I never know this until we have one in the family. All I know that baby cries because they are hungry of being or being sick. If a baby always cries fir a long period during the end of the day, the new born might have colic. Colic babies cries 3 days a week for 3 hours and 3 weeks in a month and might disappear after 3 months.
There is no scientific study about the cause of colic, but most of the expert agrees that the gut flora is the cause. Some administer pro biotic which is believe to be the cure to colic.