What did Buddha see?

The Heart of Prajna Praamita Sutra  (see English version of the full text) is the shortest  Buddhist sutra recording what Buddha experienced in his Samadhi.  What's described in this succinct text represents the highest realization a human can achieve. Over the centuries, thousands of essays and books have been written to comment on and offer interpretations on the sutra. One can write volumns in an attempt to explain Buddha's words (only about two dozens of sentences long), it still does not get anywhere near experiencing the state Buddha was experiencing oneself. I doubt how many of those buddhist abbots, adepts or masters who've commented on this sutra have actually reached Samadhi himself.

A copy of the Heart Sutra in Chinese

What Buddha saw was pure light at the beginning of the Creation (nowadays scientists call it the Big Bang). He was the light and the light was him; there was no seperation. That's why he said 'Form itself is emptiness; emptiness itself is form. So, too, are feeling, cognition, formation, and consciousness.' But remember words are not the thing. Buddha's words were recorded in Sanskrit which was translated into Chinese which in turn was translated English. So if any one gets stuck with the words, he is absolutely missing the point. He will never fully comprehend what Buddha meant until he's experienced what Buddha experienced and saw what Buddha saw in Samadhi himself.