Featured Science Threads - Page 8

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: Methane and Organic Molecules on Mars
Curiosity has found seasonal occurrences of methane and some organic molecules on Mars. Both or possible indicators of carbon based life processes, but can have other non-biological explanations. Methane has been intermittently found previously on Mars. However, lacking a continuous long term record the seasonal variations were not obvious. The seasonal variation could be explained by either biological...
Featured Thread: Basic Math Challenge - June 2018
Summer is coming and brings a new basic math challenge! Enjoy! For more advanced problems you can check our other intermediate level math challenge thread!
Featured Thread: Maxwell's equations and QFT
I have been wondering about the validity of Maxwell's equations in quantum physics. I looked in the internet and it seems from what I understood that: Maxwell's equations are valid for any situation, classical or quantum. In fact, maybe it holds more legitimacy than Schrodinger equation since it is a relativistic (invariant) set of equations...
Featured Thread: MiniBooNE results at 6.1 sigma
New evidence in the search for the 'sterile' neutrino. Can someone comment on this please.
Featured Thread: Challenges for artificial intelligence
Here I would like to see interesting challenges for artificial intelligence, which seem very hard for AI and yet in the spirit of what AI usually does. Here is my proposal: Let us feed the machine with a big sample (containing, say, a million numbers) of prime numbers and a big sample of non-prime numbers, without feeding it with a general definition of the prime number...
Featured Thread: Two-stage electron wakefield acceleration
The energy of electron-positron colliders is limited by the acceleration gradient (energy per distance) and the length of the accelerator (=the cost). In the past the energy mainly increased from making accelerators larger. Much larger accelerators than today get prohibitively expensive, however. More compact designs could keep them affordable. While conventional cavities still make some progress...
Featured Thread: Area of a circle without calculus
π is defined by the ratio of the circumference (R) of a circle to its diameter. The area of the circle is πR². Can this be derived without calculus (or Archimedes method)?
Featured Thread: CMF bulletproof body armor
The CMF armor on collision literally converts the projectile into small particles, spraying out. This is interesting and definitely not my area. Questions: the particles resulting from the hit have to have kinetic energy, if some particles are redirected to unprotected area (example: projectile hits high, just above the top of the sternum, redirect up into the lower jaw), are they a problem?
Featured Thread: Best Temperature of Water For Rinsing Dishes?
What is the best temperature water for rinsing dishes? I've googled this question, and gotten many answers, very few of which have any rational basis for them whatsoever. For example, some people say that it's better to use hot water, because the soap dissolves better in hot water. However, it's not at all clear to me that dissolving is the underlying mechanism for getting rid of the soap...
Featured Thread: Is there a plan for a search for nearby black holes?
Extrapolating to a sphere centered on Earth with a 100 ly radius, this sphere should contain about 625 stars bigger than red dwarfs and 8 black holes, of which about 4 would be in binary systems. Systematically observing the Doppler shifts for these 625 stars over a period of time should detect any invisible massive companions. Is such a search currently happening or planned?
Featured Thread: Asymptotic Safety for Quantum Gravity
Sabine Hossenfelder recently wrote about an old theory of quantum gravity due to Weinberg: asymptotically safe quantum gravity. Is anyone familiar with this idea? What I couldn't figure out from the article is whether asymptotic safety is an approach to making consistent quantum field theories, or whether some quantum field theories just happen to be asymptotically safe...
Featured Thread: Teaching Economics Without Calculus
Just a quick question. Can you really teach economics without calculus? Reviewing it now just to refresh my memory since we have a budget being delivered tomorrow here in Aus. I have reached the point where it is proven that maximizing overall profit is different from profit per unit of whatever you are considering - you can maximize one or the other - but not necessarily both...
Featured Thread: A couple of links about, not from science
We repeatedly receive some fundamental questions, some of them of philosophical nature, which we're not very keen to answer - not because they weren't legitimate questions, but because we made the experience, that they simply lead nowhere, and, I'll have to admit, because of the lack of knowledge what philosophers already had written about it...
Featured Thread: Seeking a cheap wide mouthed jar capable withstanding vacuum
I'm looking for a cheap, wide mouthed jar capable of withstanding moderate vacuum (up to 29-30" Hg). The jar I've currently been using is like this one with a rubber stopper and plumbing valve in place to hold vacuum once evacuated, which works well, but I now need something in a 3-4" width...
Featured Thread: Some Questions on Differential Forms and Their Meaningfulness
I've been trying to get a meaningful understanding of the benefits of using differential forms. I've seen examples of physics formulas that are reduced to a very simple declarative form relative to their tensor counterparts. However to me it just seems like a notation change to implied tensor indices...
Featured Thread: Propane heater behavior
I have one of these propane heaters. As months go by, it has an increasing habit of spazzing out. It will frequently do this in a strong gust. But with even a little wind, and more often when it is set on low, it will spontaneously and startlingly begin screaming like a rocket engine. When it does so, the mantle immediately starts cooling...
Featured Thread: Intermediate Math Challenge - May 2018
Math Challenge threads are back! To kick things off we have a set of "intermediate" math challenges! For more basic problems you can check our other basic level math challenge thread! Please read and adhere to the rules posted at the top of the challenge thread. Enjoy!
Featured Thread: Basic Math Challenge - May 2018
Math Challenge threads are back! To kick things off we have a set of "basic" math challenges! For more advanced problems you can check our other intermediate level math challenge thread! Please read and adhere to the rules posted at the top of the challenge thread. Enjoy!
Featured Thread: What type of bacteria evolved into mitochondria?
An important step in the evolution of plants, animals and other complex, multicellular forms of life was eukaryogenesis, the evolution of eukaryotes. Eukaryotes are one of the three major classifications of life (alongside single-celled bacteria and archaea), and are characterized by cellular compartmentalization, an extensive membrane network inside of the cells, and the presence of mitochondria...
Featured Thread: STEM Bibles List
By STEM I mean science, technology, engineering and math. By a bible, I mean a book which is comprehensive, big and heavy (both physically and intellectually), authoritative, and generally highly respected in the community as the standard book that contains more-or-less everything one need to know about the subject...
Featured Thread: One of my wheelchair motors overheats and stops working
I use an electric wheelchair to get around and can only walk a few steps with a wheeled walker. Yesterday I went to my local out of town ASDA, a 1.5 mile trip approx through an alley/Public Footpath, I have done this many times before. This time I was about 3/4 of the way there and the chair started to judder and slow down and pull to the right. It then stopped...
Featured Thread: Young Edison, or Edison's cat
Today, I'm enjoying a very good book about the young Thomas Alva Edison when he was 10-15 years old. I just came across this fun anecdote that I can't resist sharing. It reminds me of the many threads we get here on PF asking about novel ways to generate electricity.
Featured Thread: New result in high temp superconductivity
This suggests the possibility no new theory beyond BCS is necessary.
I’m interested especially in comments by members who work in this or related fields.
Featured Thread: Magnetic flux is the same if we apply Biot Savart?
Initially I am aware that magnetic flux is conserved due to divergence of magnetic field is zero and for long solenoid, magnetic field inside is uniform. So magnetic field intensity (B) at point P,Q,S, T,R,U(in the attachment) must be same. But my question is : can we obtain the same magnetic field intensity at point S or R again at the point P or U using biot savart rule for constant current?
Featured Thread: What false hints of new physics were most notable?
Sometimes experimental or observational evidence from credible physicists points to new physics and then turns out to be wrong due to statistical flukes, experimental error or a theoretical analysis mistake. What cases of this happening do you find most notable, what showed that the hints were unfounded, and why do you find them most notable? I'll start with four, to which you can add your own...
Featured Thread: Is there a local interpretation of Reeh-Schlieder theorem?
Non-philosophically inclined experts in relativistic QFT often insist that QFT is a local theory. They are not impressed much by arguments that quantum theory is non-local because such arguments typically rest on philosophical notions such as ontology, reality, hidden variables, or the measurement problem...
Featured Thread: Freeman Dyson's 1972 paper "Missed Opportunities"
I just stumbled upon the well-written 1972 paper "Missed Opportunities" by Freeman Dyson. Dyson argues that over time, people have become worse in following the mathematical hints inherent in the structure of physical theories. As an example, he compares the developments in both mathematics and physics following Newtonian physics with the "failure" to discover special relativity based purely on the transformation properties...
Featured Thread: Beauty of old electrical and measuring things, etc.
Even as a kid, I saw beauty in old devices. That made me want to understand how they worked. I had lots of old things that I keep and now reviving. Old things need to work to see the beauty. Here's what I've done so far. Here's a close up look at the meters, gauges and other measuring things...
Featured Thread: Dark Matter and who will discover it first?
While the subject has been talked about to death by many a researcher, who will discover the first dark matter scientific paper that will prove beyond theory that describes it in detail. The real discoverer will undoubtedly be the hero of physics, astrophysics, and cosmology and be awarded surely the Nobel Prize for science. Any notables that today seem on the cusp of it's discovery?
Featured Thread: LHC starts up in 2018
Yesterday the first beams this year circulated in the LHC. As every year, the machine operators start with a single low intensity bunch, checking that everything still works properly, and adjusting some parameters where the conditions changed over the winter shutdown. Meanwhile they slowly increase energy, protons per bunch and number of bunches, and finally the focusing of the beams...
Featured Thread: SuperKEKB/Belle II start up
This year we have two big particle physics accelerators running. SuperKEKB is an upgrade of KEKB, and the Belle II experiment at the accelerator is an upgrade of - you guessed it - Belle. It is located at KEK*, close to Tokyo in Japan, and it is starting up for the first time now. SuperKEKB is a B-factory...
Featured Thread: Galaxy with no dark matter? (NGC1052-DF2)
"The object, with the catchy moniker of NGC1052-DF2, appears to contain no dark matter. If this turns out to be true, it may be the first galaxy of its kind - made up only of ordinary matter. Currently, dark matter is thought to be essential to the fabric of the Universe as we understand it." - BBC
Featured Thread: Interference puzzle - Where does the energy go?
A laser beam is split into two identical beams which impinge on a half-silvered surface from opposite sides. The reflected wave is out of phase with the transmitted wave. There is destructive interference on both outputs. Where does the energy go? Normally when someone asks this question of an interference experiment I am the first to say...
Featured Thread: Quantum Theory for high-school students
I believe this could be interesting to many people here who are interested in quantum theory but are not (yet) professional physicists: "We present a conceptually clear introduction to quantum theory at a level suitable for high-school students attending the International Summer School for Young Physicists (ISSYP) at Perimeter Institute..."
Featured Thread: Bohr's complementarity is completed with entanglement?
Earlier this week, I found a very interesting paper pop up on the arXiv headed by Joseph Eberly, a notable figure in quantum optics and entanglement. In it, they look at the common treatment of wave-particle duality as a tradeoff between which-slit distinguishability, and the visibility of the resulting interference pattern...
Featured Thread: A proposed experiment to test quantum gravity
Gravity is weak - while we can study the other interactions with individual particles, for gravity we need macroscopic objects to get measurable forces. This makes it easy to measure quantum effects for the other interactions, but hard to do so with gravity. Gravitational forces are always measured with a source mass and a test mass. Quantum objects as test masses have been demonstrated quite some time ago, most notably...
Featured Thread: Neutron star collisions as a heavy element source
There was a lot of discussion after the recent observation of the merger of two neutron stars about whether or not these events are the source of the heavier elements. See this thread, for example. This recent paper has some new analysis. Especially interesting is Figure 10, that I've reproduced below. The paper's estimate of the abundance of the heavy elements is good match to the measured abundance of those elements here on Earth...
Featured Thread: Stephen Hawking has Died- 14/03/2018
"Stephen Hawking, the British theoretical physicist who overcame a devastating neurological disease to probe the greatest mysteries of the cosmos and become a globally celebrated symbol of the power of the human mind, has died. He was 76."
Featured Thread: What should be the rules to write excellent code?
I know few rules that lets me write great code: 1. "don't pollute the global namespace" when I sit down to write JavaScript code. 2. SOLID 3. KISS 4. Liskov's Open-Closed principle

Can someone help me complete the list of such rules?
Featured Thread: Television Engineering History
I was surfing the net to get some ideas involving the Kerr electro-optic effect and noticed this Wikipedia external link. It's page two from Television History - The First 75 Years. It has some cool old articles and pictures like these (images can be made larger in your browser): Just thought I share.
Featured Thread: Observation of Alfvén waves heating the Sun's corona
The corona is much hotter than the surface of the Sun, contrary what you would naively expect from the heat flow. While plasma waves were long suspected as cause, the mechanism was not well understood. How are these waves produced, and how is their energy converted to heat? Scientists now observed the second part directly, and conclude that the conversion to heat is quite efficient.
Featured Thread: Are charged batteries heavier?
Since you can add energy to a battery then extract it later, considering mass energy equivalence, it should be more massive, no?
Featured Thread: Germ Protect a Straw - New Product Idea and Book Giveaway
I would like to propose that your product ideas are posted in two categories: Professional and Amateur: If you are a professional in ME or Aero or a related field, please post using the Spoiler tags, so that the Amateur participants won't see the answers too soon If you are an Amateur/hobbyist, go ahead and post your thoughts on the design (no peaking at the spoilers please). The design challenge is to incorporate germ protection into a straw...
Featured Thread: How close is Earth to the closest black hole?
Is it astronomically known what the closest distance is between Earth and a black hole? The article... says
The Milky Way teems with black holes — about 100 million of them.Based on this estimate, and taking into account the relative density of matter based the distance from the center of the Milky Way, what would be a reasonably accurate estimate of the distance between Earth and the closest black hole?
Featured Thread: Science and math books with nice covers
Serious books on math, physics and related sciences usually have covers which are quite boring and visually not very attractive. (Books that have something to do with Universe are a common exception, but when you see a few of them you have seen them all.) But sometimes, covers are really interesting and/or beautiful. Here you are encouraged to present examples...
Featured Thread: B Level Explanation of Conduction and Resistance
Students seeking “deeper” understanding of basic electricity, frequently come with one of the following misconceptions. 1.Electrons are like balls, they start with potential energy and gain kinetic energy. They deliver their energy to the far end of the wire by filling a bucket. 2. Electrons are like pods filled with energy. The pods burst as they go through a resistor, and they are all used up by the time the wire reaches ground.
I am seeking a B level explanation of conduction and resistance that is not based on analogies...
Featured Thread: Psychology: How will we react to discovery of alien life
The pilot study analyzed news scientific reports (with software), and gave questionnaires to study subjects after reading some specially chosen reports as well. You are best advised to read the phys.org link first before generating conclusions. Limited study.
Featured Thread: The Forgotten Anniversary: 100 Years since Emmy Noether's Theorems
We shouldn't have forgotten this: On January, 25th it has been 100 years, a complete century, since Emmy Noether published her paper "Invarianten bestimmter Differentialausdrücke" (Invariants of Certain Differential Expressions, Göttingen 1918). It is still the basic concept of so many physical models, from classical mechanics to the standard model of particle physics...
Featured Thread: Can indistinguishable particles obey Boltzmann statistics
Many text books claim that particles that obey Boltzmann statistics have to be indistinguishable in order to ensure an extensive expression for entropy. However, a first principle derivation using combinatorics gives the Boltzmann only for distinguishable and the Bose Einstein distribution for indistinguishable particles (see Beiser, Atkins or my own text on Research Gate). Is there any direct evidence...
Featured Thread: Warm air goes up... reason on a microscopic scale?
I was wondering about the microscopic reason warm air rises up, while cold air comes down. I am aware of the macroscopic reason - density changes. But what happens microscopically? Decrease in density means that the gas molecules are widely spaced out, but their mass remains the same. Then why does warm air go up?

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