Probably for the umbilical cord that connects babies (from their early stages in the womb to their removal) to their mothers. The cord is cut, forming the belly button. This is analogous to astronauts in space.
Answer:
There are no gaps in space between the photons as they travel. If you were to look at a wave then you'd come to a conclusion that indeed that there aren't any gaps unless they are specifically placed.The light from a distance star indeed spreads out and weakens as it travels, but this just reduces the wave strength and does not introduce gaps.
1 watt = 1 joule per second = 1 newton meter per second = 1 kg m2 s-3
It depends who is watching it.
-- A passenger on the train says that his clock is normal, but the clock at the station he just passed is running slow.
-- A ticket agent at the station says that his clock is normal, but the clock on the train that just rolled through is running slow.
-- They're both correct, but ...
-- The difference is too small for either of them to notice, unless the train is going faster than about half the speed of light.
-- It isn't.
