Question

What is the speed of light?

Answer 1

In order to answer this question, to know the speed of light, we will go through the whole theory behind the speed of light, we will also mention the value of the speed of light in many unit systems. And we will also discuss the mass-energy equivalence equation.

Complete answer:
The universal physical constant $c$ , or the speed of light in vacuum, is essential in many fields of physics. Its exact value is defined as $299792458m.{s^{ - 1}}$ (approximately $300000km.{s^{ - 1}}$ ). It's precise because a metre is defined as the length of the route taken by light in vacuum over a time interval of $\dfrac{1}{{299792458}}\sec onds$ by international agreement. According to special relativity, the speed at which ordinary matter, energy, or any signal carrying information may travel through space is limited to $c$ .
Though it is most frequently associated with light, it is also the speed at which all massless particles and field disturbances, including electromagnetic radiation (of which light is a narrow range in the frequency spectrum) and gravitational waves, travel in vacuum. Regardless of the source's speed or the observer's inertial reference frame, such particles and waves travel at $c$ . Regardless of the frame of reference in which their speed is measured, particles with non zero rest mass can approach but never achieve $c$ . $c$ connects space and time in both special and general relativity theories, and it also appears in the famous mass–energy equivalence equation, $E = m{c^2}$ .
Objects or waves may appear to travel faster than light in some instances (e.g. phase velocities of waves, the appearance of certain high-speed astronomical objects, and particular quantum effects). Beyond a certain point, the expansion of the cosmos is thought to exceed the speed of light.

Note: We know that's the exact speed of light since we defined it to be that number. We define a metre by taking our definition of a second (the time it takes for a particular number of periods of radiation emitted in hyperfine transitions in caesium-133) and multiplying it by the number of periods. So the item we'd be measuring is the definition of a metre.