Supersonic jets are making a comeback. Here’s what that means for air passengers
Last week, первый анальный секс American company Boom Supersonic flew faster than the speed of sound with its XB-1 supersonic demonstrator aircraft. It’s now the first piloted non-military aircraft to break the sound barrier since the Concorde was retired from service in 2003.

It’s the first step in Boom’s ambitious goal to have supersonic airliners carry passengers by 2029.

But what exactly is supersonic travel? There are good reasons why it’s not more common, despite the hype.

What is supersonic flight?
The Mach number is defined as a plane’s speed divided by the speed that sound waves move through the air. To "break the sound barrier" means to fly faster than the speed of sound, with Mach numbers greater than 1.

The Mach number is an important ratio: as a plane flies, it disturbs the air in front of it. These disturbances move at the speed of sound. In supersonic flight these disturbances combine to form shock waves around the vehicle.

When people say you can see a fighter jet before you hear it, they’re referring to supersonic flight: fighter jets can travel at around Mach 2.

The sound from the fighter jet is trapped inside its shock wave; until the shock wave moves to your position on the ground, you won’t hear the plane.

The allure of supersonic travel
For efficiency reasons, most passenger jets cruise slightly slower than the speed of sound, at around Mach 0.8 (this is subsonic flight).

Boom plans to build an airliner called Overture that can fly at Mach 1.7. Flying supersonically can drastically decrease flight times. The company claims a trip from New York to Rome on Overture could take just four hours and 40 minutes, instead of eight hours.

Boom isn’t the only company working on this lofty goal. American firm Spike Aerospace is also developing a supersonic business jet, with the tagline "delivering the world in half the time".

This is the value proposition of supersonic passenger travel.

In limited ways, it did already exist in the 20th century. However, due to timing, bad luck and the laws of physics, it didn’t continue.