
How can you fall in love? Why do you even believe in love? To an atheist, love is just the chemical by-product of humans attempting to find a suitable mate with which to reproduce. Cows reproduce too, but they don't write sonnets. Also love extends far beyond just reproduction for survival, as evolution

How can you believe in art? After all, a stunning painting is nothing more than light reflecting off a mix of pigments smeared onto a flat surface. Does a provocative film create rivers of tears from an audience all because of an optical illusion of innumerable still images flashing on a blank white screen for two hours?
How can you enjoy music? Thousands of sound vibrations coming from a bunch of metal strings stretched over a hollow piece of wood can't be anything but air molecules bouncing off your eardrum.
How can you have hope in anything? The outcomes of the future are mere statistical probability without purpose.
Why do you care if you ever hurt anyone else? I've heard atheists speak of their moral foundations as sort of a common-sense "moral rules of man". In a nutshell, don't do anything if it's going to hurt

Where do you find grounds for such a romantic idea as kindness? If the universe began with random chaos, it will end in random chaos. And so will your human life. With no justice or purpose. So why bother trying to justify any acts you do with morality or kindness for your fellow man or for the earth? There is no punishment for any ill act you do, if you are the ultimate definer of justice. And it makes no difference to make the world a better place, because it will all end in uncontrollable chaos anyway.
And forget something as silly as beauty. The reason a man finds a woman beautiful could be a mate-search honed by millions of years of evolved survival instincts. But who gives a shit about a sunset? Sitting on a sandy beach and being enveloped by a burning red and pink sky certainly never helped any species survive being eaten by another. In fact, you'd think it would be a detriment. I don't know why some ravenous animal hasn't developed a camouflage of a beautiful sunset. As some dumb human stops to admire, they get torn apart and gobbled up.

Humans have the ability to transcend these worthless and otherwise chaotic tangible things into a spiritual experience unlike any animal on earth (so far as we know). And it is unlikely that many of these spiritual experiences had any effect on our chances of survival as a developing species. So it seems they may exist for another purpose (or come from another source). For one to admit that they encounter any of these human states can be admitting to experiencing a non-material, non-mathematical facet of our universe. Give me all the formulas you want, but you just can't prove love.