Flexi Says: The things we observe in space are objects that emit some type of electromagnetic radiation. However, scientists think that matter that emits light makes up only a small part of the matter in the universe. The rest of the matter, about 80%, is dark matter. Dark matter emits no electromagnetic radiation, so we can’t observe it directly. However, astronomers know that dark matter exists because its gravity affects the motion of objects around it. Like ordinary matter, dark matter exerts an attractive force on other matter. Dark energy is a hypothetical form of energy that exerts a pushing force which is causing the rate of expansion of the universe to increase. Scientists have not yet detected this source of energy.
