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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.

It is said that some physicists doubted the existence of atoms in 1900 until Einstein proved their existence a few years later. Did Mendeleev's creation of the periodic table in the 1870s already prove the reality of atoms by giving the known elements atomic masses?

I try to clarify some misunderstandings about the general structure of relativistic QFT. Particularly the important defining property of "locality".

My question is, as is with normal colour and fluorescence the effect stops immediately the light is switched off. Why does the effect linger with Glow in the dark? Why are the emissions so much slower not instant the moment the light is switched off?

Was curious if induction water heaters were a thing and if they had any benefits over a traditional electric resistance coil. On quora someone argues that a resistance coil is a near-perfect conversion of electricity to heat, therefore no benefit to induction - is this correct?

Not sure of the precise terminology to discuss different solid matter states, and also not sure if this is generally the subject of mechanical or chemical engineering.

I assume most people when they refer to Quantum Theory, they sort of referring to QFT. So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

This *[Ed.: the claim that photons have a "path"]* is a misconception of quantum theory already for massive particles. It's even more severely misleading for massless quanta of spin ≥1, which do not even allow the definition of a position observable itself...

Highschooler develops a new integration technique that works on 73% of the common integrals used in Calculus 2 named Maclaurin Integration.

The usual spacetime manifold in general relativity is a topological space that has no boundary. Manifolds that do have a boundary are discussed as well as details of doing GR with such manifolds.

Both Feynman and Einstein have famous quotes about explaining physics concepts to those not well schooled in physics. (freshman undergrad and a six-year-old respectively). Yet both hedged a bit on this: Einstein Things should be made as simple as possible but not simpler and Feynman...

De-emphasizing simultaneity in SR curriculum. Thoughts? Experiences? This thread, some earlier ones, and my signature got me thinking a bit about whether it would be a good idea to de-emphasize simultaneity when teaching SR since it is a frame-dependent concept.

In a recent thread, I said that if there was interest, I would post in a separate thread the calculations for the kinematic decomposition of the congruence of worldlines describing the rod in the "rod and hole" relativity paradox discussed in that thread. Since there was interest, I am posting that separate thread...

Countdown to launch thread

Need help with defining optical qualities of two LCD screen layers that can severely hurt eyes when the screen is disassembled (what do they do to light to make it dangerous).

One of the leading researchers in Loop Quantum Gravity discusses existing observations that should guide future quantum gravity research in a three-page paper. Rovelli points to three pieces of existing observational evidence that should guide future quantum gravity research. Bottom line...

An old clock stops working at the 41-minute mark. A new replacement, identical to the old one, also fails at the 41-minute mark. Repeated tests show that this isn’t just a fluke: the clocks always seem to fail around the same positions, so what could be the cause? Is it the defective gear? Is the motor failing to fight gravity when it lifts the hands?

Bernoulli, lift and cause & effect: looking for a clear-cut cause-and-effect and analogy.

One thing I've never got clear in my head, and which I find hard to answer using google and my textbooks on GR, is the following: how exactly is black hole formation observed by an observer sitting at a distance?

So I was trying to get a bit better handle on the definition of the difference between an event horizon and a Killing horizon. Locally they are indistinguishable, and the key difference (to my understanding) is that the event horizon is the last Killing horizon that escapes to future null infinity...

LHCb has discovered a couple of tetraquarks and pentaquarks in the last years. Recently they added one more, but this one is different from the previous discoveries. Tetraquarks have two quarks and two antiquarks. If all of them are light (up/down/strange) it's basically impossible to measure them and experimentally confirm that they actually have four quarks, so people mainly focus on tetraquarks with at least one heavy quark...

Nauka is the most recent ISS module. After docking, it unexpectedly fired thrusters, changing the orientation of the ISS. The situation has been resolved. Nauka, a Russian multipurpose science module and one of the largest ISS modules, was docked to the ISS. During the checkout procedures after docking the module suddenly fired its thrusters, rotating the ISS quite rapidly (up to 0.5 degree/s).

'Nowadays we know you can start with just about anything, and at low energies, the effective theory will *look* renormalizable. This is useful, if you want to calculate processes in low-energy physics; disappointing if you’d like to use low-energy data to learn what is happening at higher energies. Chances are, if you go to energies that are high enough, spacetime itself becomes ill-defined, and you don’t have a quantum field theory at all. But on labs here on Earth, we have no better way to describe how the world works.'

This derivation uses collisions in 1 dimension, plus rapidity. I've been noodling around with derivations of relativistic energy and momentum, and I almost got it down to just a few lines. But not quite. I'm going to work in one spatial dimension, for simplicity (even though some derivations require a second spatial dimension)...

Interesting video about interpreting 'single photon' interference experiments. Bumped into this video after admiring the falling cat by @A.T. As an experimental physicist, indeed experienced a little of the 'hole in the brain' phenomenon!

This myth has been around for a long time. (I wish I'd sent it into Mythbusters.) Do we all agree it is theoretically possible? Once we do, can we figure out a practical way of testing it? OK. I'm sure we're all in agreement that it is theoretically possible to float a cruise ship "in" a bucket of water, right? If not, maybe we need to sort that out first.

Found a cool proposal on the arXiv from the BASE collaboration. Put a proton in a Penning trap with a beryllium ion. Let the proton spin precess for a while. SWAP the proton spin state with the beryllium spin state a la quantum logic techniques. Readout the beryllium state. Get a g-2 measurement. Repeat the process for an antiproton. Look for CPT violation...

We show how one can solve most, if not all, introductory-level projectile motion problems in one or maybe two lines. To this end, we forgo convention. We demote clock time T to a parameter of secondary importance and ditch the independence of motion in the vertical and horizontal directions...

I am a 16 years old who has a dream to become a quantum physicist but I am also someone who doesn't know the beginning of the road so I thought maybe some comments will be helpful so tell me where shall I start?

The two known textbook axioms of Special Relativity are generally thought to be independent. Or are they not, really?

This is an enormous failure, comparable to the "Great Northeast Blackout of 1965". Rolling blackouts are being imposed at a time when millions of residential customers need home heating. The oil refineries shut down. Expect gasoline/diesel shortages and price spikes nation wide in a few days.

Flat slabs are weird in GR. Off the back of a recently closed thread where there was some discussion about the gravitational field of an infinite flat slab, I decided to have a play at investigating that. I've found a few interesting things.

Let me share an educational problem which I learned from my friend Prof. M. Kirsanov. Perhaps somebody finds it interesting to discuss it with students. I do. The problem is pure kinematic.

I wonder if anybody has an idea for a topology on the set of Lie algebras of a given finite dimension which is not defined via the structure constants. This condition is crucial, as I want to keep as many algebraic properties as possible, e.g. solvability, center, dimension...

Reading McGhee's excellent book on the Carboniferous period and he explains in detail the unique circumstances behind the creation of 90% of the world's coal deposits - receding ocean in an ice age that created low lying swamps, high concentrations of oxygen in the atmosphere that would have been sufficient for wildfires to turn swamps into charcoal...

A general thread to collect the latest research on mutations to the SARS-CoV-2 virus. Given the seeming increased transmissibility of the new SARS-CoV-2 variants being identified, I thought I'd start a general thread to collect and organize information on the various mutations to the SARS-CoV-2 virus.

Einstein, Infeld and Hoffman tried to derive the equations of motion of point particles in GR from Einstein's field equations. On another thread, now closed, Intrastellar asked: "Since the EFE describes the shape of spacetime, it describes the way black holes, for example, evolve. Can one derive the geodesic equation from it in some limit ?"

- What is the correct theory of neutrinos?
- Why are they almost but not quite massless?
- Do all three known neutrinos—electron, muon, and tau—all have a mass?

Here is the official peer reviewed Pfizer vaccine study published in the New England Journal of Medicine... This is a follow-up piece that describes what an emergency use authorization means and gives a perspective about follow-up...

I could use some help designing a magnetic induction power source to convert kinetic energy to DC power, for use in keeping a GPS unit with GSM SIM card independently powered inside a bicycle frame...

Starlink has begun its public beta phase, and naturally some people were more interested in the electronics than in fast internet access. Here is a video how the satellite receiver looks inside. The first half is focused on the mechanical side, the second half is looking at the electronics.