Eighteenth-century chemists famously jumped the gun by using the ancient Greek word “atoms,” referring to the indivisibly small building-blocks of matter, to label the units of chemical elements. Nowadays we know that these atoms are not fundamental, they’re themselves made of smaller particles. But why is it that the particles and fields of the Standard Model come together to form these particular atoms? Let’s find out.
The Biggest Ideas in the Universe | 18. Atoms
And here is the Q&A video, featuring both a brief appearance from Ariel and a plot of honest experimental constraints.
The Biggest Ideas in the Universe | Q&A 18 - Atoms
This is sort of here and sort of in the last video. Neutrinos have tiny masses, which means that they must have a relatively large Compton wavelength. Why don’t they interact stronger via the “Pauli force”? They should be bouncing off electrons because they are trying to avoid being in the same quantum state.
Just realized why they won’t. Stupid question, sorry about that.
Hi Sean, I saw a documentary years ago (so be prepared for me to get this all wrong), that weighed the likelihood of supersymmetry vs. parallel universes?? It said, the energy of the Higgs was going to indicate which of these hypotheses were right (e.g. heavier Higgs would imply supersymmetry). According to this doc, the discovered value for the Higgs Boson lay just in between the two theories. Could you explain why the weight of the Higgs would have implications for interpretations of the standard model / QM?
Mistake: Beryllium is Z=4, not Z=3. You invented a new element! Lithium-3 is, I think, the element you was thinking about…
Thank you again for a wonderful video.
1. “antiparticles move backward in time”… I assume this is “we can think of them as ‘moving backward in time’. ” Why? I may have missed the explanation for this in earlier videos. I think it might be illuminating. Also, is this important to understanding the imbalance in matter and antimatter?
2. A bit off topic… two questions on the discrete vs. continuous in QM. a) With regard to “energy shells….” I know Schrodinger was unhappy with “quantum jumps.” Are they Indeed instantaneous in a manner similar to entanglement? I saw a paper recently suggesting they are not. b) if spin is continuous angular momentum in the classical sense (e.g. a spinning top/gyroscope) why/how is it quantized? Shouldn’t we rethink it like “superposition” or “wavicle”?
3. I appreciate your closing discussion of why if QFT is true…. but doesn’t that seem analogous to where we were with Newtonian “classical” mechanics? Until we included high speeds (light) , high energies, or new observations all seemed well.
Thanks again for doing these.
We owe our existence and the whole universe around us to a tiny baryonic asymmetry that must have happened in the Big Bang. How comes, there seems to be no charge asymmetry or color asymmetry left over? Would we be able to observe such asymmetries if they existed?
In your Feynman diagrams I was reminded of his idea that anti-particles are just particles moving backward in time. John Cramer developed a form of QM based on this idea and Wheeler and Feynman’s absorber theory. It’s called the Transactional Interpretation, although I think it’s more than just an intepretation. You didn’t mention it in your lecture on QM. Is there something that rules it out?
This is a question about the 3 p-orbitals and their lobes. For an atom alone in the vacuum of space, what direction are the lobes aligned in? Is this a defined state of an atom, that it has a little coordinate system attached to it? Is their some symmetry breaking idea where perfectly symmetrical orbitals collapse to preferred directions?
You said something very consequential for Everettianism, namely, that every two electrons in the same orbital of an atom become entangled, in particular, the wave functions of their spins become entangled. Think of how many entanglements must have occurred since the beginning of the universe. The formation of every atom involves dozens of entanglements. The matter in a single galaxy contains some huge number of atoms. The number of galaxies in just the visible universe is some two trillion galaxies. As a result, the number of entanglements since the beginning of the universe is, to say the least, astronomical. And each entanglement results in a branching of the universe, with the result that our present universe has become minutely attenuated. Yes, I understand that relative energies and scales are maintained, and we don’t notice the branching or attenuation. But at this point, it becomes clearer that Everettians are engaged in philosophical word games of the sort that Christian theologians use to defend their belief in God. I have wasted a good portion of my life studying philosophy, and I have learned that when one encounters a system of thought that one intuits is wrong, the best thing to do is not to engage with the system and come up with rational arguments either for or against (an activity that may engage one’s whole career), but to just ignore the system and employ one’s talents in more worthy pursuits. I remain unconvinced of Everettianism.
Thanks for these great videos. A little nitpick: You stated that “most of the mass of your body is in the form of neutrons, not protons or electrons”. (At about 36:00 into the video). However, humans are composed of elements/isotopes with mostly equal numbers of protons and neutrons, O16, C12, N14 etc. plus H which is mostly an isotope with one proton. About 10% of the mass of a human is H so the majority of the mass of a human is in the form of protons. It’s true that most isotopes have more neutrons than protons but not the ones humans are mostly composed of.
Is it really fair to say baryons are made of quarks if 1) quarks have a bigger Compton wavelength than baryons and 2) given Pauli exclusion we define the minimum amount of space a fermion occupies as its Compton wavelength? We know experimentally that a proton in a hydrogen atom is ~1 femtometer, which is the proton Compton wavelength. If the proton was simply made of quarks, it would have to be the size of the up/down quark Compton wavelength. So unlike building atoms, I see hadronization as a more radical phase transition where the hadrons transcend and replace the quarks, they are not straightforward mereological composites.
Along the same lines, if there are some sort of quark stars between neutron stars and black holes, they shouldn’t be thought of as simply tightly packed (up, down, strange) quarks because this degenerate state would actually be less dense than the basic neutron state, due to the same Compton wavelength argument. Instead, doesn’t this have to be some 3rd phase of QCD, which is neither quark gluon plasma nor hadrons? I have heard this called the color superconducting phase, but I don’t know if it has or can have a perturbative description in terms of particle like subsystems.
Hi doctor Sean! Thanks for the awesome video! It took some time to do your home assignment, but I finally found out! I found it in some Russian book, translated by Google! Now the Euler constant finally makes sense!
Can gravitons show up in Feynman diagrams? On the one hand, they have no mass, no Baryon or lepton number, and no charge, so they can’t account for conserved quantities except for energy. But, the same it’s true of photons and they are all over the place.
On the other hand, they interact universally, so they ought to show up once in a while at least.
Is the real issue that we don’t have a quantum theory of gravity, so we can’t determine how likely those diagrams are?
You’ve mentioned that not only is the lepton number conserved, but the electron number, muon number, and tau number are individually conserved. However you’ve also said that the different flavors of neutrinos can change into each other. How is that possible without violating this?
Also, your diagram with quark decay seemed to suggest that the different families of quarks can change into each other, unlike leptons, is that correct?
You often say that (if entangled) every particle does not have their individual wave function, but are instead part of the wave function of the whole system. When speaking of the Pauli exclusion principle, however, you say that no two fermions can occupy the same quantum state.
Is this quantum state a different thing from the wave function? If not, how does the Pauli exclusion principle work within the wave function of the whole system?
Could you explain a little more how the quantum fields take on more stable configurations when the “particles” are more confined into nuclei, and atoms. The forces and potentials created seem to confine them in ways so multiple fields evolve in synchronized fashions.
Thank you again, Professor Carroll, for your time in educating us. I was educated in the “liberal arts” tradition (i.e. great books) and got an MA at the University of Chicago in Cognitive Science in the ’80’s. So, as a non-physicist I appreciate your pedagogy. Thanks so much for doing something you didn’t have to do.
I finally understand the outer shells of electrons. Hurray!!
Professor Carroll, this series is saving my sanity. Such as it is.
Endless thanks,
CS ~ San Francisco