My dad was unaware of how atoms are over 99.99% empty space, and asked me how physical contact works. So my question is, how does physical contact work both on the atomic and macroscopic scales? IIRC the electron clouds surrounding atoms strongly repel other atoms’ electrons (two negative fields), but that’s probably wrong (then how would they form molecules?). I hope this isn’t like wave-particle duality, where the answer is that it exists whether I like it or not :unsure:

Also, he asked “what powers the electrons in their orbits around the nucleus?” I’m guessing that the answer is that the electrons already have momentum, and that the environment of the atom has no friction or anything to reduce the energy of the system, so they keep orbiting until a photon transfers energy to them or they lose a photon. Then the orbit changes or the electron is ejected from the nucleus? :jvang:

Abandon the idea of an orbit like a planet. The orbital name has stuck. It is a probability cloud. Their shapes can be odd. s and p are easy to visualize and think of as a traditional orbit, but d and f are not racetracks for the electron.

[QUOTE=Uncwilly;498291]Abandon the idea of an orbit like a planet. The orbital name has stuck. It is a probability cloud. Their shapes can be odd. s and p are easy to visualize and think of as a traditional orbit, but d and f are not racetracks for the electron.[/QUOTE]Ooh, you're sticking your neck out here, posting to an audience which includes at least one pedantic chemist with a rudimentary knowledge of quantum mechanics.

Just as Bohr's planar elliptical orbits are easy to visualize and over-simplified, so are Schrödinger's spherical harmonic orbitals. For a start, they assume that the atom as a whole is in a stationary state and that it consists of a nucleus surrounded by electrons bound to a spherically symmetrical nucleus of infinitesimal size in a globally spherical symmetrical environment.

An atom interacting with a passing free electron is still a nucleus surrounded by electrons but is not in a stationary state --- it changes with time as the electron moves, either to be absorbed, to be scattered or to cause the ejection of one or more other electrons.

Nuclei are not points and they are not, in general, spherically symmetric --- they may have electric and magnetic dipole moments for instance.

In a molecule the separated nuclei result in further deviations from spherical symmetry and even electrons which are tightly bound to a nucleus do not occupy pure spherical harmoic orbitals.

We've not even got on to the effects of special relativity (Dirac's orbitals are not the same as Schrödinger's), or QED, or ...

I am certain that the first clause of Haldane's "My own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose." is true; the second may well be true.

[QUOTE=Uncwilly;498291]Abandon the idea of an orbit like a planet. The orbital name has stuck. It is a probability cloud. Their shapes can be odd. s and p are easy to visualize and think of as a traditional orbit, but d and f are not racetracks for the electron.[/QUOTE]

I know that the orbits are a simplified concept, but I don’t know how else to explain this stuff to my dad...

If we were to assume “a nucleus surrounded by electrons bound to a spherically symmetrical nucleus of infinitesimal size in a globally spherical symmetrical environment,” how would a system containing nothing but a single typical hydrogen atom behave? In particular, my dad thinks that the “orbit” of an electron should decay like that of a planet or a moon (which happens unimaginably slowly if I am not mistaken). I’m pretty sure that, at this scale and with nothing interacting with the system, the electron orbits the proton forever.

Then again, maybe something like gravitational interactions between the proton and electron would destabilize the system over time? Though I don’t know anything about gravity, I’m pretty sure we haven’t discovered a quantum for it yet.

Now, you do the following experience, take an electric motor, take a thick wire (2-3 mm, copper or else) about a meter long and bend it like a curved propeller, so when it rotates it should look like an upside-down bowl. Some helicopter-like toy can also be used, if you bend the propeller properly. Then put everything on the table, and add an apple under the mushroom, something like in the following picture.
[ATTACH]19154[/ATTACH]
The battery is not necessary, a wall connected 20kW motor is ok to use too. Start the motor at 10 thousand RPM, and ask Mike to get the apple with his hand. What the hack, there is mostly empty space there...

After few trials he will get the idea about matter interaction :razz:

[QUOTE=jvang;498313]In particular, my dad thinks that the “orbit” of an electron should decay like that of a planet or a moon (which happens unimaginably slowly if I am not mistaken). I’m pretty sure that, at this scale and with nothing interacting with the system, the electron orbits the proton forever.[/QUOTE]Your dad is predicting what every physicist would happen after the discovery of the nucleus by Rutherford by scattering alpha particles (helium nuclei) off atoms.

Unfortunately for them, nature just doesn't work that way and you are correct, as far as anyone knows.

The quantum theory was developed to provide a mathematical framework describing what actually happens as well as possible. Bohr's theory was much better than the classical one, Schrödinger's better than Bohrs, Dirac's better than Schrödinger's and so on.

When I confronted these issues for the first time many years ago I accepted that I had been misled by well-meaning teachers into putting too much faith in classical electrodynamics. Just because a theory works superbly well in one area does not imply that it works just as well in all areas. Compare Newtonian and relativistic dynamics, for instance.

[QUOTE=xilman;498328]When I confronted these issues for the first time many years ago I accepted that I had been misled by well-meaning teachers into putting too much faith in classical electrodynamics.[/QUOTE]

It's the [URL="https://en.wikipedia.org/wiki/Lie-to-children"]Lies we tell to children[/URL] to help them learn.

Heck, if the leading researchers don't fully understand how the Universe works, how can we expect people not already somewhat trained to jump from what they empirically observe to QED et al? Newton before Einstein, etc....

[QUOTE=chalsall;498367]It's the [URL="https://en.wikipedia.org/wiki/Lie-to-children"]Lies we tell to children[/URL] to help them learn.

Heck, if the leading researchers don't fully understand how the Universe works, how can we expect people not already somewhat trained to jump from what they empirically observe to QED et al? Newton before Einstein, etc....[/QUOTE]I fully support that approach, as long as the teachers themselves recognize that they are teaching lies (or approximations to be more accurate).

Two personal anecdotes. My mother-in-law was told dogmatically by one of her teachers that it was impossible to split an atom. This was a week or few [B]after[/B] the atom-splitting experiment had been in the world's newspapers. Peter Atkins, who taught me most of the QM I learned at Oxford, told his freshman audience words close to: "What I am about to teach you is wrong but the examiners believe it to be true so you have to learn it". Guess which teacher I respect the most.

[QUOTE=xilman;498370]My mother-in-law was told dogmatically by one of her teachers that it was impossible to split an atom.[/QUOTE]

LOL... This was, of course, before the Quark Age (a bit like the Iron Age, but different)?

[QUOTE=chalsall;498372]LOL... This was, of course, before the Quark Age (a bit like the Iron Age, but different)?[/QUOTE]Some time in the 1930's

[QUOTE=LaurV;498318]Start the motor at 10 thousand RPM[/QUOTE]

Pretty fast! :unsure: I figured that was how that worked...

What does it mean for a neutrino to interact with normal matter through only the weak atomic force and gravity? What makes a neutrino going through something different that a photon or other particle going through a material?

My dad was wondering about if it would be possible to halt the "orbits" of electrons in an atom. I'm under the impression that cooling matter to absolute zero is like trying to accelerate it to the speed of light; you can get really close but not actually to absolute zero. I just read a thingy about zero-point energy, which made very little sense. But it seems that no matter how low of a temperature you cool matter to, there will be some energy in the system. Or something about superfluid helium? :max:

He also asked me about quarks, which I know very little about. What I do know; there are 6 types: up, down, strange, charm, bottom, and top. Up and down quarks are the most stable, and the other quark types decay into up and down quarks. A hadron is a particle made up of quarks, which includes protons and neutrons. There are three in each proton and neutron; a proton has 2 up and 1 down, a neutron has 2 down and 1 up. The up quark has a 2/3 electric charge, and the down quark has a -1/3 charge (giving protons a positive charge of 1 and neutrons a neutral charge of 0). That's about all I know about quarks.

He also asked me about how we calculate energy. I think he meant how E = mc² works and what the speed of light has to do with energy. As per Wikipedia, this is mass-energy equivalence:

[QUOTE]mass–energy equivalence states that anything having mass has an equivalent amount of energy and vice versa[/QUOTE]

I took for granted what the formula means, but now I'm curious too; what does the speed of light (squared!) have to do with energy? I get that this has something to do with rest mass and special relativity or something, but that's about it...