the handy booklet of

Constantly Asked Physics Questions

Everyone gets bored of always answering the same questions over and over again. It's normal. Especially if it's Physics. That's why we have FAQs. But next to the always asked questions, there are also the often asked, those who just can not make it to big FAQs but really are popular enough to annoy the answerer, helplessly scrolling for new adventures in a sea of déjà-vus.

This is not a definitive FAQ, nor is it necessarily a good FAQ, it's just my FAQ. It's shamelessly skewed towards my view of the physical world. It is also very inconsistent in the level requested of the reader. Typically, I'd just assume the minimal background needed for the answer to be a pleasurable conversation, neither a patronizing poem nor a bored review.

You can contribute if you want! Check the README at the Github project page or just hit me up on Reddit.

Download .pdf

You can find a printable, up-to-date .pdf version of the CAPQ here. (This .pdf is a work in progress and content might be scrambled, missing, or badly laid out.)


Kinematics/General Physics

KGP1 - Why is \(c\)/\(\hbar\)/\(k_B\)/(other fundamental constant) the value it is? What would happen if it was different?

Classical Mechanics

CM1 - Why is my physics teacher so anal about centripetal vs centrifugal? Is the centrifugal force "fictitious"?

CM2 - What would happen if you were struck by a primordial (\(10^{14} \; \mathrm{kg}\)) black hole at orbital speed (\(8 \, \mathrm{km}/\mathrm{s}\))?

Thermodynamics

TD1 - How are negative temperature possible? Why are they hotter than any positive temperature? How were they acheived?

Celestial/Orbital Mechanics

OM1 - How do gravity assists/slingshots work?

OM2 - Why won't/didn't New Horizons stop at Pluto and instead had to fly by?

Fluid Mechanics

Classical Electrodynamics

CED1 - What is the Maxwell stress tensor \(\mathbf{\sigma}\) and how does it work?

CED2 - Why is current produced to a wire when moving a magnet close to it?

Analytical Mechanics

AM1 - Why are \(q(t)\) and \(\dot q(t)\) treated as indipendent in Lagrangian mechanics? Shouldn't \(\dot q(t)\) be viewed as a function(al) of \(q(t)\)?

Special Relativity

SR1 - In what sense does \(E=mc^2\), and what does it mean?

SR2 - if photons are massless, how can \(E=mc^2\)?

General Relativity

GR1 - How long does a year on Mercury last from Mercury's point of view?

General Quantum Field Theory/Many Body/Relativistic QM

QFT1 - What is "imaginary time"? And what is meant by "Euclidean spacetime"?

Nuclear Physics

Quantum Electrodynamics

QED1 - How does \(1+2+3+\ldots=-1/12\)/\(\zeta\)-regularization enter in the Casimir effect?

Particle Physics/High Energy Physics

HEP1 - Why are photons massless?

HEP2 - Why do photons not acquire a mass through the Higgs mechanism?

HEP3 - Why do photons not acquire a mass through quantum corrections/interaction with virtual particles? What is charge renormalization?

HEP4 - Is the electron a point particle, or an extended object? How sure are we of that?

Quantum Gravity/String Theory

QG1 - If the Planck length/Planck time is the smallest measurable/possible length/time, then...?

QG2 - since the electron is a point mass, is it a black hole?

List of well-known crackpots

Aether Wave Theory / Zephir

Imagining the Tenth Dimension / Rob Bryanton

The Stand-Up Physicists / Doug Sweetser

Nassim Haramein / Resonance Project / Schwarzschild proton / Haramein-Rauscher metric

An exceptionally simple theory of everything / \(E_8\) Theory / Garret Lisi

EM drive / Roger Shawyer / NASA "warp" drive