feb 23 at 20:41
• @KP99 In the context of relativity all freely falling objects gain no kinetic energy. Only one of the three other forces and tidal forces cause acceleration and relative velocities. Only objects which have accelerated absolutely have kinetic energy. So a stone falling to Earth or a star rotating in a galaxy have no kinetic energy. That's true. If I accelerate in empty space, who has kinetic energy? Me or the stars? Feb 23 at 21:00
• Tbh, I really don't know where to start from...but I'm curious where you are getting all of these interpretations or if you are cooking up all of these explanations. For now, can you provide name of the book Or any reference which you're following, I will check it out myself, because it appears to me that you are harbouring some misconceptions about fundamentals of relativity, both special and general. Conversations like this will only create confusion among fellow readers who are new to these ideas.
– KP99
Feb 23 at 21:44
• @KP99 By the way, my answer was given in the context of classical mechanics. With classical kinetic and potential energy. Feb 23 at 22:03