It’s the first thing we hear in the morning, whether it’s the birds or your alarm clock. “The only somewhat startling difference is that the acoustic waves making up the pulse move so much more slowly than light.It’s hard to imagine the world without any sound since we rely on it so much. “The effect is the same as that observed in previous electrical or optical experiments,” Robertson told Physics Web. The underlying waves that make up the pulse remain at subluminal velocities, so no information, matter or energy actually travels faster than light. Proponents of Einstein’s special relativity need not worry, though. Therefore, he says, superluminal sound is an “everyday” occurrence, although it is mostly too subtle to notice. Robertson says that such split-path interference can also occur naturally when a sound source is located near a hard wall: some of the sound reaches the listener directly, and some reaches the listener from a slightly longer path as it bounces off the wall. This gives the impression that the sound has travelled farther, and thus faster, in the same space of time. As they interfere with each other, they replicate the shape of the original pulse, only farther ahead. Inside, a loop filter splits the signal along two unequal length paths, and then recombines it to produce large amounts of anomalous dispersion. William Robertson and colleagues from Middle Tennessee State University in the US have managed to produce “faster than light” sound, however, by putting a sound pulse through a surprisingly simple waveguide. But until now, superluminal acoustic waves have existed only in theory, and would require the group velocity to increase almost a million times over. Indeed, the group velocity of light has already been shown to travel faster than the speed of light in a vacuum. Webinars Tune into online presentations that allow expert speakers to explain novel tools and applications.Video Watch our specially filmed videos to get a different slant on the latest science.Podcasts Our regular conversations with inspiring figures from the scientific community.Audio and video Explore the sights and sounds of the scientific world.Supercool physics Experiments that probe the exotic behaviour of matter at ultralow temperatures depend on the latest cryogenics technology.The science and business of space Explore the latest trends and opportunities associated with designing, building, launching and exploiting space-based technologies.Revolutions in computing Find out how scientists are exploiting digital technologies to understand online behaviour and drive research progress.Nanotechnology in action The challenges and opportunities of turning advances in nanotechnology into commercial products.#BlackInPhysics Celebrating Black physicists and revealing a more complete picture of what a physicist looks like.Artificial intelligence Explore the ways in which today’s world relies on AI, and ponder how this technology might shape the world of tomorrow.Collections Explore special collections that bring together our best content on trending topics.Innovation showcases A round-up of the latest innovation from our corporate partners.Projects and facilities Follow the latest progress at the world’s top scientific experiments.Policy and funding Understand how emerging policy changes could affect your work and career.Education and outreach Learn about novel approaches to educating and inspiring the scientists of the future.Business and innovation Find out how recent scientific breakthroughs are driving business innovation and commercial growth.Impact Explore the value of scientific research for industry, the economy and society.Personalities Find out who’s doing what in industry and academia.Interviews Discover the views of leading figures in the scientific community.Opinion and reviews Find out whether you agree with our expert commentators.Careers Consider your career options with valuable advice and insightful case studies.People Meet the people behind the science.Events Plan the meetings and conferences you want to attend with our comprehensive events calendar.

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Sound travels faster than light