Featured Science Threads - Page 10

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: Breakdown of Gauss' Law?
So, this has been bothering me for a few days and I'm having trouble understanding where the fault is. If we consider a uniform charge density ##\rho## extending through all space, then by symmetry, I would argue that ##\mathbf{E}=0## in all space. However, this does not agree with what a naive application of Gauss's Law would predict since ##\nabla\cdot\mathbf{E}=0\ne\rho/\epsilon##. So where exactly is the argument breaking down? Is there something unusual...
Featured Thread: Merging Neutron Stars
"Rumors are starting to fly that LIGO/VIRGO sees a signal of merging neutron stars, with an optical counterpart. Indeed, the thing that seems to have triggered the rumors was having a number of telescopes suddenly pointing at the same patch of sky. It's difficult to discuss the science behind the rumors pre-publication, but it might be reasonable to use this thread to discuss the science behind merging neutron stars."
Featured Thread: 10 Math Tips to Save Time and Avoid Mistakes
Exam situations are always situations of stress. It comes with our endeavor to be as good as possible together with our fear to fail. Some students handle these situations better than others. But there are some tricks I encountered over the years tutoring young students. I’m sure everybody has developed their own ways to get along with tests, so the following has to be a personal view of mine. It resulted from my experiences...
Featured Thread: Open problems in mathematical physics
"We present a list of open questions in mathematical physics. After a historical introduction, a number of problems in a variety of different fields are discussed, with the intention of giving an overall impression of the current status of mathematical physics, particularly in the topical fields of classical general relativity, cosmology and the quantum realm. This list is motivated by the recent article proposing 42 fundamental questions..."
Featured Thread: 2017 Nobel Prize in Physics - Opinions and Expectations
"Three colleagues, Rainer Weiss, Barry C. Barish, and Kip S. Thorne, have won the 2017 Nobel Prize in physics, for their contributions to work that led to the observation of gravitational waves — something that happened for the first time in 2015." - NPR
Featured Thread: 2017 Nobel Prize in Physiology or Medicine
This morning, the 2017 Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discoveries of molecular mechanisms controlling the circadian rhythm. "Their discoveries explain how plants, animals and humans adapt their biological rhythm so that it is synchronized with the Earth's revolutions."
Featured Thread: Engineering: Rethinking Evacuation Plans
The Miami Herald posted this story. Built for bottleneck: Is Florida growing too fast to evacuate ... The article made a good point that I hadn't considered. A good evacuation plan does not require 10 million people to drive 600-1000 miles away. It means driving 10-20 miles inland to a shelter. In south Florida, 10-20 miles inland puts you in the Everglades or Big Cyprus Swamp. Those are really bad places to build 10000 shelter buildings...
Featured Thread: Contest: Equations as Art 2017
The goal is to create the most beautiful or interesting equation aesthetically (pleasing to the eye).
This is not about it's mathematical significance. Get your inner designer on! Each member is allowed to post one equation. The equation can be completely made up...
Featured Thread: Solar imaging and techniques
This thread is for showing your images of solar activity taken with YOUR cameras, telescopes etc.
That is, don't post images from SDO, SOHO or any other professional sources unless you specifically want to ask "how do they do that and what are those solar features I can see? This is intended for those of you out there, like myself that get out there and do your own imaging and are looking for ways to improve...
Featured Thread: Advanced Math Problem of the Week 9/14/2017
Here is this week's advanced math problem of the week. We have several members who will check solutions, but we also welcome the community in general to step in. We also encourage finding different methods to the solution. If one has been found, see if there is another way. Occasionally there will be prizes for extraordinary or clever methods...
Featured Thread: Cassini's Grand Finale 9/15/2017
"For NASA’s Cassini orbiter—its fuel dwindling after 13 years exploring Saturn, along with the planet’s sprawling rings and dozens of icy moons—the end will come Friday at 7:55 A.M. Eastern time. That’s when mission planners project radio communications will be lost with the two-ton, bus-size spacecraft as it plunges into the giant planet’s turbulent atmosphere at more than 122,000 kilometers per hour." - sciam.com
Featured Thread: Introduction to Perturbative Quantum Field Theory
This is the beginning of a series that gives an introduction to perturbative quantum field theory (pQFT) on Lorentzian spacetime backgrounds in its rigorous formulation as locally covariant perturbative algebraic quantum field theory. This includes the theories of quantum electrodynamics (QED), quantum chromodynamics (QCD), and perturbative quantum gravity (pQG) — hence the standard model of particle physics...
Featured Thread: Staged Blackouts
Again and again we hear of the consequences of loss of electrical power. Frequently, the authors call for more redundancies in the power grid so that blackouts will not happen. No complex system can ever be 100% reliable. However, as systems grow from very reliable to extremely reliable, people come to treat them as absolutely reliable. (A psychological quirk?) Lack of preparedness grows and the actual consequences become...
Featured Thread: Double Rainbows and the direction of its colors
I just saw a double rainbow. On the brighter bow the color arcs were red on the left edge of the bow and shifted to blue on the right edge. On the dimmer bow the colors shifted from blue on the left edge to red on the right. Why were they separated oppositely like this?
Featured Thread: Comparison of tidal forces acting on the Moon vs Enceladus
I have heard about a moon Enceladus. Which is powered by tidal force. I suppose this force press back and forth on the moon and friction in the core causes heat. Can anyone explain it?
Featured Thread: Do light and sound waves roll up and break like ocean waves?
When sea waves approach the shore they roll up and break due to different velocities of water layers formed due to the gradual change in water depth. The highest wave peaks move faster than all other layers and thus falls down. All other layers fall the same way but in a delay. this ends up with wave rolling up when approaching the shore. Does light and sound wave have a similar phenomenon?
Featured Thread: Beyond LHC, future particle colliders and lasers
With LHC currently at 13TEV design energy, and a planned higher luminosity upgrade, is the current plan to double the magnet strength for the current existing LHC to arrive at a 28-33TEV collider, or is it building a completely new future 100 TEV collider near Geneva where LHC is housed but in a completely new tunnel or in China? Are future lepton collider plans, such as one in Japan, linear or circular?
Featured Thread: U(1) invariance of classical electromagnetism
This is an interesting question that popped through my mind. Some of us should know what is meant by „gauge transformations”, „gauge invariance/symmetry” and are used to seeing these terms whenever lectures on quantum field theory are read. But the electromagnetic field in vacuum (described in a specially relativistic fashion by the tensor...
Featured Thread: Automated tennis ball launcher for my dog
I thought I would post my thoughts/progress on designing and building an automatic tennis ball launcher for my dog. The little fella gets a bit bored during the day when we are at work, so I want to build him this so he has something to do other than push a basketball around the backyard. Any and all advice/criticism is appreciated.
Featured Thread: U.S. Solar Eclipse of Aug. 21, 2017
I've been waiting for this for a long time and it's just a little more than a year away now. This will be the opportunity of a lifetime for people in the U.S. The 2017 solar eclipse will be visible across the width of the entire U.S! The points of Greatest Eclipse and Greatest Duration are going to occur on opposite sides of the Kentucky - Illinois border.
Featured Thread: "probability of finding the electron"
I was trying to help (elsewhere) a student with some QM related problem and I realized something. When discussing QM we underline the fact that electron doesn't behave as a particle, it behaves as a wave. Yet when we explain wave function we say something like "square of the wave function is a density probability of finding the electron" - which seems to suggests to students the electron is a particle that can be found...
Featured Thread: A new exomoon candidate: Kepler-1625b I
The authors looked for signals of potential moons in the Kepler transit data. There is some weak evidence that a group of smaller moons exists, but the measurements are not accurate enough to pin that down on a star-by-star level. One particular planet, however, Kepler-1625b, has very curious features in all three observed transits. The Hubble telescope will observe the next transit in October this year.
Featured Thread: First Human Embryos Edited in U.S.
"Researchers have demonstrated they can efficiently improve the DNA of human embryos. The first known attempt at creating genetically modified human embryos in the United States has been carried out by a team of researchers in Portland, Oregon, MIT Technology Review has learned. The effort, led by Shoukhrat Mitalipov of Oregon Health and Science University, involved changing the DNA..."
Featured Thread: Should Algebra Be Required At Community Colleges?
The chancellor of the California Community Colleges system believes that students who are not majoring in math or science should not have to take intermediate algebra to earn an associate degree. California has the largest community college system in the US, and what goes in California sometimes spreads across the country. What do you think?
Featured Thread: Is it possible to detect a single phonon?
Is it possible to detect a single phonon? If yes, can it be detected at a well-defined position?
Featured Thread: A Poor Man's CMB Primer. Part 5: Quantum Seeds
The CMB establishes a record of ancient acoustic oscillations in the baryon-photon plasma. We’ve been studying how these primordial sound waves evolve, and how to analyze the last scattering surface to learn about them. Now it’s time to confront their origin: what process composed the cosmic symphony? A few different proposals have been advanced over the years to explain the origin of the primordial perturbations.
Featured Thread: Great Magic Triangle Math Puzzle
"The missing square puzzle is an optical illusion used in mathematics classes to help students reason about geometrical figures; or rather to teach them not to reason using figures, but to use only textual descriptions and the axioms of geometry. It depicts two arrangements made of similar shapes in slightly different configurations. Each apparently forms a 13×5 right-angled triangle, but one has a 1×1 hole in it." Can you figure out an easy way to inspect it?
Featured Thread: A propagating Majorana mode
"In a discovery that concludes an 80-year quest, Stanford and University of California researchers found evidence of particles that are their own antiparticles. These 'Majorana fermions’ could one day help make quantum computers more robust." - Stanford News
Featured Thread: Results shown at EPS
The EPS conference was a week ago, and many new results and future plans were shown. A good general overview has been collected by Paris Sphicas in his Summary slides. I had a look at some presentations and collected things I personally found interesting. Warning: The selection is heavily biased, I cannot cover everything, and I probably missed many interesting things.
Featured Thread: Super p-Brane Theory Emerging from Super Homotopy Theory
What are even the principles of the theory? Two principles worth considering: The gauge principle: No two different things are ever equal, instead they may be related by a gauge euivalence. Consequently, no two different gauge transformations are ever equal, instead they may be related by a gauge-of-gauge equivalence. And so on.Mathematically this is the principle of homotopy theory...
Featured Thread: An Integral Result from Parseval's Theorem
In this Insight article, Parseval's theorem will be applied to a sinusoidal signal that lasts a finite period of time. It will be shown that it necessarily follows that ## (\frac{\sin(2 x_o)}{x_o})( \frac{\pi}{2})=\int\limits_{-\infty}^{+\infty} \frac{\sin(x-x_o) \sin(x+x_o)}{(x-x_o)(x+x_o)} \, dx ##.
Featured Thread: Hamiltonian in Quantum vs Classical
The Hamiltonian in classical mechanics is not always equal to the total energy of the system. I believe this is only true if there is only a potential field and no vector potential. However, in quantum mechanics for a particle in an EM field, even if a vector potential is used the energy operator E -> H. Is this an inconsistency?
Featured Thread: Is Biomass Carbon Neutral?
About 9% of Germany's power is produced by wood biomass burning, second only to wind in their "renewable" sector. Clearly, wood can be "renewable", but to me the more important question is: is it green? It appears that the EU considers biomass to be "carbon netural" and thus subsidizes it as a clean, renewable energy source. But the situation is not so clear in the US and there is debate about the issue (sources below)...
Featured Thread: Solar system's path in the Milky Way galaxy
My understanding: Circuit is ~ 30 million years. Plane of solar system orbit is tilted from plane of milky way.
Is milky way plane crossed once or twice? What is error bar for 30 million? How much does dark matter density vary along solar system path?
Featured Thread: Counting intersections of lines in a triangle
Divide each side of a triangle into n equal lengths. Connect the ends of each length to the opposite vertex with straight lines, thereby forming 3n overlapping triangles of equal area. (The problem at the link is an example with n=3.) At how many points will three lines intersect?
Featured Thread: Double field theory: Where is the extra space?
Double field theory [1] is an attempt to realize T-duality of string theory at the level of field theory. For instance, if a field in ordinary field theory lives in 4 non-compact space-time dimensions, then a field in double field theory lives in 8 non-compact space-time dimensions. I don't understand it from the physical point of view...
Featured Thread: The Sleeping Beauty Problem: Any halfers here?
The sleeping beauty problem is a well known problem in probability theory. Allegedly, there are many "thirders" who think that the correct answer is 1/3, but also many "halfers" who think that the correct answer is 1/2. For me, it is quite obvious that the correct answer is 1/3. Is there anybody here who is convinced that the correct answer is 1/2? If you are one of them, what is your argument for 1/2?
Featured Thread: Inertia and Mach's Principle
Mach, Newton and others observed that centrifugal forces appear in a object when it rotates in relation to the stars. Einstein was convinced by this and tried, unsuccessfully as far as I understand, to incorporate what he called Mach’s Principle into General Relativity...
Featured Thread: LHC starts 2017 data-taking
"Stable beams" has been declared. Similar to 2016, the initial collision rate is low (0.2% the design rate). The machine operators have to check that everything works and nothing presents a danger to the machine before more protons can be filled in. It will probably take a few weeks to reach the same collision rates as achieved last year. Meanwhile, the experiments start collecting some initial data...
Featured Thread: Advances in Machine Intelligence
Recently, I came across an individual who claimed to research AI professionally and who expressed to me the following view after some discussion of various technologies and the rate of advancement of such tech... I would very much love to read what anyone has to say regarding this, and would also greatly appreciate where you think machine intelligence will be in the next 10 year span...
Featured Thread: Einstein's definition of time
It so happens that last night I was rereading Einstein's famous 1905 paper On the Electrodynamics of Moving Bodies. I think this is one of the most fascinating scientific papers in history, but some people say it's not at all clear. In any case I love reading Einstein's papers. I would be interested in reactions to how Einstein defines time in the first section of this paper. Is it clear? Is it confusing?
Featured Thread: Challenges to QED from hyperfine measurements
Does this really challenge QED? Or does this mean that we miss certain contributions to QED calculations? The authors are speculating "new effects might appear in the interaction of the electron with itself, the vacuum or the nuclear fields in this regime, that is, the hyperfine interaction might be affected by the existence of new particles not included yet in the current standard model and therefore not considered in state-of-the-art...
Featured Thread: Educating the General Public about pro Nuclear Energy?
Why would nuclear energy be better option, I hear a lot of fears from the general public of why it is not safe?
How would someone convince someones fear about the safety of nuclear power, considering what happened in Japan?
Featured Thread: Interview with Astronomer Pamela Gay
For every person who says “I hate science” there is at least one person saying, “I once wanted to be a scientist.” Life keeps a lot of people from following their desires, and a lot of these people go on to be artists or engineers, or… something other than a scientist. Citizen science lets these people fulfill their dream, and lets them contribute to our understanding of the world and the universe around us...
Featured Thread: New ideas on the mechanism of solar CME's
Solar activity has been a love of mine since the early 1970's and am always looking out
for new research info. Some recent studies and lots of computer animations have come up with new understandings of the mechanisms that instigate CME's and other mass ejections from the sun.
Featured Thread: Residential Fuel Cells: Japan vs US/EU
For several years, I've been seeing mention of growing number of residential fuel cells in Japan. But in the USA and the EU, hardly a mention. Does anyone know why the puzzling discrepancy?
Featured Thread: Thermochemistry Challenge Problem - Chet's Paradox
I have a reversible chemical reaction described by the balanced equation: ##aA+bB=cC+dD##. I devise a reversible process to take a closed system containing these species (and its surroundings) from thermodynamic equilibrium state 1 to thermodynamic equilibrium state 2...
Featured Thread: Using CRISPR to cut HIV out of infected cells
A major impediment to curing patients with HIV is the fact that the virus integrates its DNA into the genome of the cells it infects. While antiretroviral drugs and therapies can prevent infection of new cells and kill cells that are actively producing virus, a "latent reservoir" remains that can be cause an active infection to re-emerge after drug treatment has stopped. Therefore, current treatments for HIV-infected individuals requires...
Featured Thread: Life on the Edge: is it still alive?
I recently read ' Life on the Edge" by Jim Al-Khalili and Johnjoe McFadden. It was very readable and it got me quite convinced about the whole idea. Al-Khalili is a very presentable broadcaster / writer and offers an attractive case. But it was written some while ago and Google hasn't much to offer... I would love to read some well informed opinions about this.
Featured Thread: Niches for Publishable Undergraduate Research
Undergrads struggle with research ideas, because they often tend to assume their work needs to be within the domain of new fundamental science of the sort that would be suitable for the Physical Review, when often their skills and scientific maturity have not yet really empowered them for that level of contribution. As mentors of a lot of undergrad (and high school) research, we’ve found that...

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