Faster than lighta
The speed of light is the universe’s ultimate speed limit, but could there be a way to get around it?
Pick up any book on physics or astronomy and you’ll read that light is the fastest thing in the universe and that immutable laws P prevent anything else from ever matching its speed through space. The limited speed of light sets the rules of cause and effect across the universe, and even affects how we see the distant cosmos. But what are the rules behind this cosmological speed limit? How exactly does it apply? Could there be natural phenomena that break this apparently universal rule, and might we one day find a way of doing the same?
Light travels through an empty vacuum with astonishing speed, crossing 299,792 kilometres (186,282 miles) of empty space in a single second. This means that light – and other related forms of electromagnetic radiation such as radio waves – seems to move instantaneously; it’s only when we look into the depths of space that the effects of its finite speed become apparent. Radio commands sent to rovers on Mars may take up to 20 minutes to reach the Red Planet, while light from the nearest stars has travelled several years to reach us. Distant galaxies are hundreds of millions and even billions of ‘light years’ away.
The idea of the speed of light as an ultimate cosmic speed limit only emerged around 1905 through Albert Einstein’s special theory of relativity. “We’d had, at that point in the early 20th century, a fairly complete theory of classical electromagnetism for about 40 years or so,” explains Dr Erik Lentz, a physicist at the Pacific Northwest National Laboratory (PNNL) in Washington. “And so Einstein had a notion of how electromagnetic fields could create a propagating light beam that travelled at a particular speed. But that speed, interestingly, didn’t seem to depend on what frame of reference you calculated it from. Whether someone was trying to measure the speed of a light beam relative to themselves in a laboratory or on board a moving train, it didn’t seem to matter.”
Einstein’s special theory described how this fixed or ‘invariant’ speed of light can affect other types of measurements, usually in circumstances where two objects are moving at very high or ‘relativistic’ speeds in relation to each other. For instance, objects moving at high speeds relative to an outside observer appear shortened along their direction of travel, experience time dilation and even increase their mass rather than
