Why Do We See Distinct Lines in Atomic Emission and Absorption Spectra?

[black hole 123]

just watched this

how i don't see the atoms quantum tunnel instaneneously to another location? how come i don't see waves? how come i see billiard balls?

 

[ZapperZ]

You are ignoring a significant part of this. You should not just focus on the object being looked at, but also the INSTRUMENT that is used to look at it. This is an image from a TEM - transmission electron microscope.

After you read what a TEM is, do you still have the same question?

Besides, what "waves" were you expecting? If you think QM wavefunction is "real", then we have a different and separate problem to deal with here.

Zz.

 

[black hole 123]

You are ignoring a significant part of this. You should not just focus on the object being looked at, but also the INSTRUMENT that is used to look at it. This is an image from a TEM - transmission electron microscope.

After you read what a TEM is, do you still have the same question?

Besides, what "waves" were you expecting? If you think QM wavefunction is "real", then we have a different and separate problem to deal with here.

Zz.

when u said wavefunction isn't real, are u talking about many world? i think many world is nonsense because which world is our consciousness in? but ofc scientists as usual just ignore consciousness and focus on a purely material world.

i think the microscope should at least "see" if something is there or not, so while its meaningless to ask whether atoms really look like what's in the video, it's fully meaningful to ask why atoms aren't tunnelling away from the lattice. i watched a couple of these video and i never see atoms suddenly disappearing. I am sorry if i sound childish, i just want to see quantum effects with my good old eyes instead of reading abstract descriptions of it.

is the reason this: there aren't many atoms in the video and the time lapse is just a few minutes? because if one atom poofed in a sample size that large in a few minutes, a person's body would vanish in a day at most? is it true if 10^30 atoms were observed then poofings would happen regularly?

 

[PeterDonis]

when u said wavefunction isn't real, are u talking about many world?

No. What you see in the microscope can't depend on any particular intepretation of QM, since all interpretations make the same predictions for experimental results.

i think many world is nonsense because which world is our consciousness in?

As you seem to recognize, this is not really within the realm of science at this point. Please stay on topic.

 

[PeterDonis]

how i don't see the atoms quantum tunnel instaneneously to another location?

Why would you expect to see quantum tunnelling in this experiment?

 

[ZapperZ]

when u said wavefunction isn't real, are u talking about many world? i think many world is nonsense because which world is our consciousness in? but ofc scientists as usual just ignore consciousness and focus on a purely material world.

i think the microscope should at least "see" if something is there or not, so while its meaningless to ask whether atoms really look like what's in the video, it's fully meaningful to ask why atoms aren't tunnelling away from the lattice. i watched a couple of these video and i never see atoms suddenly disappearing. I am sorry if i sound childish, i just want to see quantum effects with my good old eyes instead of reading abstract descriptions of it.

1. Your eyes are a horrible detector!

2. Why would the atoms tunnel away? These are in a lattice, as in a solid. They are in a fixed location within the material. It is why a solid holds its shape! Your fingers didn't "tunnel" away while you were tying all that, did it?

3. You are not seeing ANYTHING directly here. If you had bothered reading the link I gave you on TEM, you'll realize that these are images made by electrons passing through the material, and then causing the generation of visible light when they hit a CCD. This is the image that was then recorded! I do both SEM and TEM. None of these will show any "waves" that you are thinking of.

4. This has nothing to do with many worlds. Rather, you have not explained any you expect to see "waves". I merely indicated that if YOUR "waves" have anything to do with the QM wavefunction, then you have a severely erroneous understanding of QM.

is the reason this: there aren't many atoms in the video and the time lapse is just a few minutes? because if one atom poofed in a sample size that large in a few minutes, a person's body would vanish in a day at most? is it true if 10^30 atoms were observed then poofings would happen regularly?

You need to stop bastardzing quantum mechanics, and then impose your misunderstanding upon the rest of us.

Zz.

 

[black hole 123]

then when do they tunnel? only when they are free particles? why do the atoms not spread out their waves when they are in a lattice?

 

[DennisN]

i just want to see quantum effects with my good old eyes instead of reading abstract descriptions of it.

Ok, you asked for quantum effects for your eyes, so here you go:
(though it's not the tunnelling effect)

Superfluid helium:



and the double slit experiment performed with electrons:

 

[Nugatory]

then when do they tunnel? only when they are free particles?

Tunneling happens in situations where the potential energy is the same at two points but higher in between - imagine two valleys separated by a hill. A classical non-quantum ball in one valley can roll up the hill to the top and then down into the other valley, but only if it starts out with enough energy to roll all the way up to the top and keep going - otherwise it will just fall back into the valley where it started. A quantum particle, however, can be found in either valley; we call this "tunneling" because it's as if the particle gets to the other side of the hill without going over the top. However, none of this has anything to do with the atoms in the lattice that you're looking at, because the potential energy here doesn't look like two valleys separated by a hill, it's more like each atom is in the bottom of its own very deep valley and doesn't have any other valley to tunnel into.

why do the atoms not spread out their waves when they are in a lattice?

When you set up and solve the equations of quantum mechanics for a gold atom surrounded by other gold atoms, the solutions will be waves that are near as no never mind zero except In a small region for each atom. So you have waves but they only spread out over a very small region, corresponding to the dots in that photograph.

The quantum mechanical behavior of atoms in a solid is a very challenging problem. There's no way of doing the topic justice without going through several years of college-level math, and you don't want to take it on without a pretty good understanding of the quantum mechanics of single particles. There's no substitute for a first-year QM textbook, but if you don't want to deal with that then Giancarlo Ghirardi's book "Sneaking a look at god's cards" is a more friendly introduction.

 

[black hole 123]

Tunneling happens in situations where the potential energy is the same at two points but higher in between - imagine two valleys separated by a hill. A classical non-quantum ball in one valley can roll up the hill to the top and then down into the other valley, but only if it starts out with enough energy to roll all the way up to the top and keep going - otherwise it will just fall back into the valley where it started. A quantum particle, however, can be found in either valley; we call this "tunneling" because it's as if the particle gets to the other side of the hill without going over the top. However, none of this has anything to do with the atoms in the lattice that you're looking at, because the potential energy here doesn't look like two valleys separated by a hill, it's more like each atom is in the bottom of its own very deep valley and doesn't have any other valley to tunnel into.

When you set up and solve the equations of quantum mechanics for a gold atom surrounded by other gold atoms, the solutions will be waves that are near as no never mind zero except In a small region for each atom. So you have waves but they only spread out over a very small region, corresponding to the dots in that photograph.

The quantum mechanical behavior of atoms in a solid is a very challenging problem. There's no way of doing the topic justice without going through several years of college-level math, and you don't want to take it on without a pretty good understanding of the quantum mechanics of single particles. There's no substitute for a first-year QM textbook, but if you don't want to deal with that then Giancarlo Ghirardi's book "Sneaking a look at god's cards" is a more friendly introduction.

now i get it, it's got to do with the potential energy. if a particle suddenly disappeared from the lattice and reappears in empty space, it would have higher total energy and it would be getting that energy from nothing, which is impossible. is this how u look at it?

sorry for the low quality of my questions, I am a layman and really want to know lol.

 

[Nugatory]

now i get it, it's got to do with the potential energy. if a particle suddenly disappeared from the lattice and reappears in empty space, it would have higher total energy and it would be getting that energy from nothing, which is impossible. is this how u look at it?

That's the classical explanation for why atoms in a solid stay put. The quantum mechanical explanation is completely different (although potential energy is still an important part).

There's really no way of learning this stuff except to start with the basics and build from there.

 

[member 648030]

just watched this

how i don't see the atoms quantum tunnel instaneneously to another location? how come i don't see waves? how come i see billiard balls?

I did not understand exactly the mechanics of the video experiment.
In any case, I can think that you do not see "waves", for the same motive, for which, in the double-slit experiment you see the "dots" of the electrons on the final screen

 

[fluidistic]

I think Nugatory gave a pretty good explanation of why you did not notice "waves" instead of what seemed to be to you well defined dots. I wish to add that I've watched a video of atoms almost in real time, where atomic diffusion -so involving both translation to vacant sites and quantum tunelling, to name a few - was explicitely visible. I do not remember which apparatus it was, I am not sure it was as common as usual SEM/TEMs.

 

[DrClaude]

If you want to see waves, check out the second figure here: https://www.researchgate.net/publication/238552666_In_Touch_with_Atoms/figures?lo=1

 

[ZapperZ]

then when do they tunnel? only when they are free particles? why do the atoms not spread out their waves when they are in a lattice?

What waves?! What are these waves that you kept bringing up?

If you want to see waves, check out the second figure here: https://www.researchgate.net/publication/238552666_In_Touch_with_Atoms/figures?lo=1

Unfortunately, a lot of people get the wrong ideas from this picture. I've had to tackle explaining this picture many times.

First of all, this is an STM image. It means that the STM tip is either sampling a constant current, or a constant voltage profile of the surface (and it is ONLY the surface). From the scan, the electronics then create an image.

The "waves" in this case are regions of "modulations" where the surface electrons are confined. This is not the "wavefunction", i.e. it is not the wavefunction of single electron, or even many electrons. In other examples, one can show similar profile for what is known as "charge density waves". So it is like you piling sand in a periodic pattern, or you see "waves" of sand pattern on the beach. It really isn't a "wave", but rather a periodic arrangement of "things".

Note that if these are traveling waves that move over time, the STM imaging will wash out, because the STM tip will be sampling a time varying average over an entire period at every "wavy" location.

Zz.

 

[DennisN]

i just want to see quantum effects with my good old eyes instead of reading abstract descriptions of it.

And here are some more quantum effects for your eyes:
(still not tunneling, though)

Atomic emission spectra, where the lines in the spectra correspond to the different energy levels of the electron(s) in the atom(s):
(the early, outdated Bohr model failed to explain all that could be observed)

• Hydrogen
• Neon and Mercury

and here is a video demonstration:

Spectrum Demo: Continuous and Emission (Physics Demos, Utah State University)


and a demo of absorption lines:

Sodium Absorption Lines (Harvard Natural Sciences Lecture Demonstrations)


and last, but not least here is a demonstration of electron diffraction, which originally was made in the Davisson-Germer experiment:

Electrons (Sixty Symbols)
(I tried to timestamp the video link, but it did not work, please jump to 4 m 56 s in the clip, and then to 6 m 20 s)


Enjoy!

 

[vanhees71]

I am sorry if i sound childish, i just want to see quantum effects with my good old eyes instead of reading abstract descriptions of it.

It's not childish at all but very reasonable. I wish the discussions about QT would be as reasonable as that question! The problem is that many popular-science treatments of QT (as well as relativity) try to emphasize the "weird properties of the modern theories" rather than to provide the notion, why these abstract looking theories are necessary in the first place.

To answer your question: Everything you see around you in everyday-life concerning the properties of matter are, to the best knowledge we have today, described not by classical but by quantum physics. Already the quite common notion that we live in a pretty stable world, where we can sit behind our stable desk on a stable chair and hack nice forum postings into our laptops cannot be understood in terms of classical physics to begin with.

Given the empirical fact that all of matter is made of a few "fundamental building blocks" (on the most fundamental level all of the matter around us is "made up" of up- and down quarks and electrons), it is not understandable from classical physics, why the macroscopic matter around us (and finally also making up ourselves) is as stable as observed. This is explained by quantum theory only. Importantly, because nothing needs to move in a atom in a ground state (in clear contradistinction to the outdated Bohr model of the atom!) there's no necessity for the electron in a hydrogen to crash into the proton because it looses all its energy to the synchrotron raditiona which would have to be necessarily emitted according to classical electrodynamics if it really were running in circles around the proton. Another important fact that can even be described adequately only with quantum theory is the indistinguishability of particles of the same kind and that the fundamental building blocks are all fermions, following the Fermi-Dirac statistics and the Pauli exclusion principle. The fact that the table I'm sitting at when writing this posting is pretty much due to the Pauli principle. I cannot simply reach through the table, because the electron levels of the solid are all occupied, and it's not possible to put more electrons there, i.e., the electrons in my hand cannot be at the same place where the electrons of the table are and that what makes it impossible to simply reach through the table.

The fact that for everyday-life experience almost always classical mechanics and electrodynamics is a very good description of what we see is that we don't look at the microscopic details but at rather "coarse-grained" macroscopic observables like the center of mass of a solid body or the macroscopic electromagnetic field we perceive as light when it comes to optics etc. Then the apparently "weird" properties of quantum theory are averaging out, and QT leads to the classical effective behavior of the macroscopic observables.

 

[DennisN]

Atomic emission spectra, [...] and a demo of absorption lines

Hi again, @black hole 123!

I reread the thread, and since this was marked as a "B" thread and you said you were a layman, I thought I could have been more descriptive regarding my post about spectral lines and the video demonstrations.

First, a line in a spectra is made of light (photons) with a distinct, particular energy and frequency, which are related (see this equation).
(Note: this is a little bit simplified for the purpose of this B thread).

The electrons in atoms can be excited, which means they can absorb energy (from e.g. incoming light or via an applied voltage, as demonstrated in the videos) and then they reach higher energy states. After that, they can transition back to a lower energy state by emitting a photon (light).

The emission spectra show lines where each line is the result from an electron transitioning from a higher energy state to a lower energy state. The lines are made up of photons which got emitted by the atoms, which equals the energy difference between the higher energy state and the lower energy state.

In contrast, the absorption spectra in the other video shows how the electrons in the sodium atoms absorbs a discrete, particular amount of energy, that is, photons of a particular energy in the incoming light. Thus a distinct, particular line is removed from the continuous spectrum, which then appears as having a black line in it.

In short, here is the quantum thing of it:

Since the energy levels of the electron(s) in the atom(s) are quantized, the emission and absorption lines appear as clear, distinct lines in the spectrum, where each line is representing a particular energy and frequency.

So this shows that electrons in atoms can not be in any arbitrary state, which means they can not have any arbitrary energy between 0 and x Joule (or eV). They can only be in a number of well defined, discrete energy states.