Sometimes, there are things that shouldn’t arrive at the same time.
On a stormy day, you might see a silent flash of lightning appear in the sky, and about 4 seconds later, you hear the booming thunder, occasionally startling you. Perhaps you already know the reason for this phenomenon: light travels much faster than sound. Light moves at a speed of up to 300,000 km/second, while sound waves travel through the air at a sluggish speed of 0.3 km/second.
But what would happen if the speed of sound in the air were a million times faster, matching the speed of light?
Of course, if that were the case, you would be able to hear the thunder at the same time as the flash, which might seem grand and perfect, but in reality, you wouldn’t want to experience that feeling.
Sound waves consist of particles, each moving slightly enough to collide with the adjacent particle. George Gollin, a physics professor at the University of Illinois, explains that this creates areas of higher and lower density within the sound wave. He uses the example of a spring toy: as it moves, the coils continuously compress together and then expand. Sound waves work similarly. At slow speeds, these density changes are imperceptible. At the speed of light, however, it’s a different story.
Returning to the story of lightning and thunder, if light and sound traveled at the same speed, you would see and hear simultaneously, but at that moment, the lightning would take on a strange shape. “In the humid air conditions of a storm, sound waves pass through and compress everything, then expand and significantly decrease the pressure. Since pressure corresponds to temperature, a sudden drop in pressure after thunder would cause the humid air to freeze. You would see the flash through a thick mist of ice crystals,” Gollin said.
The extremely fast speed of sound would completely change the sounds in our world. Our voices would sound very different. When we speak, our vocal cords vibrate to create sound waves with many different frequencies, which are then directed into the larynx. There, waves of the same frequency combine to create much larger waves—resulting in louder sounds. However, not all frequencies combine in the same way. Some synchronize perfectly, while others interfere with each other, producing smaller waves and quieter sounds.
If sound were to travel faster through the air, it would change how these waves combine, making some frequencies louder and others quieter. In sound waves, frequency corresponds to pitch, so what you would get is a very peculiar high-pitched voice.
To imagine what our voices would sound like then, think of the voice after inhaling a helium balloon, similar to Mickey Mouse’s voice. William Robertson, a professor in the physics and astronomy department at Middle Tennessee State University, explains that this is because sound waves travel only three times faster through helium. And if sound waves matched the speed of light, they would move over a million times faster.
The way sound-producing instruments work would also change. For example, wind instruments (like trumpets and flutes) would produce sound waves that accelerate, leading to increased frequency and higher pitch, creating sounds so high that humans could not hear them. We would need to design these instruments to be over a million times longer to harmonize with violins and cellos. With instruments like violins and cellos, Robertson states that the change in sound speed as it moves through the air would not affect the sound speed along a string.
However, you also don’t need to think too much about the changes that would occur if sound traveled at the speed of light, as humans would not survive if this happened. Even the gentle sound of a flute could blow everything around it into fragments.
While light travels in electromagnetic waves, which are not matter, sound waves are mechanical, consisting of particles colliding with each other. Gollin states: a molecule moving at the speed of light would have “almost infinite energy.” It would fly through every particle it encounters, releasing electrons and creating an eruption of matter and antimatter—particles created in high-speed collisions that have properties opposite to those of matter.
“The consequences would be catastrophic,” Gollin concludes. Perhaps we should be satisfied with the fact that thunder arrives after lightning; it wouldn’t be wonderful at all if both arrived simultaneously.
