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I was reading "The holographic universe" by Michael Talbot and it said that most scientists believe, and there is proof of the fact that an electron is only a particle when we are observing it. Now, when an electron is zooming around an atom it is not being observed (Usually) So an electron on, say, the couch I am sitting on should be a wave instead of a particle, but we are taught from a young age that an electron is a particle zooming around the nucleous of an atom. So why is an electron in an atom a particle and not a wave?

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    $\begingroup$ Quantum objects aren't "waves" or "particles", they're quantum states. Thus, this question isn't really meaningful. See also e.g. Is the wave-particle duality a real duality? $\endgroup$ – ACuriousMind Jul 9 '15 at 20:31
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    $\begingroup$ @ACuriousMind funny how although this question "isn't really meaningful" it's also one of the most interesting questions in physics and one of the most often asked and closed, despite the lack of any really good answers to it :-) $\endgroup$ – DanielSank Jul 9 '15 at 21:10
  • $\begingroup$ Someone should write a really good explanation of the experimental reasons we sometimes think of electrons as particles and sometimes as waves, and then discuss the role of measurement, entanglement, and decoherence in the transition from wave-like to particle-like behavior. Wouldn't that be nice... $\endgroup$ – DanielSank Jul 9 '15 at 21:11
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    $\begingroup$ @DanielSank: are you volunteering yourself? $\endgroup$ – Kyle Kanos Jul 9 '15 at 22:53
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    $\begingroup$ Don't close as unclear. The OP is basically asking why we concentionally treat fermions as particles (and implicitly we we conventionally treat gauge bosons as waves - well, photons as waves :-). That is, why do electrons appear particle like more often than they appear wave like? $\endgroup$ – John Rennie Jul 10 '15 at 5:24
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In quantum mechanics, things are not "particles" or "waves" - they may behave like both, or like neither. But a quantum object "is" neither of those - it is a quantum state, usually described as a vector in a Hilbert space.

The Bohr model of the electron orbiting the atom is false (for one inconsistency, that of moving charges classically radiating, see this question) - there is no orbiting in the classical sense going on at this scale.

Quantum objects don't really "become particles" when we observe them, but they are forced into a state that is sharply localized, usually, and this is what we intuitively would call a particle - a small blob with a more or less definite position in space.

Conversely, their wave-like characteristics are more pronounced when their position is not definite, but rather their momentum (by the uncertainty relations, these two states are mutually exclusive at scales where $\hbar$ is large).

It is very difficult to cast the classical concepts of "wave" and "particle" into precise enough terms to discuss them in quantum mechanical settings, and it doesn't help that there is no consensus about the measurement problem. The quote you read that "an electron is only a particle when we are observing it" is probably meant to mean that most of our measurement procedures force the electron into a sharply localized state, but that "usually", i.e. for instance when undisturbed in an atom, it is in a very smeared out state, an atomic orbital, and has no position to speak of (and hence can't be talked about as a classical particle).

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    $\begingroup$ Good way to answer this. I will add that if you look at the electron in the ground state of a Hydrogen atom, it has $\ell = 0$ hence $\langle L^2\rangle = {\hbar}^2 \ell(\ell+1) = 0$; it's not "orbiting" at all in the conventional sense and its only angular-momentum is spin-angular-momentum: so the inconsistency with the classical picture can at times be 100%. $\endgroup$ – CR Drost Jul 10 '15 at 19:57
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Who says electrons are not waves in the atom?

Discard your bygone, quaint, outdated, perplexing, stupifying, nonsense idea that electrons move in a solar-system sort of orbits. That model(attributed to Rutherford) was an attempt to understand the atomic arena of Nature; unfortunately it was far from being correct as it had many in-built flaws.

Then the age of Quantum Mechanics began. That ushered in a new perspective to look at the phenomenon at the atomic scale which not at all follow classical determinism.

Everything at the quantum level is ruled by probability-uncertainty. The probability is not due to our ignorance but it is rather fundamental. The matter of irony is that despite being deterministic, classical physics is but approximation of Quantum Mechanics(see complementarity Principle).

Caution:Electrons are not waves.

They do, however, behave as wave. Waves of what? Waves of probability. These waves are described by $\Psi(x,y,z,t)$, a complex-function known as wavefunction. It tells you all the possible states the electron may be at now. Since there is uncertainty in the present, we cannot predict the future by certainty. This wave is spread in the whole space. The probability of finding the electron at a certain point at a certain time is the square of the amplitude of the wavefunction there i.e. $\Psi\cdot \Psi^*$, where $\Psi^*$ is the complex conjugate.

Caution: There is a huge difference between the probability of the event & the event itself; Probability wave of electron doesn't mean that it is smeared throughout the space; it can be at any place but we are not sure where it is. The probability wave just provides the probability of finding the electron at a certain place at a certain time.

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I think the default that electron is a particle is taught us first because of historical reason. You have to understand the newtonian universe before the quantum mechanics; else it would be too complicated.

The atomic model was first made with electron on discrete observable routes. The next step was the thinking that they have to be stable and quantized so that they are not emitting photons as default. So the orbital model follows.

So after this with quantum mechanics it turned out to be, that everything has the wave particle duality and these behave also like waves, but the de broglie wavelength is mostly so small that it isn't measurable. But scientists proved that the double slit experiments also works with carbon molecules.

It would be nice if the kids are learning all this, but also in maths you don't start with unknown variables; you make them first understand actions like addition, multiplication etc. Afterwards you can build up your system step by step. But our brain just needs first a simple model before it can imagine more complicated things.

Also the quantum mechanics is not the least and best theory. I think the quantum field theory adds a bit more to the states of the quantum mechanics since there are fundamental problems when combining it with relativity.

But, you don't can add up just the theory; you have to find new ones and an interesting question is, if we find them be seeking valid equation and put them together. In "Emperor's Mind" Roger Penrose makes a good approximation with Goedel theory. Goedel actually proved that not everything which is valid is proofable so you have to assume that some of your things are true and build your universe upon it. But at the end every theory is either disproved or not already disproved.

Hopes this helps. Greetings

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  • $\begingroup$ In your first sentence, don't you mean to say we are first taught that electrons are particles, not waves. $\endgroup$ – Dr Chuck Jul 10 '15 at 11:58

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