it's a good question and one that puzzled me when I was at school. We talk about matter and energy being equivalent and related by Einstein's famous equation$E=mc^2$ but it is not at all clear how matter and energy can interconvert and how particles can turn into other particles.

To understand this you need to understand how particles are described in quantum field theory. I have already described this in some detail in previous answers, so rather than go through it again let me refer you to the previous answers:

• What keeps mass from turning into energy?

• Do photons truly exist in a physical sense or are they just a useful concept like $i = \sqrt{-1}$?

To briefly reprise the above, the general idea is that we can create a particle by adding energy to its quantum field, and we can annihilate a particle by removing energy from its quantum field. The end result is that particles are a lot more ephemeral than we might think, though we should note there are conservation rules that have to be obeyed such as conservation of charge and angular momentum.

To understand processes like the decay of muons to electrons we need to know that quantum fields can interact with each other and exchange energy. This interaction means the fields become mixed up with each other, so if we start with a muon then with time it will evolve into some mixture of a muon with all the other fields that a muon can interact with. If we observe this mixture then most of the time our observation will just collapse the state to a muon, but every$2.2\mu\text{s}$ or so we'll observe an electron and two neutrinos instead i.e. we observe that the muon has decayed to an electron and two neutrinos. Or put another way, one muon's worth of energy got removed from the muon quantum field and added to the electron and neutrino quantum fields.

The muon can interact with many different quantum fields, but the interaction has to conserve charge, momentum, etc and those conservation rules mean that the decay of an isolated muon to an electron and two neutrinos is the only path possible. If we changed the rules e.g. by colliding a muon and anti-muon at high energy this would allow many other decay paths to be taken.

And this addresses your previous questionWhy would particles resulted from high energy collisions appear in larger mass first then breakdown later? Suppose we collide two quarks at a very high energy (which is what we do in theLarge Hadron Collider). As the two quarks interact they evolve into a mixture of all the quantum fields that the quark field can interact with, which is basicallyall quantum fields. Since we have added lots of extra energy in the form of kinetic energy of the quarks there is plenty of energy to form massive particles as well as lighter ones.

We can do a scattering calculation and this tells us the probabilities of creating the different products. In general the probability of creating light particles is greater than the probability of creating heavy particles, but even for the heavier particles the probability is not zero (again, subject to conservation laws). That means a collision that can create electrons can also create muons and (if there is enough energy) even tau particles, though we will usually see the lighter products more often than the heavier ones.

• $\begingroup$(+1) Re: "The muon can interact with many different quantum fields" but there are as many as 17 fields all coexisting in the same quantum vacuum medium according to QFT... Without mutually agreed bandwidth allocation or complicated multiplexing schemes, why don't the airspace get crowded / rendered unusable by these 17 fields which all broadcast using the same quantum vacuum medium?$\endgroup$

  James

  – James

  2025-11-16 09:45:36 +00:00

  CommentedNov 16 at 9:45
• $\begingroup$Thank you and appreciate your answer very much.$\endgroup$

  Kanokpon Arm

  – Kanokpon Arm

  2025-11-22 09:27:52 +00:00

  CommentedNov 22 at 9:27

• particle-physics
• standard-model
• radiation
• leptons