What exactly is gravity? Why is Newton’s law of gravitation the way it is?
Why does the gravitational constant G have exactly the value it does?
Is the effect of gravity “instantaneous”, meaning no time passes (this is Newton’s implicit assumption), or is there perhaps a certain time span involved, e.g., a delay
on the order of the speed of light?
To give a concrete example: what would happen if the Sun suddenly disappeared?
According to Newton’s laws, we would immediately feel the disappearance of the Sun, while the last emitted light particles would still take a while to reach Earth.
We would then see the Sun shining for another 8 minutes while the Earth is already leaving its orbit.
Why does the speed of light have the same value for every observer?
Why is this speed approximately 300,000 km/s?
And more generally: why do the other physical constants, for example, Planck’s and Boltzmann’s constants, have the values ​​they do?
What is ‘space,’ what is ‘time,’ and what is ‘curvature of space-time’?
Why do the Einstein equations from general relativity have the form they do?
What exactly is ‘energy’?
Why does the Schrödinger equation have the form it does?
What is a ‘(elementary) particle’ and what is a ‘wave’? And so on.

Difficult, quite fundamental questions, to which a definitive answer has not always been formulated.
These fascinating questions inspired me, a retired mathematician and software developer, to try to understand classical and modern physics, up to about the second half of the 20th century.
Not that I expected or expect to find answers to the above questions by doing so.
I saw and still see it primarily as an enjoyable personal hobby. This set of programs (models), as well as the documents on the website, reflect my studies.

I have attempted to create models for many topics I have encountered, which will hopefully make the physical theory clearer.
In these models, by setting a number of general and initial variables, the consequences of these changed settings can usually be examined.
Creating these models has forced me to delve deeper into the subject matter.
This also allows me to directly test my understanding.
Moreover, my experience is that actually calculating with formulas or laws
clarifies the concept considerably.
Simply reading and trying to memorize often, at least for me, does not lead to sufficient insight. This does have the disadvantage of being time-consuming.
But then again, what is time?

Panta Rhei ouden menei, “everything flows, nothing is permanent,” is a statement attributed to the Greek philosopher Heraclitus (c. 540–480 BC). Parmenides, a more or less contemporary of Heraclitus, conversely, stated: “The universe is immovable.”
Parmenides placed particular emphasis on reason and also believed that one could only discover anything through reason (logic).
To me, the latter seems more the domain of mathematics.
Heraclitus’s world seems more applicable to physics.
Therefore, I have given this set of models the name Panta Rhei.
Most models (and also physical theories) also deal with motion or, more generally,
changes (position, velocity, momentum, energy, etc.).

In the menu pages you can download for free the relevant programs (or apps) and you can also download the theory related to that topic in the form a pdf. These documents contain the theory in my own words, gratefully utilizing numerous available sources.

In these apps, one can generally learn or experience the following:
– understand how the relevant physical laws work in practice
– discover how certain parameters (initial values ​​and physical constants) influence changes (e.g., motion, energy, …)
– compare different physical theories

The programs will initially be available for Windows (32 and 64 bit). I intend to make these programs available for Android, iPad (iOS) and macOS as well
All programs are developed in the Delphi Firemonkey development platform from Embarcadero.

Finally, I have included screenshots of a number of programs below so you might get an idea.