What If You Travelled at the Speed of Sound?

Pick an altitude, pick a speed of sound

Sea level uses 343 m/s. Eleven kilometres uses ~295 m/s because the air is cold, not because Mach is magic. Faster true airspeed at the ground for the same Mach is a temperature story. The hours slider is then ordinary distance = speed × time. Earth's equatorial circumference is about 40 075 km if you want a lap count. No wind, no great-circle routing, no Coriolis on the flight plan.

A boom is a shock, not a sound effect

When you travel at Mach 1 you are keeping pace with your own pressure waves, which pile up. Past Mach 1 they form a cone that sweeps the ground as an N-shaped pressure jump — the boom. Intensity depends on altitude, mass, length, and atmosphere. Concorde was loud; a hypothetical you-sized dart would be a different dart. The boom is real, and it is a shock wave, not the sound of the aircraft itself.

Not a performance chart

Jets that cruise near Mach 0.85 do so for economics and for the drag rise toward Mach 1. Sustained Mach 1 in dense air is expensive. At 11 km the air is thinner and colder. None of that is modelled as thrust, lift or specific fuel consumption. If you wanted walking versus driving, that is another experiment. If you wanted sound itself to be faster, see the experiment that speeds up sound.

Worked example: London to New York at Mach 1

Heathrow to JFK is about 5,540 km in a straight line over the Earth’s surface (a great circle).

1. At sea-level Mach 1 (343 m/s, about 1,235 km/h or 767 mph): 5,540 ÷ 1,235 ≈ 4.5 hours.
2. At Mach 1 in the cold air near 11 km (295 m/s, about 1,062 km/h): about 5.2 hours. Same Mach number, slower true speed.
3. Concorde cruised at about Mach 2 and around 60,000 ft and usually made the crossing in about three and a half hours, including climb and descent.
4. A typical airliner at around Mach 0.85 takes roughly seven hours, helped or slowed by the wind.

Travelling at the speed of sound would get you from London to New York in about four and a half to five hours, before wind, routing or take-off and landing.

What people get wrong

“A sonic boom happens once, when a plane breaks the sound barrier.”

A supersonic aircraft makes a boom for as long as it flies faster than sound. The shock waves trail behind it like a boat’s wake and sweep the ground as a ‘boom carpet’ that can be about 50 miles wide.

“The speed of sound is always 767 mph.”

That figure is for air at about 15 °C. Sound speed depends on air temperature, so it is slower high up where the air is colder, even though Mach 1 still means ‘the local speed of sound’.

“Nobody went supersonic until jets.”

The first piloted supersonic flight was by Chuck Yeager in the rocket-powered Bell X-1 on 14 October 1947, reaching Mach 1.06 at about 43,000 ft.

Common questions

How we calculated this

Sea-level speed of sound is 343 m/s. Tropopause speed is 295 m/s, a rounded figure for ~216 K in the standard atmosphere (c ∝ √T). Distance = v × hours × 3600. Laps use 2π times WGS 84 equatorial radius. Sonic boom is qualitative. Not a flight-performance integration, not a noise certification.

Assumptions and limitations

Sources

• NOAA JetStream — layers of the atmosphere

  Tropopause height and the idea of a standard atmosphere.

• NOAA NGS — WGS 84

  Earth's equatorial figure; the train formula uses the IUGG mean radius.

• NASA Earth fact sheet

  Earth mass and radius for orbital and gravity-train numbers.

• NASA — Science of sonic booms

  Why a supersonic aircraft drags a continuous boom carpet behind it.

• NASA — First generation X-1

  The first piloted supersonic flight, 14 October 1947.

• Science Museum Group — Concorde prototype aircraft

  Concorde cruised at Mach 2 at about 60,000 ft.

All IfSketch sources · Methodology