If the universe is constantly expanding, how could the big crunch happen ?
In: 6
In the Big Crunch hypothesis the idea is that the there are two forces in play – an initial outward momentum of everything caused by the Big Bang and the small and persistent gravitation attraction trying to pull everything back in. Like a model rocket launched upwards at first the initial momentum is so huge everything flies outward, but gradually overtime gravity sucks away this momentum, the mass eventually stops, and then starts to rebound in on itself, eventually recollecting in a Big Crunch.
But that’s not what we are observing in the real world. We are observing the outward expansion *accelerating*. So *something* else must be in play, some sort of anti-gravity outwards repelling force. The issue we can’t *find* the source of this force, but we can estimate the size of it. So we can say there is a force of size “x” out there, being caused by unseeable, undetectable things that we have no physical understand of. We call these unseeable, undectable things “Dark” energy and matter. We currently believe that “Dark” energy is the biggest factor in the mysterious expansion force, but remember, we can’t *find* it.
So we currently don’t accept the Big Crunch theory, because it doesn’t fit with our observations, and we accept that the universe is expanding, increasingly quickly, and will do so for ever. Eventually this expansion with result in everything just being so spread apart and dispersed that nothing meaningful can ever happen again. We call this theory the “Inevitable Heat Death of the Universe”, you can have some fun googling researching that topic.
Latest Answers