What can someone use to stop an asteroid attack

A very high powered nuke.

Explanation:

The sheer force,as used in "Armageddon",will have to be more powerful than Tsar Bomba,the largest nuclear bomb to detonate in history.In order to make this bomb,you would need a lot of nuclear fission.This is a delicate process,so we must do it carefully,but not too slowly.Next:The detonation.It would either have to be rocket powered to the asteroid cluster,asteroid,etc,or it would have to be transported.Once near the target,it would have to be remote detonated from a far distance,because radiation travels FAST through space,therefore,if not a far enough distance away,you would melt into nothing,probably.Once detonated,there are multiple possibilities,the rock could split in half and go separate ways around the earth,reattach,and keep going.Or maybe the bomb would do nothing and just put another crater in the asteroid,and we all die.There are way more,but to the point,a nuclear bomb has a 50% chance of working,but its the best way.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.