The ability to observe space allows scientists to essentially look back in time, thanks to the way light travels across vast distances in the universe. Telescopes like the James Webb Space Telescope enable us to capture light from distant celestial bodies, acting as time machines that reveal what the universe looked like in the past. This phenomenon is rooted in the fact that light, despite traveling at incredible speeds, still requires time to travel across the vast expanses of space.
Light travels at approximately 186,000 miles (300,000 kilometers) per second, which is incredibly fast in human terms. However, even at this speed, the immense distances between objects in space mean that the light we see today actually left those objects millions or even billions of years ago. For example, light from the Moon takes just 1.3 seconds to reach Earth, while light from Neptune, the furthest planet in our solar system, takes about four hours. This delay in light’s arrival means that when we observe these objects, we are seeing them as they were in the past, not as they are right now.
When we look beyond our solar system, the distances become even more staggering. Within our galaxy, the Milky Way, distances are often measured in light-years—the distance that light travels in one year. For instance, Proxima Centauri, the closest star to Earth after the Sun, is over four light-years away. That means when we observe Proxima Centauri, we are actually seeing it as it was over four years ago. The light that reaches us today from that star began its journey back in time, traveling through space at a constant speed.
The James Webb Space Telescope, with its advanced instruments and capabilities, is able to observe objects that are far further away than ever before. By studying the light emitted from galaxies, stars, and other celestial bodies billions of light-years away, Webb allows scientists to peer into the distant past of the universe. The further the light travels, the further back in time we are able to see, offering a glimpse into the early stages of the universe, helping us understand its origins and evolution over time.