Future astronauts travelling to distant stars and galaxies at near-light-speed would be unable to receive communications from Earth until their ship reached its destination, with the exception of a brief period following launch, according to the results of a newly published scientific study.
When it comes to near light speed communication, the laws of physics appear to be very much against us. Granted, on Earth, the time lag between sending a message and receiving it is barely noticable. However, with greater distances come greater problems. For example, it can take a satellite orbiting Mars 5-20 minutes to receive a message from NASA, and over 22.5 hours to reach the Voyager 1 probe, which is currently making its way through the interstellar medium at a distance of over 15 billion miles from Earth.
According to the results of a recent paper published to the research-sharing platform arXiv, the issue of long range communication becomes orders of magnitude trickier when the spaceship you’re trying to talk to is travelling at a velocity close to the speed of light. As it stands, near-light-speed travel remains firmly in the realm of science fiction. However, just because a technology currently seems impossible, doesn’t mean it won’t one day be invented, especially when you take into account our species’ rate of technological progression.
After all, a mere 66 years separated the invention of powered flight in 1903 and humanity’s first steps on the Moon in 1969. Who is to say what we’ll be capable of in a few centuries time? In preparation for such an eventuality, the authors of the arXiv study sought to examine the communication difficulties that could be faced by spacecraft travelling at near-light speed.
The study took into account two distinct mission scenarios in which spacecraft sent messages while travelling from a launch/starting point to a distant landing site. The first scenario explored the lonely fate of a spacecraft impossibly experiencing constant, neverending acceleration, while the second, more realistic mission involved a spacecraft accelerating on the first half of its journey, before decelerating in preparation for landing.
In both cases, the communications sent to and from the spacecraft are encoded in photons (light particles), which travel constantly at the speed of light (670,616,629 miles per hour) whilst in the empty vacuum of space, as per Einstein’s theory of special relativity.
This cosmic speed limit — along with other relativistic effects — would create profound issues for the near-light-speed starships when trying to stay in touch with the civilization that it had left behind. According to the researchers calculations, a spacecraft experiencing constant acceleration would be capable of receiving messages during the early stages of a mission, with signal latency increasing until the crew eventually hit an ‘event horizon’ point. After this, photons sent from the launch site would never be detected by the travelling spacecraft, leaving it isolated as it ploughed onwards through the void of space.
The second, more realistic mission profile proved to be more complex. In this scenario, the outgoing spacecraft was able to receive communications from its launch site for a relatively short time, before it too was plunged into a communication blackout, after which any further messages from the point of origin wouldn’t be intercepted by the ship until it reached its destination.
Meanwhile the ship would be capable of sending one way transmissions to the launch site, and receiving messages from its eventual destination throughout the mission. However, messages sent to the destination by the spacecraft wouldn’t be received until shortly before the ship itself arrived.
The relative nature of the passage of time would add another layer of complexity to interstellar travel. Experiments have shown that time progresses differently depending on where you are in the universe, and what you are doing.
For example, clocks placed near extremely massive celestial objects, or set upon a spaceship travelling at close to the speed of light, would appear to tick slower when compared to one held by an outside observer watching from a relatively stationary location in the void of space. This is an effect known as time-dilation, which is constantly at work, but barely noticeable on a day to day basis on Earth.
However, on a spacecraft moving at a fraction of the speed of light, time-dilation — paired with other effects — could act to warp incoming communications, making them stretched or compressed depending on who was transmitting or receiving the messages. It would also cause less time to pass for astronauts aboard a near-light-speed spacecraft than it would for the people crewing a planetary outpost.
The issues listed in the paper would make an autonomous robotic mission preferable to one with a human crew, who would undoubtedly keenly feel the effects of isolation from the civilization that they had left behind during prolonged blackout periods.
For the relatively brief periods where communication is possible with home, the extreme wait times between messages would make two-way communications challenging to say the least. Instead, the authors suggest that missions could rely on one-way communications.
Anthony is a freelance contributor covering science and video gaming news for IGN. He has over eight years experience of covering breaking developments in multiple scientific fields and absolutely no time for your shenanigans. Follow him on Twitter @BeardConGamer
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
