The Universe is incredibly big and seems full of potential for life, with billions of habitable planets.
If an advanced civilization had the technology to travel between the stars, at just 0.1% of the speed of light, It could colonize our galaxy in roughly 100 million years. Which is not that long given the billions of years the milky way has existed – so in principle any spacefaring civilization should be able to spread rapidly over huge sectors of the galaxy.
And yet we see nothing, hear nothing, the universe seems empty. Devoid of others. This is the Fermi Paradox, which we have discussed in more detail in other videos.