Sound waves can travel through different mediums, such as air or water, and move at different speeds depending on what they’re traveling through.įor example, they move through solids much faster than they would through liquids or gases, which is why you’re able to hear an approaching train much faster if you listen to the sound propagating in the rail track rather than through the air.Īlbert Einstein’s theory of special relativity sets the absolute speed limit at which a wave can travel which is the speed of light, and is equal to about 300,000 km per second (186,000 miles per second). Waves, such as sound or light waves, are disturbances that move energy from one place to another. show that a combination of two dimensionless fundamental constants results in a new dimensionless constant that provides the upper bound for the speed of sound in condensed phases. For now, the speed of light remains the same as it has for centuries, constant and fixed… but watch this space.Trachenko et al. Studies into these ideas are ongoing, and we don't know for sure one way or the other yet. These particles create electromagnetic ripples along the way, the hypothesis goes, and could potentially cause variations in the speed of light. Quantum field theory says that a vacuum is never really empty: it's filled with elementary particles, rapidly popping in and out of existence. However, the story doesn't quite end there, thanks to quantum theory, that branch of physics hinting that the Universe might not be quite as constant as we think. Scientists have measured it by bouncing lasers back from objects and watching the way gravity acts on planets, and all these experiments come up with the same figure. We don't just have the word of Maxwell and Einstein for what the speed of light is, though. It matches the speed of a gravitational wave, and yes, it's the same c that's in the famous equation E=mc 2. What's more, this constant underpins much of what we understand about the Universe. Today the speed of light, or c as it's commonly known, is considered the cornerstone of special relativity – unlike space and time, the speed of light is constant, independent of the observer. Unfortunately for Beeckman and the progress of science, the results were inconclusive, but then in 1676 Danish astronomer Ole Rømer noticed strange variations in the eclipse times of one of Jupiter's moons over the course of a year.Ĭould this be because light took a longer time to travel from Jupiter when Earth was further away? Rømer thought so, and his rough calculations put the speed of light at about 220,000 kilometres per second – not a bad estimate at all, especially considering the data he would have had on planet sizes wasn't all that accurate. First, by Dutch scientist Isaac Beeckman in 1629, who set up a series of mirrors around a gunpowder explosions to see if observers noticed any difference in the when the flashes of light appeared. To start at the start though, some history: at the beginning of the 17th century, the general consensus was that light didn't have a speed, that it just appeared instantaneously, either present or not.ĭuring the 1600s this idea was seriously challenged.
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