# Sorry for my question

abdullahbameh
when can we stop using classical mechanics and turn to QUANTUM MECHANICS AND RELATIVTY instead of classical and if not why?!

i am in lovewith the result of quantum and relativity and i feel that classical is good but less accurately and it is for the old days

may be your question will be to me why i don't like classical the answer is because classical is having too much mathematics and calculation and less accurate results as we live in the universe

Staff Emeritus
Gold Member
may be your question will be to me why i don't like classical the answer is because classical is having too much mathematics and calculation and less accurate results as we live in the universe
Wait, you think that classical physics has too much mathematics? Do you think classical physics has more mathematics that Quantum Mechanics or General Relativity?

Classical physics is a very good approximation for most 'everyday' uses, i.e. moving at non-relativistic speeds in flat space time with macroscopic bodies at standard temperatures, why should we over complicate calculations or models for every day uses when we obtain sufficiently accurate solutions from significantly simpler models?

Last edited:
abdullahbameh
my answer is general relativtey and quantuam mechanics is having more maths than classical but the value of rightness can be hundred thousands of decimals but under the classical we do not take all the hidden variables so it is left incompleted job so what is the use of solving

indr0008
because in everyday use, do we need that accuracy at all?

Staff Emeritus
Gold Member
my answer is general relativtey and quantuam mechanics is having more maths than classical but the value of rightness can be hundred thousands of decimals but under the classical we do not take all the hidden variables so it is left incompleted job so what is the use of solving
Refer to my previous post,
Classical physics is a very good approximation for most 'everyday' uses, i.e. moving at non-relativistic speeds in flat space time with macroscopic bodies at standard temperatures, why should we over complicate calculations or models for every day uses when we obtain sufficiently accurate solutions from significantly simpler models?
Furthermore, I'd be interested to know if you've ever come across a Quantum Mechanical description of fluid mechanics, say a turbulent flow in a pipe? Or the motion of a rigid body? The answer is of course no, because it is far too complicated and unnecessary to find a Quantum mechanical description of such phenomena. Furthermore, for most application classical physics describes the phenomena we observe as accurately as we measure.

Edit: There's no need to apologise for asking a question, that's what we're all here for

Last edited:
Feldoh
Because in real life, you can have a certain percent error in things. Normally we're not moving close to the speed of light, in super hot/cold areas, or dealing with microscopic objects.

Because we are not dealing with this constraints the accepted amount of percent error is large enough that it doesn't require us to use quantum or relativity. In some cases as Hootenanny stated, it would be pretty much impossible to model the situation using quantum mechanics.

You say you don't like classical physics because of the math, and yet quantum and relativity math is even harder.

Poop-Loops
The ratio of benefit vs. work involved is too small. Meaning, it takes a LOT of work to calculate any real system using General Relativity or Quantum Mechanics, but the accuracy you get from it will not be used in daily life.

One of the most important skills a physicist needs is the ability to know when and how to use an approximation.

Homework Helper
Gold Member
because in everyday use, do we need that accuracy at all?

Exactly. All physical theories have a range of validity in which they work. Some theories have larger ranges than others, but that does not mean the others are not useful.

Classical mechanics is valid for situations we deal with in everyday life. Theoretically, quantum mechanics would give a correct answer to any classical situation, but the answers would not be noticeably different. Thus, we use the theory that is more easier and practical to use, which, in this case, is classical mechanics.

NeoDevin
Probably the best answer to your question is to simply suggest that you try to work out the behaviour of a mass on the end of a spring, from quantum mechanics. Take into account all the inter-atomic forces, and the wave function of each particle. Don't forget that some/all of the particles may be entangled as well. When you finish this, let me know.

abdullahbameh
ok i can except that classical is very perfect to ous daily life but what i concluded that we use classical mechanics for our daily life and quantum mechanics for macroscopis world because classical mechanics does not have any validity in the macroscopic world but i still see in some macroscopic phenomenas we still use classical mechanics to explain it or to get its equations like effective mass in the conductor during the time of conductivity m* we explaine it by using F=ma ! how is this possible and we are dealing with macroscopic world where classical mechanics failed that means what

indr0008
i don't quite understand the effective mass part, but in the classical mechanic we picture things as a whole and quantitatively, don't know how to explain it...

it is just about what gains what magnitude of force

Feldoh
like effective mass in the conductor during the time of conductivity m* we explaine it by using F=ma !

Huh?