Question

What is the point of SETI? If we received a signal from an intelligent alien planet, it would take lets say, 30,000 light years to reach us. By then their civilization would have advanced 30,000 years. After 30,000 years, shouldn't they have the ability to travel to Earth and wouldn't we have made contact?

It is always hard to imagine what intelligent aliens would think or what would motivate them to seek contact. In your example, we could only detect a signal from a distance of 30,000 LY if they were transmitting a very powerful beacon — something intended to advertise their presence. If so, they must have considered the problem of the long time delay. Most of the SETI targets we are searching are much closer, within a few hundred LY. Either way, we don’t think any aliens are likely to undertake interstellar travel, because the time delays would be much worse — in your example, even if they traveled at 30% the speed of light, an extraordinary speed, the trip would take nearly 100,000 years. When we apply our understanding of physics, and our logic, we conclude that no matter what the stage of development, sending light signals is much more practical and efficient than sending spacecraft over interstellar distance. Maybe we are wrong in guessing what an alien civilization would try to do. But right now, searching for radio or light pulses is the one thing we can do. And we can be sure that if we don’t try to detect such signals, we won’t know whether they are there or not.

David Morrison
NAI Senior Scientist
October 22, 2009