I’ve noticed that in some topics people mention something in the line of: “Oh, my universe is purely hard sci-fi, there’s no FTL, people use cryo-sleep to travel long distances between the stars”.
That makes no sense, how is cryogenics or any other method for “freezing” someone or making him/her sleep over decades without aging “hard” sci-fi? There’s no known mechanism on how this can be done in any conceivable way today by any medic or scientific standard. There’s no known way how to keep someone from aging medically or technologically over long periods of time, nor there’s any known way to keep someone sleep for long periods of time without all kinds of health issues including calcium loss in the bones, skin sores and possible brain damage.
People in a coma, for example, are moved every day by nurses in order to let their skin rest, do you remember that scene in The Walking Dead with Rick waking from a coma? Well, he won’t be able to walk and his back would be covered in open, maybe bleeding sores. Now imagine that having someone into a machine not moving for decades or even centuries?
It baffles me because I heard people saying that a movie like Passengers is “hard sci-fi” because it doesn’t have FTL, but they do show a magical machine that can keep people sleeping and frozen in their age for more than a century. Yeah, very hard!