In 1976 Candian scientist, apparently obsessed with the idea of the Spring thaw, averred that relativistic travelers would be irradiated in transit. That they might come to serious harm away en route due to erosion caused by quantum effects. This was called the Unruh Effect after Bill Unruh, the Canuck making the prediction.
The accelerating reference frame generates heat from the surrounding empty space. A special effect was predicted by Unruh, an effect created by the acceleration of an electromagnetic field. Such a field is maintained by photons and it is these photons and other particles that cause the heating. Ultimately the “heat bath,” given sufficient time, will destroy the traveler.
Unruh was challenged. His work was declared untenable and the result of a mathematical error, but no satisfactory adjudication has been had.
A group of Brazilian scientists has proposed an experiment to decide the question. If the Unruh effect is real, scientists have a new problem to consider and Sci-Fi authors have more stories to write. They will study relativistic particles and look for radiation. Wavelength differentials will reveal the presence (or lack thereof) of the Unruh Effect.
Three years ago, John Varley wrote Dark Lightning, a story about a generation ship (a hollowed out asteroid) that had to limit its speed. The genius in residence detected that passing a certain speed would cause serious problems. Varley speculated on Dark Energy. Quite off the mark but not bad.
The Unruh Effect, if true, is a real problem that no ablation shield will solve. Its effect is not just a bow shock but an effect of the space-time in which all that travel move. If anything melts, everything melts.
In case you’re worried about your first trip to Proxima Centauri, don’t worry. Too even feel the effect, a traveller must accelerate at a rate of approximately 10^21 m/s^2. That will warm you 4°C but you’ll be flatter than a crepe if your mode of transportation happens to survive.
Don’t buy those personal air conditioners yet. The vapor spritzers can stay in the drawer. Heat pumps won’t help beat the stifling heat on the warm-up trip to Trappist 1. (If it’s not too volatile, that is. If it’s not one thing, then it’s another!)