It would be difficult for light-speed spacecraft to communicate, which would be bad news for interstellar travel.

It would be difficult for light-speed spacecraft to communicate, which would be bad news for interstellar travel. We may have been spoilt by science fiction when it came to space communication. Even if we could build a spacecraft that traveled at almost the speed of light, we would struggle to keep in touch with it.

The key is to communicate. Both on Earth and in space, that is true. But there's a vital fact of life in space that you have to deal with. The distances between worlds are fairly large and between star systems are very large because the speed of light has a finite value. A recently conducted analysis, which has not yet undergone peer review, imagines the experience of communicating with a spacecraft that is approaching the speed of light. Furthermore, this is undoubtedly bad news.

Two scenarios involving a spaceship traveling near the speed of light are imagined by researchers David Messerschmitt, Ian Morrison, Thomas Mozdzen, and Philip Lubin. Although this vehicle doesn't exist (yet), nothing in physics rules out the possibility that it could be constructed. It is a vehicle that accelerates at a rate of one g, or the same force as gravity when we stand on Earth, and never runs out of thrust.

In the first scenario, a spacecraft continues to accelerate as it gets farther from Earth. Due to the finite speed of light, communication will initially function, albeit slowly. Eventually, however, messages from Earth will no longer be able to reach the spacecraft. The craft will always be one step ahead of the message as it approaches the speed of light. At that point, communication between the spacecraft and Earth will cease.

Another odd effect exists as well, but it is inherent to the craft. Time dilation occurs when an object approaches the speed of light. Its clock becomes slower. Therefore, if the spacecraft accelerates at 1g, it would only take a person on board 20 years to travel 26,000 light-years to the galactic center. And it will only take 45 years to travel tens of billions of light-years to reach the edge of the visible universe.

In the second scenario, the spacecraft accelerates for a while at 1g and then decelerates as it gets closer to its destination at 1g. Similar to the first instance, communication from Earth would be impacted until the spaceship's deceleration phase, when all of the messages caught up with it. Alternatively, the spaceship could communicate with the destination, but as it approaches, the messages will likely pile up. Before they get very close, you won't receive a beautifully spaced set of messages announcing their arrival.

"The authors of the paper stated that except for a brief period after launch or before landing, interstellar spacecraft and their crews must accept highly autonomous operations and give up notions of maintaining operational and social interactions with those at the origin or destination throughout the mission."

Although a few classical and relativistic effects were examined, there are still more that have not been taken into account that could have an impact on communications. When a ship is moving, its signals will exhibit a Doppler effect, similar to how the pitch of an ambulance siren changes when the ship is driving toward or away from you.

Thus, you require antennas that are capable of detecting light whose frequency varies with time. Additionally, there is a relativistic aberration, which is the conic concentration of light in the direction of motion of an object in motion.

In other words, the crew of any spacecraft we build will eventually be left on their own.

This research has not yet been peer-reviewed in a paper.