are we surrounded by some kind of spacetime horizon? we are unable to witness a part of the universe. the boundary that separates us from this part of the universe is the 'cosmological horizon'. anything that lies beyond our cosmological horizon, cannot influence us in any way, not even by gravity. the world outside that just seems unreal. do you know that we create a horizon around ourselves whenever we accelerate? yes! that's true, when we move or accelerate in flat spacetime (away from any gravitational influence) we actually create a horizon called 'the rindler horizon' around ourselves. outside this rindler horizon like the event horizon, the part of the universe just seems unreal or non-existent. do you know, our planet heats the moon? yes, our planet increases the temperature of the moon.... further continued in this book......