A YouTuber’s DIY device captures light’s journey in ultra-slow motion, reigniting viral fascination with a mind-bending physics demo.
In a cluttered garage, a green laser pulse doesn’t zip across the space it crawls, inch by inch, revealing the finite speed of light. This captivating footage, created by YouTuber AlphaPhoenix, shows a beam propagating at an effective 2 billion frames per second, turning an invisible phenomenon into a visible spectacle.
A tweet from X.
The video, posted in October 2025, depicts the laser moving about 15 centimeters per frame, matching light’s near-vacuum speed of 299,792,458 meters per second.
“Light moves about six inches, or 15 centimeters, per frame of this video,”
Says creator Brian Haidet in the footage.
Brian Haidet, PhD in Materials Science and Engineering, runs the AlphaPhoenix YouTube channel with over 500,000 subscribers. Known for DIY physics experiments and Hawaiian-shirt flair, he focuses on making science accessible. This project upgrades his 2024 1-billion-FPS setup.
“I spent roughly a year iterating to achieve 2 billion FPS, improving optics, timing, illumination, and control software,”
Haidet explains.
Built for under $1,000, Haidet’s streak camera uses a modified green laser for nanosecond pulses, a fog machine to scatter light, and parallel mirrors 3-5 meters apart. A spinning mirror (15,000-20,000 RPM) sweeps light through a slit to a single-pixel sensor like a photomultiplier tube. Arduino and Python code stitch thousands of pulses into video.
“The spinning mirror sweeps the image of the slit across the sensor once per rotation,”
He details. It’s a spatial-to-temporal conversion, not full-frame capture.
The clip features a “mirror ladder” where the beam bounces, forming glowing rungs in fog. Outgoing light seems slow returning appears fast. Light in air travels at 99.97% vacuum speed, but the demo approximates it.
Uploaded October 17, 2025, as
“A laser pointer at 2 billion fps makes the speed of light look… kinda weird,”
It exploded with millions of views. It recirculated on X in December via @dom_lucre’s “BREAKING” post, hitting 321,000 views quickly. Reactions mix awe and humor, boosting shares.
The “weird” effects stem from perspective.
“When you look toward the laser, the outgoing pulse appears to move slowly because photons scattered far away take longer to reach your eye/sensor,”
Haidet notes. Incoming light looks faster due to closer points. It’s geometry, not speed variation mind-bending as light defies instant intuition.
Haidet’s work democratizes science.
“It’s a resourceful, low-cost way to approximate ultrafast imaging,”
Per Interesting Engineering. It educates on relativity, inspires DIY efforts, and combats misinformation with transparency.
From historical estimates to modern labs, capturing light’s pace captivates. Haidet’s garage feat brings it home, reminding us of nature’s wonders in everyday settings.
