Fasting is a physical worship that cannot be divided into parts. Therefore, fasting cannot be shortened by fasting for half a day and then eating and drinking for the other half. Rather, the command in the Quran is that if you are traveling and cannot fast, then break your fast and make up for it later, and it is better to fast afterward.
As it is a divine command:
فَمَن شَهِدَ مِنكُمُ الشَّهْرَ فَلْيَصُمْهُ وَمَن كَانَ مَرِيضًا أَوْ عَلَى سَفَرٍ فَعِدَّةٌ مِّنْ أَيَّامٍ أُخَرَ يُرِيدُ اللّهُ بِكُمُ الْيُسْرَ وَلاَ يُرِيدُ بِكُمُ الْعُسْرَ
(الْبَقَرَة ، 2 : 185)
” He who witnesses this month must fast it, and he who is ill or on a journey should complete the count by (fasting on equal number of) other days. Allah desires ease for you and does not desire hardship for you”
