Changes

The "[[mass]]" on the right side of Einstein's equation <math>E=mc^2</math> is invariant (or rest mass) for a physicist and generally '''relativistic mass''', or ''"inertial mass"'', for non physicists, which is rather non intuitive arrangement but luckily the Einstein's equation works for both kinds of mass (unless one wants spacially accurate terminology, which then may to involve also [[curvatures of spacetime]]).

The "[[mass]]" on the right side of Einstein's equation <math>E=mc^2</math> is invariant (or rest mass) for a physicist and generally '''relativistic mass''', or ''"inertial mass"'', for non physicists, which is rather non intuitive arrangement but luckily the Einstein's equation works for both kinds of mass (unless one wants spacially accurate terminology, which then may to involve also [[curvatures of spacetime]]).

Now we have a problem which ''"[[invariant mass]]"'' or '''relativistic mass''' is responsible for gravitation? It turns out it is '''relativistic mass''' and therefore it is the energy content of mass. And that's why for light the gravitational effects are the same as for other "masses". Photons (articles of light) don't have ''"[[invariant mass]]"'' (their [[invariant mass]] is equal zero, and that's why they are called "massless" particles) yet they have '''relativistic mass''' (energy) and therefore they may take part in gravitational phenomena (as they do). Energy of each photon is <math>E_\nu=h \nu</math>, where <math>h</math> is Planck constant, and <math>\nu</math> if frequwncy of light carried by this photon.

Now we have a problem which ''"[[invariant mass]]"'' or '''relativistic mass''' is responsible for gravitation? It turns out it is '''relativistic mass''' and therefore it is the energy content of mass. And that's why for light the gravitational effects are the same as for other "masses". Photons (articles of light) don't have ''"[[invariant mass]]"'' (their [[invariant mass]] is equal zero, and that's why they are called "massless" particles) yet they have '''relativistic mass''' (energy) and therefore they may take part in gravitational phenomena (as they do). Energy of each photon is <math>E_\nu=h \nu</math>, where <math>h</math> is Planck constant, and <math>\nu</math> if frequency of light carried by this photon.

==See also==

==See also==

[[Gravitation demystified]].

[[Gravitation demystified]].