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: AI, do you fear it?
I think that a lot of people fear AI because we fear what it may reflect about our very own worst nature, such as our tendency throughout history to try and exterminate each other.
But what if AI thinks nothing like us, or is superior to our beastial nature?
Do you fear AI and what you do think truly sentient self-autonomous robots will think like when they arrive?
Featured Thread: Quantum analog of Boltzmann entropy?
In classical statistical physics, entropy can be defined either as Boltzmann entropy or Gibbs entropy. In quantum statistical physics we have von Neumann entropy, which is a quantum analog of Gibbs entropy. Is there a quantum analog of Boltzmann entropy?
Featured Thread: How do I become a mathematician?
I’m currently a senior in high school. All of my applications are finished and I am now in the waiting zone. At the same time, I started to wonder what my future will be and frankly I was quite inspired by the discussion in 2006 about what it takes to become a mathematician...
Featured Thread: Black hole mass coupled to expansion source of dark energy?
A recent article proposes observed black hole growth in ellipticals being coupled to expansion, and sourcing dark energy. Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy..
Featured Thread: Chess fundamentally harder to "effectively" solve than Go?
Typically, the converse is claimed - Go is harder to solve than chess for (among other reasons) simple combinatorics. But for a perfect knowledge player to play effectively against "near-perfect players" I think the reverse may be true...
Featured Thread: Why unitary evolution?
Why is the fundamental evolution of systems postulated to be unitary rather than a more general CPTP map? The usual justification for why the evolution of physical systems is unitary in quantum mechanics involves arguments like "probabilities must sum to 1" or similar arguments that apply equally to any CPTP map. I'm just curious what justifications people here would use for selecting out unitary evolution in particular...
Featured Thread: Staff and Member Appreciation
Did you know we're entering Physics Forums' 22nd year!? Incredible and it keeps getting better and better! We welcomed the MHB community a few months ago and Insight authors published 26 Insights this year! Physics Forums is nothing without the amazing support from you, our members. You make the community.
Featured Thread: Big announcement made fusion energy
The US Department of Energy is set to reveal a “major scientific breakthrough” this week after scientists were reportedly able to produce a fusion reaction that created a net energy gain for the first time.
Featured Thread: How can you tell the spin of a particle by looking at the Lagrangian?
It is extremely mysterious to me how to tell that one Lagrangian should govern one spin as opposed to another. The only thing that sticks out to me at all here are the gamma matrices, which act on spinors. However, a similar term is also present in the Dirac equation, so this can't be the full story. How does the "spin content" drop out...
Featured Thread: Are we living in the matrix? No.
David Tong gives an interesting talk about the lattice chiral fermion problem here. Abstract: Are we living in the matrix? No. Obviously not. It's a daft question. But, buried underneath this daft question is an extremely interesting one: is it possible to simulate the known laws of physics on a computer...
Featured Thread: Most commonly misspelled science and math words
I'm looking for a list of commonly misspelled engineering, science, and math words. What do you see often? Using the list we generate maybe I can clean up Physics Forums along the way.
Featured Thread: Group like operations that are not associative
Is there any example of an operation that fails the associativity test, but meets the other two tests? I'll refer to this hypothetical entity as an almost-group for the purposes of this post lacking any knowledge of a better name. While my specific motivation is in Lie groups, an example of such an operation that is a finite almost-group but not associative would be helpful.
Featured Thread: Extending Newton's laws -- Is the concept of force still defined?
It is argued that the correct interpretation of Newton's 2nd Law for one body of mass m reads "The dynamics (i.e. vector sum of all external forces acting on the body = "all its interactions") dictates the kinetics (i.e. time derivative of the momentum vector = "motion")", under the assumption that the body's mass will not change during the action of the external forces and after that. Now let us assume that the effect of the external forces is to dictate the motion of the body by making it lose mass, i.e. we step out of Newton's 2nd law's assumptions.
Featured Thread: Sabine Hossenfelder on the search for new particles
In private, many physicists admit they do not believe the particles they are paid to search for exist – they do it because their colleagues are doing it. Note: Please read what she is talking about before commenting.
Featured Thread: Artemis 1 going to the Moon: News and Reactions
For the first time in 50 years, a crew capsule is sent towards the Moon again. The Flight Readiness Review (FRR) for Artemis 1 concluded - the rocket is on track for a launch on August 29, 12:33 UTC (08:33 local time) or in the two hours afterward. Backup launch windows are daily from September 2 to September 6.
Featured Thread: Introducing Math Problem of the Week
One of the best things to migrate over from MHB is their Problem of the Week program. Let me introduce the POTW director anemone! anemone had been running the POTW at MHB for 8 years and we're very glad to have her continue the great program here. I'll let her say hi and tell you what to expect!
Featured Thread: What is the correct way of measuring remaining battery capacity?
I was searching for a way to measure the remaining charge of a battery using Arduino. Most (almost all) of the tutorials are simply measuring the battery voltage using the ADC on the Arduino. Is there any better method of measuring the remaining battery capacity that does not use the voltage at the terminals as a reference? (The solution does not have to use an Arduino.)
Featured Thread: Legally Regulating AI
It seems to me that one needs a highly specific definition of what AI is before enforcing such a law. I prefer a very broad definition. I would include James Watt's flyball governor from 1788 as an AI. It figured out by itself how to move the throttle, and it displaced human workers who could have done the same thing manually...
Featured Thread: What New Experiments, If Any, Would Help Determine Light Quark Masses?
Given already high-precision experimental data about hadrons with light quarks, the main barrier to determining u, d, and s quark masses is doing the QCD calculations. But, are the new experiments that could be done that would advance the measurement of these masses?
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.

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