PeterDonis said:This Usenet Physics FAQ article may be helpful:
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/constants.html
The speed of light in a vacuum is approximately 299,792,458 meters per second, or about 670,616,629 miles per hour. This is the fastest speed at which energy can travel through space.
The speed of light plays a crucial role in the Big Bang theory as it is the speed at which the universe is expanding. This expansion began at the moment of the Big Bang and continues to this day. Additionally, the speed of light also helps us determine the age and size of the universe.
The speed of light in the early universe was measured by studying the cosmic microwave background radiation (CMB), which is the leftover radiation from the Big Bang. Scientists observed the temperature fluctuations in the CMB and used that data to calculate the speed of light at different points in the early universe.
There is no evidence to suggest that the speed of light has changed since the Big Bang. In fact, the speed of light has remained constant throughout the history of the universe, according to our current understanding of physics. However, there are some theories that suggest the speed of light may have been different in the very early stages of the universe.
The speed of light is a fundamental constant in Einstein's theory of relativity. This theory states that the laws of physics are the same for all observers, regardless of their relative motion. The constant speed of light is a crucial component of this theory, as it is the same for all observers regardless of their motion. This has been confirmed by numerous experiments and observations, providing strong evidence for the theory of relativity.