Stop Time with Light: From Edgerton's Strobe to Attosecond X-ray Movies

Overview

In this video, Veritasium reveals three unusual ways of stopping time and what you can see when you slow things down. Beginning with Harold Edgerton's strobe photography from the 1930s, he shows how a tiny, bright flash can freeze fast motion and produce sharp photos of spinning motors and flying tennis balls. The discussion then moves to a one-pixel camera that can capture nearly a trillion frames per second, enabling ultra slow motion of light traveling through scenes. Finally, the talk ventures into attosecond X-ray pulses generated at large facilities to image electron densities and simulate molecular movies. The thread tying the segments together is how physics and imaging technology push temporal and spatial resolution to reveal hidden dynamics.

Introduction

Veritasium walks through three distinct approaches to capturing moments that are normally too fast for the eye. The common theme is using timing to reveal motion and structure at scales ranging from milliseconds to attoseconds.

Edgerton's Strobe: A Century-Old Breakthrough

The video recounts Harold Doc Edgerton's development of a strobe light that creates a bright, ultrashort flash by momentarily ionizing gas in a tube. Triggered by a high voltage pulse, the gas becomes a conductor and the capacitor's energy is dumped into the flash, lighting the scene for about 10 microseconds. This allows photographers to freeze motors, tennis rackets, or even balloons in action. The strobe dramatically improved image sharpness for fast-moving subjects and was used widely in Life and National Geographic magazines to communicate fast processes to the public. Edgerton's genius lay not just in the hardware, but in his photographic eye and timing tricks that made his shots compelling and informative.

The 1 Trillion FPS Frontier: Single Pixel Imaging

The film then introduces a different extreme: a camera that can see nearly one pixel at a time but at around 1 trillion frames per second. In a single pixel camera the sensor counts photons arriving at a very high rate, with each frame lasting about a picosecond. By scanning the scene point by point with fast mirrors and collecting many measurements, the system reconstructs a full high-speed visualization of light propagation. This approach trades spatial resolution for temporal resolution, enabling direct observation of light wavefronts as they travel through a simple room with shapes like a cone and a sphere. The key is the repeatability of the scene enough times to build a coherent image when the sensor position changes slightly between measurements.

Attosecond X-ray Pulses: Imaging Electron Dynamics

At Slack, a 3.2 kilometer long electron accelerator, researchers generate relativistic electron pulses and pass them through undulators to emit X-ray pulses in the femtosecond and even attosecond regime. These pulses are used to probe molecules by ionizing core electrons with energies tuned to element-specific ionization thresholds. The resulting kinetic energy of ejected electrons encodes information about electron density in the molecule. By driving a molecule with a laser and then probing it with X-ray pulses at controlled delays, scientists can construct a molecular movie that depicts how electron densities evolve over time. This attosecond technique can produce frames separated by hundreds of attoseconds, allowing a possible movie with a quadrillion frames per second in principle when assembled across time delays. The video emphasizes the importance of repeatable dynamics, because each shot must recreate the same process for the data to be stitched into a movie.

Takeaways

The three approaches illustrate a spectrum of strategies for stopping time: traditional strobes that capture sharp snapshots, single-pixel ultrafast imaging that resolves light in motion, and attosecond X-ray techniques that reveal electron motion in molecules. Together they show how advances in imaging physics expand our ability to visualize processes that are essential to materials, chemistry, and physics, from the level of gears turning to electrons dancing in atoms.