The highest possible velocity of electromagnetic phenomena and light is the speed of light in a vacuum, which is approximately 299,792,458 meters per second (m/s).

This value is often rounded to 3 x 10⁸ m/s for simplicity. It's a fundamental constant in physics, denoted by the letter c.

Here's why this is the limit:

* Einstein's Theory of Special Relativity: This theory states that the speed of light in a vacuum is the ultimate speed limit for any object or information in the universe. Nothing can travel faster than light.

* Mass-energy equivalence: As an object approaches the speed of light, its mass increases infinitely, requiring an infinite amount of energy to accelerate it further. This makes exceeding the speed of light impossible.

Important Note:

* While the speed of light in a vacuum is constant, light can travel slower in other mediums like water or glass.

* The speed of light is a theoretical limit. It's impossible to reach it in practice.