The time it takes to receive a response back from a message sent into space using lights or radio waves depends on the distance between Earth and the recipient and the speed of light.
The speed of light is approximately 299,792 kilometers per second (186,282 miles per second) in a vacuum. If we consider the scenario of sending a message to a target that is relatively close, such as the Moon, which is about 384,400 kilometers (238,900 miles) away on average, the round trip time for a response would be approximately 2.56 seconds (assuming the response is sent immediately upon receiving the message). This includes the time it takes for the message to travel to the target and the response to travel back to Earth.
If we were to send a message to Mars, the time for a response would vary depending on the relative positions of Earth and Mars. The distance between Earth and Mars can range from about 54.6 million kilometers (33.9 million miles) at their closest approach (opposition) to around 401 million kilometers (249 million miles) at their farthest distance (aphelion). At their closest approach, it would take approximately 3 minutes and 6 seconds for a round trip communication (message sent to Mars, response received back on Earth). At their farthest distance, this round trip time would increase to around 22 minutes and 12 seconds.
For more distant targets, such as other star systems, the time for a response becomes significantly longer due to the vast distances involved. The nearest known star system, Alpha Centauri, is about 4.37 light-years away. This means that it would take approximately 8.74 years for a round trip communication with our current technology.
It's important to note that these estimates assume direct communication without any delays due to transmission or processing times. In practice, various factors such as signal strength, potential obstacles, and the time required for the recipient to decode and respond to the message can also affect the overall communication time.