By Abigail Degn, October 28, 2025
BYU is marking its 150th anniversary with a creative spin on a classic celebration: blowing out birthday candles in BYU style.
Instead of a traditional breath to extinguish the flames, BYU turned to science. Physics and Astronomy professor Brian Anderson helped “blow out” the 150 candles on a BYU-themed cake with remotely placed loudspeakers using a process he studies and teaches at BYU: time reversal acoustics. Others have blown out candles with sound, but this technique can be used to blow out candles anywhere in the room, even far away from the loudspeakers.
This technique works by first recording how sound travels from a distant source, like a loudspeaker, to a receiver, like a microphone. Then, playing the recorded sounds backward with the last sound played first, and the first sound played last, creates focused sound waves back at the microphone location where they originally were recorded. This experiment is done in a reverberation chamber where sounds bounce around the room in an intentionally complex manner, but amazingly time reversal can create a coherent, focused wave among the chaos, like a reversed circular ripple in a pond from a thrown rock.
“To blow out each candle, we generated 180 decibels of sound at each candle location. For reference, a rock concert is about 120 decibels. So, this is about a thousand times louder than a rock concert at each of those candle locations,” Anderson shared.
Time reversal acoustics has many practical uses, such as destroying a kidney stone without invasive surgery; however, for this birthday celebration, the technique is used for fun.
This demonstration works because of the heat rising from the candles, which creates a small channel of warm air, and that helps jets of air to form in the focused sound to blow the candles out. Recently, Anderson and one of his students published a paper on the physics behind this process. Although it looks simple, Anderson says it’s surprisingly complex.
With the festivities continuing throughout this sesquicentennial year, Anderson says he’s grateful to be a part of it. He hopes this demonstration is a small way to show appreciation for the university.
“The 150th birthday of BYU allows all of us to think about the heritage that we have all benefited from, from all the people that have contributed over the years” Anderson says, “I like to think of this demonstration as providing a metaphor for how Christ can focus on and minister to each of us one by one, even in a noisy and chaotic world.”
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