Light travels through the universe at the fastest speed that scientists can measure. In fact, the speed of light acts as a universal speed limit, with nothing known to move faster. This speed is measurable, and it plays a crucial role in our understanding of the universe’s size and age.
What exactly is light: a wave or a particle?
Light travels at an astounding speed of 299,792,458 meters per second. To grasp this, it’s important to understand what light truly is, a concept that became clearer in the 20th century.
For centuries, the nature of light remained a mystery. Scientists struggled to understand how it moved and whether it could be described by wave or particle physics. How could light seem to travel at the same speed everywhere? It wasn’t until Albert Einstein’s explanation of the theory of special relativity in 1905 that things began to make sense. Einstein proposed that space and time are interconnected, and the speed of light is the constant that binds them.
What is the speed of light?
The speed of light is commonly described as fixed, with nothing able to exceed it. This is absolutely true. The speed of light in a vacuum is 299,792,458 meters per second, or 186,282 miles per second. However, light does slow down when it travels through different substances. For instance, when it passes through glass, its speed reduces to about two-thirds of its speed in a vacuum. Even in the near-vacuum of air, light slows down ever so slightly. As it moves through space, it encounters clouds of gas and particles, as well as gravitational fields, all of which can slow its speed just a little bit. Additionally, some of the light is absorbed by these gas clouds and particles as it passes through.
This behavior is related to the nature of light itself, which is an electromagnetic wave. As light moves through a medium, its electric and magnetic fields interact with the charged particles it encounters. These interactions cause the particles to scatter the light at the same frequency but with a phase shift.
Interestingly, despite its incredible speed, light’s path can be altered when it passes through regions in space with strong gravitational fields. This effect is clearly observed in galaxy clusters, which contain vast amounts of matter, including dark matter, that bends the light from more distant objects, such as quasars.
Lightspeed and gravitational waves
According to current physics laws, gravitational waves also travel at the speed of light, although this is still under study as scientists examine the phenomenon of gravitational waves created by the collisions of black holes and neutron stars. There are no other known objects that travel faster than the speed of light, though some can come close.
One puzzling exception involves space-time itself. It appears that distant galaxies are moving away from us faster than the speed of light. This presents a “dilemma” that scientists are still working to understand.
