Based on our current knowledge of physics, another intelligent species visiting our planet would have to be from our own galaxy. So how many potential species exist?

For that,we turn to the Drake Equation. The current estimate is 2.3 potential civilization in the entire galaxy capable of detection. Capable of interstellar travel? There is no calculation for that, but based not the trending of every new variable reducing the odds by 10%, it would be .23 - or no civilization that has the capability for interstellar travel.

My problem with the Drake Equation is that it takes into account the solar habitable zone, but not the galactic habitable zone. If we add that back into the equation, the number of potential civilizations reduces to .23 and the chance that they ever meet is .023.

This doesn't take into consideration the number of civilizations that would observe, but chose to remain undetected, have a non-interference policy, etc.

So no, I don't believe ET has visited us or ever will. We are alone.

Can that change? Sure. If humanity every reaches the point where near-light travel is possible, and we begin to colonize other solar systems, then the whole equation changes. Over time, we would change into unique species in each solar system. But for now?

ET won't be iPhoning home.