Light traveling in a straight line
Light travels in a straight line due to the property of light known as rectilinear propagation. This means that light rays move in a straight path unless they are reflected or refracted by an object or medium.

Wave nature of light
Light is an electromagnetic wave that propagates through space. When light waves encounter an obstacle or a medium with a different refractive index, they can be reflected or refracted, causing them to change direction.

Reflection and refraction
When light hits a smooth surface, it undergoes reflection, bouncing off at an angle equal to the angle of incidence. This property allows us to see objects by reflecting light into our eyes. Refraction, on the other hand, occurs when light passes from one medium to another, causing it to change direction.

Principle of least time
Light follows the path that takes the least time to travel from one point to another. This principle, known as Fermat's principle or the principle of least time, explains why light travels in a straight line when not influenced by external forces.

Conclusion
In conclusion, the straight-line path of light is a result of its wave nature, the principles of reflection and refraction, and the principle of least time. These factors work together to ensure that light travels efficiently and predictably through space.