minutephysics

The Bizarre Physics of Electric Guitars

Jun 14, 2023

To try everything Brilliant has to offer—free—for a full 30 days, visit http://brilliant.org/MinutePhysics The first 200 people get 20% off a premium subscription! I was sent a magnetic guitar pick to review, so I reviewed it. Does it work? How? Why? What's the physics of electric guitar strings and pickups? Are magnets useful? Do they affect the strings? The pickups? Thanks to Pete B. for loaning me the guitar. Here are links to the youtube channel for the people who make the magnetic pick: https://www.youtube.com/@xpick And the videos critiquing it Samurai Guitarist: https://www.youtube.com/watch?v=zXTHRh1bQsg Forlorn Hope: https://www.youtube.com/watch?v=2E8rrt5gE8Q Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Geosynchronous Orbits are WEIRD

Dec 22, 2022

Go to https://givewell.org/minutephysics to have your first donation matched up to $100! This video is about the physics of geosynchronous and geostationary orbits, why they exist, when they don't, when they're useful for communication/satellite TV, etc. REFERENCES Fraction of a sphere that's visible from a given distance https://math.stackexchange.com/questions/1329130/what-fraction-of-a-sphere-can-an-external-observer-see Orbital period https://en.wikipedia.org/wiki/Orbital_period Kepler's third law https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion#Third_law Kepler's 3rd law (which can be derived from Newton's law of gravitation and the centripetal force necessary for orbit as mr\omega^2=G\frac{mM}{r^2}, and using \omega=\frac{2\pi}{T}) is T = 2pi Sqrt(r^3/(GM)) where M is the mass of the central object, G is the gravitational constant. Alternatively, we can solve for r, r = (T^2/(4pi^2) GM)^(1/3) ~ T^(2/3)/M^(1/3) = (T^2/M)^(1/3). There is a limit (kind of like the Roche limit but for rotations). A rotating solid steel ball or other chunk of metal that has tensile strength (ie that isn't just a pile of stuff held together by gravity like most planets) would be able to spin faster. Calculate how much of a planet's surface you can see from a given geosynchronous orbit/radius? (Obviously for lower ones you can see less, etc) - d/(2(R+d)) where d is distance to surface, ie, R is sphere radius, R+d is object radius from sphere center. Let's plug that in with r being the geostationary orbit radius. That is, we have \frac{1}{2} \left(1- \left(\frac{4 \pi^2 R^3}{T^2 G M }\right)^{1/3}\right) Average density of a sphere \rho is given by \rho =M/(\frac{4}{3}\pi R^3), ie \rho=\frac{3M}{4 \pi R^3} aka \frac{M}{R^3}=\frac{4}{3}\pi \rho. So we can convert the "fraction of planet surface seen" to \frac{1}{2} \left(1- \left(\frac{3 \pi}{G \rho T^2}\right)^{1/3}\right) So as either \rho or T\to \infty, the fraction goes to a maximum of \frac{1}{2}. And the point of "singularity" where the orbit coincides with the surface is where G\rho T^2=3\pi, aka \rho=\frac{3\pi}{GT^2}. For a rotation period of 3600s, that corresponds to a density \rho \approx 11000kg/m^3, which is roughly twice the density of the earth. For a rotation period of 5400s, we have \rho\approx 4800kg/m^3, which is basically the density of the earth. Alternately, if we plug the density of the earth in to an orbit of period 5400s, we get as a fraction of the planet seen: \frac{1}{2} \left(1- \left(\frac{3 \pi}{G \rho T^2}\right)^{1/3}\right) = 0.02 aka 2\% of the earth's surface. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Why Penrose Tiles Never Repeat

Dec 1, 2022

The first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant. Thanks to Brilliant for their support. This video is about a better way to understand Penrose tilings (the famous tilings invented by Roger Penrose that never repeat themselves but still have some kind of order/pattern). This project was a collaboration with Aatish Bhatia (https://aatishb.com). REFERENCES Explore Penrose and Penrose-like patterns: https://aatishb.com/patterncollider Video by Derek Muller/Veritasium about Penrose Patterns: https://www.youtube.com/watch?v=48sCx-wBs34 Music algorithmically generated, algorithm designed by Henry Reich N.G. de Bruijn’s paper introducing the pentagrid/Penrose idea: https://www.math.brown.edu/reschwar/M272/pentagrid.pdf De Bruijn, N.G., 1981. Algebraic theory of Penrose’s non-periodic tilings of the plane. Kon. Nederl. Akad. Wetensch. Proc. Ser. A, 43(84), pp.1-7. Here are some excellent in-depth references on how to construct Penrose Tiles Using the Pentagrid Method: Penrose Tilings Tied up in Ribbons by David Austin: http://www.ams.org/publicoutreach/feature-column/fcarc-ribbons The Empire Problem in Penrose Tilings by Laura Effinger-Dean: http://www.cs.williams.edu/~bailey/06le.pdf Pentagrids and Penrose Tilings by Stacy Mowry & Shriya Shukla: https://web.williams.edu/Mathematics/sjmiller/public_html/hudson/HRUMC-Mowry&Shukla_Pentagrids%20and%20Penrose.pdf Penrose Tiling by Andrejs Treibergs: http://www.math.utah.edu/~treiberg/PenroseSlides.pdf Algebraic Theory of Penrose's Non-Periodic Tilings of the Plane by N. G. de Bruijn: https://www.math.brown.edu/reschwar/M272/pentagrid.pdf Particularly good and helpful, and (we think) an undergrad thesis which is impressive!: http://www.cs.williams.edu/~bailey/06le.pdf An interesting popular science read on the discovery on quasicrystals and their connection to Penrose Tilings: The Second Kind of Impossible by Paul Steinhardt: https://bookshop.org/books/the-second-kind-of-impossible-the-extraordinary-quest-for-a-new-form-of-matter-9781476729930/9781476729930 Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Freezing water expands. What if you don't let it?

Oct 14, 2022

The first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant. Thanks to Brilliant for their support. REFERENCES Page with TONS of info about water and ice https://water.lsbu.ac.uk/water/water_density.html Specifically, a graph showing density & temperature & pressure along the phase line!!!!! https://water.lsbu.ac.uk/water/images/ice_water_density_1.gif Water freezing in isochoric conditions (theory): https://www.nature.com/articles/s42005-020-0303-9 Water pressure/density calculator https://www.omnicalculator.com/physics/water-density http://www.csgnetwork.com/water_density_calculator.html Article about pressure vs temperature vs volume expansion: Using freezing as a source of energy https://link.springer.com/article/10.1007/s42452-018-0139-z#:~:text=It%20is%20well%20known%20that,energy%20using%20a%20hydraulic%20motor. Latent heat of water at 0C https://link.springer.com/referenceworkentry/10.1007/1-4020-3266-8_124#:~:text=A%20total%20of%20334%20J,the%20latent%20heat%20of%20fusion. Mariana Trench https://en.wikipedia.org/wiki/Mariana_Trench#:~:text=At%20the%20bottom%20of%20the,atmospheric%20pressure%20at%20sea%20level. Regelation on wikipedia https://en.wikipedia.org/wiki/Regelation#:~:text=Regelation%20is%20the%20phenomenon%20of,heavy%20weight%20attached%20to%20it. Using Ice VI to freeze meat without tissue damage https://www.sciencedirect.com/science/article/abs/pii/S0309174003001931 Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

You're Technically HOTTER Than The Sun (with XKCD!)

Sep 8, 2022

Where to buy WHAT IF? 2 by Randall Munroe – Amazon: https://bit.ly/3Rk5Vy2 Barnes and Noble: https://bit.ly/3AKwXIl Penguin Random House: https://bit.ly/3HgfucP Books-A-Million: https://bit.ly/3Q4bEH3 Bookshop: https://bit.ly/3q26vVk IndieBound: https://bit.ly/3TyhX8W Apple Books: https://bit.ly/3wNNBp9 FOR INTERNATIONAL EDITIONS, Including the UK and Germany, click here: https://xkcd.com/what-if-2/ The #1 New York Times bestselling author of What If? and How To answers more of the weirdest questions you never thought to ask The millions of people around the world who read and loved What If? still have questions, and those questions are getting stranger. Thank goodness xkcd creator Randall Munroe is here to help. Planning to ride a fire pole from the Moon back to Earth? The hardest part is sticking the landing. Hoping to cool the atmosphere by opening everyone’s freezer door at the same time? Maybe it’s time for a brief introduction to thermodynamics. Want to know what would happen if you rode a helicopter blade, built a billion-story building, made a lava lamp out of lava, or jumped on a geyser as it erupted? Okay, if you insist. Before you go on a cosmic road trip, feed the residents of New York City to a T. rex, or fill every church with bananas, be sure to consult this practical guide for impractical ideas. Unfazed by absurdity, Munroe consults the latest research on everything from swing-set physics to airliner catapult–design to answer his readers’ questions, clearly and concisely, with illuminating and occasionally terrifying illustrations. As he consistently demonstrates, you can learn a lot from examining how the world might work in very specific extreme circumstances. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ What if Pluto were plutonium? And Uranus uranium? And Mercury mercury? This video is based off of a chapter of the new xkcd book "What If? 2" MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Passing A Portal Through Itself

Sep 1, 2022

Nebula Classes - Great classes by your favorite creators on a creator-owned streaming service: https://nebulaclasses.com/minutephysics This video is about what happens if you try to pass a portal (like in the video game Portal or Portal 2) through itself - do you get a paradox? Infinite recursion? Impossibility? Contradiction? The end of the world? Collapse of the wavefunction? Ultimately it ends up looking beautiful and weird and recursive and... just watch the video :) Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

How Many Fossils to Go an Inch? (ft. Robert Krulwich)

Aug 18, 2022

A beautiful guest video by Robert Krulwich and Nate Milton Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Another Portal Paradox

Aug 4, 2022

We have a course on Brilliant! And the first 200 people to https://brilliant.org/minutephysics get 20% off an annual premium subscription to Brilliant, with full access to all courses, including ours. What happens if you extend a piston through a portal? Or try to sandwich a cube between two portals? That's right, it's time to explore more portal paradoxes! Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Trinity of Quality

Jun 29, 2022

The first 200 people to https://brilliant.org/MinutePhysics/ get 20% off an annual Premium subscription to Brilliant. MinutePhysics is on Patreon: https://patreon.com/minutephysics In order to make something good, you need to have the right combination of three things: Quality, Discernment and Taste. This video is about quality vs quantity, the paradox of quality, how to make good content and good videos, etc. Based on my experience over the last decade running a collaborative creative business, MinuteEarth, where we do regular internal reflection and training on the craft of science communication. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Announcing...

Jun 16, 2022

Check out MinuteFood! https://youtube.com/minutefood and support MinutePhysics: https://patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Most Collisions Are Secretly in One Dimension

May 26, 2022

The first 200 people to https://brilliant.org/MinutePhysics/ get 20% off an annual Premium subscription to Brilliant. This video is about elastic and inelastic collisions in 1D, 2D and 3D - and how the collision of conservation of energy with conservation of momentum, plus a secret direction, results in a completely predetermined behavior for most collisions. REFERENCES 1D Collision Calculator: http://hyperphysics.phy-astr.gsu.edu/hbase/col1d.html#c1 Elastic collision of spheres Wolfram https://demonstrations.wolfram.com/ElasticCollisionsOfTwoSpheres/ Oblique collisions of two 2D spheres https://iopscience.iop.org/article/10.1088/1361-6404/aab330 Ballistic Pendulum http://hyperphysics.phy-astr.gsu.edu/hbase/balpen.html Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Is Anything on the Internet Real?

Dec 22, 2021

GiveWell is matching donations from first-time donors dollar for dollar up to $250. Click on https://bit.ly/3DvVik8 to donate and be sure to use the fundraiser code MINUTEPHYSICS at checkout to make sure your donation gets matched. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Problem With The Butterfly Effect

Oct 21, 2021

The first 200 people to go to https://brilliant.org/minutephysics get 20% off a Premium subscription to Brilliant Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

(A book with the answer)

Oct 8, 2021

Get the new MinuteEarth book at: https://www.minuteearth.com/books !! Support MinutePhysics on Patreon: http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Rocket & String Paradox

Aug 18, 2021

The first 200 people to go to http://brilliant.org/minutephysics get 20% off a premium subscription to Brilliant. This video is about Bell's Spaceship Paradox of Special Relativity, wherein a pair of rockets (or spacecraft) connected by a weak thread accelerate with uniform acceleration, maintaining the same separation, and the question is: does the thread break? And if so, why? REFERENCES Interactive Spacetime Globe by Alexander Wu: https://alexonscience.com/projects/spacetimeglobe/ Read an overview on Wikipedia: https://en.wikipedia.org/wiki/Bell%27s_spaceship_paradox John Baez on Bell's Spaceship Paradox, Rindler Acceleration, etc https://math.ucr.edu/home/baez/physics/Relativity/SR/BellSpaceships/spaceship_puzzle.html Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

A Better Way To Picture Atoms

May 19, 2021

Thanks to Google for sponsoring a portion of this video! Support MinutePhysics on Patreon: http://www.patreon.com/minutephysics This video is about using Bohmian trajectories to visualize the wavefunctions of hydrogen orbitals, rendered in 3D using custom python code in Blender. REFERENCES A Suggested Interpretation of the Quantum Theory in Terms of "Hidden" Variables. I David Bohm, Physical Review, Vol 85 No. 2, January 15, 1952 Speakable and Unspeakable in Quantum Mechanics J. S. Bell Trajectory construction of Dirac evolution Peter Holland The de Broglie-Bohm Causal Interpretation of Quantum Mechanics and its Application to some Simple Systems by Caroline Colijn Bohmian Trajectories as the Foundation of Quantum Mechanics http://arxiv.org/abs/0912.2666v1 The Pilot-Wave Perspective on Quantum Scattering and Tunneling http://arxiv.org/abs/1210.7265v2 A Quantum Potential Description of One-Dimensional Time-Dependent Scattering From Square Barriers and Square Wells Dewdney, Foundations of Physics, VoL 12, No. 1, 1982 Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Windmills Are NOT Like Dams

Apr 1, 2021

Watch the bonus material cut from this video at https://nebula.tv/minutephysics The Solution to the Windmill Paradox. This video is about the tradeoff of Windmills: the fact that the more kinetic energy you extract from the wind the slower the wind goes, the less wind you have to extract energy from, etc. How much energy is the sweet spot to extract from the wind?? Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Why Do Boats Make This Shape?

Mar 21, 2021

Go to https://nebula.tv/minutephysics to get access to Nebula (where you can watch the extended version of this video), plus you'll get a 20% discount on an annual subscription. This video is about the "Kelvin wake" shape of water wakes behind boats - we talk about mach angle, dispersion, superposition of many waves, and how these all lead to the pattern of a wake. We don't get into Froude number though... REFERENCES Boat Wake Wikipedia Page: https://en.wikipedia.org/wiki/Wake Interactive Boat Wake Simulation: https://observablehq.com/@rreusser/dispersion-in-water-surface-waves Feynman Lectures on Water Waves: https://www.feynmanlectures.caltech.edu/I_51.html#Ch51-S4 Building up a Boat Wake from V-Shaped Wakes: https://editor.p5js.org/aatish/full/bDiykicsC Wave Dispersion: https://en.wikipedia.org/wiki/Dispersion_relation Mach angle shock waves: https://www.sciencedirect.com/topics/engineering/mach-angle Ship Wakes - Kelvin or Mach Angle? Rabaud and Moisy Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.214503 Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Physics of Windmill Design

Mar 2, 2021

This video was created in partnership with Bill Gates, inspired by his new book “How to Avoid a Climate Disaster.” Find out more here: https://gatesnot.es/3u7UUVU This video is about how physics dictates the design of modern windmills - why they are so big, have so few blades, and have such skinny blades. REFERENCES H. Glauert: Aerodynamic Theory, 1935 Division L (Airplane Propellers), Chapter XI: Windmills and Fans Wind power extraction fundamentals https://home.uni-leipzig.de/energy/energy-fundamentals/15.htm Betz's Law https://en.wikipedia.org/wiki/Betz%27s_law Tip Speed Ratio https://en.wikipedia.org/wiki/Tip-speed_ratio Aerodynamics of Wind Turbines Book https://www.amazon.com/Aerodynamics-Wind-Turbines-Physical-Analysis/dp/1119405610 Penn State Wind Turbine Aerodynamics Lesson https://www.e-education.psu.edu/aersp583/node/469 Wind Power Physics youtube video https://www.youtube.com/watch?v=qx_M0nvDIGU Why do Wind Turbines Have Three Blades? https://rosemary-barnes.medium.com/why-do-wind-turbines-usually-have-3-blades-f7f95d714869 Wind Power Fundamentals http://web.mit.edu/windenergy/windweek/Presentations/Wind%20Energy%20101.pdf Wind Power Explained https://www.calcunation.com/blogs.php/the-physics-behind-wind-turbines/ Drag Coefficient http://dx.doi.org/10.1615/AtoZ.d.drag_coefficient Reynolds Number and Drag http://www2.eng.cam.ac.uk/~mpj1001/learnfluidmechanics.org/LFM_blank_notes/handout_8_v3.pdf Reynolds Number https://en.wikipedia.org/wiki/Reynolds_number Viscosity of Air https://en.wikipedia.org/wiki/Viscosity#Air Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

General Relativity Explained in 7 Levels of Difficulty

Feb 18, 2021

Go to https://nebula.tv/minutephysics to get access to Nebula (where you can watch the extended version of this video), plus you'll get a 20% discount on an annual subscription. This video covers the General theory of Relativity, developed by Albert Einstein, from basic simple levels (it's gravity, curved space) through to the concepts of how curved spacetime is represented by psuedo-Riemannian manifolds with Lorentzian signature (that is, special relativity and minkowski space are the local tangent space), how matter and energy are represented by an energy-momentum tensor, and how these two together obey the Einstein Field Equations. The solutions to the Einstein Field Equations (including the schwarzschild metric, kerr metric, freedman-lemaitre-robertson-walker metric, etc) represent gravity around massive objects like the sun, earth, and black holes, but also the history and expansion and future evolution of the cosmos. The universe on a large scale is described by general relativity - on a small scale, quantum mechanics. And where they meet... there's still work to be done. REFERENCES Wald's textbook - General Relativity Hartle's textbook - Gravity: An Introduction to Einstein's General Relativity Carlo Rovelli History of Quantum Gravity: https://cds.cern.ch/record/442809/files/0006061.pdf Leon Rosenfeld 1930 paper on quantum gravity: http://www.edoc.mpg.de/438547 Kerr Metric Solution - https://en.wikipedia.org/wiki/Eddington%E2%80%93Finkelstein_coordinates Schwarzschild Metric - https://en.wikipedia.org/wiki/Schwarzschild_metric Eddington-Finkelstein Coordinates - https://en.wikipedia.org/wiki/Eddington%E2%80%93Finkelstein_coordinates Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Why LESS Sensitive Tests Might Be Better

Jan 14, 2021

Thanks to Brilliant for sponsoring this video - the first 200 people to click on https://www.brilliant.org/MinutePhysics will get 20% off a Premium subscription to Brilliant. This video written & produced in collaboration with Aatish Bhatia, https://www.aatishb.com This video is about how cheap, fast, and LESS sensitive rapid antigen tests might be better for screening (& maybe surveillance) than PCR COVID tests due to the nature of contagiousness/infectiveness at various points on the viral load trajectory of symptomatic and asymptomatic COVID sars-COV-2 carriers. REFERENCES Thanks to Daniel Larremore for feedback on early versions of this video https://larremorelab.github.io/ Rapid Antigen Testing: COVID-19 testing: One size does not fit all. https://science.sciencemag.org/content/371/6525/126 Rethinking Covid-19 Test Sensitivity — A Strategy for Containment. https://www.nejm.org/doi/full/10.1056/NEJMp2025631 Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening. https://advances.sciencemag.org/content/7/1/eabd5393.abstract The effectiveness of population-wide, rapid antigen test based screening in reducing SARS-CoV-2 infection prevalence in Slovakia. (pre-print, not yet peer reviewed) https://www.medrxiv.org/content/10.1101/2020.12.02.20240648v1 Effective Testing and Screening for Covid-19. https://www.rockefellerfoundation.org/wp-content/uploads/2020/09/A-National-Decision-Point-Effective-Testing-Screening-for-Covid-19-Full-Report.pdf Brown University & Harvard University modeling of COVID-19 testing shortfall. https://globalepidemics.org/testing-targets/ Fast Coronavirus Tests are coming. https://media.nature.com/original/magazine-assets/d41586-020-02661-2/d41586-020-02661-2.pdf Open letter signed by epidemiologists and infectious disease experts supporting widespread & frequent rapid antigen testing for COVID-19: https://www.rapidtests.org/expert-letter More information on various COVID-19 tests: https://chs.asu.edu/diagnostics-commons/testing-commons Field performance and public health response using the BinaxNOW Rapid SARS-CoV-2 antigen detection assay during community-based testing. https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1890/6052342 Performance of an Antigen-Based Test for Asymptomatic and Symptomatic SARS-CoV-2 Testing at Two University Campuses. https://www.cdc.gov/mmwr/volumes/69/wr/mm695152a3.htm Asymptomatic Spread: People without symptoms spread virus in more than half of cases, CDC model finds https://www.washingtonpost.com/science/2021/01/07/covid-asymptomatic-spread/ (More than half of all) SARS-CoV-2 Transmission From People Without COVID-19 Symptoms. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2774707 Three Quarters of People with SARS-CoV-2 Infection are Asymptomatic: Analysis of English Household Survey Data. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7549754/ Viral Load Curve: SARS-CoV-2 viral dynamics in acute infections. (pre-print, not yet peer reviewed) https://www.medrxiv.org/content/10.1101/2020.10.21.20217042v2 Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Why Masks Work BETTER Than You'd Think

Sep 8, 2020

Thanks to the Heising-Simons foundation for their support: https://www.hsfoundation.org (their COVID-19 grants: https://www.hsfoundation.org/grants/covid-19-response-grants/ ) Check out https://aatishb.com/maskmath to explore and for references. This video is about how masks (whether surgical, or N95, or cloth) are counterintuitive and actually work much better epidemiologically than one might expect. Masks do double-duty, and the fraction of interactions with masks is much higher than the fraction of people wearing masks, so partially adopted, partially effective masks are able to reduce the basic reproduction number surprisingly well. REFERENCES: Aatish’s detailed writeup on github: https://github.com/aatishb/maskmath/blob/master/model/mathmodel.ipynb Amid the Coronavirus Crisis, a Regimen for Re-entry: https://www.newyorker.com/science/medical-dispatch/amid-the-coronavirus-crisis-a-regimen-for-reentry Face Masks Against COVID-19: An Evidence Review https://www.preprints.org/manuscript/202004.0203/v3 Mask FAQ Test Results: https://www.maskfaq.com/test-results The Effect of Mask Use on the Spread of Influenza During a Pandemic: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1539-6924.2010.01428.x Calibrated Intervention and Containment of the COVID-19 Pandemic: https://arxiv.org/ftp/arxiv/papers/2003/2003.07353.pdf Cloth Mask Breathability and Filtration Efficiency Technical Report: https://static1.squarespace.com/static/5e8126f89327941b9453eeef/t/5f2c4463a5c9f75a38d2b26f/1596736614213/N95DECON_cloth_mask_breathability_filtrationtechnical_report_v1_200804.pdf What kind of mask should I be wearing to protect against COVID-19? http://built-envi.com/what-kind-of-mask-should-i-be-wearing-to-protect-against-covid-19/ Masks for all? The science says yes. https://www.fast.ai/2020/04/13/masks-summary/ The Real Reason to Wear a Mask: https://medium.com/the-atlantic/the-real-reason-to-wear-a-mask-e6405abbc484 Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Astounding Physics of N95 Masks

Jun 18, 2020

Head to https://brilliant.org/MinutePhysics to sign up for free and get 20% off a Premium subscription to Brilliant! This video was written in collaboration with Aatish Bhatia - https://aatishb.com To learn more about using & decontaminating N95 masks: https://www.n95decon.org Thanks to Manu Prakash for useful discussion and feedback (Manu is involved with the N95 decontamination project) Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ The physics & engineering of N95 mask design is pretty incredible. REFERENCES 10X efficiency of electrically charged fibers "The electrostatic charge of N95 masks is a major contributor to their filtration efficiency, improving it at least 10-fold over uncharged fabric" (Tsai et al., Journal of Electrostatics 2002; Peter Tsai, personal communication). Prakash Lab COVID-19 Response Group Working Draft Document on N95 masks: https://docs.google.com/document/d/1aACcbkyZjR7nZy_wWeGQ9U2iGy0y4QajBeOL8RqAZIQ/edit “Electrostatic charge contributes as much as 95% of the filtration efficiency” Molina, A., Vyas, P., Khlystov, N., Kumar, S., Kothari, A., Deriso, D., ... & Prakash, M. (2020). Project 1000 x 1000: Centrifugal melt spinning for distributed manufacturing of N95 filtering facepiece respirators. arXiv preprint arXiv:2004.13494. https://arxiv.org/pdf/2004.13494.pdf Tsai, P. P., Schreuder-Gibson, H., & Gibson, P. (2002). Different electrostatic methods for making electret filters. Journal of electrostatics, 54(3-4), 333-341. https://www.researchgate.net/profile/Phillip_Gibson/publication/222659741_Different_electrostatic_methods_for_making_electret_filters/links/5a5912cba6fdcc3bfb5ab21e/Different-electrostatic-methods-for-making-electret-filters.pdf History of Electrets Jefimenko, O. D., & Walker, D. K. (1980). Electrets. The Physics Teacher, 18(9), 651-659. https://aapt.scitation.org/doi/abs/10.1119/1.2340651 Physics of Air Filtration Hinds, W. C. (1999). Aerosol technology: properties, behavior, and measurement of airborne particles. John Wiley & Sons. https://www.wiley.com/en-us/Aerosol+Technology%3A+Properties%2C+Behavior%2C+and+Measurement+of+Airborne+Particles%2C+2nd+Edition-p-9780471194101 Scientific consortium for data-driven study of N95: https://www.n95decon.org/ N95 & virus particle sizes Bałazy, A., Toivola, M., Adhikari, A., Sivasubramani, S. K., Reponen, T., & Grinshpun, S. A. (2006). Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?. American journal of infection control, 34(2), 51-57. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.488.4644&rep=rep1&type=pdf Harnish, D. A., Heimbuch, B. K., Husband, M., Lumley, A. E., Kinney, K., Shaffer, R. E., & Wander, J. D. (2013). Challenge of N95 filtering facepiece respirators with viable H1N1 influenza aerosols. Infection Control & Hospital Epidemiology, 34(5), 494-499. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4646082/ Liao, L., Xiao, W., Zhao, M., Yu, X., Wang, H., Wang, Q., ... & Cui, Y. (2020). "Can N95 respirators be reused after disinfection? How many times?. ACS nano. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7202248/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

How To Tell If We're Beating COVID-19

Mar 27, 2020

This video made possible with support of Brilliant - the first 200 subscribers to go to http://Brilliant.org/MinutePhysics get 20% off a Premium subscription to Brilliant. Go to http://aatishb.com/covidtrends to explore the graph from the video yourself! RESOURCES Grant's 3Blue1Brown Video: Exponential Growth and Epidemics: https://www.youtube.com/watch?v=Kas0tIxDvrg Aatish's Exponential/Logistic Curve-Fitting Site: https://github.com/aatishb/covid/blob/master/curvefit.ipynb Data Source: https://github.com/CSSEGISandData/COVID-19 Our World in Data Page on Coronavirus: https://ourworldindata.org/coronavirus How many tests for COVID-19 are being performed around the world? https://ourworldindata.org/covid-testing Understanding logarithmic scales: https://www.nytimes.com/2020/03/20/health/coronavirus-data-logarithm-chart.html What we can learn from the countries winning the coronavirus fight: https://www.abc.net.au/news/2020-03-26/coronavirus-covid19-global-spread-data-explained/12089028 (Great explainer on log scales and growth curves explained in the context of COVID-19 in different countries) This video is a collaboration with Aatish Bhatia about how to see the COVID-19 tipping point - we present a better way to graph COVID-19 coronavirus cases using a logarithmic scale in "phase space" - plotting the growth rate against the cumulative cases, rather than either of these against time. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

How to Tell Matter From Antimatter | CP Violation & The Ozma Problem

Feb 26, 2020

This video was made with the support of the Heising Simons Foundation. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ This video is about the Ozma problem of distinguishing the chirality (ie left-handedness or right-handedness) of matter using weak interaction processes like beta decay (for example in uranium), or neutral kaon/k-meson decay. This is wrapped up in the phenomenon of CP violation, by which charge and parity are both violated by certain weak interaction processes - this enables antimatter to be unambiguously distinguished from matter, and left handed chirality from right handed. REFERENCES The Ozma Search for Extraterrestrial Intelligence (SETI) Project https://www.seti.org/seti-institute/project/details/early-seti-project-ozma-arecibo-message Sean Carroll on CP Symmetry (& why we shouldn’t trot out baryogenesis all the time) https://www.preposterousuniverse.com/blog/2010/06/04/marketing-cp-violation/ Electroweak CP Violation on Scholarpedia http://www.scholarpedia.org/article/CPviolationinelectroweakinteractions The Wu Experiment https://en.wikipedia.org/wiki/Wuexperiment Martin Gardner, The New Ambidextrous Universe https://books.google.com/books?id=kdLGa8cPPUC&lpg=PP1&pg=PR2#v=onepage&q&f=false Lecture notes on CP Violation and the CKM Matrix, Cambridge (Mark Thomson) https://www.hep.phy.cam.ac.uk/thomson/lectures/partIIIparticles/Handout122009.pdf Homochirality https://en.wikipedia.org/wiki/Homochirality L-glucose (vs D-glucose) https://en.wikipedia.org/wiki/L-Glucose Radioactive Nucleus Decay http://www.radioactivity.eu.com/site/pages/RadioactiveSeries.htm CP Violation in Semi-Leptonic Decays (SEE PAGE 426 for reference to definition of MATTER) https://www.hep.phy.cam.ac.uk/thomson/lectures/partIIIparticles/Handout122009.pdf Kaon Decay Modes http://pdg.lbl.gov/2012/listings/rpp2012-list-K-zero-L.pdf Flipped bowling Jesus scene in Big Lebowski https://www.youtube.com/watch?v=lWz8NGIisMo Isotopes of Uranium https://en.wikipedia.org/wiki/Isotopesofuranium Beta Decay https://en.wikipedia.org/wiki/Betadecay The Wu Experiment https://en.wikipedia.org/wiki/Wuexperiment Kaons https://en.wikipedia.org/wiki/Kaon CP Violation in Symmetry Magazine https://www.symmetrymagazine.org/article/charge-parity-violation Physics Stack Exchange on CP Violation https://physics.stackexchange.com/questions/160511/what-cp-violating-processes-do-we-know-of MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Reimagining the Periodic Table

Dec 20, 2019

Go to https://Brilliant.org/MinutePhysics to gift Brilliant Premium for the holidays, and for 20% off! This video is about cutting, taping, and rearranging the periodic table into the Left Step form, the Mendeleev's flower form, the cake form, the wide form, the standard form, and so on. A great holiday craft!! REFERENCES Alternate Periodic Tables https://en.wikipedia.org/wiki/Alternative_periodic_tables Electronegativity https://en.wikipedia.org/wiki/Electronegativity Atomic Radius Radii https://en.wikipedia.org/wiki/Atomic_radius First Ionization energy https://en.wikipedia.org/wiki/Ionization_energy Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Why Do Mirrors Flip Left & Right (but not up & down)?

Dec 6, 2019

Go to https://nebula.tv/minutephysics to get access to Nebula (where you can watch MinuteBody) plus you'll get a 20% discount on an annual subscription. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ This video is about why words flip left & right (aka horizontally) in a mirror but not up & down (aka vertically). The answer has to do with specular reflection, mirrors being like windows into another world (alternate universes, just with in and out flipped!), and transparency of the things we write on. REFERENCES Specular Reflection https://en.wikipedia.org/wiki/Specular_reflection PhysicsGirl video about mirrors https://www.youtube.com/watch?v=vBpxhfBlVLU Fermat’s principle http://electron6.phys.utk.edu/optics421/modules/m1/Fermat's%20principle.htm Thomas-Fermi screening https://en.wikipedia.org/wiki/Thomas%E2%80%93Fermi_screening MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

Do Photons Cast Shadows?

Nov 6, 2019

Thanks to Nebula for their support. Go to https://nebula.tv/minutephysics to get Nebula! Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ This video is about two-photon (gamma-gamma) physics, and how photons can interact with each other - either mediated by a passing lepton, or gravitationally via lensing, or via vacuum fluctuation pair production of vertical particles (electron-positron pair, for example). This is the so-called "box diagram" feynman diagram. REFERENCES Water waves interact with each other (weakly nonlinear shallow water waves) https://en.wikipedia.org/wiki/Korteweg%E2%80%93deVriesequation http://mathworld.wolfram.com/Korteweg-deVriesEquation.html Paper: Absorption of Very High Energy Gamma Rays in the Milky Way https://arxiv.org/pdf/1608.01587.pdf Paper: Observing light-by-light scattering at the Large Hadron Collider (LHC) https://arxiv.org/pdf/1305.7142.pdf Mass-Energy Scale http://labs.minutelabs.io/Mass-Energy-Scale/ Optical Depth https://en.wikipedia.org/wiki/Opticaldepth The electromagnetic spectrum and photon energies http://labman.phys.utk.edu/phys222core/modules/m6/The%20EM%20spectrum.html Gravitational Lensing http://andybohn.com/research/lensing.html Ask an Astrophysicist on gamma ray scattering and energies in cosmology http://teacherlink.ed.usu.edu/tlnasa/reference/imaginedvd/files/imagine/docs/askastro/answers/970412e.html Measuring Vacuum Polarisation with High Power Lasers https://arxiv.org/pdf/1510.08456.pdf Detecting vacuum birefringence with X-ray free electron lasers and high-power optical lasers https://indico.desy.de/indico/event/12654/session/2/contribution/8/material/slides/0.pdf Vacuum birefringence in the head-on collision of XFEL and optical high-intensity laser pulses https://arxiv.org/pdf/1807.03302.pdf ATLAS makes first direct detection of Light-by-light scattering at the LHC https://atlas.cern/updates/press-statement/atlas-sees-first-direct-evidence-light-light-scattering-high-energy Two Photon Physics http://www.hep.ucl.ac.uk/opal/gammagamma/gg-tutorial.html https://en.wikipedia.org/wiki/Two-photonphysics Thesis: The Opacity of the Universe for high and very high energy γ-rays http://inspirehep.net/record/1254304/files/desy-thesis-13-033.pdf MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

The Man Who Corrected Einstein

Oct 15, 2019

Sign up for Brilliant FOR FREE at http://brilliant.org/minutephysics - the first 200 people get 20% of a premium subscription. This video is about how Russian physicist Aleksandr Fridman corrected Albert Einstein about the expansion of the universe. Einstein thought that general relativity implied that space had to be static and unchanging, but he had made a technical error regarding the differentiation of the metric (in particular, I believe he mistook the determinant of the metric for a scalar rather than a tensor density of weight 2). Friedmann didn't make this differential geometric mistake, and the cosmologies he found from the Einstein Equations were more varied in their properties - they could be expanding, or contracting, or (with the cosmological constant), static. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ REFERENCES Alexander Friedmann https://en.wikipedia.org/wiki/Alexander_Friedmann Einstein Wrongly Criticizes Alexander Friedmann https://einsteinpapers.press.princeton.edu/vol13-trans/301 Alexander Friedmann Corrects Einstein https://einsteinpapers.press.princeton.edu/vol13-trans/363 Einstein Admits his Mathematical Mistake https://einsteinpapers.press.princeton.edu/vol14-trans/77 Interrogating the Legend of Einstein’s “Biggest Blunder” https://arxiv.org/abs/1804.06768 Cosmological Considerations in the General Theory of Relativity https://einsteinpapers.press.princeton.edu/vol6-trans/433 On the General Theory of Relativity (Einstein) https://einsteinpapers.press.princeton.edu/vol6-trans/110 The Field Equations of Gravitation https://einsteinpapers.press.princeton.edu/vol6-trans/129 The Einstein Field Equations https://en.wikipedia.org/wiki/Einstein_field_equations Presentation about the Sequence of Events http://web.mit.edu/8.286/www/slides07/Einstein-and-Friedmann.pdf Tensor Densities: https://en.wikipedia.org/wiki/Tensor_density MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

When It's OK to Violate Privacy

Sep 21, 2019

Go to http://www.dashlane.com/minutephysics for a free 30 day trial and 10% discount with offer code 'minutephysics' Watch the main video here: https://www.youtube.com/watch?v=pT19VwBAqKA Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ REFERENCES Cynthia Dwork (key inventor of Differential Privacy), giving a great intro talk about differential privacy https://www.youtube.com/watch?v=lg-VhHlztqo Hazards of Smoking: the Effect on Life Span https://www.nejm.org/doi/pdf/10.1056/NEJMsa1211128 NHL Hockey Birth distributions https://www.quanthockey.com/nhl/birth-month-totals/nhl-players-career-stats.html MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich