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: 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.
Featured Thread: Quiescent voltage of op-amps
Estimate the quiescent voltages at the inputs and outputs of the two op-amps and the overall voltage gain (in decibels) of the circuit at the frequency of operation. State any assumptions made.
Featured Thread: Math Challenge - November 2020
Summary: Diffusion Equation, Sequence Space, Banach Space, Linear Algebra, Quadratic Forms, Population Distribution, Sylow Subgroups, Lotka-Volterra, Ring Theory, Field Extension.
Featured Thread: Octonions and the Standard Model
A survey of attempts to connect the octonions to the Standard Model - mainly explaining the math and having fun, not advocating any particular theory. I've slowly been writing a thread on octonions and particle physics, just to explain some facts in a self-contained way, with all the proofs. I don't know where this will lead. I'm certainly not presenting a theory of physics, much less advocating one. Mainly it's just fun.
Featured Thread: Automation Ethics: Should your car serve you or serve society?
Tesla’s Autopilot a ‘distant second’ to GM’s Super Cruise system in Consumer Reports testing. I think this is very interesting because of Consumer Report's reason for their evaluation. The GM autopilot aggressively monitors the driver to make sure he/she is alert and paying attention. The GM autopilot can be used only on preplanned roads and not on residential suites.
Featured Thread: NASA discovers water on the moon!
"NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) has confirmed, for the first time, water on the sunlit surface of the Moon. This discovery indicates that water may be distributed across the lunar surface, and not limited to cold, shadowed places."
Featured Thread: US Schools Are Changing Their Grading System. Is It A Good Idea?
A discussion of whether or not it is a good idea to modify the U.S. K-12 educational system with the new "Equitable Grading System" now being implemented in, for example, San Diego, CA ?
Featured Thread: Number of known asteroids reaches 1 million!
We find asteroids faster than ever before. By 1921 astronomers knew 1000, then it took almost 70 years to extend that to 10,000 (1989). Just 16 years later we reached 100,000 (in 2005), and 15 more years later we reached 1 million. Early discoveries were people looking at analog photos, but now most discoveries are done by computers analyzing giant datasets...
Featured Thread: Introduction to Pitot-Static Systems in Gliders
Like many others, I have been seeking new and fun things to do during a pandemic. I decided on the new Microsoft Flight Simulator 2020, but the Condor 2 Soaring Simulator is my intermediate step. I am certified as a pilot, including gliders, but I have not flown for many years because of the expense. These simulators will allow me to join much of the fun and to greatly increase my skills, while semi-quarantined...
Featured Thread: 2020 Nobel prize in physics
The Nobel Prize in Physics 2020 was divided, one half awarded to Roger Penrose "for the discovery that black hole formation is a robust prediction of the general theory of relativity", the other half jointly to Reinhard Genzel and Andrea Ghez "for the discovery of a supermassive compact object at the centre of our galaxy."
Featured Thread: Math Challenge - October 2020
Summary:: Functional Analysis, Algebras, Measure Theory, Differential Geometry, Calculus, Optimization, Algorithm, Integration. Lie Algebras.
Featured Thread: This is why EM interference can be an issue...
Good story about hunting for an interfering RF source, where you are trying to track down an interfering signal. We do them frequently for practice (as HAM radio operators), and have used the skills a few times for real. I haven't done it in the rain yet, though...
Featured Thread: There's Gold in Them Neutron Stars - or - Maybe Not
When humanity finally detected the collision between two neutron stars in 2017, we confirmed a long-held theory - in the energetic fires of these incredible explosions, elements heavier than iron are forged. But a new analysis has revealed a problem...
Featured Thread: Parents' frustration with distance learning -- "Common Core Math Methods"
Interesting article. At first I thought the article was saying that for many parents, helping their kids with their math homework was the hardest because maybe they weren't all that great at math themselves.
Featured Thread: Math Challenge - September 2020
Summary: group theory, number theory, commutative algebra, topology, calculus, linear algebra
Featured Thread: Spectroscopy of positronium fine structure: 4.5 sigma deviation
A recent study measures a transition frequency in positronium higher than predicted. They produce very slow positronium excited by a laser, that suppresses uncertainties previous measurements had and improves the statistics. They also have ideas how to reduce the uncertainties that are still relevant. No indication of the measurement time that went into the study, but taking data for a longer time will certainly help even if they don't make larger upgrades.
Featured Thread: Your favorite Eureka moment for proofs
What was your favorite proof or Eureka moment you remember? Mine was about normal subgroups.. You learn the definition and prove a few properties and go to the next subject. I remember that I once tried to teach the concept to someone and in the middle of my explanations I all of a sudden realized...
Featured Thread: The mathematical definition of "wave"?
What is the mathematical definition of a "wave" and the quantities associated with a wave, such as group velocity, phase velocity etc.? Is there a standard mathematical definition for "wave"? What is the definition? Assuming that there is a definition, what are the mathematical definitions of the properties of waves? For example, how is the "group" of a wave defined? ( as in the "group" that has a "group velocity").
Featured Thread: Computer languages as examples in formal logic
A computer language is not a clear example of a formal language, a formal system, or a formal logic. Can we modify the rules for a computer language to create clear examples?
Featured Thread: 5x5 Magic Squares
A magic square is a NxN array of numbers from 1 to N2 such that the sum of elements of each row, column and diagonal adds up to the same number, 65 in the case of 5x5's. An example would be...
Featured Thread: A bit confused about significant figures
Suppose I took a pile of measures of length: 18, 19, 20, 21, 22, 23, 24, 25 giving a mean of 172/8 = 21.5 on my calculator. If I have to give the mean to the lowest number of significant figures then that would give an answer of 20 - which feels wrong. I think I should work to 2 sig fig so 22 - which makes sense. So I guess my question is how how many sig fig does 20 have? Can it depend on the context?
Featured Thread: ATLAS and CMS see signs of Higgs->muons decay
The Higgs boson couples to mass, muons are relatively light, that makes a decay to a pair of muons (muon+antimuon) very rare. In addition there are many other processes that produce pairs of muons, making this decay mode challenging to find. For a long time it was expected that the experiments would need the high luminosity upgrade for a clear signal...
Featured Thread: Math Challenge - August 2020
functional analysis, operator theory, topology, measure theory, calculus
Authors: Math_QED (MQ), Infrared (IR), Wrobel (WR), fresh_42 (FR).
Featured Thread: Difference between Physics and Mathematics
Our forums are full of physics and mathematics. One cannot talk about the former without getting into calculations and mathematics sooner or later: Hilbert spaces, differential operators and linear algebra all over the place. Students of both faculties have normally a similar motivation, foundation and interests in both - more or less...
Featured Thread: Face shield bleach disinfection
Face shield or respirators are getting to be as common as masks in public. What kind of bleach in basin can theoretically kill the covid-19 virus? What should be the concentration of bleach and now does it kill it?
Featured Thread: Starting to Learn Python: Development Tools and Environments
There is a dizzying array of editors and IDE's out there. What is a good option to get started? I've never programmed (or done anything technical) on Windows. Is there any general advice about using the Windows environment for programming? I don't want to get into installing Linux at this stage. Do I need to be able to find my way around the Windows O/S, or does an IDE make that unnecessary?
Featured Thread: Twin paradox explained for laymen
As a layman I also have conceptual difficulties with the twin paradox. It would allow me to move on if some one could quickly answer the rather obvious question: would there be any time dilation if the earth was removed entirely from the thought experiment so that the twins are in a symmetrical relationship of inertia or relative motion. I cannot see how there could be but would then have to look to gravity to explain it.
Featured Thread: Using Far-UVC Light To Kill Airborne Human Coronaviruses
This paper was published in Nature, and it presented a rather fascinating result if it is true. The researcher used far-UVC light (222 nm wavelength) to kill the viruses in airborne aerosol with a claim based on the current guidelines that far-UVC is not as harmful as UVA and UVB.
Featured Thread: LHCb discovers a new tetraquark state
In a recent paper submitted by the LHCb collaboration at arXiv, they have reported a tetraquark state composed of charm quarks and antiquarks. The statistical significance of the data is more than 5σ...
Featured Thread: Math Challenge - July 2020
Functional Analysis, Topology, Differential Geometry, Analysis, Physics
Authors: Math_QED (MQ), Infrared (IR), Wrobel (WR), fresh_42 (FR).
Featured Thread: Meaning of quark mass
What is the meaning of the mass assigned to an individual quark?
A hydrogen atom is less massive than the sum of an unbound proton and an unbound electron. If I add energy to the atom the system becomes more massive, and when I add enough then I have an unbound electron and proton, each of which has the usual mass...
Featured Thread: Dark matter experiment XENON1T sees an excess at low energies
XENON1T sees an excess of events at low energies that doesn't have a good explanation at the moment.
Featured Thread: A Competitor to the Drake Equation
A alternative to the Drake Equation for thinking about how likely intelligent life on other planets has been recently published. The Astrobiological Copernican Weak and Strong Limits for Intelligent Life proposes a different way to think about the possibility of intelligent life other places than earth.
Featured Thread: PF has donated to support black STEM organizations
In honor of Juneteenth , PF has donated $50 to Black Girls Code and $50 to The National Society of Black Engineers. See what you can do today and beyond to further the support for african-americans in STEM!
Featured Thread: Differential Forms or Tensors for Theoretical Physics Today
There are a few different textbooks out there on differential geometry geared towards physics applications and also theoretical physics books which use a geometric approach. Yet they use different approaches sometimes. What are the advantages of one over the other? Do theoretical physicists today tend to prefer one over the other and is it field specific?
Featured Thread: Math Challenge - June 2020
Normed, Banach and Hilbert spaces, topology, geometry, linear algebra, integration, flux.
Authors: Math_QED (MQ), Infrared (IR), Wrobel (WR), fresh_42 (FR).
Featured Thread: Elevators and airflow
Elevators are a problem in this post COVID world. It is impossible to maintain social distancing while also meeting the passengers-per-hour needs of the building. Skyscrapers without efficient elevators are not practical.
Featured Thread: SpaceX Crew Dragon Launch Try #2 3:22PM EST
Watch history unfold on Saturday, May 30, as NASA and SpaceX launch astronauts Robert Behnken and Douglas Hurley to the International Space Station. Here we go again! Set for 3:22PM EST. Lots of analysis in this live video already!
Featured Thread: Project Loon, Stratospheric balloon
Project Loon is a network of stratospheric balloons designed to bring Internet connectivity to rural and remote communities worldwide. There is one being tracked, between Reunion and Mauritius in the Indian Ocean. Another one over Equador, 6 over Peru, 1 over Puerto Rico, 3 over Kenya and 1 near the Seychelles.
Featured Thread: Crew Dragon Demo-2: Launch at 4:15PM EST
It doesn't happen every day decade that people are being launched to orbit in a new spacecraft. The last time it happened was 2003 (Shenzhou), and the last time before that was the Space Shuttle in 1981. The next time will be in 12 hours, if the weather stays good. And for the first time it is a private spacecraft. Going to orbit is no longer the exclusive domain of governments. You can call SpaceX if you want a ride (and have maybe 100 million dollars).