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Old Mar 22nd 2018, 11:13 AM   #1
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What do we know about an undisturbed atom?

Hello,
can I say:we know only facts about how atoms do react after or during a disturbance? We do not know what an undisturbed atom is!? The properties of an undisturbed atom are in general unknown.
Can I conclude: an undisturbed atom can be something completely different compared to how we understand it in science.

Thank you in advance
Lothar
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Old Mar 22nd 2018, 11:54 AM   #2
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Originally Posted by LotharSchuh View Post
Hello,
can I say:we know only facts about how atoms do react after or during a disturbance? We do not know what an undisturbed atom is!? The properties of an undisturbed atom are in general unknown.
Can I conclude: an undisturbed atom can be something completely different compared to how we understand it in science.

Thank you in advance
Lothar
Quantum mechanics (QM) is the theory which applies here. According to QM nothing can be said or known about the state of an unobserved system. Therefore nothing can be understood about an undisturbed atom. So you're correct. Do what know what an undisturbed atom is? That's a question for metaphysics, not physics.

Metaphysics is the branch of philosophy that deals with the first principles of things, including abstract concepts such as being, knowing, substance, cause, identity, time, and space.

I guess we can say that atoms still exist when not being observed, they have energy, etc. But we have no way of making this determination experimentally and that's why physics can't be applied.
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Old Mar 23rd 2018, 06:36 AM   #3
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Everything that we know about atoms comes from their interactions,
indeed I think it would be correct to say that anything we know about anything comes from it's interactions.

In a meta-physics sense anything that does not interact cannot be of any importance to us, and so if it exists or not does not matter.

On another level, an atom is always subject to interactions (even if only tiny gravitational interactions) with the rest of the universe.

See my first ever post (under a different name) on this forum: <new take on an old question>
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Old Mar 23rd 2018, 10:58 AM   #4
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Originally Posted by LotharSchuh View Post
Can I conclude: an undisturbed atom can be something completely different compared to how we understand it in science.
PMB's answer is correct. I just want to add that even though quantum mechanical observables are obtained via perturbation (and therefore a disturbance), quantum mechanics makes predictions for all of the possible states that an atom, once measured, can potentially give. Therefore, although we have no experimental evidence of the undisturbed state, and probably never will, we know through experiment whether the set of possible states predicted by the theory is upheld. This set of possible states can be said to be something which describes the behaviour of the unobserved thing.

Consider the following thought experiment: there's an opaque box that apparently has an object inside of it, but no one knows what the object is. Nobody is allowed to open the box and look at it at any time to confirm what it is. However, someone tells you that if you shake the box, something happens inside it and a result appears on the top of it.

You might shake that box a bunch of times... 10 times, 100 times, 10,000,000 times and find that in every single case, the result is always "My reply is so", "It is decidedly so", "Cannot predict now", "As I see it, yes", "It is certain" or "Outlook not so good". What can you conclude?

You could conclude the following:

- The set of possible states of the object in the box is the set:
1. "My reply is so";
2. "It is decidedly so";
3. "Cannot predict now";
4. "As I see it, yes";
5. "It is certain"; and
6. "Outlook not so good"

You might even hypothesise that the box is called a "magic 8-ball" and the object inside the box is a 6-sided die and that shaking the box is equivalent to rolling the die. You can even compare the box results to other experiments involving dice rolling and conclude that the hypothesis is sound. Then, since your theory of the statistics agrees with experimental evidence, it makes it into the textbooks. However, all of this is on the presumption that we can never truly be certain about that state of that object inside the box without being able to open the box, which is impossible.

Similarly, in QM, even though we can never truly know what undisturbed atoms are like, we can certainly know the sets of their possible states and make predictions about which state we might see if we "shake them"

Last edited by benit13; Mar 23rd 2018 at 11:06 AM.
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Old Mar 23rd 2018, 11:46 AM   #5
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Thanks you for your helpful comments. So far I got the point.
I like to go a step further and increase the extent of the disturbance: a particle accelerator/Collider/LHC.
What is now the rationale to claim, that we understand the structure of matter. Can 2 colliding protons etc with GeV tell us really something about matter ?
and
Are'nt those particles of the standard-model something absoloutly exotic we create?
I understood, that one must say "we know the standard-model of 2 colliding protons" and this might not occur anywhere else in the world". But we can make predictions.

I just think..
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Old Mar 23rd 2018, 12:15 PM   #6
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Originally Posted by LotharSchuh View Post
Thanks you for your helpful comments. So far I got the point.
I like to go a step further and increase the extent of the disturbance: a particle accelerator/Collider/LHC.
What is now the rationale to claim, that we understand the structure of matter. Can 2 colliding protons etc with GeV tell us really something about matter ?
and
Are'nt those particles of the standard-model something absoloutly exotic we create?
I understood, that one must say "we know the standard-model of 2 colliding protons" and this might not occur anywhere else in the world". But we can make predictions.

I just think..
It'd be a good idea if you picked up an intro level text and read a little about it. You'd learn a great deal more that way than asking us here. The purpose of a text is to explain to the reader exactly what you're asking and that takes many pages by experts in that subfield. I know the basic physics and quantum mechanics but I'm not a particle physicist. I wouldn't do as much justice to the subject as a text can since they not only work in the field but they also teach it. They've spent many years honing their lecture notes to get the story straight and understood correctly.

That said, physicists who know the theory can use it to make predictions. That means they can smash particles together and predict what should come out of the collision. They then compare theory with observation. They also know what to expect when they do scattering experiments. For example; chromodynamics is defined as follows. From: https://en.wikipedia.org/wiki/Quantum_chromodynamics
In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks and gluons, the fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory, with symmetry group SU(3). The QCD analog of electric charge is a property called color. Gluons are the force carrier of the theory, like photons are for the electromagnetic force in quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. A large body of experimental evidence for QCD has been gathered over the years.
A short history is important here: When Murray Gell-Mann was working in particle physics trying to make sense of the data coming from accelerator labs. So many particles were being created and thus discovered. There was a desire to understand it all and make predictions. As he was working on this it occurred to him that it could all be described in terms of what he called quarks (he chose the pronunciation to rhyme with fork). Later on he chose to take the risk and say "quarks are particles." He was nervous about it too. He had no idea if they existed or whether what he came up with was clever bookkeeping. The quarks were assigned a charge whose magnitude was one third the magnitude of the electron charge.

Experimentalists used this theory to predict what the results of deep inelastic scattering. In the 60's electrons were fired into protons using the Stanford Linear Accelerator and in the 70's they used beams of neutrinos and protons at CERN. Lo and behold - the results were consistent with scattering off of three charged particles which make up the proton.

Gell-Mann won the Nobel Prize for it.
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