Featured Science Threads - Page 8

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...

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...

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...

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...

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!

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!

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...

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...

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...

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.

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.

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?

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...

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...

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...

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...

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?

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...

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...

"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

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...

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..."

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...

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...

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...

"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."

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?

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.

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.

Since you can add energy to a battery then extract it later, considering mass energy equivalence, it should be more massive, no?

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...

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?

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...

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...

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.

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...

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...

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?

Why did you decided to learn physics? What was your motivation? What is your personal physics story?

"Years in the making, the commercial spaceflight company is preparing to launch its first Falcon Heavy rocket, which as its name implies, is a heavy-lift booster built from a core stage and two of SpaceX's Falcon 9 recoverable rockets. According to SpaceX, when the Falcon Heavy lifts off, it will be "the most powerful operational rocket in the world by a factor of two."

For many years, the measurements of the Landé g-factor of the muon have been puzzling, as the experimental value and the theoretical predictions showed some disagreement - 3.6 standard deviations for the last years. Experimental and theoretical uncertainties have a similar size, so work on both sides helps.
Muon g-2 at Fermilab is currently taking more data to improve the experimental result...

I just wanted to see anybody's opinion on the super blue blood moon yesterday night (at least for me). I couldn't catch a glimpse of it in Sydney since it had been very hot for a few days and clouds had taken over the sky. Did anybody see it? Anywhere in the world besides Oceania?

What book are you reading now, or have been reading recently? Only STEM (science, technology, engineering and mathematics) books are counted.

I have been reviewing GR lately because as a mentor I find myself now answering more of those questions. I learnt GR years ago from Wald and other sources, but since then have been exposed to the symmetries of the Standard Model. What struck me during this review is I now have a different perspective...

The contest task is to share an account of your best educational experience. It may be something you experienced as a student or as a teacher, but should be a good example of how your education or that someone you were teaching benefited from the actions described in the account. Your account may be as long or short as necessary, but make sure to include as much information as is needed to properly appreciate it...

I’m taking physics II and discrete math this semester. Long story short: I’m probably not going to be able to rely on the professors to teach me this semester. I’m really, really hoping that I can get all A’s this year. What do you guys recommend I do? I should note that I’m also working this semester (15-20 hours/week).

An article in Quanta Magazine discusses the math behind the Navier Stokes equations, why they are so difficult to solve and whether they truly represent fluid flow...

I ran across several YouTubes that claim, and apparently demonstrate, that you can clean carbon deposits from a car engine by simply spraying or pouring (very slowly) water into the intake when the engine is fully warmed and running. I've never heard this from a reliable source and my reaction is... What is the real story on this?

The Hypatia Stone is a small meteorite from SW Egypt. Petrographic and chemical analysis by a group of researchers mostly from University of Johannesburg found element abundances and other unique chemical anomalies in the meteorite. They suggest that the object originated in the interstellar dust cloud, likely before the formation of Earth.

An understanding of Newton's laws is integral to the design and operation of the modern-day helicopter. The first modern-day helicopters came about in the 1940s so the laws were well known by then...but here's the thing. Newton published his laws in the Principia in 1687, but Leonardo Da Vinci had already invented the 'Aerial Screw'...