Featured Science Threads - Page 3

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 Challenge - May 2020
Test your skills in this month's math challenge thread! Topological spaces and metrics, integrals, abstract algebra (groups and rings), heat equation, geometry .
Featured Thread: Almost Plausible Solar Takeover Plan
I'm normally among those who think that renewable advocates lack realism when they advocate 100% wind+solar grid. This article is the first I've seen that comes close to being plausible. I do doubt the article's numbers for storage and for wind, but the basic idea of massively overbuilding solar is in the right direction...
Featured Thread: What Have Educators Learned About Distance Learning?
The cumulative experience with distance learning must have soared in the past 2 months.
  • What has been learned?
  • What works? What doesn't work?
  • Are there new distance learning methods or strategies for the coming fall term?
Featured Thread: T2K sees ~3 sigma evidence for neutrino CP violation
Previous measurements already hinted at this, now we have a relatively strong single measurement. CP violation is linked to matter/antimatter asymmetries. They are small for quarks, but it looks like they are larger in the neutrino sector. The measurement favors the maximal CP violation that was still within the range set by other parameters. DUNE will measure this parameter more precisely in the future.
Featured Thread: Why do boats have a pointy bow?
A (displacement) boat hull has a design goal of making as little water resistance as possible with the required volume for load carrying capability. To achieve this the hull is given the shape similar to a vertical symetrical airfoil. But as the leading edge of a boat (it's bow) seems to be made as sharp as possible, the leading edge of airfoils are round. Why aren't boats bow round as the airfoil?
Featured Thread: Physics Challenge April 2020
Can solve solve one of these 3 physics challenge problems? This is an experiment if we could establish a little physics competition. Topics include, Classical Physics, Special Relativity Theory
Featured Thread: Clarification of accelerator physics terminology
I have been reading some papers on accelerator physics recently, especially those on the LHC and the upcoming FCC-hh. As a beginner, I am not supposed to know everything, but there are a few terms that I feel I have to know in order to penetrate further into this field...
Featured Thread: How can I measure the terrestrial tide on my place?
How can I measure the terrestrial tide on my place? Since i don't have a MEMS gravimeter or a laser spectometer what will be the simplest method to measure the local earth tide variations?
Featured Thread: Math Challenge - April 2020
Calculus (Polynomials, Series and Functions), Differential Equations, Operators, Normal Distribution, Number Theory (Authors: Infrared - IR; QuantumQuest - QQ; fresh_42 - FR)
Featured Thread: Can dx be negative?
This is more of a "housekeeping" question (i.e. it's not particularly interesting), though I haven't studied much in the way of infinitesimals so apologies in advance for my lack of rigour! As far as I'm aware, an infinitesimal can be thought of as a small change in some quantity. Changes can be either positive or negative, so subsequently it also seems reasonable for ##dx## to potentially represent a negative change...
Featured Thread: Can large Black Holes ever spaghettify? (and more)
So Alice and Bob are hanging out near a really large black hole. It's quiet. Nothing has entered the BH is a while. Alice tosses Bob in and then waits long enough for him to collide with the singularity. Of course, Bob is keeping time differently than Alice - so I rather doubt that the time period Alice calculates for Bob to reach the "center" has any real meaning to Bob. But Alice's real goal is to enter the BH herself and to never seen Bob again...
Featured Thread: Innovations to help COVID-19 treatment efforts
I didn't see a thread so far in the Medical forum that addressed the specific innovations that are being worked on to help combat this pandemic, so I thought I'd start this thread. One such innovation may be using plasma from Pts who have recovered from the virus to help treat new Pts. I don't know much about that, so hopefully Bill or Jim or others can comment...
Featured Thread: Why is rolling easier than sliding?
I learned that rolling involves the coefficient of static friction unlike sliding that involves the coefficient of kinetic friction. It's known that the coefficient of static friction is always higher than the coefficient of kinetic friction. This should result in rolling to be more difficult than sliding as it involves higher frictional force, which is not the case in real life...
Featured Thread: Math Challenge - March 2020 (Part II)
This is an extra round of questions, because the ones in part I had been solved so fast. However, we still have some easy ones here. They are from calculus, abstract algebra, algebraic geometry, and topology. (Authors: Infrared- IR; fresh_42 - FR)
Featured Thread: Quickly Transitioning to Teaching Online Due to COVID-19
There's a good chance that the spread of the COVID-19 virus will cause colleges and universities to suspend on-ground class meetings. I know that UC Berkeley and UCLA have already done so to some degree, and the schools I teach at have suggested instructors prepare the possibility by getting ready to teach courses online...
Featured Thread: What makes the current coronavirus different than others?
An interview on NPR with virologists discussed the reasons that this current viral pandemic is different than others in the past. Key differences were: - Ability of make new viruses - apparently 1000 times more prolific than flu...
Featured Thread: Tidal effect of Sun on Earth
It's well known that the tidal effect of the Moon on the Earth causes the Earth's rotation to slow down and the radius of the Moon's orbit to increase over time. However, the Sun also exerts a tidal effect on the Earth, which should also contribute to slowing down the Earth's spin. This raises two questions...
Featured Thread: Students Engaged In Active Learning Think They Learn Less
My classes are a blend of both. My students had to do a pre-lecture in which they had to read up something or watch a video, followed by a short quiz based on the material that was presented. When to come to class, I give them a "traditional lecture", but heavy on (i) clicker questions and discussions, (ii) in-class problem solving where they work in groups to solve problems, and (iii) in cases where we have "labs", the experimental work is often incorporated within the lecture as they are observing the result...
Featured Thread: Math Challenge - March 2020
We have a variety of areas this month: calculus, trigonometry, topology, algebra (geometry, linear, abstract), so I hope you all will find an interesting one. Authors: QQ (QunatumQuest), IR (Infrared), FR (fresh_42)
Featured Thread: Debris found in fuel tanks of 70% of inspected 737 Max jets
Yes, that 737 Max. News. It's unclear if these airplanes were supposed to be delivered to customers already if the 737 Max wouldn't be grounded for other reasons, but foreign objects in more than half of the inspected planes is certainly nothing customers want to see. There are 350 more aircraft waiting they have to check.
Featured Thread: E=mc^2 before Einstein
A short historical paper gives evidence that Einstein was not the first who discovered E=mc2E=mc2. "The mass-energy relation E=mc2 has a dual origin, one grounded in the postulate of the existence of an aether made of "ultramondane particules" moving in space at the speed of light, c; the other, a consequence, first deduced by Henri Poincare, of John Poynting's electromagnetic Theorem."
Featured Thread: Ptolemaic Model of Solar System
Why did the Ptolemaic model coupled the motion of Venus to the sun? You notice that the center of the smaller orbit of Venus is always in line with the sun. Anyone knows why those folks back then forced it to move this way? There must be a reason why they thought Venus was always very close to the sun and can't move too far away from it.
Featured Thread: FFT scaling vs analytical FT
How does the scaling of the numerical output of a forward FFT compare to the mathematical definition of the Fourier transform?
Featured Thread: Proper barograph linkage settings for maximum pen displacement?
What would the settings be for both the linkage and the screw so that the smallest change in the aneroid disc causes the largest change in the movement of the recording chart pen? Currently, I have the screw screwed all the way into the axle up to the lock nut and I am utilizing the last hole in the linkage.
Featured Thread: Math Challenge - February 2020
A lot of calculus questions this month, but a bit (linear and abstract) algebra, too. The functional analysis question is a bit tricky.
Featured Thread: Amateur microscope mostly for children
When I was a child I used to have a microscope. I don't remember the maximum zoom it could do. Nowadays when I look up for amateur microscopes on the web, they seem to go up to either 1000x or 2000x. Do you think it's enough to get some fun by looking at bugs and cells of onions for example? The use would not be for research, only to have fun. Is there any recommendations you could provide?
Featured Thread: An observer passing the event horizon of a black hole
I am not particularly well aquainted with GR and my questions are concerning the often mentioned statement that an observer that passes the event horizon won't notice it. But is this really correct? I have recently thought about different scenarios and I have three particular ones below that I would like others to consider...
Featured Thread: LIGO+Virgo saw something unknown
Not much is known so far. It was a very short burst seen by all three detectors, with a false alarm rate of 1 per 25 years - a good chance this is something real. The burst was 14 milliseconds long and the fitted central frequency is 65 Hz, which means they had just about a single cycle in the signal. Expect more updates in the following days.
Featured Thread: Math Challenge - January 2020
Topics include Useful Equations And Inequalities, Calculus, Functional Analysis, Small Groups
Featured Thread: Betelgeuse unusual dimming, ready to supernova?
The red giant, and semi-regular variable, Betelgeuse is the dimmest seen in years, prompting some speculation that the star is about to explode.
Featured Thread: Innovative Scientific Uses of GPS
New ways to use GPS for scientific purposes. Feel an earthquake, Monitor a volcano, Probe the snow, Sense a sinking, Analyze the atmosphere. What are some that you can come up with?
Featured Thread: See the first precise pulsar surface map
Using NICER data, scientists have obtained the first precise and dependable measurements of both a pulsar’s size and its mass, as well as the first-ever map of hot spots on its surface.
Featured Thread: A second Genesis more likely if life is found on Europa or Enceladus.
Life on Europa has been discussed on threads on pf previously. This post relates to models (Jay Melosh) looking at whether life on Europa/Enceladus would be the result from lithopanspermia or from scratch, abiogenesis. Some NASA missions in the pipeline may shed some light on this in the next decade with 'Dragonfly' scheduled for 2026.
Featured Thread: NASA is going to assemble a quiet supersonic aircraft: X-59 QueSST
The final approval to build the X-59 QueSST has been given. It will be reviewed in late 2020 for a flight in 2021. What do you think - is there still a market for civilian supersonic aircraft? They are faster, but they are more expensive and offer less comfort than subsonic aircraft.
Featured Thread: How to prepare my camera for a solar eclipse
There will be a solar eclipse on 26th December that can be viewed from my city. In addition to buying safety glasses, I also want to prepare my camera, if possible.
Featured Thread: Does the statistical weight of data depend on the generating process?
If we have two identical data sets that were generated by different processes, will their statistical weight as evidence for or against a hypothesis be different?
Featured Thread: Math Challenge - December 2019
Test your skills with challenging problems on Topology, Calculus, Group Theory...
Featured Thread: Help with Building a Vacuum Chamber
A client asked me to look into designing a vacuum chamber for drying out lumber. I am a decent fabricator but sadly not so great at the physics side of things. I know the chamber I'm building will need pretty thick material and a lot of reinforcement. He wants it to be roughly 10'x3'x3' inside dimensions...
Featured Thread: Scientists engineer E. coli that eats carbon dioxide
E. coli is one of the best studied and most widely used bacteria in biotechnology. This week, published in the journal Cell, researchers report having engineered the bacterium to be able to generate all of its carbon from CO2, opening the way toward using these bacteria for replacement of petrochemicals in manufacturing...
Featured Thread: Compilation of severe errors in famous textbooks
For the sake of helping student to avoid confusions, I wonder if we can make a compilation of known errors made in standard and commonly used textbooks. Not talking about some random typos, but more when like the entire treatment of a subject is fundamentally flawed...
Featured Thread: Effects of a Change of Direction of Rotation of the Earth?
What would be the effects/consequences if the Earth rotated about its axis in a North-South ( or South-North) direction instead of an East-West one as it currently does, and at the same rate, i.e., with a period of around 24hrs( while keeping the same rotation about the sun unchanged)s...
Featured Thread: New measurement of the Hubble constant is consistent with the CMB value
This paper just came out with a new measurement of the Hubble constant based on the technique of gamma ray attenuation. The result is consistent with the lower (CMB-based) value. Interestingly, they also do a joint analysis of several non-CMB techniques (BAO+BBN+SN+γ-ray attenuation), and find a value completely consistent with the CMB value...
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...