"Hey, another atom. I'm hydrogen, nice to meet you.
How are you feeling about the jump?"
"Hi there, I'm antihydrogen, your antiatom,
and to be honest, I'm feeling kind of neutral.
My positron and antiproton balance out, just like your electron and proton, right?"
"Hey, yeah! You look just like me, but different somehow."
"Whoa, be careful! If we get too close, we'll disappear in a spark of energy.
I'd like to stay in one piece."
"Oh wow, sorry."
"It's okay. I was just thinking,
it's kind of weird for us to be
chatting like this before our jump above CERN."
"Why's that?"
"Well, for starters, how do we know we'll both fall?"
"Of course we'll fall. It's gravity,
you know, the force of attraction between masses.
I even know how fast we should fall.
Galileo showed in that tower experiment
that all falling objects accelerate at the same rate, regardless of mass."
"That's for bigger objects.
It's a different story for small particles like us.
Our mass is so tiny that the gravitational force we experience is miniscule,
and if the particles are charged, like my antiproton or your proton,
then it becomes impossible to detect
compared to the much greater electromagnetic force acting on them."
"But that's only for charged particles. You and I are both neutral.
Our charges balance out, so the electromagnetic force is small
and the gravitational force should be detectable.
I know mine's been measured."
"Because you're everywhere, but I'm kind of hard to find."
"Why is that, anyway?
Shouldn't there have been an equal amount
of matter and antimatter created in the Big Bang?"
"You'd think so, but then all of those particles
would have annihilated each other into energy, remember?
And the Universe is obviously full of matter.
No one knows why there is more matter than antimatter,
which is why scientists are so interested in studying me."
"So where do they find you anyway?"
"Actually, I was made in that lab down there.
They needed an accelerator to make my antiproton because it's so heavy,
just as heavy as your proton.
Getting my positron was easier.
It's much lighter, like your electron, and there are materials
that naturally decay by emitting one.
Then they just had to put the two together and they got me.
But it's only recently
that they've been able to keep me
around long enough to study my properties."
"And now they've sent you on this jump with me. Hey, wait a minute."
"That's right. We're reenacting Galileo's experiment,
but with matter and antimatter instead of two objects made of matter."
"So what's going to happen?
Are you going to fall upwards or something?"
"Only one way to find out!"