# When is energy converted to mass? What are the required conditions to do so? [duplicate]

I want to know whether every kind of energy is converted to mass like kinetic and potential energy? Is it only possible for particles like electrons and protons or even either for big objects like a car or bus. Please consider the minutest / smallest change in mass even 0.000000000000000000000001 kg of gain in mass? I mean "relativistic mass" in case when the object is moving and "rest mass" in case when the object is at rest. Can Rest mass too can increase when the gravitational potential energy of an object increases

• Mass is simply a property of physical objects: things aren't converted to mass. The idea of converting things "to mass" is a one hundred year old idea, that really looks a bit shabby nowadays. Mass as a concept just isn't that important outside Newtonian mechanics anymore and there are no rigorous concepts of mass that aren't simply another way of expressing total energy. Mass is useful as an ID tag for subatomic particles and atoms, but it has some thorny, awkward properties which make it not useful anymore otherwise: see my answer here – Selene Routley Aug 21 '17 at 8:59

I'm going to answer this from the perspective of quantum field theory.

Basically, there are these things called quantum fields which permeate everywhere in the universe. Each field has its own respective particle. You can think of a field like a pond. A ripple in the pond is a particle. In other words, a particle is a disturbance in a field. For example, a disturbance in the electron field is called an electron.

To create a ripple, energy must be used. By 'giving' energy to a field, you get a particle. Some of these particles have mass. Energy isn't really 'converted' into mass.

This answer strays a bit away from your particular need/special relativity, but hopefully, gives a fundamental view of the question.

Here are a few videos on the topic:

• So if you are moving at the speed of about 1000m/s somehow will there be increase in your mass? And if yes why you experienced a gain in mass – Arpit Bhardwaj Aug 22 '17 at 0:16
• So how does QFT tell me about the gain in mass of a body while moving – Arpit Bhardwaj Aug 23 '17 at 0:20
• +Arpit Bhardwaj Not exactly. Special relativity tells us that motion is relative, and if we are going in a car, and we pass a tree, the observer inside can say that the tree is in motion. Which object's mass increases - the car or the tree? There is something in special relativity called 'relativistic mass', which is based on m = E/c^2, i.e, the energy of motion turns into mass. This is true, but this definition of mass was disliked by Einstein, and modern physicists dislike it as well. Check out this Wikipedia page: en.wikipedia.org/wiki/Mass_in_special_relativity#Controversy – Aditya Radhakrishnan Aug 23 '17 at 11:31
• So what really happens in this case – Arpit Bhardwaj Aug 23 '17 at 11:42