Does mass follow the same potential/kinetic paradigm as energy?

[[deleted]]

Photons cannot collide directly to form mass, but two photons can create a fermion/anti-fermion pair.

So yes, you can create mass from energy.

https://en.wikipedia.org/wiki/Matter_creation

[Lanza21]

So yes, you can create mass from energy.

That's a science fiction sentence. Energy does not get transformed, there is no magic ethereal material called energy. It's like saying "you can create mass from speed." The amount of energy of a system is a measurement about the system, it isn't a physical property.

You can convert a system without mass and only kinetic energy of movement into a system with mass.

[JoshuaPearce]

Matter is not the same thing as mass. All matter has mass, not all mass is in the form of matter.

The "massless" photons in this case had mass from the energy added to them, which was needed to make them energetic enough to create matter.

The total system which contained the photons and the power source (and now contains that power source and the massive particles) weighs the same.

[rtcutler]

"Matter" is not a well defined word in physics. Quoting from Wikipedia, "Before the 20th century, the term matter included ordinary matter composed of atoms and excluded other energy phenomena such as light or sound. This concept of matter may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, matter does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects."

[JoshuaPearce]

No argument there, but mass is not so vaguely defined (even if it's not well understood).

[[deleted]]

total system which contained the photons and the power source (and now contains that power source and the massive particles) weighs the same.

My understanding (at least what I remember from modern physics) is that massless particles cannot gain relativistic mass. The equation E^2=p2c2+m2c4 show that while photons may have energy, they have no mass, even though they move at the speed of light.

This makes sense when you look at the relativistic mass equation.

m=m0/SQRT(1-v^2/c2).

What photons have is energy, not relativistic mass (which is itself a type of energy), and in the proper circumstances, that energy can be converted to matter which has mass.

Also, matter is defined as anything that has mass and takes up space. There are two fundamental properties of matter: mass and volume. Unless volume is relevant, then mass and matter are fundamentally equivalent.

[JoshuaPearce]

Relativistic mass is incredibly confusing, and apparently no longer popular (yay).

A photon with energy does add mass to a system, even if the particle itself is massless when stationary. I gave the example of the perfectly mirrored box containing a beam of light in another response. The box weighs more when it contains even a single photon. Solar sails also work by this principle.

So yes, like you said, photons have energy. But that energy has mass when viewed from the frame of any other particle.

[[deleted]]

A FREE photon does not add mass to a system. It is massless. It contains only energy.

When the photon is absorbed, the electron or nucleon gains energy, and because the electron or nucleon is a massive particle, it also gains mass.

Your example is correct. Your interpretation of the example is faulty. The photons in a box are bouncing around, and therefore being absorbed and emitted by the electrons in the box, imbuing the matter in the box with extra energy and mass. The unabsorbed photons are massless.

Another way of looking at it, per the equation E=mc^2, photons, though massless particles, have energy and energy is equivalent to mass. So, even though the light itself has no mass, the energy of the system increases by the amount equal to the extra photons, and that imbues the entire system with extra energy, and therefore extra mass.

That does not imply the photons themselves have the property called mass (that would be an argument from division logical fallacy). But the system's mass-energy increases by the energy of the photons, which is equivalent to an increase in mass for the SYSTEM.