The reason light has a limited reach in space is primarily due to the expansion of the universe and the finite age of the universe. Let's break it down:
Expansion of the universe: The universe has been expanding since the Big Bang. As space itself expands, the distances between galaxies and other cosmic objects also increase. This expansion causes the light from distant objects to become stretched, resulting in a phenomenon called cosmological redshift. As the light travels through expanding space, its wavelength increases, shifting it toward the red end of the electromagnetic spectrum. Eventually, for objects that are extremely far away, the cosmological redshift becomes so significant that the light is shifted beyond the visible spectrum and into longer wavelengths, such as microwaves or radio waves. This phenomenon is known as the cosmic microwave background radiation.
Finite age of the universe: The universe has a finite age, estimated to be about 13.8 billion years. This means that the light we receive from distant objects has been traveling for a finite amount of time to reach us. The farther away an object is, the longer it takes for its light to reach us. As a result, there is a limit to how far back in time we can observe with light. This limit is often referred to as the observable universe, which is currently estimated to have a radius of about 46 billion light-years, given the expansion of space over time.
It's important to note that the observable universe is not a physical barrier or a hard limit on the size of the entire universe. It simply represents the portion of the universe that we can currently observe due to the constraints of the finite speed of light and the age of the universe. Beyond the observable universe, there may be more distant regions that we cannot observe because their light has not reached us yet, or it has been shifted beyond detectable wavelengths due to cosmic expansion.