Maybe we haven't found alien life because it's all evolving in other universes. A group of astronomers have just released a research paper suggesting that other universes could be far more habitable than our own. It all depends on a few conditions right when those universes were born.
There is now a lot of evidence that we live in a multiverse, where there are as many universes as there are galaxies. Each universe will probably have different physical laws and properties too. As University of Michigan physicist Fred C. Adams and his colleagues say in their paper on arXiv, one of the major differences might be in each universe's "amplitude of primordial density fluctuations", known as Q for short.
Basically, Q describes the difference between dense and empty regions of space — in this case, in a universe. A high Q means there are high fluctuations, with extremely dense areas and extremely empty areas. In our universe, Q isn't all that high, which is why we have a lot of matter spread out everywhere, with big spaces in between stars and galaxies. But what if we lived in a universe with a high Q, and our galaxies were far denser than they are in this universe?
First of all, stars would be extremely close together so you'd be getting sunlight from all around — not just from your local star. It might be a lot more dangerous, with more giant rocks zooming around and smashing into things, and more stars colliding with each other in mega-explosions. But this kind of high Q galaxy would also be much warmer and more hospitable than our current ones. In fact, it's possible that you could live on a free-floating planet just sort of drifting around the galaxy, bathed in the light of hundreds of nearby stars.
There is another opportunity for galaxies with a higher Q than ours. If stars are just the right distance apart that all the free-floating planets in the galaxy are bathed in gentle, warming radiation, a planet won't even need a host star to be in the 'habitable zone'! There could potentially be millions of free-floating, habitable planets, heated purely by starlight. These planets would need to be far enough from the galactic centre that they avoid collisions and extreme radiation, but not so far that they aren't heated enough bt starlight. They need to lie in, what the authors call, the 'Galactic Habitable Zone'.
So you might have a much more habitable galaxy than we have right now. Life could emerge almost anywhere, even drifting between the stars.