In the realm of physics, there is a fundamental distinction between something that can travel at the speed of light and something that cannot be seen by humans. According to our current understanding, electromagnetic radiation, including visible light, travels at the speed of light in a vacuum.
If there is an object or phenomenon that emits or reflects visible light but cannot be seen by humans, it would typically be due to factors other than its speed. For example, if an object is transparent or emits light outside the visible spectrum (e.g., ultraviolet or infrared), humans may not be able to see it directly. However, this doesn't mean that the light itself is not traveling at the speed of light.
In certain circumstances, such as when an object is moving close to the speed of light relative to an observer, relativistic effects can come into play. These effects can cause changes in the perceived color, intensity, or direction of the light, making it difficult for humans to detect or interpret. However, this does not alter the fundamental speed of light itself.
It's important to note that there may be phenomena in the universe that are beyond our current understanding or detection capabilities. These could include hypothetical particles or forces that interact with matter and have properties we are not yet aware of. However, until such phenomena are observed and studied, we cannot make definitive statements about their properties or whether they can travel at the speed of light.