Featured Science Threads - Page 2

Below is a curated list of some of the most interesting and highest quality science news and discussions on Physics Forums. News and discussions are added weekly. Also check the Hot Threads page for discussions choosen algorithmically.
Featured Thread: Proof of the existence of atoms
It is said that some physicists doubted the existence of atoms in 1900 until Einstein proved their existence a few years later. Did Mendeleev's creation of the periodic table in the 1870s already prove the reality of atoms by giving the known elements atomic masses?
Featured Thread: The general structure of relativistic QFTs
I try to clarify some misunderstandings about the general structure of relativistic QFT. Particularly the important defining property of "locality".
Featured Thread: Why does the effect linger with Glow in the dark?
My question is, as is with normal colour and fluorescence the effect stops immediately the light is switched off. Why does the effect linger with Glow in the dark? Why are the emissions so much slower not instant the moment the light is switched off?
Featured Thread: Is induction heating more efficient than resistance heating for a water heater?
Was curious if induction water heaters were a thing and if they had any benefits over a traditional electric resistance coil. On quora someone argues that a resistance coil is a near-perfect conversion of electricity to heat, therefore no benefit to induction - is this correct?
Featured Thread: How to describe and discuss different solid matter states?
Not sure of the precise terminology to discuss different solid matter states, and also not sure if this is generally the subject of mechanical or chemical engineering.
Featured Thread: What sort of an experiment can refute QM or QFTs?
I assume most people when they refer to Quantum Theory, they sort of referring to QFT. So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?
Featured Thread: What do physicists mean when they say photons have a "path"?
This [Ed.: the claim that photons have a "path"] is a misconception of quantum theory already for massive particles. It's even more severely misleading for massless quanta of spin ≥1, which do not even allow the definition of a position observable itself...
Featured Thread: High schooler Develops new Integration Technique
Highschooler develops a new integration technique that works on 73% of the common integrals used in Calculus 2 named Maclaurin Integration.
Featured Thread: Manifold with a boundary
The usual spacetime manifold in general relativity is a topological space that has no boundary. Manifolds that do have a boundary are discussed as well as details of doing GR with such manifolds.
Featured Thread: Approaches for teaching Modern Physics in Grade School and University
Both Feynman and Einstein have famous quotes about explaining physics concepts to those not well schooled in physics. (freshman undergrad and a six-year-old respectively). Yet both hedged a bit on this: Einstein Things should be made as simple as possible but not simpler and Feynman...
Featured Thread: Teaching SR without simultaneity
De-emphasizing simultaneity in SR curriculum. Thoughts? Experiences? This thread, some earlier ones, and my signature got me thinking a bit about whether it would be a good idea to de-emphasize simultaneity when teaching SR since it is a frame-dependent concept.
Featured Thread: Kinematic Decomposition for "Rod and Hole" Relativity Paradox
In a recent thread, I said that if there was interest, I would post in a separate thread the calculations for the kinematic decomposition of the congruence of worldlines describing the rod in the "rod and hole" relativity paradox discussed in that thread. Since there was interest, I am posting that separate thread...
Featured Thread: The James Webb Space Telescope
Countdown to launch thread
Featured Thread: Optical qualities of prism sheet and glass substrate (LCD screen)
Need help with defining optical qualities of two LCD screen layers that can severely hurt eyes when the screen is disassembled (what do they do to light to make it dangerous).
Featured Thread: Rovelli on Quantum Gravity
One of the leading researchers in Loop Quantum Gravity discusses existing observations that should guide future quantum gravity research in a three-page paper. Rovelli points to three pieces of existing observational evidence that should guide future quantum gravity research. Bottom line...
Featured Thread: The 41 second clock failure syndrome
An old clock stops working at the 41-minute mark. A new replacement, identical to the old one, also fails at the 41-minute mark. Repeated tests show that this isn’t just a fluke: the clocks always seem to fail around the same positions, so what could be the cause? Is it the defective gear? Is the motor failing to fight gravity when it lifts the hands?
Featured Thread: Bernoulli, lift and cause & effect
Bernoulli, lift and cause & effect: looking for a clear-cut cause-and-effect and analogy.
Featured Thread: Math Challenge - November 2021
Summary: Analysis. Projective Geometry. C∗-algebras. Group Theory. Markov Processes. Manifolds. Topology. Galois Theory. Linear Algebra. Commutative Algebra.
Featured Thread: Math Challenge - October 2021
Summary: Functional Analysis. Project Management. Set Theory. Group Theory. Lie Theory. Countability. Banach Algebra. Stochastic. Function Theory. Calculus.
Featured Thread: Black hole formation watched from a distance
One thing I've never got clear in my head, and which I find hard to answer using google and my textbooks on GR, is the following: how exactly is black hole formation observed by an observer sitting at a distance?
Featured Thread: Future null infinity confusion
So I was trying to get a bit better handle on the definition of the difference between an event horizon and a Killing horizon. Locally they are indistinguishable, and the key difference (to my understanding) is that the event horizon is the last Killing horizon that escapes to future null infinity...
Featured Thread: Math Challenge - September 2021
Summary: Gamma function. Combinatorics. Stochastic. Semisimple Modules. Topological Groups. Metric spaces. Logarithmic inequality. Stochastic. Primes. Approximation theory.
Featured Thread: Doubly charming tetraquark
LHCb has discovered a couple of tetraquarks and pentaquarks in the last years. Recently they added one more, but this one is different from the previous discoveries. Tetraquarks have two quarks and two antiquarks. If all of them are light (up/down/strange) it's basically impossible to measure them and experimentally confirm that they actually have four quarks, so people mainly focus on tetraquarks with at least one heavy quark...
Featured Thread: Math Challenge - August 2021
Summary: countability, topological vector spaces, continuity of linear maps, polynomials, finite fields, function theory, calculus
Featured Thread: Chaotic ISS attitude after Nauka misfires thrusters (resolved)
Nauka is the most recent ISS module. After docking, it unexpectedly fired thrusters, changing the orientation of the ISS. The situation has been resolved. Nauka, a Russian multipurpose science module and one of the largest ISS modules, was docked to the ISS. During the checkout procedures after docking the module suddenly fired its thrusters, rotating the ISS quite rapidly (up to 0.5 degree/s).
Featured Thread: Could QM Arise From Wilson's Ideas
'Nowadays we know you can start with just about anything, and at low energies, the effective theory will look renormalizable. This is useful, if you want to calculate processes in low-energy physics; disappointing if you’d like to use low-energy data to learn what is happening at higher energies. Chances are, if you go to energies that are high enough, spacetime itself becomes ill-defined, and you don’t have a quantum field theory at all. But on labs here on Earth, we have no better way to describe how the world works.'
Featured Thread: A short derivation of the relativistic forms of energy and momentum
This derivation uses collisions in 1 dimension, plus rapidity. I've been noodling around with derivations of relativistic energy and momentum, and I almost got it down to just a few lines. But not quite. I'm going to work in one spatial dimension, for simplicity (even though some derivations require a second spatial dimension)...
Featured Thread: How big is a photon -- revisited
Interesting video about interpreting 'single photon' interference experiments. Bumped into this video after admiring the falling cat by @A.T. As an experimental physicist, indeed experienced a little of the 'hole in the brain' phenomenon!
Featured Thread: Floating a cruise ship in a bucket of water
This myth has been around for a long time. (I wish I'd sent it into Mythbusters.) Do we all agree it is theoretically possible? Once we do, can we figure out a practical way of testing it? OK. I'm sure we're all in agreement that it is theoretically possible to float a cruise ship "in" a bucket of water, right? If not, maybe we need to sort that out first.
Featured Thread: Math Challenge - July 2021
Summary: Group Theory, Lie Algebras, Number Theory, Manifolds, Calculus, Topology, Differential Equations.
Featured Thread: Math Challenge - June 2021
Summary: Lie algebras, Hölder continuity, gases, permutation groups, coding theory, fractals, harmonic numbers, stochastic, number theory.
Featured Thread: Search for CPT violation with protons/antiprotons using quantum logic
Found a cool proposal on the arXiv from the BASE collaboration. Put a proton in a Penning trap with a beryllium ion. Let the proton spin precess for a while. SWAP the proton spin state with the beryllium spin state a la quantum logic techniques. Readout the beryllium state. Get a g-2 measurement. Repeat the process for an antiproton. Look for CPT violation...
Featured Thread: How to Solve Projectile Motion Problems in One or Two Lines
We show how one can solve most, if not all, introductory-level projectile motion problems in one or maybe two lines. To this end, we forgo convention. We demote clock time T to a parameter of secondary importance and ditch the independence of motion in the vertical and horizontal directions...
Featured Thread: Where shall I start? (16 y/o wanting to become quantum physicist)
I am a 16 years old who has a dream to become a quantum physicist but I am also someone who doesn't know the beginning of the road so I thought maybe some comments will be helpful so tell me where shall I start?
Featured Thread: Math Challenge - March 2021
Summary: Lie Algebras, Commutative Algebra, Ordering, Differential Geometry, Algebraic Geometry, Gamma Function, Calculus, Analytic Geometry, Functional Analysis, Units.
Featured Thread: One more talk about the independence of Einstein's SR axioms
The two known textbook axioms of Special Relativity are generally thought to be independent. Or are they not, really?
Featured Thread: Grim Day on the Texas Power Grid
This is an enormous failure, comparable to the "Great Northeast Blackout of 1965". Rolling blackouts are being imposed at a time when millions of residential customers need home heating. The oil refineries shut down. Expect gasoline/diesel shortages and price spikes nation wide in a few days.
Featured Thread: Gravitational field of an infinite flat slab
Flat slabs are weird in GR. Off the back of a recently closed thread where there was some discussion about the gravitational field of an infinite flat slab, I decided to have a play at investigating that. I've found a few interesting things.
Featured Thread: Math Challenge - February 2021
Summary: Calculus, Measure Theory, Convergence, Infinite Series, Topology, Functional Analysis, Real Numbers, Algebras, Complex Analysis, Group Theory
Featured Thread: Two disks -- An educational problem
Let me share an educational problem which I learned from my friend Prof. M. Kirsanov. Perhaps somebody finds it interesting to discuss it with students. I do. The problem is pure kinematic.
Featured Thread: Topology on a space of Lie algebras
I wonder if anybody has an idea for a topology on the set of Lie algebras of a given finite dimension which is not defined via the structure constants. This condition is crucial, as I want to keep as many algebraic properties as possible, e.g. solvability, center, dimension...
Featured Thread: Coal and the Fermi Paradox
Reading McGhee's excellent book on the Carboniferous period and he explains in detail the unique circumstances behind the creation of 90% of the world's coal deposits - receding ocean in an ice age that created low lying swamps, high concentrations of oxygen in the atmosphere that would have been sufficient for wildfires to turn swamps into charcoal...
Featured Thread: SARS-CoV-2 Mutations
A general thread to collect the latest research on mutations to the SARS-CoV-2 virus. Given the seeming increased transmissibility of the new SARS-CoV-2 variants being identified, I thought I'd start a general thread to collect and organize information on the various mutations to the SARS-CoV-2 virus.
Featured Thread: Einstein-Infeld-Hoffman paper
Einstein, Infeld and Hoffman tried to derive the equations of motion of point particles in GR from Einstein's field equations. On another thread, now closed, Intrastellar asked: "Since the EFE describes the shape of spacetime, it describes the way black holes, for example, evolve. Can one derive the geodesic equation from it in some limit ?"
Featured Thread: Math Challenge - January 2021
Summary: Linear Programming, Trigonometry, Calculus, PDE, Differential Matrix Equation, Function Theory, Linear Algebra, Irrationality, Group Theory, Ring Theory.
Featured Thread: Neutrino Puzzles and Open Questions about Neutrinos Today
  • What is the correct theory of neutrinos?
  • Why are they almost but not quite massless?
  • Do all three known neutrinos—electron, muon, and tau—all have a mass?
Featured Thread: Pfizer/Moderna vaccine research paper
Here is the official peer reviewed Pfizer vaccine study published in the New England Journal of Medicine... This is a follow-up piece that describes what an emergency use authorization means and gives a perspective about follow-up...
Featured Thread: Math Challenge - December 2020
Summary: Circulation, Number Theory, Differential Geometry, Functional Equation, Group Theory, Infinite Series, Algorithmic Precision, Function Theory, Coin Flips, Combinatorics.
Featured Thread: Motion-powered GPS tracker to install permanently inside bicycle frame
I could use some help designing a magnetic induction power source to convert kinetic energy to DC power, for use in keeping a GPS unit with GSM SIM card independently powered inside a bicycle frame...
Featured Thread: Starlink phased array antenna
Starlink has begun its public beta phase, and naturally some people were more interested in the electronics than in fast internet access. Here is a video how the satellite receiver looks inside. The first half is focused on the mechanical side, the second half is looking at the electronics.