The upper limit for the speed of light in a vacuum, denoted by the symbol "c," is considered a fundamental constant of nature. In the theory of special relativity, proposed by Albert Einstein, the speed of light in a vacuum is postulated to be the maximum speed at which information or causality can propagate through spacetime. Its value is approximately 299,792,458 meters per second (or about 186,282 miles per second) in a vacuum.
As for the speed of sound, it is dependent on the medium through which it propagates. In general, sound travels at different speeds in different materials, as the speed is determined by factors such as the density, temperature, and elasticity of the medium. For example, in dry air at a temperature of about 20 degrees Celsius (68 degrees Fahrenheit), the speed of sound is roughly 343 meters per second (or 1,125 feet per second).
It's important to note that the speed of sound is significantly slower than the speed of light. In most cases, the speed of sound is several orders of magnitude lower than the speed of light. The difference in their velocities is due to the nature of the propagation mechanisms involved. Sound requires the physical interaction of particles in a medium, while light is an electromagnetic wave that does not require a medium for propagation.
In summary, the upper limit for the speed of light in a vacuum is considered to be a constant value in our current understanding of physics, while the speed of sound varies depending on the properties of the medium through which it travels.