> Even at very low speeds, a civilization with a 10 million year "head start" (which is nothing on the timescale of the universe) would be able to send autonomo

> Even at very low speeds, a civilization with a 10 million year "head start" (which is nothing on the timescale of the universe) would be able to send autonomous robots across the galaxy. I see this sort of statement all the time, and we have no empirical evidence it is true. As this article says, even this simple "Starshot" concept is "a monumental engineering challenge that will require huge leaps in technology for spacecraft design, propulsion and communication." And all the challenges are fundamentally physical, involving issues of weight, strength, density, power density, thermodynamics, etc. Unless they make some near-magical breakthrough in physics, a civilization one million years older than our own would find it just as difficult as we will! And what if some galactic civilization has already done this? Are we likely to detect a spacecraft "just 3 to 12 feet across and weigh as little as a thimbleful of water" passing somewhere through our solar system at 20% C?