The Result

Approximately 2.63487577492127810833×10^{10,275,621,677,278,468,246} worlds are possible in Minecraft. That is an immense number. Here, I'll put into perspective on how truly big this number is. If 100 is 3 digits long, 1,000,000 is 7 digits long, and 1,000,000,000,000( a trillion) is 13 digits long, then this number is 10,275,621,677,278,468,246 digits long. Absolutely Mind-blowing. This is by far the largest number, in terms of absolute numerical value, I've ever worked with personally. I also did some rooting and found that this number is approximately 2×10^1079.649, which I can roughly round to 10¹⁰⁸⁰ or as I like to call it 10^{Every particle in the observable Universe}.

The Process

So, first what I did was find out how many blocks there are in the game. The Debug world type made this rather easy because it had every block( or at least I'd assume considering it has every orientation of Fire), so all I needed to do was count how many block there were. I did some multiplying and found that there are 5,207 blocks in Minecraft. Now, that may seen surprising, but keep this in mind: That number also counts for blocks like the bottom half of an open birch door facing east.

After I knew how many blocks there were, I need to find how many positions there can be for these blocks AKA the possible building area for the game. Now, most of you would think "Well, the corners of the world are (-30000000, -30000000),(30000000, -30000000), (-30000000, 30000000), (30000000, 30000000), so you double 30000000 then square it", but that's not entirely accurate. See, there are blocks with a value of 0 for either the X or the Z axis( with the 1 block that has 0 for both), so there's a whole cross section that most people forget about when calculating the size of the world. After some multiplying and adding that 1 (0,0) block I have 120000001. That's the size of the cross section. Now, I have to take 120000001+4×30000000² x256 to get the total amount of buildable volume within the world. 9.21600030720000256×10¹⁷ meters^3. Good, now I know the volume of the world. So now what I need to do is that the number of blocks, 5,207, and raise it to the power of the volume of Minecraft, 9.21600030720000256×10^17. 5,207^{9.21600030720000256×1017}=2.97568334933857917827×10^{3,425,207,225,759,489,415.} BUT WAIT, what about the nether and the end? Well, that's easy: 5,207^{3×9.21600030720000256×1017}=2.63487577492127810833×10^{10,275,621,677,278,468,246.} Bouya, that's every possible combination of every possible block in Minecraft.

Here are the more accurate numbers, BTW:

Overworld: 2.975683349338579178278709876854225869199696307643362303617165285854668543102199327286257580596139967022938343419744095612228466645145730675046167798155674721164492186264854236548984514237496428705384751649551808712996492200824439157019898205348943604663160788475612024403792924257624044650275069342548798421736317272938214975883066631283312999492865662726535620758779618254932299944117005437127024453922576771432902872297214260120331057854245653151232176117788300536798993105678109308635247488033161567309846083380171218107628839023346700547937980580509484016163009508388710472993412931852472669836200968790550428662×10^{3425207225759489415}

Overworld+Nether+End: 2.634875774921278108332860641293157908840476761859821246449175762500316882638905178010620891988297923409114522837336059751030762922394720528789007184877011399551128228958309542631380066918588006431223267353700092534033897482069307663279385163767021130422606902099212930204498702305492129992025199456819612911703040071273909570170699802096297832729263850956489160159620962161179674925754029602349619262438683071475299948246777605609113454086518491719792990007526829586352252558658871213455879990355374287527739199221574871802719107775608037845644354292823477320888670997749861427768560437955808883470548734768828919676×10^{10275621677278468246}