# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: annie123 on 05/02/2012 19:26:53

Title: How can Newtonian mechanics and quantum mechanics coexist?
Post by: annie123 on 05/02/2012 19:26:53
Can anyone explain to a layman why the Newtonian view of the world - laws etc.- still work n an everyday level when quantum discoveries/theories show that things work quite differently and sometimes contrarily at the quantum level?
Title: Re: Newton versus Bohr
Post by: Geezer on 06/02/2012 03:27:58
What! Are you trying to put all the scientists out of a job?

I'm not really qualified to answer this, but I don't think there is any dividing line. The quantum level is not about absolutes. It's about probabilities. As you move towards a larger scale, those probabilities create the illusion of absolutes, and, at some point, the probabilities are so constrained that they might as well be absolutes.
Title: Re: Newton versus Bohr
Post by: Soul Surfer on 06/02/2012 08:37:09
It is simply that the Newtonian view is an excellent approximation of what things are like for the precisions and velocities involved in everyday life.  Relativity and quantum effects are only corrections for this view when you look at things in a great deal more detail precision and under extreme conditions.

It annoys me greatly when people and textbooks say that Newton was wrong, the later discoveries just proved him to be almost right, they just added corrections to the model.
Title: Re: Newton versus Bohr
Post by: JP on 06/02/2012 13:12:04
I'm not really qualified to answer this, but I don't think there is any dividing line. The quantum level is not about absolutes. It's about probabilities. As you move towards a larger scale, those probabilities create the illusion of absolutes, and, at some point, the probabilities are so constrained that they might as well be absolutes.

Exactly right.  It's impossible to generalize to all cases, but for most cases quantum effects are very very very small.  When we look at everyday objects, they're big.  They also consist of many particles.  Averaging out tiny quantum effects over large sizes and over billions and billions of particles makes the total quantum effect too tiny to notice with in everyday life.
Title: Re: Newton versus Bohr
Post by: annie123 on 06/02/2012 21:16:22
Thanks for the input. But when I read that things can exist as a wave or a particle, and that what things are is influenced by whether they are being observed or not, (and the cat thought expt. didn't help much) this doesn't help when I'm in a plane and think is this a collection of particles that could change into a lot of waves? And what about entanglement? If this can happen to a quantum particle why not to a collection of them?
Title: Re: Newton versus Bohr
Post by: Geezer on 06/02/2012 22:07:53
I think one of those cats gets into my drier and entangles my socks with my shorts.
Title: Re: Newton versus Bohr
Post by: Soul Surfer on 06/02/2012 22:12:35
Everything is particles AND waves all the time and there is nothing weird about it because stuff just behaves the way it does.  What we know about it has no effect on everyday life and the way things behave.  For big things the waves are so tiny that you never really see them.  As for the observation.  It does not have to be a person that makes this observation.  One particle can "observe" another just by bumping into it and this is happening for the atoms all around us millions of times every second.
Title: Re: Newton versus Bohr
Post by: wolfekeeper on 08/02/2012 07:39:24
Can anyone explain to a layman why the Newtonian view of the world - laws etc.- still work n an everyday level when quantum discoveries/theories show that things work quite differently and sometimes contrarily at the quantum level?
This has no completely agreed upon answer on this.

To some extent, the answer is that a lot of the time, the different things that can happen don't make any difference to what happens in the end, and then the quantum effects (which are sometimes described as being in different universes) join back up (we can see the joining back together again in many quantum mechanical experiments).

But in some cases the effect of the different things that can happen get multiplied up (the classic being Schroedinger's cat) and then the cat dies (and you get very sad) or it lives. Then the universe (possibly) splits into two at least locally, and the effects of that dead/live cat spread out through every transaction that that matters for. However, whether that dead or live cat matters to an alien on alpha centauri or not or even the other side of the Earth in most cases- probably not, so the quantum 'ripples' stop spreading at some point, the split universe thing really only happens locally.

And make no mistake, quantum mechanics really matters and has observable consequences, whether you're looking at laser diffraction patterns or superconductive levitation or simply using a computer (transistors work by quantum mechanics) it really does make a big difference to the real world, we don't live in a Newtonian world.
Title: Re: Newton versus Bohr
Post by: syhprum on 08/02/2012 12:07:20
Do transistors really require quantum mechanics to describe their operation, please give some references.
Title: Re: Newton versus Bohr
Post by: wolfekeeper on 08/02/2012 15:01:43
Yeah, Solid-state physics

http://en.wikipedia.org/wiki/Solid-state_physics

Basically the flow of electrons and holes in transistors and semiconductors came out of research into quantum mechanics applied to crystalline matrixes like silicon. (I think they were trying to work out how cat's whiskers worked, and why they weren't very reliable, which lead to study of doping of crystal structures which was then analysed using QM theory, and this lead directly to transistors.)
Title: Re: How are Newtonian physics and Einstein's theories different?
Post by: annie123 on 10/02/2012 05:00:35
Hello
Thanks for more replies. But I do ask why the topic title was changed. Hasn't the change made a difference to the meaning? EInsteins theories and Bohrs - I didn't think they were the same.
Anyway, another reason i asked is because in the discussion about teleportation I have read here and there a particle can be reconstituted in a completely different place, annihilated at point of origin, and I heard on the infinite Monkey show (another science podcast) that there is no reason in theory why a package of particles can't do this. But Newton's schemata  wouldn't support this.
And if something can be a wave and a particle at the same time (is this the twin slits experiment?) how can anything remain solid and relied upon to stay so?
Title: Re: How are Newtonian physics and Einstein's theories different?
Post by: imatfaal on 10/02/2012 10:26:41
Hi Annie - I guess the title was changed because for many people Bohr is associated with his model of the atom (http://en.wikipedia.org/wiki/Bohr_model) and the "old form (http://en.wikipedia.org/wiki/Old_quantum_theory)" of quantum theory which are a bit outdated.   I think newtonian v quantum is the best way to describe the differences - its very wooly but most people will get the idea that it is the difference between the deterministic "pseudo-clockwork" world and the stochastic random ideas of quantum mechanics.  This is the same difference as classical and non-classical physics.  Not really sure about using Einstein as a name for the non-deterministic side of physics - he never really settled with that, although his work on photoelectric effect was massively important

On your two questions - there is no reason that the bunch of particles shouldn't move, but it is mindbogglingly unlikely that they will.  I seem to remember on IMC they were also talking about recreation of particles with the same properties (and as fundamental particles are completely alike this basically amounts to teleportation) - my worry in this would be the necessary uncertainty through heisenburg.  The double slit experiment does show the wave characteristics of light - and it still works when using individual particulate photons - which shows the duality.  Things remain everyday normal and solid because the probability for them to do so is so overwhelmingly high
Title: Re: How are Newtonian physics and quantum mechanics different?
Post by: JP on 10/02/2012 23:44:38
Hi Annie,

I see my earlier post didn't take.  I think you're right about the post title--it shouldn't be Newton vs. Einstein, so I changed it to Newton vs. quantum mechanics.  Einstein's most famous theories were relativity (special and general) which are still called classical theories because they don't involve quantum mechanics.  While Bohr was one of the founders of modern quantum mechanics, he was just one of many involved in working out the theory, so its probably most accurate to say Newton vs. quantum rather than Newton vs. Bohr, which is what I've done.
Title: Re: How are Newtonian physics and quantum mechanics different?
Post by: annie123 on 11/02/2012 20:14:57
HI
I'm not sure the new title is any better. I know how the theories are different. I wanted to know how they can coexist since they often seem to contradict each other.
Title: Re: How are Newtonian physics and quantum mechanics different?
Post by: JP on 11/02/2012 21:30:16
HI
I'm not sure the new title is any better. I know how the theories are different. I wanted to know how they can coexist since they often seem to contradict each other.

I think this is a case of the moderators trying to clear it up and ending up mucking it up.  I'll change it to "How can Newtonian mechanics and quantum mechanics coexist?"  If you can think of a better title, go ahead and change it, if you can edit your first post.  If not, shoot me a PM and I'll change it for you.

(I didn't make the original edit--Chris did--so I can't speak to his motivations.  However, using the term Newtonian mechanics is pretty clear, but Bohr's theories aren't really synonymous with modern quantum theory, so I kept his name out of both my edits.  :p )
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: imatfaal on 14/02/2012 12:32:54
HI
I'm not sure the new title is any better. I know how the theories are different. I wanted to know how they can coexist since they often seem to contradict each other.

They do contradict each other to an extent - but we know in what realms to use one and where to use the other.  These theories are all models - and a useful way to think of them is as analytical toolboxes.  They are not final descriptions of underlying reality - they are mathematical models that allow us to predict outcomes and explain behaviour.

When you want to calculate where a field gun shell will land you use Newtonian mechanics.  To plot the course of a satellite you use Newtonian mechanics with a few modifications (and bear in mind the time dilations from einstein's relativity) - or at least you used to, maybe they use more Einstein than Newton now.  To calculate a planetary orbit to max precision you use General Relativity.  These are all classical theories - so which is right and which is wrong; the answer is neither really - they are varying toolboxes with strengths and weaknesses.  GR is most precise and most unwieldy, Newtonian mechanics is less precise (although pretty amazing) but is usable without an extra brain.

Your question of classical physics v quantum mechanics is similar.  On the very small scale QM is a much better model for predicting the outcome of experiments - but it rapidly becomes impossible to use when dealing with more complex systems.

QM does make some underpinning claims that are completely at odds with classical physics - the ultimately stochastic/random nature of nature, the fact that some(all) quantities are quantised (ie come in small lumps), the uncertainty principle etc; but when we are doing a job we can ignore the philosophical problems and use the kit that will best give us an answer.  The theoretical physicists though are massively concerned with trying to pull all the strands together - in reality it means getting gravity to fit into a quantum model (not the other way around).  To an extent a very famous way this is being attempted exemplifies the model/toolbox idea - this is string theory; rather than work piecemeal, this is an attempt to set up an overarching framework of maths and modelling that could possibly explain many differing areas of physics, make it mathematical self-consistent and ONLY THEN see if we can get it to work in the real world.

Its complicated and fascinating - in the end you choose the best tool for the job and try not to worry about theoretical problems
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: annie123 on 18/02/2012 23:09:56
Thanks imatfaal. I guess without the training in theoretical physics and the math. brain of a Feynman  the lowly plebs don't have much chance of really getting a handle on all this. But it is frustrating to get a glimpse of the implications of the different theories and not be able to relate them to the realities of daily life. IN the end, who will know what reality is? Only a very few highly evolved packets of grey matter? Seems rather hard on most of the human race.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: yor_on on 18/02/2012 23:19:58
See them as evolving, like building a stair. Newtons definitions works very well on earth although becomes modified at relativistic speeds. The biggest difference is the one about time, Newton saw time as a unchanging river same for all. Einstein introduced 'frames of reference' that, when compared to each other, delivered different 'clock beats'. But from a strictly local 'frame of reference', meaning the one that we all have relative our local clocks (wrist watch) time never change its pace. so Newton can, with some modification, be said to have got that one right too :) Although it now becomes a result of the fact of lights unvarying speed in a vacuum, no matter what 'frame of reference' you measure that speed from.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: yor_on on 18/02/2012 23:31:54
As for QM versus Newton?

That's a big jump, Newton looked at macroscopic phenomena, and light of course :) QM has a very different outlook on how macroscopic phenomena comes to be, which still is a hypothesis. We do not know how the microscopic transits into macroscopic phenomena.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 19/02/2012 01:03:34
Thanks for the input. But when I read that things can exist as a wave or a particle,
Not really... things are both a wave and a particle. And not really A wave, more like every possible wave, simultaneously.

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and that what things are is influenced by whether they are being observed or not, (and the cat thought expt. didn't help much)
No, not according to whether they are observed, unless you include the particles (which are waves/particles) observing each other.

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this doesn't help when I'm in a plane and think is this a collection of particles that could change into a lot of waves?
The best I can explain it, it's kinda like a sea wave made up of lots of ripples and swirls all sloshing along, it's all waves all the time. Each wave represents all possible positions and movements, of the particle, which varies bearing in mind the positions and movements of all the other particles that have interacted with it.

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And what about entanglement? If this can happen to a quantum particle why not to a collection of them?
Yup. It can. That's what the Schroedinger's cat is, the cat ends up entangled with the radioactive decay event (and dies) AND doesn't, and lives, and then when you open the box, so do you get entangled with the dead moggie/radioactive decayed or live moggie/no radioactive decay.

The thing is, once the different waves have deviated enough, you've got no access to the opposite state, you either have a dead cat, or a live cat; the only way you could see the other one is if these two universes interacted in some way, but they're actually too far apart in quantum mechanics terms to do that, whereas the dual slit experiment, the two different universes can join back together so you can see the join from the interference fringes.

The thing is, Schroedinger's cat isn't a theoretical thing, it happens all the time, if you listen to a geiger counter, it's happening to you.

But the waves still, more or less obey Newton, because the ensemble of particles follow Fermat's principle, which pretty much explains things like momentum, so things take the quickest way from a->b in most situations, given their initial speed, so Newton's laws pretty much fall out.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: annie123 on 21/02/2012 01:12:56
Curiouser and curiouser and through a glass darkly etc etc. My comment remains - re the average /reasonably educated person has no chance of ever making sense of it all and only the very favoured few are able to get even a glimpse of what it's all about. The Jest of God . . .(not that I believe in him/her . . .) I wonder sometimes how the elite physicist can even function in an everyday life, eating his cornflakes and taking out the garbage when reality is ....well, only they know. Thanks everyone anyway for trying . . .
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: Geezer on 21/02/2012 02:41:21

My comment remains - re the average /reasonably educated person has no chance of ever making sense of it all and only the very favoured few are able to get even a glimpse of what it's all about.

Annie,

I don't think that's true at all. It's simply about preconceived ideas.

Most people are smart enough to understand that preconceived ideas are very often completely wrong. You don't need to have a pointy head to get a grip on the basics of quantum mechanics. It's certainly all counter-intuitive, but our inate intuition is entirely limited by the resolution of our senses. They are simply not designed to let us detect the quantum level.

What I think is remarkable is that humans have been able to create a set of extended senses that allow us to observe what's really going on "behind the scenes", and we are nowhere near done yet!
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: yor_on on 22/02/2012 16:00:31
Most things in life are 'through a glass darkly' Annie :)
Subtly altered as you learn new things and become experienced. And I think that goes for everything, from emotions and relations to physics.
Physics is about how and why we exist at all. It's our try for making some sense out of it. And I doubt that you will find anyone that never wondered about that.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: JP on 23/02/2012 14:26:31
Physics is about how and why we exist at all. It's our try for making some sense out of it.

I disagree.  Physics is about coming up with scientific models to describe nature.  It might happen to answer questions about how and why we exist along the way, but directly answering questions about how and why we exist is more in the realm of metaphysics or religion.  One of the reason questions like this one come up (why are Newton's laws still around if we have quantum mechanics?) is that there's a misconception that physics is about answering fundamental questions, which would require throwing out all previous models when a more fundamental one comes along.  But the aim of physics is to provide useful models, so we keep and use Newton's laws because they work well for many problems, even though we know that quantum mechanics is more fundamental.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 23/02/2012 15:41:00
I wonder sometimes how the elite physicist can even function in an everyday life, eating his cornflakes and taking out the garbage when reality is ....well, only they know. Thanks everyone anyway for trying . . .
Pretty much like this:

Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: Soul Surfer on 26/02/2012 10:09:16
Please do not give up Annie most of it is quite understandable by ordinary people it is just that some scientists like to enhance the air of mystery by choosing extreme examples ant putting them into the context of normal life.  For example from your replies you seem to think of waves as insubstantial things that are liable to fly off in all directions unheeded and particles as nice solid lumps that stick together and give solidity to materials.  the real point is that as I said earlier everything is all waves and particles all the time it is just the way you look at it that creates the difference.

Firstly let me clear up one important fact whatever people tell you the cup you are drinking your coffee from is going to stay being a cup for as long as you want it and not fly apart as a load of waves and drop the coffee in your lap (that is unless you drop the cup :)).  Physical laws stay the same as far as we are concerned.

Next about waves and particles.  We are all very familiar with electromagnetic waves.  These are in order of longest wavelength and lowest frequencies  Radio waves, microwaves,  infra red, visible light, ultra violet light, x rays, and gamma rays.

They are all exactly the same thing electric and magnetic fields oscillating and there is a continuous spectrum right from the lowest frequencies  the longest waves that is radio waves (remember long wave radio 1500 metres or fm radio 100 Megacycles that's about 3 metres )  right through the mid range of heat radiation which is measured in micrometers to gamma radiation where the waves can be less than the size of an atom.  The shorter the wave the easier it is to think of it as a particle however it is quite possible to measure radio waves as particles a good example is the 21cm wavelength radiation emitted by cold hydrogen atoms in the depths of space.  on the other hand the gamma rays are almost always thought of as particles but Mossbauer spectrometer measures them as waves to make incredibly precise measurements.

Now the wavelength of electrons protons and atoms involves more fields than just the electromagnetic but their wavelengths are very short so it is much easier to think if them as particles however with very low temperature and precise measurements it is quite possible to observe them as waves.  This does not in any way change the properties of things.

one of the problems nowadays there is so much science fantasy and so much very realistic computer generated graphics that it is possible to create images of anything happening quite easily.  This tends to cause some people to loose their grip on reality and start to think that the laws of physics can be bent and changed. This is just not true in our environment.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 26/02/2012 11:31:55
Curiouser and curiouser and through a glass darkly etc etc. My comment remains - re the average /reasonably educated person has no chance of ever making sense of it all and only the very favoured few are able to get even a glimpse of what it's all about. The Jest of God . . .(not that I believe in him/her . . .)
I suspect that that's true of practically everything. If you go along to watch a complex play at the theatre, you might think you understand it, but there may actually be a hidden meaning that is really what the play is really about. Or there may be bits which you didn't quite get but that didn't change the overall plot so you didn't bother about it, that an expert would know.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: Geezer on 26/02/2012 18:47:54
A frequent question is "yes, but why does it work that way?" Unfortunately, Science is more focused on "what it does" in ever greater levels of detail, and the greater the detail, the weirder it seems.

QM is a really strange subject, and at some point I suppose you just have to accept "what it does" and run with it. That's why the people that work in this field are called quantum mechanics!! (footsteps running towards exit)

I think it's time for one of JP's favs

Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: annie123 on 26/02/2012 18:59:44
Yes, I've watched a lot of Feynman's videos and read the bio by L Krauss. And I agree that one doesn't have to be a genius to have a glimpse of what's going on when geniuses have helped to open the windows, but it's frustrating to know that reality is 'so hard to know' as Feynman puts it even at a basic level because so many people don't have the time or resources to even touch on the edge of it all. And quantum theories may be superceded or improved upon in the coming centuries (if we survive or for whatever survives). I know this is starting to get philosophical in terms of human purpose/satisfaction/self knowledge etc. so i won't go on. But despite knowing I'm hardly skimming the surface somehow it's still more exciting than most other things out there, and I guess I'm lucky to have 'the time and resources' to look at these things.I just think it seems rather sad that so many people don't have the opportunity to even start looking.Thanks  to all contributors.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: greeniemax on 27/02/2012 10:45:14
Newtonian physics works on macro level and QM works on Quantum level, when you look at the world everything is logical and makes perfect sense, everything seems perfectly normal. When we look at Quantum level everything is weird and doesn't make logical sense, logic dies out.

1. Physicist say you other lay people are too stupid to understand what is being talked about, you have to learn high level math and it gives right answers...
2. Lay people say or people with little knowledge that it doesn't make sense, it could be all wrong if its not making sense.
3. Totally lay people don't even care because it doesn't bother them.

Everything though is fine till the point we think that where does it all change? When you talk about single atom does the law change or is it when you talk about multiple atoms? What happens when the laws change, this middle level actually has balanced laws something between two laws or is the change abrupt? Does this change over layer has its own law, in case it does how many layers are there?

The whole "science" we have today is based on "say" of few people, even if direction seems wrong same laws are followed without bothering about where we are heading or looking at alternative root, it doesn't matter just keep walking as long as you get answers right even if it involves 100 different constants.

People say "we are going the wrong way", scientist say "we study, this is why we know that we are going the right way" and still others don't care.

But a person who studies is better than a person who doesn't even though it doesn't apply to church but what the heck.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 11:44:38
Newtonian physics works on macro level and QM works on Quantum level, when you look at the world everything is logical and makes perfect sense, everything seems perfectly normal. When we look at Quantum level everything is weird and doesn't make logical sense, logic dies out.
I don't know if any physicist has ever said that, only that everyday intuitions about how things are aren't much use.

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1. Physicist say you other lay people are too stupid to understand what is being talked about, you have to learn high level math and it gives right answers...
It's not a question of stupidity, it's just a question of them not having studied it, and looked at the experiments.

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Everything though is fine till the point we think that where does it all change? When you talk about single atom does the law change or is it when you talk about multiple atoms? What happens when the laws change, this middle level actually has balanced laws something between two laws or is the change abrupt? Does this change over layer has its own law, in case it does how many layers are there?
The many worlds theory (which Hawking says is 'trivially true' if quantum mechanics applies to the universe) doesn't seem to require any other layers; I'm not saying that there aren't any other layers, but we don't seem to need them, based on the experiments to date.

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The whole "science" we have today is based on "say" of few people, even if direction seems wrong same laws are followed without bothering about where we are heading or looking at alternative root, it doesn't matter just keep walking as long as you get answers right even if it involves 100 different constants.

People say "we are going the wrong way", scientist say "we study, this is why we know that we are going the right way" and still others don't care.
There is no particular direction that scientists are going on; they just follow the clues they find, given by nature, and that takes them in particular directions with their theories; determined by nature. The whole point of science is to work out what nature is doing.

Scientists don't get to decide how nature works!!!
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: greeniemax on 27/02/2012 12:32:01
I think that I can safely say that nobody understands quantum mechanics.
The character of physical law (Cambridge, USA, 1967) - Richard Feynman

If you claim you understand QM than seriously one of you is wrong, QM is something you can't understand its not logical, people who claim its logical should be simply asked to explain entanglement, with logic.

String theory with 10 different ways to look at the world with 10 different formulation of same mathematical theory, logical?

I would personally love to understand QM, yes GR is simple and it is logical can be understood but QM please.

I would like to know what was expertise of Newton before he created Calculus and Formulation for Gravity? What was expertise of Galileo? I agree study of any subject is important but if you walk with rules that were given to you, you can never think out of the box because you automatically assume that rules given to you are correct. Lots of people give lots of weird theory that doesn't make sense but they can think out of the box for sure, unlike scientist.

So if there is no layer than where do the laws change? Where does the light was wave becomes photons? That is what I mean by layers, when the laws change from macro to micro where it happens? Does these law work for 1 atom, 2 atoms, 10 atoms or billion atoms? Maybe I'm bad at making my point clear but the laws have to change at some point, what is that point, do laws change abruptly or is there a middle layer of laws? I hope you understood what I'm trying to say.

Science considers whatever explained before as perfect flawless theories, no one has poked his nose to explain photo electric effect and keep light as waves, but science simply changed its understanding of elementary particles and take word of Albert Einstein for light to be photons even though that doesn't work in macro environment, because we can clearly see Doppler shift in light we never bother say how could color of a release photon change but we simply say it got elongated, how? No one bothers. Its a problem when we take older theories for their word of mouth values and try to apply them to current experiments, we don't know what's going on so it doesn't matter where we fit the results.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 13:41:05
What does understand mean?

Did Newton understand his theory of gravity?

I mean his theory involved action at a distance. How did that work?

Now it's understood in terms of theory of curved space. How does space work?

I'm sure entanglement will be eventually understood in terms of simpler things, but just because we have entanglement that we don't understand in simpler terms, doesn't mean we don't understand quantum mechanics, or if we don't, Newton didn't understand gravity either.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: greeniemax on 27/02/2012 14:03:09
I'm sure action at a distance is hard to understand if you think deeper because we "still" have no clue about it, we could say "gluons" are responsible for it but we still have no mechanism to say this is how it works.

We could say space-time is responsible for gravity but its something that would confuse the person at first but if you try to understand it, its not a problem its totally explainable, it gives reasons for why we feel gravity, why light bends and why planets have the orbits they do, but almost everything in quantum mechanics don't have any explanation of why they behave the way its does. For instance what produces light? What's the actual working mechanism behind it? Why less dense objects rise?

These things might be explained in QM but wouldn't make logical sense.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 14:42:18
On the contrary, QM is perfectly logical, you just start with the right axioms, and you can derive the theory from it.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: greeniemax on 27/02/2012 16:04:11
I'll give it another shot, I mean simple things like light doesn't make any sense in Young's Double slit experiment, when light behave's like particle it interfere with itself, which is impossible but if you put detector on slits you find them going through single slit.

The problem can't be solved logically, but if you accept these things as result it's perfectly fine and go ahead with the problem.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 16:19:57
It can and is resolved logically, you just have to start with the right axioms.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 16:31:25
I mean, for example the idea that a light particle only goes through one slit is obviously wrong.

Feynman says that light particle behaves as if it goes ALL ways from the emitter to the receiver, including apparently crazy ways like going above the screen in a curve, and spiralling around in big arcs, and going completely the wrong way, and then coming back again... it's just that most of those crazy ways tend to cancel out, and he suggested a physically plausible way of adding them all up which gives the right answers; the photon carries a spinny thing that spins at a constant rate (depending on its frequency), and to add up all the routes you just add the spinny things together.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: JP on 27/02/2012 17:31:18
The double slit experiment brings it back to your earlier point, wolfekeeper: what does it mean to "understand" the physics?  I think Annie's confusion comes down to the basic problem of having an intuitive grasp on the physics based on our life experiences.  I can watch objects move about under Newton's laws and I feel gravity everyday.  Even if I don't study Newtonian mechanics exhaustively, I can get understand what its models are saying intuitively from these experiences.

But even in the simple two-slit experiment, the particle behaves like a wave and goes through both slits at once.  Even though we can intuitively understand waves and particles as separate things, we have no intuitive framework to understand something that can be both at once.  What physics training really gets you in this case is a very good understanding of the model, rather than an intuitive understanding of what quantum particles are.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: wolfekeeper on 27/02/2012 17:43:14
I don't think Newtonian mechanics was even that intuitive, I mean, how many thousand years did mankind take to come up with it?

It's only intuitive to us because we were all trained in it as children. It wouldn't surprise me if we didn't start training school children in a qualitative understanding of QM eventually, and then it won't seem nearly so weird.

you know like: there's waves, there's particles, there's waveparticles!!! and all the kids will go: OK

I mean they won't completely get it, they probably don't completely get waves either, but it will break it to them gently, and when they do need to know it, it will have had longer to settle in.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: yor_on on 27/02/2012 23:56:36
I lean towards JP:s view. A good understanding of the model is foremost, and that never seems to end, does it? :)

As for the rest, I think everyone 'knew' about gravity even if the mathematics describing it was Newtons. Even babies can differ between a normal fall and a fall/curve that is 'wrong'. They've tested this with a white board using magnets and then letting them 'fall' correctly, versus using a magnet behind the board influence the object in front to take a 'wrong' course/curve. The way they measured was by measuring the babies eye movements, and see their movement to the 'right position' for a 'fall', versus the 'wrong' curve/fall that magnetic object in fact did
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: greeniemax on 28/02/2012 04:23:44
Wolfekeeper doesn't it ever occurred to you that we really need a different description of something that isn't explainable? You said that if children are taught QM they would simply say yes, but what if QM is wrong? What if there is no double state of Photon, electrons or atoms?

Still it doesn't matter if children say "OK"?

This is exactly what happens to people who go and study QM, even if they don't get it they say "OK", because if Feynman couldn't get it I'm sure others who say "We get it" are either lying or are totally lost. Its also a problem of society if a person is physicist and he/she says QM doesn't make sense than everyone in the Scientific society will attack that person, he/she would be considered dumb and stupid.

Maybe QM is right but scientist aren't even ready to look at other approaches where Quantum duality doesn't have to exist, no one want to risk explaining Photo Electric Effect in wave, because everything underneath will change and has to be change to understand another model.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: zmth on 16/07/2018 02:29:44
In the limit of large quantum numbers it will lead to the classical result. Simply put it's solution will agree with the classical for those subjects in which the classical theory is a good enough approximation. Nothing bizarre about it.
Title: Re: How can Newtonian mechanics and quantum mechanics coexist?
Post by: PmbPhy on 17/07/2018 02:43:31
Can anyone explain to a layman why the Newtonian view of the world - laws etc.- still work n an everyday level when quantum discoveries/theories show that things work quite differently and sometimes contrarily at the quantum level?
There's an analogy which I like to use. I ask the question "Is this table flat?" and to all of my senses and the best mechanical equipment and optical microscopes tells me that it is. However there are ()in principle) other ways of looking at the surface of a table and that's with a scanning tunneling electron microscope. That is so accurate that what you see on the viewing monitor is a bunch of atoms making the surface bumpy and "seeing a bunch of atoms" has a whole different meaning now.