Why Can Light Pass Through Light Without Colliding?
Lights Out Physics
17,937 views
Hey guys! We’re now live on Spotify🎧
Listen here: https://open.spotify.com/show/3qYsIDs...
Cross the beams of two flashlights in a dark room and they pass straight through one another, untouched, as though neither were there. Water would splash, thrown balls would bounce, cars would crash, yet light walks through light and comes out the far side unchanged. But physics does not actually forbid two beams of light from colliding, and in the last few years that collision has been caught on camera at the largest machines ever built. So why does light so very nearly never collide with light?
Tonight we take that quiet, everyday moment apart, floor by floor, from the wave that simply adds to the flickering emptiness underneath it, following the one hidden door through which a beam of light can finally reach another. What has to happen for two beams to touch, and what does light become when they finally do?
Get comfortable, close your eyes if you like, and let this slow walk through the physics of light keep you company tonight. Subscribe to Lights Out Physics if you enjoy taking the long way around the universe.
CHAPTERS
0:00 Introduction
1:44 The Two Beams That Pass Through
11:30 Everything Else Collides
21:43 Waves Simply Add
31:53 The Missing Handhold
42:48 The Word That Was Too Tidy
52:25 What We Have and What We Don't
1:02:10 The Secret Handshake Through Matter
1:12:30 How Rare Is Never
1:22:33 Caught in the Act
1:32:31 When Light Becomes Matter
1:42:09 The Vacuum Was Never Empty
1:51:45 The Transparent Universe
SOURCES
ATLAS: Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions (arXiv) — https://arxiv.org/abs/1904.03536
ATLAS: Evidence for Light-by-Light Scattering in Heavy-Ion Collisions (arXiv) — https://arxiv.org/abs/1702.01625
ATLAS observes light scattering off light (CERN) — https://atlas.cern/updates/briefing/a...
Making Matter from Collisions of Light — STAR at RHIC (U.S. Department of Energy) — https://www.energy.gov/science/np/art...
STAR Ultraperipheral Collision Results (arXiv) — https://arxiv.org/pdf/2503.06357
SLAC Experiment E-144 Home Page — http://kirkmcd.princeton.edu/e144/
Evidence for vacuum birefringence from the neutron star RX J1856.5-3754 (MNRAS) — https://academic.oup.com/mnras/articl...
Vacuum birefringence, RX J1856.5-3754 (arXiv) — https://arxiv.org/abs/1610.08323
Photon-photon scattering: a tutorial (Canadian Journal of Physics) — https://cdnsciencepub.com/doi/10.1139...
Photon-photon scattering and related phenomena: the early period (arXiv) — https://arxiv.org/pdf/1711.05194
Quantum Vacuum Experiments Using High Intensity Lasers — the Schwinger limit (arXiv) — https://arxiv.org/pdf/0812.3087
Hans Heinrich Euler — the first calculation of light-by-light scattering (Euler & Kockel, 1935) — https://en.wikipedia.org/wiki/Hans_He...
—
Disclaimer: Lights Out Physics is an education and relaxation channel. Factual material is based on peer-reviewed research and official scientific bodies; any speculation, fringe theory, or personal analysis is identified as such when it appears. This is not a news channel. Viewer discretion advised.
#LightByLightScattering #QuantumElectrodynamics
15 Comments
Why Can Light Pass Through Light Without Colliding?
Lights Out Physics
17,937 views
Hey guys! We’re now live on Spotify🎧
Listen here: https://open.spotify.com/show/3qYsIDs...
Cross the beams of two flashlights in a dark room and they pass straight through one another, untouched, as though neither were there. Water would splash, thrown balls would bounce, cars would crash, yet light walks through light and comes out the far side unchanged. But physics does not actually forbid two beams of light from colliding, and in the last few years that collision has been caught on camera at the largest machines ever built. So why does light so very nearly never collide with light?
Tonight we take that quiet, everyday moment apart, floor by floor, from the wave that simply adds to the flickering emptiness underneath it, following the one hidden door through which a beam of light can finally reach another. What has to happen for two beams to touch, and what does light become when they finally do?
Get comfortable, close your eyes if you like, and let this slow walk through the physics of light keep you company tonight. Subscribe to Lights Out Physics if you enjoy taking the long way around the universe.
CHAPTERS
0:00 Introduction
1:44 The Two Beams That Pass Through
11:30 Everything Else Collides
21:43 Waves Simply Add
31:53 The Missing Handhold
42:48 The Word That Was Too Tidy
52:25 What We Have and What We Don't
1:02:10 The Secret Handshake Through Matter
1:12:30 How Rare Is Never
1:22:33 Caught in the Act
1:32:31 When Light Becomes Matter
1:42:09 The Vacuum Was Never Empty
1:51:45 The Transparent Universe
SOURCES
ATLAS: Observation of Light-by-Light Scattering in Ultraperipheral Pb+Pb Collisions (arXiv) — https://arxiv.org/abs/1904.03536
ATLAS: Evidence for Light-by-Light Scattering in Heavy-Ion Collisions (arXiv) — https://arxiv.org/abs/1702.01625
ATLAS observes light scattering off light (CERN) — https://atlas.cern/updates/briefing/a...
Making Matter from Collisions of Light — STAR at RHIC (U.S. Department of Energy) — https://www.energy.gov/science/np/art...
STAR Ultraperipheral Collision Results (arXiv) — https://arxiv.org/pdf/2503.06357
SLAC Experiment E-144 Home Page — http://kirkmcd.princeton.edu/e144/
Evidence for vacuum birefringence from the neutron star RX J1856.5-3754 (MNRAS) — https://academic.oup.com/mnras/articl...
Vacuum birefringence, RX J1856.5-3754 (arXiv) — https://arxiv.org/abs/1610.08323
Photon-photon scattering: a tutorial (Canadian Journal of Physics) — https://cdnsciencepub.com/doi/10.1139...
Photon-photon scattering and related phenomena: the early period (arXiv) — https://arxiv.org/pdf/1711.05194
Quantum Vacuum Experiments Using High Intensity Lasers — the Schwinger limit (arXiv) — https://arxiv.org/pdf/0812.3087
Hans Heinrich Euler — the first calculation of light-by-light scattering (Euler & Kockel, 1935) — https://en.wikipedia.org/wiki/Hans_He...
—
Disclaimer: Lights Out Physics is an education and relaxation channel. Factual material is based on peer-reviewed research and official scientific bodies; any speculation, fringe theory, or personal analysis is identified as such when it appears. This is not a news channel. Viewer discretion advised.
#LightByLightScattering #QuantumElectrodynamics