If Alexander had faced a unified Indian empire

I completely agree with you. If you keep in mind that according to royal inscriptions, Only Egypt under Ptolemy B' had an army of 40,000 cavalry, 200,000 infantry and 300 elephants, well-trained under Macedonian standars you can imagine what size of army could Alexander had taken from every quarter of his empire.

Even the coalition army at Ipsus didn't reach such a huge figure (save for in the way of elephants, of which they had 400).  And certainly, the solely Ptolemaic army at Raphia wasn't anywhere near that.

Originally posted by Anujkhamar Out of curiosity, how many people in this thread actually know something about ancient indian militaries? And how many people are just here to advertise Hellenism?

 In the land of the blind, the one-eyed man is king (or something like that)

Somebody actually knows something, but that something is easily applied to another parallel universe yet not to our own

We shouldnt take for granted that the number of troops taking part in a battle is the ultimate proof of the entire size of Ptolemy's army.

The numbers stated before could be explained, if we have in mind that in Ptolemaic Egypt there was in use the system of allotment-holders - machimoi, an equivalent term to cleirouchoi -  in the model of Athens. Each allotment-holder was also a soldier, who could easily help in Ptolemaic Egypt military services when needed on special occasions.

Despite this, Ptolemies before Philopator, had a kind of tradition not to put native soldiers in the field but rather prefer as the great majority of regular soldiers, Macedonians, Thracians, Cretans, Greek mercenaries and a small amount of Asiatic troops due to the wealth of Ptolemy royal house.

We do know also that one of the deeds of Ptolemy II, was to organize expeditions for capturing African elephants in the regions of South Africa, even though the use of African elephants in the battlefield against the Indian elephants of Seleukides proved finally to be a failure.

Generals of the day generally gave invasions all of what they could muster.

Well, Polybius tells us Raphia (troops numbered 75,000 plus 73 elephants) was in fact the first time the native machimoi had been used in battle.  Though, modern scholars disagree and say Raphia was just the first time they had been armed as phalangites.  Certainly, we know native machimoi had been used for various roles before Raphia.  Ptolemy I Soter is even mentioned as using native troops at Gaza.  At any rate, native troops never became the majority of the army. 

Anyway, I'm not sure how this is supporting your number. 

Originally posted by Aeolus Simply, Machimoi in 5th century according to Herodotus amounted to 410,000. Surely the number wouldnt be as huge in Ptolemaic Egypt but enought to verify the stats of Egyptian records.

This number is obviously high.  Not even the Nandan dynasty with their massive kingdom in India could field such an army.

Anyway, the native phalanx at Raphia was only 20,000 strong.