What's the smallest unit of measurement?

Let’s say you want to measure something really, really, really tiny. How do you do that? With inches? Centimeters? Millimeters? What if it’s so tiny you can’t even see it? Particle physicist Jessica Esquivel helps us solve this teeny tiny mystery!Got a question that seems too big to answer? Send it to us at BrainsOn.org/contact, and we’ll try to measure up!