like how everything bounces off of each other. or collides.. (a pebble dropped onto the sand at the beach for example.. every single particle of sand including the pebble interact with each other.) why does the known physics exist? what if there was no interactions between various materials? (various objects passing through each other like the other isn't there?)
We don't know why anything works the way it does, only HOW they work. If nothing interacted...well, you wouldn't exist. Atoms wouldn't exist. Everything would simply pass right through everything else.
Wow! That's a very difficult question to answer. I'll give my thoughts on it though. We have observed that everything in the universe obeys mathematical (i.e. logical) rules, which are the "laws of physics". Quantum physics encapsulates this quite nicely - "objects" have "states", and they are said to have interacted when states have changed. All of this happens in a coordinate space we call "space" and "time". Now I will speculate: Why does anything exist at all? I think the universe exists for the same reason logic and mathematics exist - because of itself. They are self generating systems. Imagine then that the universe began with some sort of self generated chunk of logic. That piece of logic would generate "conclusions", which would then interact through their relationships to each other and their "parent" to generate new "conclusions". At some point we might expect this system to reach some sort of steady state, with "chunks" being steadily created, destroyed, and modified. Note that logic has embedded in it the notion of causality, since it takes an input and generates an output. Using this we can establish both a direction, and a LOCAL quantization of time. 1 unit of local time would be 1 evaluation of the logic. Now we look at the overall network of logic. Certain pieces are more connected than others - I will call this their interaction strength. Imagine that each "chunk" has "nodes" that it uses to talk to other "chunks". If all the nodes on one chunk can talk to all the nodes on another chunk, we get an interaction strength of n^2. Distance is fundamentally defined in physics as the inverse of relative interaction strength between objects, so we have just produced the 1/r^2 rule of field forces. By extension we have also generated a LOCAL 3D quantized space. Seems almost too good to be true, doesn't it? It gets better. Quantum mechanics gives us the Heisenberg Uncertainty Principle, which basically tells us that trying to constrain certain parameters of a particle causes other parameters to become more uncertain. For example, constraining the position of a particle causes the momentum to go wild. Where would this come from in the system I have given above? Note that I said space and time are locally quantized in this model. This is not true in general for models of this type. Depending on how you set up the system, different particles will see each other as being in different spatial positions. In other words, a particle doesn't actually have a "globally defined position". This means that the dimensionality of the space is actually a decimal very close to 3, but probably less than 3, like 2.999999999 etc. Applying methods of thermodynamics will give the dimensionality of the space, and just like temperature we expect it to become VERY sharply peaked at 3 when the system becomes large. (to put this more succinctly, a universe with only 2 particles can only be 1D - a universe with 3 particles can be 1D or 2D - add more particles and you get an asymptote approaching 3 assuming you follow the rule for interaction strength) The lack of a globally defined position means that the position a particle occupies is dependent on what it's interacting with. So in other words, you get things like electron shells and probability waves, but they do not represent truly undefined parameters. It's just that the result of a test is dependent not only on which atom in your equipment interacted, but also on the target's relationship with everything else in the entire universe. Needless to say, this means that detecting any deviation from the probability waves in quantum mechanics is probably impossible (at least in the near future). Well, that was my rant. It's very hard to present it without a chalkboard, but I tried. Enjoy.
there is an anthropic principle which tells that, if there is no physics, then you and your question will not be exist, so causality between these two should be clarified.