3Blue1Brown

But Why Would Light 'Slow Down'? Visualizing Feynman's Lecture on the Refractive Index

Published 30 Nov 2023 · 25 daily observations recorded · last updated 2026-09-29

Views
2,864,688
Avg views / hour
115.5
since publish (lifetime average)
Recent velocity
45.5
+1,093 views over 24h (2026-09-28 → 2026-09-29)
vs channel baseline
—
Channel median
—

Recent growth

Last 7 days
+7,319 views
measured 2026-09-22 → 2026-09-29 (168h)
Last 30 days
+27,918 views
measured 2026-08-27 → 2026-09-29 (792h)

Performance history

Every observation TubeSum recorded, plotted as measured.

Views over time — 25 observed points, 2.8M to 2.9M views 0 1M 2M 3M Aug 10, 2026 · 2,830,364 views Aug 17, 2026 · 2,832,919 views Aug 27, 2026 · 2,836,770 views Sep 1, 2026 · 2,840,800 views Sep 4, 2026 · 2,843,346 views Sep 7, 2026 · 2,845,818 views Sep 11, 2026 · 2,849,003 views Sep 12, 2026 · 2,849,840 views Sep 13, 2026 · 2,850,389 views Sep 14, 2026 · 2,851,245 views Sep 15, 2026 · 2,852,074 views Sep 16, 2026 · 2,852,709 views Sep 17, 2026 · 2,853,964 views Sep 18, 2026 · 2,854,743 views Sep 19, 2026 · 2,855,259 views Sep 20, 2026 · 2,855,971 views Sep 21, 2026 · 2,856,786 views Sep 22, 2026 · 2,857,369 views Sep 23, 2026 · 2,858,192 views Sep 24, 2026 · 2,859,123 views Sep 25, 2026 · 2,860,085 views Sep 26, 2026 · 2,861,365 views Sep 27, 2026 · 2,862,640 views Sep 28, 2026 · 2,863,595 views Sep 29, 2026 · 2,864,688 views Aug 10 Sep 17 Sep 29

Based on 25 observations · last observed Sep 29, 2026 · straight lines connect consecutive observations — TubeSum does not measure the days between them.

All observations

The same points the chart plots, as exact numbers. Gaps mean no observation was taken that day.

Date Views Avg views / hour Channel median
2026-09-29 2,864,688 115.5 —
2026-09-28 2,863,595 115.6 —
2026-09-27 2,862,640 115.6 —
2026-09-26 2,861,365 115.7 —
2026-09-25 2,860,085 115.8 —
2026-09-24 2,859,123 115.8 —
2026-09-23 2,858,192 115.9 —
2026-09-22 2,857,369 116.0 —
2026-09-21 2,856,786 116.0 —
2026-09-20 2,855,971 116.2 —
2026-09-19 2,855,259 116.2 —
2026-09-18 2,854,743 116.3 —
2026-09-17 2,853,964 116.4 —
2026-09-16 2,852,709 116.5 —
2026-09-15 2,852,074 116.6 —
2026-09-14 2,851,245 116.6 —
2026-09-13 2,850,389 116.7 —
2026-09-12 2,849,840 116.8 —
2026-09-11 2,849,003 116.9 —
2026-09-07 2,845,818 117.2 —
2026-09-04 2,843,346 117.5 —
2026-09-01 2,840,800 117.7 —
2026-08-27 2,836,770 118.1 —
2026-08-17 2,832,919 119.2 1,262,848
2026-08-10 2,830,364 119.9 1,262,848

Content analysis

Transcript, chapters and structure for this video live on its analysis page — performance and content are separate documents on TubeSum.

Read transcript & analysis →