explain how all in quantum phys. all possibilities exist at once until someone observes .?

Answer 1

Our intelligence has evolved over millions of years to deal with physics intuitively as it applies to common things like throwing rocks and hurling spears. We have an inborn grasp of such things which allows us to deal with the world around us, on a very human scale.

When you get into scales that are very large, or very small, this inborn feel for how things should work becomes increasingly inaccurate. We simply aren't adapted to the truth of the very, very small scale interactions that occur at the quantum level.

This is fine in ordinary life, since the net result of quantum interactions is evened out when you employ large enough numbers to make rocks and spears work as you expect.

Basically, the universe isn't doing anything 'illegal' when it allows for uncertainty in the wave/particle duality of light, for example. The misunderstanding is not the universe's fault, its your own, brought about by your limited awareness.

The mistake is to assume that the rock and the spear are solid, immutable concepts. That's just an illusion brought on by your ancestral genetic conditioning. The truth is simply more subtle than your awareness.

Answer 2

This is the way quantum theory works. It may not be true, but it works out in the lab. When you say how does it work, that is a question that may await us when we have shuffled off this mortal coil.
In a quantum system, playing a game of darts, the dart hits the board before you throw it.
Look up the Heisenberg Uncertainty Principle in your quantum I book.

Answer 3

It comes down to interpretation of quantum mechanics you subscribe to. According to Copenhagen interpretation, for example,
the act of measurement causes an instantaneous "collapse of the wave function". This means that the measurement process randomly picks out exactly one of the many possibilities allowed for by the state's wave function, and the wave function instantaneously changes to reflect that pick.