In modern Arabic the correct spelling would be:
الحمد لله رب العالمين
But this is not the way how the Sahaba wrote it more than 1400 years ago.
The picture below shows (a copy?) an early version of a hand written copy of surah al-Fatiha -I've marked the corresponding word:
This corresponds to writing the word al-'Alameen العالمين without alif in the middle:
الحمد لله رب العلمين
Therefore only the second one is conform to the Rasm al-'Uthmany unless it appeared in other copies of al-Moshaf al-Imam and was confirmed by scholars of rasm like abu 'Amr ad-Dani -who as far as I know is among the last scholars that have seen most (if not all) of these copies himself-. And only this is allowed to be used in a Moshaf according the majority view. Some scholars allow to add a pending alif in order to show for examples different qira'at, which is usually practiced in nowadays copies.
Mainly there are three known views about whether or not the rasm is binding:
- Majority: regard it binding: Among the reasons they brought up is that this was an agreement of the Sahabah, and those who came later beside the confirmation of the prophet(), there's a bit doubtful hadith on the authority of Mu'awiyah in which the prophet() ordered this -it doesn't appear in any reliable hadith sourec-. This is the safest view of all.
- Ibn Khaldun, ibn Qutaybah and al-Baqilani and others regard it as not binding. Their argument is the lack of any textual order to follow one specific codex.
- A middle view saying that in order to learn it or for private purposes the qur'anic text could be written for laymen according the (correct)known orthography. Among the scholars defending this position are al-'Izz ibn 'Abd as-Salaam and a-Zirkashy.
For further information take a look at the following posts:
How many spellings do exist for Quran's text? How many rasm-al-mushaf do we have?
How many writing styles of Mushaf Quran that exist?
Is it allowed to erase Harakat or Waqf marks from the Quran?
Different versions of Arabic Qur'an