Other anatomical changes associated with long-duration space flight are definitely negative: the immune system weakens, the heart shrinks because it doesn't have to strain against gravity, eyesight tends to degrade, sometimes markedly (no one's exactly sure why yet). The spine lengthens as the little sacs of fluid between the vertebrae expand, and bone mass decreases as the body sheds calcium. Without gravity, we don't need muscle and bone mass to support our own weight, which is what makes life in space so much fun but also so inherently bad for the human body, long-term.
Chris HadfieldBy looking at the difference between perceived danger and actual danger, you can fundamentally change your reaction.
Chris HadfieldIt's good to have a fear of heights. I mean, it's kind of crazy not to because if you just lean out a little bit and there's a gust of wind or somebody bumps you or something and you fall, you're splat.
Chris HadfieldIn my experience, fear comes from not knowing what to expect and not feeling you have any control over whatโs about to happen. When you feel helpless, youโre far more afraid than you would be if you knew the facts.
Chris Hadfield