That is the question. Humans want to know why something exists or happens; philosophy and the sciences have thinking processes to help us determine "why". We try to find underlying reasons "why". We do have to recognize, however, that at a deep level, some concepts are simply there - they exist.
A simple example is the number, one, i. e., 1. Asking why 1 exists is a pointless exercise in sophism. 1 simply exists as the representation on unity, the existence of something: je pense, donc je suis, or in Latin, cogito, ergo sum, or in English, I think, therefore I am. Axioms are necessary as the foundation of a system of knowledge. For you metaphor lovers, one cannot build a strong house on sand, even if you build it of bricks. A house built on sand will fall ... eventually.
Now in high school physics, one learns about conservation of energy. And conservation of momentum. And conservation of angular momentum. Those concepts are supremely useful in understanding the motion of bodies and actions of all kinds of materials and our world.
Why? Why are those quantities - energy, momentum, and angular momentum - conserved (i. e., constants of motion).
This is something one can prove from deeper, more obvious axioms. All it takes is a bit of multivariable calculus and knowledge of mechanics at the level of an advanced undergraduate or first year graduate student at a good college science program. Here is a reference: Mechanics, by L. D. Landau and E. M. Lifshitz, which is Volume I of Course of Theoretical Physics (translated from Russian). In my second edition, which I read in 1974, pages 13-19 cover this material. Hmmm ... in 1974, this book cost me $10 for a hardcover copy.
I won't show you the math or how those conservation laws are derived, as typing equations and Greek letters is beyond my computer skills. Here are the results.
The more fundamental axioms upon which classical mechanics are founded are the homogeneity of time, the homegeneity of space and the isotropy of space.
Homegeneity of Time
In simple terms, homogeneity of time means that under very general conditions, the motions of particles or behavior of physical systems will be the same whether one does the experiment or actions now or next year or in ten years or in a billion years in the future or in the past. From the axiom of homogeneity of time one can prove that energy is conserved.
Homgeneity of Space
In simple terms, homogeneity of space means that under very general conditons, the motions of particles or behavior of physical systems will be the same whether one does the experiment or actions here or in Nebraska or in the galaxy Andromeda. From the axiom of homogeneity of space, one can prove that momentum is conserved.
Isotropy of Space
In simple terms, isotropy of space means that under very general conditions, the motions of particles or behavior of physical systems will be the same whether one orients the system rightside up or upside down or to the left or right or at a 30 degree angle or whatever direction. From the axiom of isotropy of space, one can prove that angular momentum is conserved.
At the deepest level of the tree of knowledge are sound philosophical concepts. One needs to understand what are the questions and what are the deepest concepts; scientists - good scientists - try to understand "why" by standing on solid ground. And if one finds the unexplainable, one needs to re-examine the ground for ... holes.
Skepticism is essential, but once one finds good ground, one must move on to build the structures of knowledge, and fight the good fights.
The axioms of homogeneity of time and space, and isotropy of space are good ground.
[Btw, of course all this can be extended into relativistic space-time by simple generalizations of the definitions of energy, momentum and angular momentum.]
Word of the Day
"Durst" - verb [$10] archaic or dialect
Durst is an archaic past tense of 'dare', showing the old germanic foundations of English.
Sentence: Obama durst to order the killing of a US citizen without trial in blatant violation of the US Constitution: resign!