For those who want to learn just enough about it so they can solve problems, that is all there is to the theory of relativity – it just changes Newton’s laws by introducing a correction factor to the mass.                 Richard Feynman – Nobel Prize in Physics

Dear reader, anyone who is familiar with the conventional derivation method of Relativity Theory may at first be skeptical about the approach described on this website.

Nevertheless, we advise the reader to dwell on this site long enough so that he/she can convince himself/herself of the consistency of the method used.

#### We confirm the special theory of relativity with a new method

Here the Theory of Special Relativity is not questioned, but confirmed.

The results are the same as in the conventional procedure, but the approach, the path taken, and the method of derivation are different.

There are two fundamental physical phenomena that led to the birth of the Theory of Relativity and characterized its development.

The first is the postulate of constancy of the speed of light for all inertial frames of reference. The second is the variability of mass as a function of speed.

The conventional method of derivation of the theory starts from the postulate of the constancy of the speed of light and uses kinematics with the Lorentz transformations.

#### Our approach to relativity is based on the variability of mass

Instead, we start from the principle of mass variability and alternatively derive the most important relations of Special Relativity, with the help of dynamics, using the conservation laws of energy and momentum.

The approach to relativistic mechanics described here is easier to understand than the conventional one for uninformed readers on the subject.

For physicists and readers who are already familiar with the Theory of Special Relativity, it is fascinating to note that relativistic equations can also be derived from Newton’s law(1), using only the momentum of the electromagnetic wave.

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(1) On this website, Newton’s Second Law of Motion is used consistently in its original form, according to which the force is equal to the time derivative of the momentum:

$\vec{F}=\frac{d(m\vec{v})}{dt}=m\frac{d\vec{v}}{dt}+\vec{v}\frac{dm}{dt}$

In this form, Newton’s law is also compatible with variable masses, as it occurs at relativistic velocities.