Can you scientifically rule out sentient extraterrestrials?

Science is about facts and probabilities one can measure, test, and deduct by evidence. Using that same deductive power back by mathematics how can one be totally sure there are no other sentient life forms out there? Off science life started here eons ago when some primordial soup of enzymes got zapped by a bolt of lightning under the right condition and then WHA LA! We had single celled organisms. Then over many more eons these single celled organisms decided to be multi-celled organisms to the point where they thought cell splitting and such was boring and that some should be female and others male and reproduction should happen by boinking. So on and so on, until we are here, the year 2011.

Given the amount of starts that are known how could you rule out the chance that the lotto win that happened here on Earth could not or did not happen anywhere else? Using the laws of averages and mathematics would that not be true. What are the odds, that with all the stars know and unknown, sentient higher life could have only happened here? That would be like someone winning the lotto then no one else ever winning; it just keeps rolling over, and over in perpetuity. How do you scientifically debunk the math of it?

Wouldn’t thinking humans are the only intelligent sentient beings in all of the universes a bit self-centered and arrogant? Are all the other planets and stars there just for the benefit of humans?