[Update: See comment]
Some sci-fi stories involve spaceships that carry biological life forms through interstellar space under the speed of the light for many years. In fact it was a hobby for people of one generation to speculate that this type of technology was just around the corner.
However there is one thing they failed to consider. A spaceship that carries biological life is, by definition, a thermodynamically closed system for all practical purposes. It does not exchange mass or energy (see next para) with the universe. And second law of thermodynamics predicts that total unusable energy (entropy/disorder) in a closed system keeps increasing until no information processing or life is possible.
Even if his spaceships used nuclear reactors and kept exchanging unusable energy with the interstellar space to avoid the problem of the second law, they would never reach anywhere before either: the entropy goes very high, OR before nuclear reactor runs out of fuel which will force the travelers to conserve energy exchange with interstellar space and end up with maximum entropy.
Even the best nuclear reactors of today that need the least fuel would never run for, say 20 years without needing more fuel.
So I think, before even we start considering interstellar space travel of biological life, we need to have extremely reliable nuclear energy that consumes very less fuel but gives loads of usable energy (think fusion reactors). OR we need faster than light travel, which has not been observed under normal physics.
The point I was trying to make is: biological life is an enormous energy guzzling, entropy vomiting system and is not the ideal thing to be carried around in spaceships in energy deserts of interstellar space.
A much more ideal solution would be to download our consciousness into machines that need much less energy like a matrix/robot, and use that for inter-stellar space travel.
These problems might also explain the Fermi’s paradox.