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Greg Bernhardt submitted a new PF Insights post
"Classical Physics Is Wrong" Fallacy
Continue reading the Original PF Insights Post.
"Classical Physics Is Wrong" Fallacy
Continue reading the Original PF Insights Post.
If a new theory does not produce approximately same answers as the classical theory in the realm where the classical theory has been tested experimentally and demonstrated to be accurate then that new theory must not be correct.Lincon Ribeiro said:- "any new theory or description must somehow converge and look like the classical physics description under such ordinary conditions.". Who said this "must" be true?
jbriggs444 said:If a new theory does not produce approximately same answers as the classical theory in the realm where the classical theory has been tested experimentally and demonstrated to be accurate then that new theory must not be correct.
Experiment is the final arbiter of correctness.
I think you are rather missing the point. If you are traveling at 30mph down the road and a car passes you going 30mph faster, you can calculate its road speed using Newtonian or Einsteinian relativity. You will get the same answer to the precision you can plausibly measure. You need to take into account the velocity variation from flies crashing into the front of the car long before you need to care about Einstein. So simplifying the maths and using Newton isn't wrong. How can it be? Unless you're saying it's wrong to neglect the flies. And if you believe that then you will get nothing done ever.Lincon Ribeiro said:It does not matter if you derivade classical physics from modern theories, they have different assumptions! they do not talk about the same thing!
Ibix said:I think you are rather missing the point. If you are traveling at 30mph down the road and a car passes you going 30mph faster, you can calculate its road speed using Newtonian or Einsteinian relativity. You will get the same answer to the precision you can plausibly measure. You need to take into account the velocity variation from flies crashing into the front of the car long before you need to care about Einstein. So simplifying the maths and using Newton isn't wrong. How can it be? Unless you're saying it's wrong to neglect the flies. And if you believe that then you will get nothing done ever.
So your objection is to the term "convergence", taken as an indication that the new theory must, in the appropriate limit, be precisely identical to the old theory and not merely identical to within current experimental uncertainties.Lincon Ribeiro said:I never said that Newtonian mechanics was wrong. never said that. I said that there is no such a thing as a convergence from a new theory to an old one based on some arbitrary limit as they start from different assumptions.
We also know that they are not complete. Although they are well tested in some domains, in others uncertainties remain about their detailed application. Indeed, we expect that they will be modified or extended to explain new evidence. But they will not disappear; just as Newton's laws did not become invalid when we understood special relativity, but rather were seen to be a very accurate approximation under well-defined conditions. Theories such as those listed in the previous paragraph are strong enough that we can use them to say we know certain things - we know that protons and neutrons are composed of quarks and gluons, we know the relationship between mass and energy, we know that Earth's surface is not a single rigid structure. These are facts, but not just simple observational facts. They come from the amalgam of observation and theory development and testing that is the essence of scientific knowledge development. It diminishes the status of our understanding greatly to say that scientists "believe" these things. We know them!
When we seek to extend and revise our theoretical frameworks, we make hypotheses, build models, and construct untested, alternate, extended theories. These last must incorporate all the well-established elements of prior theories. Experiment not only tests the new hypotheses; any unexplained result both requires and constrains new speculative theory building - new hypotheses. Models, and in the modern world computer simulations too, play an important tole here. They allow us to investigate and formulate the predictions and tests of our theory in complex situations. Our hypotheses are informed guesses, incorporating much that we know. They may or may not pan out, but they are motivated by some aspects or puzzles in the existing data and theory. We actively look for contradictions.
Obtaining examples where a theory works or doesn’t work is the whole purpose of experiments in the scientific method. We don’t usually use the word “prove”, but examples do verify or falsify theories.Lincon Ribeiro said:do examples prove that a theory is correct?
I am sorry, but this is just ignorant and the limit is not arbitrary. Obviously you will not recover classical mechanics in the ultra-relativistic limit, you will recover it in the classical limit where speeds are much smaller than the speed of light.Lincon Ribeiro said:I said that there is no such a thing as a convergence from a new theory to an old one based on some arbitrary limit
The first of these follows directly in the classical limit of SR. The second also falls out of the theory as separate conservation of mass and kinetic energy at small velocities.Lincon Ribeiro said:Apart from that:
- Newton considered space as an R³ euclidean and time as absolute.
- Mass and energy were not connected the way we know now.
When it comes to light it is very well explained using Maxwell's theory. When it comes to particles such as electrons, it is not a prediction of the classical theory but your logic is completely flawed. You have taken one of the shortcomings of the classical theory that inspired people to QM and presented it as a counter argument to the quantum theory having to reduce to the classical theory in the limits where we know that the classical theory works. We already know that the classical theory does not work in this limit and so your argument is empty. Essentially you argument to the statement "A must give the same predictions as B when C is true" is to say "but it does not give the same predictions when C is not true". We come back to your assertion that the limit is arbitrary which, again, is not the case.Lincon Ribeiro said:- How would we explain the double slit experiment?
Obviously it is not wrong. It has been experimentally verified by a large number of experiments.David Neves said:Well obviously Newtonian mechanics is "wrong"
What difference does it make if you get the old theory from an upper limit or any other arbitrary direction? My point was that SR is considering space and time as completely different things comparing to old mechanics. This does not make any sense. If I say that the assumptions are: time is relative and space is Riemaniann and you say: time is absolute and space is euclidian, how can we be talking about the same theory?Orodruin said:I am sorry, but this is just ignorant and the limit is not arbitrary. Obviously you will not recover classical mechanics in the ultra-relativistic limit, you will recover it in the classical limit where speeds are much smaller than the speed of light.
No, you are wrong. What I said was that the assumptions are different! If you look at how we treat all the experiments and particles / waves in quantum world, we see that space, time, energy and whatever are all different from what we knew from classical mechanics, which means, we cannot start to say that there exists a derivation from one to another, as they were talking, ever, about the same thing. Again, if you start with different assumptions how can you end up with theories converging at a limit that has been chosen to find a connection between them?Orodruin said:When it comes to light it is very well explained using Maxwell's theory. When it comes to particles such as electrons, it is not a prediction of the classical theory but your logic is completely flawed. You have taken one of the shortcomings of the classical theory that inspired people to QM and presented it as a counter argument to the quantum theory having to reduce to the classical theory in the limits where we know that the classical theory works. We already know that the classical theory does not work in this limit and so your argument is empty. Essentially you argument to the statement "A must give the same predictions as B when C is true" is to say "but it does not give the same predictions when C is not true". We come back to your assertion that the limit is arbitrary which, again, is not the case.
Lincon Ribeiro said:I am not saying that Newtonian Mechanics is wrong. this has nothing to do with being right or wrong.
Uhmmm ... Are you serious or just trolling? Obviously it matters that you recover the old theory in the limit where the old theory is known to be applicable or if you do so in the opposite limit.Lincon Ribeiro said:What difference does it make if you get the old theory from an upper limit or any other arbitrary direction?
We are not. We are only talking about the limit of one of the theories. In the classical limit you do recover the very same things as the classical theory. That SR is applicable to a larger set of situations is not the issue here.Lincon Ribeiro said:This does not make any sense. If I say that the assumptions are: time is relative and space is Riemaniann and you say: time is absolute and space is euclidian, how can we be talking about the same theory?
This is just wrong. As already illustrated in the actual Insight. You can start from different assumptions, but in the end what it boils down to is to make identifications of what concepts in a theory that correspond to the concepts of the previous. A theory is not its underlying assumptions - which can never be tested, it is its predictions.Lincon Ribeiro said:No, you are wrong. What I said was that the assumptions are different! If you look at how we treat all the experiments and particles / waves in quantum world, we see that space, time, energy e whatever are all different from what we knew from classical mechanics, which means, we cannot start to say that there exists a derivation from one to another, as they were talking, ever, about the same thing.
I am sorry but you are not making any sense here. The point is that the "old" theory typically has made a large number of verified predictions that are well studied enough that we know how experiments behave in a certain range - at least to within experimental uncertainty. Under the same type of conditions, the "new" theory must therefore reproduce exactly the same results up to corrections that are smaller than the experimental uncertainty. This is what it means having the "old" theory as a limiting behaviour. It has absolutely nothing to do with what "basic assumptions" have been made, just about predictions.Lincon Ribeiro said:I'm talking about how do we explain an theory evolution without wanting to find convergencies that were created just to make understanding easier.
Well, that's where we don't agree. I guess we are going nowhere here. anyway, thanks for the chat. I will think about the insights you all gave. see ya.Orodruin said:A theory is not its underlying assumptions - which can never be tested, it is its predictions.
Physics is an empirical science and what you can test are the predictions of a theory. If two theories make fundamentally different "assumptions" but give rise to the same observables, then there is no way of telling them apart and for empirical purposes the two are identical. You can never test assumptions (unless those assumptions are directly observable - but other assumptions could also lead to those testable assumptions being predictions as well).Lincon Ribeiro said:Well, that's where we don't agree. I guess we are going nowhere here. anyway, thanks for the chat. I will think about the insights you all gave. see ya.
I don't know how we separate assumptions from predictions. If I say that space-time is an entity and can be distorted, if we can't find a way to test it, the theory won't last. In my point of view the assumptions will direct affect what we are going to observe.Orodruin said:Physics is an empirical science and what you can test are the predictions of a theory. If two theories make fundamentally different "assumptions" but give rise to the same observables, then there is no way of telling them apart and for empirical purposes the two are identical. You can never test assumptions (unless those assumptions are directly observable - but other assumptions could also lead to those testable assumptions being predictions as well).
Lincon Ribeiro said:I don't know how we separate assumptions from predictions. If I say that space-time is an entity and can be distorted, if we can't find a way to test it, the theory won't last. In my point of view the assumptions will direct affect what we are going to observe.
When I started to discuss your article, my point was: If we want to explain why Newtonian Mechanics is not wrong, why do we need to use the convergence of new theories for that? that's where I do not agree, as I said on previous arguments. it makes no sense to me.
ZapperZ said:First of all, it was MY article..
Orodruin said:A theory is not its underlying assumptions - which can never be tested, it is its predictions.
By working the math. A lot of things that we may verbally or philosophically consider different are mathematically equivalent. You may think that you are drawing an important distinction between Newtonian and Relativistic mechanics, but in the v<<c limit this distinction is only in your mind and does not appear in either the math or experiment.Lincon Ribeiro said:If I say that the assumptions are: time is relative and space is Riemaniann and you say: time is absolute and space is euclidian, how can we be talking about the same theory?
The incorrect idea being addressed is that Newtonian mechanics is wrong because it has been superseded by correct theories: relativity and QM.Lincon Ribeiro said:If we want to explain why Newtonian Mechanics is not wrong, why do we need to use the convergence of new theories for that?
Orodruin said:Obviously you will not recover classical mechanics in the ultra-relativistic limit, you will recover it in the classical limit where speeds are much smaller than the speed of light.
JohnNemo said:By 'classical limit' do you mean the slow speeds for which we now regard classic physics as providing a good approximation? If so that appears to be a modern definition of 'classical'. Newton, for example, did not regard his theories as so limited.
Something all serious physicists do, but nearly no crackpot even tries. Typically because the crackpots don't even know what is known.Val28 said:I have a warning to all future Einsteins: Make sure you explain what we already know (which is now quite a lot) and your new theory recover ours in some limiting case.
Exactly, but I’m not sure this point comes out clearly in your article. To say thatZapperZ said:That’s because he didn’t know any better. WE now know the limits where it is valid.
Zz.
It doesn't "just so happen". It's a necessary feature of any theory that it looks like Newton in the classical limit because the real world looks like Newton in the classical limit. If it doesn't look like Newton it doesn't look like the real world.JohnNemo said:It just so happens that within certain limits
But that's true of relativity and quantum too. And we will always have to suspect that any future theory may be invalid outside the regime we have tested. So we can describe every theory as wrong and regard it as mere coincidence that it works. Or we can take @Orodruin's point that a theory is better regarded as its testable predictions, not its untestable assumptions, and regard it as right when those predictions are accurate to available precision.JohnNemo said:parts of his theory are mathematically correct to a very good approximation and very useful in fields of engineering.
Ibix said:It doesn't "just so happen". It's a necessary feature of any theory that it looks like Newton in the classical limit because the real world looks like Newton in the classical limit. If it doesn't look like Newton it doesn't look like the real world.