The speed of light in a vacuum is approximately 299,792,458 meters per second (about 186,282 miles per second). This value is often rounded to approximately 300,000 kilometers per second or 186,000 miles per second for simplicity.
According to our current understanding of physics, the theory of relativity, specifically Einstein's special theory of relativity, states that the speed of light is an absolute constant in the universe. In this theory, it is postulated that nothing can travel faster than the speed of light in a vacuum. This fundamental principle is denoted by the equation E=mc², where "c" represents the speed of light and is a fundamental constant of nature.
As for natural phenomena that limit our ability to exceed the speed of light, there are a few important concepts to consider. First, as an object approaches the speed of light, its mass appears to increase, making it more and more difficult to accelerate further. This effect is known as relativistic mass increase. As an object with mass accelerates, its energy increases, and so does its inertia, making it harder to achieve even higher speeds.
Another significant phenomenon is time dilation. As an object approaches the speed of light relative to an observer, time slows down for that object compared to the observer's time. This means that for a traveler near the speed of light, time would appear to pass more slowly, and therefore their journey would seem shorter from their perspective. However, this effect is symmetric, so both the traveler and the observer would perceive the other's time as dilated.
These principles, along with others described in the theory of relativity, create what is commonly known as the "cosmic speed limit." As of now, no experiment or observation has shown that anything with mass can surpass the speed of light in a vacuum. It is important to note that this limitation applies to objects with mass, and there are hypothetical particles called tachyons, which have never been observed, that are thought to travel faster than light. However, their existence and properties are still speculative and not well-understood within the current framework of physics.