Don't let the silence fool you; there is absolutely nothing calm or serene about space travel. Space is the harshest environment known to man, and even routine trips to the International Space Station are one mistake away from killing all the astronauts involved. Now take all the problems involved in near-Earth space travel, multiply that by a trillion, and you'll start to get an idea of how impossible extra-solar exploration really is.
The realities of interstellar space travel are bleak, especially to all the science fiction fans who dream of one day taking a trip to the final frontier. Health issues, isolation, and micrometeorites are just the tip of the iceberg for any would-be astronauts hoping to colonize an alien world. The laws of physics and biology are working in tandem to make sure we stay put in our little solar system, despite humanity's best efforts. Life on Earth might be disappointing sometimes, but it is nowhere near as terrifying as life beyond the stars.
Like it or not, we need gravity to survive. The effects of prolonged exposure to zero gravity environments have been well documented, and the results are clear. Without gravity, our muscles begin to atrophy at an astonishing rate. An astronaut in orbit can lose as much as 5% of their muscle mass every week, and weightlessness also has an extremely negative effect on bone density.
Zero gravity also has some terrifying effects on your blood pressure. On Earth, your blood tends to concentrate around your feet. That's not the case in space, where blood flow tends to equalize throughout the body. This can mean too much blood in your brain, which can send your biological systems into a total panic. Your body will start disposing of the "excess" blood, and astronauts can lose as much as 22% of their blood volume. Less blood means less work for the heart, so that muscle also begins to atrophy. While it is possible to restore your body after returning to Earth, it's a long and laborious process that is not always guaranteed to bring you back to full health.
Who doesn't love radiation? The answer is every cell in your body, which is unfortunate for anyone stationed off our planet. While on Earth, our planet's atmosphere and magnetic field shields all of us from all sorts of deadly radiation zipping through the cosmos. People in space don't have that layer of protection, so they are at a greater risk of exposure to harmful forms of radiation. Space travelers can look forward to all sorts of fun side effects caused by this radiation, like radiation sickness, increased cancer risks, and defects of the central nervous system. This is one of the largest issues that is preventing humanity from traveling to Mars. If we don't crack the radiation enigma, we might be stuck on this planet for good.
If humanity is to break free of the clutches of our solar system, we're going to have to travel at incredible speeds. The closest star system to our own is Alpha Centauri, but even that is about 4.3 light-years from Earth and there is no guarantee that the system contains a habitable planet. Interstellar travel will require us to travel vast distances at near light-speed in order to make any significant progress, but great speed comes at a great price.
One of Einstein's greatest achievements was introducing the world to the theory of relativity, which first proposed the idea that time travels slower for objects traveling closer to the speed of light than objects that remain still. So for an interstellar traveler moving at near light-speed, they would age at a significantly slower rate than everyone back on Earth. By the time you reach your final destination, there might not be a single person left on Earth who was alive when you first departed.
Interstellar space travel sounds like a recipe for intimacy in theory: long periods alone with a handful of physically fit people who all have way too much free time on their hands. The problem isn't about desire, however; it all comes down to biology. The way blood flows through the body is altered in space, and these conditions make it extremely difficult to maintain an erection. Yup, zero gravity basically gives you erectile dysfunction. The problem isn't exclusive to men however, as many female fluids necessary for intercourse require some help from gravity to get where they need to be.
Even if you could sustain arousal, physics is going to make sex a serious challenge. Every action requires an equal and opposite reaction, so bumping uglies is likely to send your partner flying away from you. Then there is the problem of sanitation. Sweat and other fluids produced by intercourse are going to float around uncontrollably, and all that salt and moisture could interfere with the electrical systems of a spacecraft. Unless you want to risk a short circuit that can kill the entire crew, it's best if you just keep it in your pants.