The local group is only one of many, many clusters of galaxies. all of the galaxies are all moving away from each other causing more and more space to come between them. this means the universe is expanding. that discovery is what led to

This is what i found on google “according to the collision theory, the following criteria must be met in order for a chemical reaction to occur: molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break. molecules must collide with the proper orientation.” i hope this information you.