Featured Science Threads - Page 5

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: Math Experiment: Let's Prove Something!
This is an experiment. I thought of a way to bridge the gap between the usual challenge threads. Of course we could shorten the monthly period, but given that there are almost always untouched problems, more of them might not be the solution. Today we had a thread "Is math a language"...
Featured Thread: Is weight a better way to derive energy than flow?
I am trying to figure out the total energy a system of falling buckets can produce, and whether it would be a system that can replace or enhance a system of turbines in a hydroelectric dam situation. I need to figure out the total energy that a system of buckets, suspended on a chain system around pulleys, assuming the pulleys are 10 meters in radius, and that each bucket is 1000 cubic meters, falling for 30 meters...
Featured Thread: Math Challenge - November 2019
Topics include: Stochastic, Topology, Algebra, Analysis
Featured Thread: What Do Newton's Laws Say When Carefully Analysed
Newtons first law follows from the second which is a definition of force. So it has no actual testable physical content. The third law is equivalent to conservation of momentum as is proven in most texts on Classical Mechanics. This is not just a definition, but a testable statement about nature. However we know of this dandy theorem called Noether's Theorem...
Featured Thread: Local flatness pet peeve
I see many posts by several different people referring to spacetime being "locally flat" with the intended meaning of being locally indistinguishable from Minkowski space, i.e., being able to rewrite the metric on orthonormal form and not being able to measure curvature on some local scale. I do not think this is an appropriate nomenclature and the more appropriate nomenclature would be to refer to a local inertial frame. I am aware that some textbook authors, such as Schutz, use the term in this way as well...
Featured Thread: New CRISPR-based tool for find-and-replace editing of DNA
Scientists have developed an improved CRISPR-based gene editing tool that can edit DNA more efficiently and flexibly than existing tools.
Featured Thread: California Fires and Electrical Reliability Around The World
Are the blackouts in California the result of inferior design and practices in the USA electricity grid? One of the big news stories this week is the pre-emptive blackouts in California. Some commentators have said such events could never happen in their country. Why do we read of USA electric supply problems more often than in some other countries?
Featured Thread: Is Lowering School Starting Age To 3 A Good Idea
Over in Scotland you can start prep school at 3 (even younger at some private schools). There is a bit of discussion out here in Aus, due to profiteering in day care centers and the belief it lays a better foundation, that the government lowers school starting age, like Scotland, to 3...
Featured Thread: Is there a quantum uncertainty to the number of atoms in a marble?
Quantum field Theory gives each Fermion and boson its own field, which can be in different quantum states.. what does that mean for the uncertainty of particle number applied to atoms?
Featured Thread: Why isn't back-reaction receiving more study?
The idea that backreaction (the effect of inhomogeneities in matter and geometry on average cosmic evolution) is the source for the apparent late-time accelerated expansion of the Universe is known as the backreaction conjecture.
Featured Thread: Nobel Prize in Chemistry 2019
The Nobel Prize in Chemistry 2019 was awarded jointly to John B. Goodenough, M. Stanley Whittingham and Akira Yoshino "for the development of lithium-ion batteries."
Featured Thread: Nobel Prize in Physics 2019
One half to James Peebles "for theoretical discoveries in physical cosmology", the other half jointly to Michel Mayor and Didier Queloz "for the discovery of an exoplanet orbiting a solar-type star."
Featured Thread: 2019 Nobel Prize in Physiology or Medicine
Today, the 2019 Nobel Prize in Physiology or Medicine was awarded to three scientists who study how cells sense and respond to changes in oxygen levels. These three scientists were previously awarded the Lasker Prize for Basic Medical Research in 2016 for these discoveries.
Featured Thread: Math Challenge - October 2019
Topics include number theory, geometry, stochastics, calculus, topology, functional analysis
Featured Thread: What Are The Economics Of Pebble Bed Reactors
One proposal struck me was talk of using Pebble Bed Reactors which I had never head of. I now have learned about them, and the articles said they produce electricity for about the same price as gas. But in the discussion it was mentioned while expensive to build initially compared to coal powered plants, the new ones have a life of 100 years making it the cheapest form of base-load power generation over its life cycle...
Featured Thread: NASA's Black Hole Visualization/Explanation
NASA's video and annotated image of a black hole simulation. NASA's website has a video and annotated image of a black hole simulation. I found the explanations of some aspects of the weirdness of black hole images interesting.
Featured Thread: Security Versus Programming Language
The following quote caught my eye. "It seems clear that trying to write secure operating systems in C does not work. Very smart people have tried for 50 years, and the solution to the problem is not reduced to practice." I presume that buffer overflow, heap management, and pointer validation are the shortcomings of C that lead to insecurity. But the broader implications make me curious...
Featured Thread: Is there an alternate fuel that de-emphasizes carbon?
Is there a potential fuel, for some kind of engine, not necessarily similar to existing car or diesel engines, that does not have carbon in it? That is, that you might manufacture from water and air without having to concentrate the carbon dioxide somehow. And that's liquid at ordinary temperatures and pressures one might find walking around in an ordinary town...
Featured Thread: New proton radius measurement with electrons favors "muon value"
Previously most measurements using electrons favored a larger value while measurements with muons found a smaller value for the radius. Now a second electron measurement measured a result that agrees with the muon-based measurements...
Featured Thread: Water found on potentially habitable exoplanet
Water found on potentially habitable exoplanet. "Astronomers have for the first time discovered water in the atmosphere of a planet orbiting within the habitable zone of a distant star." - from the BBC
Featured Thread: Authorities in science
Highly respected journals and books are the authorities in science. But they can be challenged by arguments based on other facts. The latter are also taken from highly respected journals and books. Thus one cannot dispense with the authorities....
Featured Thread: When Leaders in a Science Field Die
What happens to research when a leading researcher passes away? A new study looked at this in the Life Sciences . The study observed that when a leading expert in a field died there was a significant increase in publications by new researchers (with new ideas?). it was also determined that those researchers who were coauthors with the expert had a dramatic decrease in their publications...
Featured Thread: Solution Manuals For The Math Challenges
We are often asked for solution manuals of various textbooks. Unfortunately we can't answer those requests, as they are either not existent, from questionable sources, or breach the copyright law. There is no other way than to contact the author or publisher in these cases. The situation, however, is different for our own exercises. I will therefore upload solutions to math challenge questions from the past in this thread...
Featured Thread: Feynman Lectures on Physics Photos posted online
I'm happy to announce that the entire collection of (3043) photos taken of Richard Feynman giving his famous 1961-64 introductory physics lectures at Caltech (including his blackboards - original source material for the book, The Feynman Lectures on Physics [FLP]) have been posted in deep-zoomable format, along with a modified "FLP Notes Viewer" application (now renamed, "FLP Image Viewer") suitable for perusing them...
Featured Thread: Math Challenge - September 2019
Topics: ring of functions, arithmetic-geometric mean, geometry, Hilbert space, quaternions, prime, convergence, curve, gauge transformation
Featured Thread: The Higher Dimensional Analysis of Embryonic Development
It is now possible to obtain almost complete information of important aspects of embryonic development. This includes location and movement of all cells in a embryo as well as which genes are active in each cell. Important information in any attempt to understand ow embryos make adult forms...
Featured Thread: How do entanglement experiments benefit from QFT (over QM)?
A number of posters have asserted that Quantum Field Theory (QFT) provides a better description of quantum entanglement than the non-relativistic Quantum Mechanics. Yet I don't see QFT references in experimental papers on entanglement. Why not?
Featured Thread: Why is p^4 not Hermitian?
Why is p^4 not hermitian for hydrogen states with l=0 when p^2 is?
Doesn't this contradict the following theorem?
The product of two hermitian matrices, A and B, is hermitian if and only if they commute, AB=BA.
Featured Thread: Strong candidate for neutron star + black hole merger found
Found August 14. LIGO/Virgo estimate 99.8% chance that it is such a collision and only 0.2% chance that one of the objects is in the "mass gap": Between 3 and 5 solar masses, heavier than known neutron stars but lighter than known black holes. The chance for every other type of event is negligible. This is certainly something new and will keep astronomers busy for months...
Featured Thread: Russian rocket accident releases radiation
Radiation has been released following a Russian rocket explosion at the Nyonoksa naval ballistic missile test site. Could a short burst of radiation be released if there was no critical nuclear reaction?
Featured Thread: New source of space radiation
Interesting article ...... NEW SOURCE OF SPACE RADIATION: Astronauts are surrounded by danger: hard vacuum, solar flares, cosmic rays. Researchers from UCLA have just added a new item to the list. Earth itself...
Featured Thread: Mathematical Model finds Acoustic Signal that May Predict Earthquakes
"Previous machine-learning studies found that the acoustic signals detected from an earthquake fault can be used to predict when the next earthquake will occur," Ke Gao, a computational geophysicist at Los Alamos National Laboratory..."
Featured Thread: How does green screening technology handle secondary reflection of green?
I get the basics of green screening. The processing software recognizes a small range of green and can substitute a different image where it occurs. Here's what I don't get: if a subject is standing in front of a green screen, they will have reflections of green...
Featured Thread: Part of the Hubble discrepancy can be explained by local underdensity
Interesting paper on the arXiv today. The authors claim that there is observational evidence that we live in a region with slightly lower density than the universe average, just by chance. Taking this into account can explain as much as 5.5% of the discrepancy in the Hubble constant between the local measurements and the CMB measurement. If you shift the local measurements to lower values by 5.5% (about 3.8 km/sec/Mpc), then the discrepancy is within the experimental errors...
Featured Thread: Math Challenge - August 2019
1. - 2. posed and moderated by QuantumQuest
3. - 8. posed and moderated by Math_QED
9. - 10. posed and moderated by fresh_42
Keywords: calculus, abstract algebra, measure theory, mechanics, dynamical systems
Featured Thread: Two White Dwarfs in a seven minute mutual orbit
The rare discovery is the second-fastest pair ever discovered, whipping around each other at speeds reaching hundreds of kilometers per second. The two white dwarf stars complete an orbit around each other every seven minutes. It's also known as an eclipsing binary system because one of the stars repeatedly crosses in front of the other...
Featured Thread: Why randomness means incomplete understanding
Suppose we want to create a device that faithfully simulates some aspect of Nature. To do so, we need to know enough about the working of this aspect so that we know how to build the simulation. Being able to create a detailed blueprint for a perfect simulation means that we understood this aspect. Not being able to do this implies lack of understanding...
Featured Thread: Is quantum theory a microscopic theory?
Quantum theory is widely thought to be a theory of the fundamental microscopic constituents of matter. It is supposed to tell us something about how matter behaves at the fundamental microscopic level, from which the classical macroscopic behavior should somehow emerge...
Featured Thread: The Story behind the Apollo 11 and the 1202 Computer Error Code
Perhaps the most dramatic moment of Apollo 11's mission to the moon was when the Eagle began its final descent to the lunar surface and the Apollo Guidance Computer became overloaded. Few were more nervous than the young computer programmer who had written the code for the landing...
Featured Thread: SI meter definition changed?
The wording of the definition of the meter has apparently changed recently. I'm wondering about the motivation for the change. The current definition is...
Featured Thread: New H0LiCOW result: Hubble constant is 73.3 +1.7-1.8 km/(s*Mpc)
The collaboration with the questionable acronym improved their measurement with a joint analysis of the whole dataset of six gravitationally lensed quasars. Measurements based on supernovae (measuring the Hubble constant "now") and measurements based on the cosmic microwave background (needing an extrapolation to get the current value) have been in disagreement for a while now...
Featured Thread: Member jim hardy has died
It is with profound sadness that I must report that we've learned legendary PF brother @jim hardy passed away earlier this week. Jim was loved by countless members here and was an incredible positive force for the community and all our outside readers...
Featured Thread: Math Challenge - July 2019
1. - 4. posed and moderated by QuantumQuest
5. - 8. posed and moderated by Math_QED
9.+10. posed and moderated by fresh_42

keywords: calculus, polynomials, trigonometry, diagonalizability, projective linear spaces, finite vector spaces, Brownian motion, Galois groups, matrix decomposition, Hilbert spaces
Featured Thread: Interval between double sonic booms
Yesterday afternoon I heard (and so did every bird in the district) a very loud, low frequency, double boom which was very vigorous and I suspected all sorts of things but then I thought "double boom!!" and (engaging smartarse mode) I informed my wife that it was only a sonic boom. I was later proved right...
Featured Thread: Anti the Anti-Vaxers
Article with data showing immunizations save more than they hurt. Vaccines are one of the great benefits of biology has bestowed upon humanity, in that they have saved many lives and greatly reduced suffering...
Featured Thread: Crystal with two different melting points
Back in 1896, acetaldehyde phenylhydrazone (APH) kept melting at two very different temperatures. A batch he produced on Monday might melt at 65 °C, while a batch on Thursday would melt at 100 °C. Here's why...
Featured Thread: What is the value in visiting the Moon again?
Just interested in what may be achieved by putting a man/men on the moon again.
Featured Thread: Quantum Jumps and Schrodinger's Cat are predictable
Quantum Jumps are predicted using microwave monitoring. Weird. "Yale researchers have figured out how to catch and save Schrödinger's famous cat, the symbol of quantum superposition and unpredictability, by anticipating its jumps and acting in real time to save it from proverbial doom." - physorg
Featured Thread: Math Challenge (with prizes!) - June 2019
Test your skills on 15 math challenges! We have a prize this month donated by one of our most valued members, and that's what the points are for. The first who achieves 6 points, will win a Gold Membership!
Featured Thread: Early moment detection that marks the start of massive tremor events
"Whether earthquakes of different sizes are distinguishable early in their rupture process is a subject of debate. Studies have shown that the frequency content of radiated seismic energy in the first seconds of earthquakes scales with magnitude, implying determinism "

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