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What you state is incorrect.

As I said, the mass is a property of any particle. An error on a measurement is one thing, and you can make an error in measuring a mass. This is right. But the mass itself is always well defined.

This is also what special relativity tells us. If you take any elementary particle, its mass is one of its properties. The mass of the photon is zero, no matter what you try.

All you said is correct, but here we speak about theory of relativity so rest mass is absoulte, but relativistic mass is not As the name suggest

The relativistic mass is a confusing concept that should be avoided at all cost.

Physicists use the wording mass for the invariant mass or an object, or its rest mass. This consists of an intrinsic property of it.

What is abusively called the relativistic mass is nothing but another name for the energy of the object (divided by the speed of light squared). Therefore, it is better to use the wording energy instead.

I hope this clarifies.

Absolutley..also, I express better on my languange- so, if you speak croatian we can have better discusion 😂😂😂
But, I agreed with you, energy is better choice.

I can speak English, French, a little bit of German and a little bit of Dutch,. Therefore... sorry ;)

Its forgiven..Thanks for some great inputs...As I Said on beggining of my post- im not educated in science so This comes As a little class for me ☺️

The purpose of my comment was not to attack you, but to help making the point clear. It is my pleasure helping people in this way :)