Quantum mechanics and relativity do describe what happens at the intersection of Ford and Buick. The reason we don't use them to explain the collision is because they provide far more detail than is necessary for a sufficiently approximate explaination; Newtonian physics is enough.
Kinda like asking "what did you do today": I'm content with an answer of "got up, went to work, wrote some documentation", a detailed "first I opened my eyelids, then rolled right, then lifted the blanket, then ..." does indeed answer the question but goes far beyond what we find useful, and answering "the following sequence of neuro-chemical reactions caused my eyelid to open..." takes the answer into a whole different realm of understanding, totally obfuscating the answer originally sought.
Physics, via quantum mechanics and relativity, is attempting to somehow determine the ultimate answer to "what happened and how", pushing toward the supposed Grand Unified Theory - which will be fascinating and (presumably) correct, but using it to explain the Ford and Buick collision is unnecessarily detailed ... but that doesn't mean that the rediculously detailed explaination isn't true.
I don't disagree.
Here's the problem.
My original comment was on Einsteinian Relativity and Heisenberg Uncertainty Principle in that wreck.
Now, as to Einsteinian Relativity in a second, as to whether it REALLY has any effect on the crash, or whether we are so far down the curve towards the asymptote of zero that it doesn't, really, and only does mathematically. Certainly mathematically there is an effect, but math is a model. Just because the math curve doesn't hit zero doesn't mean that the real world effect isn't zero. This question is one for empirical science to try and determine.
So long as the mathematical effect is so small that it's orders of magnitude below anything we can detect empirically, it's speculative. Rational, logical, but speculative.
The problem with the Quantum Physics bit is that I wasn't commenting on Quantum Physics as a whole. I referred only to the Heisenberg Uncertainty Principle, which is a special subset of the whole grand edifice.
My point was not that quantum physics have no effect. I didn't comment there at all. My point was to keep the effects of things bounded by what they apply to. When two cars come into an intersection at constant bearing, decreasing range, they are going to collide with each other. Quantum mechanics may indeed give us some level of detail down at the asymptotes which may (or may not) be meaningful, but grosso modo, Heisenbergian uncertainty has no more to do with the outcome of that collision than nuclear fusion on the Sun does.
That was really my point: that our spheres of knowledge are bounded, and we can get into pretty interesting and pretty wrong beliefs when we start looking at graphs of outcomes that show asymptotes, and then extrapolate from the fact that it doesn't quite reach zero that "everything is possible". Empirically, everything is NOT possible. That our math doesn't quite get to zero does not mean that the observed world is wrong and the math is right. It means that the math is a model, and when you get way out on the fringes of things, the model starts to talk about things that the eyes don't see, and won't see.
Somehow this got turned into a discussion of quantum physics, by a grand conflation of Heisenberg's Uncertainty Principle with Quantum Mechnics as a whole discipline.
But I wasn't the one who did that.
Really my point was much more precise, limited, and intended to be humorous.
And don't forget a full quantum description of the cars is currently "beyond the state of the art"--just think of trying to get a complete Hamiltonian which correctly handled all the molecules in both vehicles during the course of a collision--and of course it would get worse as glass or the odd fender flew off during the crash--and positively horrible if one of the gas tanks blew up.
Not to mention the as-yet-unresolved problem of the consciousness of the drivers: which brings us back to the topic of this thread.
Cheers!