Space is not just a big ball of light because light requires a source and a medium through which to propagate. In the vast expanse of space, there are areas where light sources exist, such as stars, galaxies, and other celestial objects. However, space itself is mostly empty, devoid of matter and energy density in most regions.
Light travels in straight lines unless it encounters an object or interacts with particles or gases that can scatter or absorb it. In the absence of any objects or particles, light will continue to travel indefinitely until it encounters something or is affected by cosmic phenomena such as gravitational lensing.
Moreover, the expansion of the universe plays a role. As space expands, the light from distant sources also experiences a phenomenon known as cosmological redshift. This means that the wavelengths of light are stretched as space expands, causing the light to shift toward longer, redder wavelengths. Consequently, the light from very distant sources, such as galaxies billions of light years away, can be redshifted to the point where it falls outside the visible spectrum and becomes undetectable to human eyes.
While space itself may appear dark in the absence of light sources, there is still a pervasive background glow called the cosmic microwave background radiation. This radiation is the remnant of the early universe and is spread uniformly throughout space. However, it is in the microwave frequency range and not visible light.
Therefore, space is not a continuous ball of light because light requires sources, objects to interact with, and specific wavelengths to be visible. In the vastness of space, there are regions that are dark and devoid of light sources, making space appear mostly black or empty to our eyes.