If someone is talking and facing away from you while you are outside, you can still hear them to some extent, although the sound might be fainter compared to if they were facing towards you.
When a person speaks, sound waves are emitted in all directions from their mouth. These sound waves spread out as they propagate through the air. Some of the sound waves will travel directly towards you, while others will disperse in different directions.
Even if the person is facing away from you, some of the sound waves they produce will still reach your ears. This is because sound waves can bounce off objects and surfaces in the environment, including the ground, buildings, and other objects. These reflections can redirect the sound waves towards you, allowing you to hear the person speaking.
The sound waves that reach your ears from the person facing away from you do not actually travel backward. Instead, they follow a path that involves bouncing off various surfaces before reaching your ears. The specific path and intensity of the sound waves reaching you will depend on the environment, including the presence of obstacles and the distance between you and the speaker.
It's worth noting that the further away you are from the person and the more obstacles there are between you, the more the sound waves will attenuate and become less audible. Additionally, if the person is speaking softly or there is a lot of ambient noise, it may further affect your ability to hear them clearly.