LAUSR

F ans of Star Wars will recognize this quote from the opening sequence in the celebrated film series. The line occurred to me as I read a recent report [1] that Voyager 1, launched by NASA in 1977, has now left our solar system and is cruising through deep space at a distance of more than 13 billion mi (approximately 0.0022 light-years) from Earth. To put that distance in perspective, it may be noted that the one-way travel time for radio signals from the spacecraft to Earth is more than 19 h. And yet, thanks to some superb antenna engineering, NASA continues to receive data from Voyager 1; though to compensate for the increased free-space path loss, the data rate has dipped to about 1 kb/s from its peak of 115 kb/s decades ago [1]. Jill Tarter, a scientist at the Search for Extraterrestrial Intelligence (SETI) Institute and the inspiration for Jodie Foster’s character in the film Contact, once speculated [2] that the proposed Square Kilometer Array (SKA) project, comprising antennas scattered over an area of 1 million km2 with an effective aperture diameter of about 1,000 km, “would be powerful enough to detect the leakage into space from a standard terrestrial TV transmitter at a range of half a dozen light-years. Therefore, any neighboring civilization with comparable TV transmitters would leak enough signal into space for detection by the SKA, even if it were not intentionally broadcasting for our benefit.” I am afraid that Dr. Tarter might have been indulging in a bit of Madison Avenue hype when she said that. As discussed in [3], there are severe technical challenges to watching interstellar TV. Even if we set aside the alluring notion of being able to watch alien TV shows, it is puzzling to find that, despite decades of increasingly sophisticated radio listening, we have not picked up any radio signals of extraterrestrial origins. In his 2010 book on the subject of SETI [4], British physicist Paul Davies offered an explanation. He imagined an alien community just 1,000 light-years away (the Milky Way is roughly 100,000 light-years across). At 1,000 light-years away, aliens today would see Earth as it was 1,000 years ago. They might detect signs of agriculture and large buildings such as the pyramids, but it would have made little sense for them to start beaming powerful and expensive radio messages at Earth circa 1,000 A.D. In his poem “Andrea del Sarto,” Robert Browning once pondered, “Ah, but a man’s reach should exceed his grasp, Or what’s a heaven for?” It was thrilling to learn that the 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Barry Barish, and Kip Thorne [5] “for decisive contributions to the Laser Interferometer Gravitationalwave Observatory (LIGO) detector and the observation of gravitational waves.” LIGO recently [6] detected gravitational waves (which also travel at the speed of light) linked to a violent collision between two neutron stars 130 million years ago. So, what happened a long time ago in a galaxy far, far away is still breaking news for planet Earth!