Thanks to CuriosityStream for their support. Go to http://www.curiositystream.com/minutephysics to watch Particle Fever and 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 ... https://www.youtube.com/watch?v=Fv1JJ227CQk

Get "Into Thin Air" for free on Audible at http://www.audible.com/minutephysics And Subscribe to MinutePhysics MinutePhysics is on Google+ - http://bit.ly/qzEwc6 And facebook - http://facebook.com/minutephysics And twitter - @minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Music by Nathaniel Schroeder http://www.soundcloud.com/drschroeder Created by Henry Reich ... https://www.youtube.com/watch?v=NafbGOQBlQs

Get a free trial of Audible at https://audible.com/minutephysics or by texting 'minutephysics' to 500500 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 This joke video is about how Internet Service Providers (aka ISPs, internet companies, telecommunications companies, etc) violate the basic axioms of Zermelo-Fraenkel set theory. Like the axiom of choice (sometimes Well-ordering theorem), the Axiom of extensionality, Axiom of regularity (also called the Axiom of foundation), Axiom schema of specification, Axiom of pairing, Axiom of union, Axiom schema of replacement, Axiom of infinity, Axiom of power set. ... https://www.youtube.com/watch?v=Z3IPVWN-1ks

Why is the past different from the future? Caltech physicist Sean Carroll explains how the arrow of time is not an intrinsic property of physics, but rather an emergent feature. Trying out a new feature: English Transcript! Let me know how it works Tweet it - http://bit.ly/vJRWOo Facebook it - http://on.fb.me/tHwjDU minutephysics is now on Google+ - http://bit.ly/qzEwc6 And facebook - http://facebook.com/minutephysics And twitter - @minutephysics ... https://www.youtube.com/watch?v=GdTMuivYF30