The concept of the James Webb Space Telescope (JWST) "seeing back in time" is related to the vast distances of astronomical objects and the finite speed of light.
Light travels at a finite speed, approximately 299,792 kilometers per second (or about 186,282 miles per second) in a vacuum. This means that when we observe distant objects in space, we are actually seeing them as they were in the past, because the light emitted by those objects takes time to reach us.
The universe itself is around 13.8 billion years old, and the Big Bang is believed to have occurred about 13.8 billion years ago. Since the universe has been expanding since that time, the objects in the universe, such as galaxies, have also been moving away from each other.
The JWST is designed to observe the universe in infrared light, which is less affected by dust and allows us to observe more distant and faint objects. By observing extremely distant objects, the telescope can capture the light that has traveled for billions of years to reach us.
When we look at objects located billions of light-years away, the light we receive has traveled for billions of years. This means that the light we observe from these objects was emitted billions of years ago, providing us with a glimpse of the universe's past. In a way, by observing these ancient light sources, the JWST allows us to look back in time and see the universe as it existed billions of years ago, including the early moments after the Big Bang.
By studying the light from distant galaxies, the JWST can provide valuable insights into the formation and evolution of galaxies, the early universe, and the processes that occurred shortly after the Big Bang, helping scientists unravel the mysteries of our cosmic origins.