Featured Science Threads - Page 4

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...

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...

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...

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)

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...

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...

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...

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...

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)

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.

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."

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.

How does the scaling of the numerical output of a forward FFT compare to the mathematical definition of the Fourier transform?

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.

A lot of calculus questions this month, but a bit (linear and abstract) algebra, too. The functional analysis question is a bit tricky.

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?

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...

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.

Topics include Useful Equations And Inequalities, Calculus, Functional Analysis, Small Groups

The red giant, and semi-regular variable, Betelgeuse is the dimmest seen in years, prompting some speculation that the star is about to explode.

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?

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.

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.

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.

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.

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?

Test your skills with challenging problems on Topology, Calculus, Group Theory...

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...

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...

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...

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...

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...

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"...

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...

Topics include: Stochastic, Topology, Algebra, Analysis

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...

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...

Scientists have developed an improved CRISPR-based gene editing tool that can edit DNA more efficiently and flexibly than existing tools.

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?

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...

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?

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.

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."

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."

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.

Topics include number theory, geometry, stochastics, calculus, topology, functional analysis

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...

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.

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...

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...