According to the Fermi paradox, the milky way should have been colonized by dozens of different civilization a over a billion years before humanity even evolved. If these are the number of intelligent societies that should have developed, there should be tens of thousands of planets with multicellular life, and tens of millions of planets with some form of simple single-celled life in our galaxy alone. A number of objects within our own solar system are thought to contain primeval life, including: Mars, Titan, Europa, Ceres, and Ganymede. If you are referring to the entire universe, it is out of the question that we are not alone. The question we should be asking is why no one has found us yet.
There are hundreds of billions of stars in our galaxy. There could be trillions upon trillions of planets in the Milky Way alone. Add to that billions of galaxies in the known universe and there are a lot of possibilities for life outside of Earth. Surely at least one of those places harbors some form of life. The life forms don't have to be intelligent or advanced. Yet at least one other planet in the universe has at least bacterial life on it that could evolve into complex life forms later.
Scientists have proven that the galaxy is very big, bigger than we can even imagine, and it keeps getting bigger. There are also many planets out there that we believe to resemble earth. With all this in mind i just think that it would be ignorant to say that we are the only life in the universe.