Here's why:

* Light is an electromagnetic wave: It doesn't need a medium (like air or water) to propagate.

* Vacuum is the absence of matter: Since there are no particles to interact with in a vacuum, light can travel unimpeded.

While light can travel through other materials like air, water, and glass, its speed is slower than in a vacuum. The speed of light in a vacuum is a fundamental constant, approximately 299,792,458 meters per second.