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# Were Newton's laws superseded by quantum mechanics?

2 years ago

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Kara Johnston

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Newton's laws are like rules for how big things move around, like cars and balls. They work really well for most things we see every day.

But when we look at really tiny things, like atoms and particles, we need different set of rules. These tiny things follow a set of rules called quantum mechanics. It's like a different set of instructions for how very small stuff behaves.

So, Newton's laws are still really useful for big stuff, but when we're talking about the tiniest things in the universe, we need to use quantum mechanics instead. Both sets of rules are important for understanding how everything in the world works!

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Gavin Rodger

quantum mechanics is the study of the very small and the very fast (relativistic speeds). newtons laws dictate the mechanics we expect from respectively large bodies (i.e. a 'body' of particles) moving at relativitly low speeds (non-relativistic speeds).

basically,

physics research can be split into 4 groups: small and fast (quantum mechanics); small and slow (atomic/nuclear physics); big and fast (general relativity); and big and slow (newtonic physics)

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An interesting question and the answer is all about the scale at which you are observing the world. Newton's Laws are still valid and are still used today, because they describe the world that we can see all around us. For example, a car cruising down the motorway, or a gymnast spinning round a high bar. Quantum mechanics, however, describes things that are happening on a much smaller scale, way beyond what we can see - the subatomic scale.

So, for the moment at least, we need to use both sets of theory to help us understand our world.

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Gabriel Pinheiro Sanchez

Hi Kara,

This is an interesting question. Maybe trying to reframe it would make you understand it better. You can think of Mechanics as a subfield of Physics, it deals primarily with static or moving bodies inserted into a certain space. Newton's Laws of Mechanics apply in a specific area of this subfield, that of the visible world, anything from an ant to a jet will comply to Newton's equations just fine with little to no error.

However, when we move our observed space into smaller or bigger objects, these equations, while still somewhat valid, start to break apart and return wrong results when measured experimentally. That is where quantum mechanics comes in. The equations that Dirac, Plank, among others developed, work very well for objects inside this size scale, for example an atom can have a radius of 0.1 nanometers (that's 10000000000 times smaller than a meter!), here quantum mechanics works perfectly.

Now, for an extra thought, if we go to a large scale, a whole planet for example, General and Special relativity become the standard Mechanical equations we deal with. While Newton's equations work relatively better than for quantum scales, it still does not account for many phenomena we observe with objects so massive.

TL;DR It is not a matter of superseding one another, these theories complement each other to provide a complete view of our universe and the phenomena around us. As Newton famously said “If I have seen further it is by standing on the shoulders of Giants".

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Not really. In terms of A-level Newton's Laws are fully correct for macroscopic objects-even those requiring a microscope to see-i.e persons, planets, vehicles, tiny oil drops etc. Quantum physics only applies to subatomic particles. Additionally, subatomic particles conserve momentum in the Newtonian was...

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Newton's laws remain a valid approximation that work well in everyday situations. We can still safely use our three laws of motion when doing problems about things like the motion of cars on the road.

Einstein's theory of relativity provides a more complete framework that takes into account the behaviour of objects as they approach the speed of light, and is needed for understanding how astronomical phenomena like black holes work.

Quantum mechanics provides insight into the behaviour of matter on a very small scale, and does in some sense supersede Newton's laws for the behaviour of atoms and other particles. We can't really treat atoms like billiard balls that simply bounce off each other - at a quantum scale things are different and more 'fuzzy'.

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Majd Yousof

Newton's Laws are inapplicable in atomic and subatomic scales, due to the added consideration of strong, weak and electromagnetic forces. So ultimately, at a larger scale, Newton's Laws are applicable, however on the quantum scale they aren't.

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Newton's laws of motion apply to macroscopic objects, while quantum mechanics describes the behavior of particles at the atomic and subatomic scales. They coexist and are not superseded by each other.

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Pooja Uday Naik

Newton's laws were not superseded by quantum mechanics. They hold true for classical mechanics and particles in the geometric regime. However, when we consider particles that are really small, like those of subatomic atoms, Newton's law collapses and the laws of quantum mechanics are more suited to describe the motion and behavior of these particles.

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Chidozie Kingsley Edoziem

No they weren't.

Newton's Laws were part of classical or Newtonian mechanics which was more or less the foundation and dealt with the idea or concept of large or macro bodies such as cars, buildings etc, while quantum mechanics which is more modern, came afterwards and applies to the energy and interactions of very small bodies such as at the subatomic level.

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Louis Houseman

Quantum mechanics do violate newtons laws, spesiffically his first law. However, quantum mechanics hasn't nessacarily 'superseded' newtons laws as quantum mechanics essentially describes different scales than what newtons laws describe. Newtons laws describe earthy mechanics (things that we may see and experience) quantum mechanics on the other hand deals with the extremely small, mostly they do not adress the same problems. Something that could be said to have superseded Newtons laws is relativity, (get in contact with me for a conversation about that).

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Joel Douglas-Jones

No they weren’t, Newtonian mechanics are very useful and accurate on the scales we work with generally in day to day life, Quantum mechanics on these scales produce the same answers as Newtonian mechanics, we only see large disparities between the two at the ~atomic scale

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Sidra Shuja

No. Newton's laws are used to explain our daily life while at the atomic level, they fail to explain the motion and nature of atoms and that is where quantum mechanics come in. Therefore, Newton's laws are still in use.

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Savio Antonio Vogt

No. Newton's laws are derterministic for objects in space-time that operate in everyday life. However, Quantum Mechanics describes the unseen world. It seems absurd that QM in principle, superseeds Newton's laws but, if one digs deeper, QM does make use of Newton's Laws or Newtonion Mechanics when they are 'Generalized'. Some examples are Hamiltonion, Lagrangian, and Routhinian Mechanics. Hope this answers your question.

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Ryan Barwell

For most purposes both Newton's laws and quantum mechanics are valid explanations for how systems behave, however it's best to think of the quantum scale world and the sort of scale we recognise and see on larger scales as different things. Newton's laws were discovered way before the advent of quantum mechanics, this does not mean that they were superceded though, they just solve decrepancies in the quantum world that newton's laws might not not predict. The major thing that separates the laws of motions and quantum mechanics is that newton's laws are deterministic, this means that when the same conditions are given, the same output will be given. Quantum mechanics is probablistic, if you observe a particle in could be in a different place each time you observe it. Either way they're both correct but when applied to different frames of reference

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