so we can go visit them - for dinner, or interstellar diplomacy, or whatever. Of course we'll

need to be able to talk with them about what to make each side of the portal out of, how

big to make the various pieces, and so on. But since we've never been to Alpha Centauri,

and they've never been here, this is tricky – I mean, if you tell me to make you an

arc that's 300 cubits long, and I don't know what a cubit is, you'll probably get

an arc that's not exactly what you were hoping for .

So we'll have to build, from the ground up, an easily sharable way of communicating

about the universe, where distances and such are based on ideas, rather than specific artifacts

. We'd probably start with basic materials, you know, like how instead of sending a vial

with a chunk of lithium in it across interstellar space, we can just say “use the atom that

has 3 protons, 3 neutrons, and 3 electrons.” Water would be “the molecule that's a

combination of one atom with 8 protons and two atoms with 1 proton.” And so on.

Once we have materials down, we can do clocks – we just tell the aliens that if they take

the atom with 55 protons and 78 neutrons , make it emit a photon of light in a certain way

, and wait for that photon to oscillate 9,192,631,770 times: that's what we call one second.

Once we have clocks, we can do distances: just tell the aliens to see how far light

goes in one 299,792,458th of a second – that's what we call a meter.

But this is when we would run into a massive roadblock – literally. Pretty much the

rest of our communication about the universe requires knowing what mass is, and what we

currently call a kilogram isn't an idea we can just tell distant aliens, the way we

can say “the atom with 3 protons”. A kilogram is just a particular lump of metal sitting

in a particular room in a particular place on our planet , and if you want to know how

many kilograms of say, antimatter, you have, you have to take it there and weigh them against

each other . In the very near future, we're going to

settle on a more sensible way of talking about mass, so instead of saying “in order to

build this teleporter you have to come to the part of earth with good cheese so we can

show you our shiny lump of metal,” , we'll either be telling the aliens to just get a

pile of something like 21.5253873 septillion of the atom that has 14 protons and 14 neutrons,

or we'll tell them to weigh how much mass an atom or molecule loses after emitting a

photon of light that oscillates roughly 135.6392534 septillion septillion times each second. One

of these two concepts will be our new kilogram, and even though the pile of atoms option sounds

simpler in principle, it's actually kind of harder and more expensive to do in practice.

Whichever way it is, once we have our new way of communicating about mass as an idea

instead of an object, we'll be able to build our wormhole teleporter with the alpha centaurians

. And then we can bring them here to earth, have dinner, and afterwards, show them the

chunk of metal that used to be THE THING that we used to talk about the mass of all other

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