Question for you regarding quantum physics vs “Newtonian” physics…
I read an article the other week that described the distinction between the two as an analogy to ** the engineering techniques required to build a motor car vs a motor car less than 1 cubic mm in size. IE you need to do things differently to achieve the same effect at different scales **. (Sorry, I don’t recall the site it was on and my history doesn’t go back that far.)
This is all fine but in primary school I got the impression that the laws of physics (as opposed to the principles of engineering for example) were supposed to be “universal” and that whatever applied to one applied to all, EG like an apple falling from a tree so the moon orbits the earth sort of thing.
Do modern physisits reject this notion as some kind of wishful superstition or is it still considered dogma?
Do they pay lip service to the idea and ignore it in practice? Is there a contention in the sci community about this issue or is it pretty much accepted as described above? Is there a supportable alternative interpertation of the difference between quantum and “Newtonian” physics that maintains the same laws should apply at any size?
I think the intuitive feeling is that there should be universal rules that apply to everything. The fact that we have different rules for different scales at present is thought to be because we haven’t found the theory that ties it all together satisfactorily. I believe that a significant goal of physicists is to come up with an all inclusive theory.
I’m sure someone who actually knows what they’re talking about will be in soon.
Just wait for someone to make up some conversion constant and give it a greek letter so we can all start contemplating a few thousand other things we’ll never know for sure.
See, here’s the deal. In a very real sense, Newtonian mechanics is wrong, and quantum mechanics is right (or at least, more right). Quantum mechanics is the universal that you’re talking about. But that’s hardly a reason to ditch Newtonian concepts. The wrongness of Newtonian mechanics only become apparent on the microscopic scale, or in certain situations where something that happens on the macroscopic scale depends on what’s happening microscopically. For most applications in the macroscopic (say, everything bigger than dust), Newtonian mechanics is so close to right that you’d never, ever be able to tell the difference. Additionally, quantum is really hard, and what’s worse, it gets harder the bigger the system gets. By the time you get to the macroscopic, you would never want to use quantum, since Newtonian formulae work just as well. So in summary, on the small scale, we use quantum because it’s more accurate, and on the large scale, we use Newtonian because it’s much easier.
A similar thing happens with regard to relativity. At very fast speeds, like 10% the speed of light, or in very strong gravity wells, like black holes, you use relativity because it’s right. And at slower speeds, you use Newtonian gravitational theory because it’s easier.
Funnily enough Achernar, that’s kinda always been how I imagined it… I have always been fascinated with the idea of quanta and found it a much more interesting way to describe reality than just a bunch of bodies banging into each other, but when I read that article it kinda threw me.
For the most part classical physics can be derived from quantum properties when Planck’s constant (h) goes to zero. This is because the Heisenberg Uncertainty principle disappears and therefore so does quantum mechanics. Wouldn’t that be great news?
However, this is not true of spin (intrinsic) angular momentum. The spin quantum number is a fixed quantity (s = ½) and so cannot be increased to infinity as h tends to zero. The property analogous to electron spin therefore disappears for classical objects, and spin most definitely cannot be thought of as an electron spinning on its axis. And it, therefore, is a strictly quantum mechanical construct.
Adam K, would you try to describe the operation of a CD player with laws of planetary motion ? NO.
are the laws the govern the operation of a CD player universal ? YES. Are those that govern motion of planets universal ? YES. But they do not form a complete set of rules that can describe any phenomenon, they are just a small part.
when you go to a smaller scale you need ADDITIONAL rules, rules that tend to cancel-out on a large scale and thus are not observed there, and not used in the formulas, laws etc.
