At the system demo, each team demonstrates their own work but the system is not integrated. they say they underestimated the integration effort, but they cannot integrate every iteration and meet the planned scope. what should the scrum master suggest?

The scrum master can suggest that:

Postpone the work on system integration for a while until the train is in sustain  and enhance the section of road map of implementation

Explanation:

System Demo:

It is such a software that is used to measure the progress of Agile Release Train.

As the teams didn't expect that the integration of system will be a difficult task  and they ultimately failed to accomplish the goal of integration so that scrum master asked them to stop working on the system integration until the Agile Release Train's sustainability and to improve and optimize the  implementation of road map.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.