Why You Can't Use Entanglement To Make An Ansible

I've been disappointed that I didn't grok why you couldn't use entanglement to make an ansible, so I asked around on the Viable Paradise Yahoo! Group, and got some insight. Thanks to Laura, Meredith, Calvin, and Leo.

Here's what I've got in my head:

In order to transmit information, one party must set (that is, determine) a property of the universe, and another must read (that is, measure) that same property. When each party is in possession of one particle of an entangled pair, neither party can set any entangled state of the particles (like, say, spin). One party (A) can set the property whether-the-waveform-has-collapsed-yet, by reading any of the entangled states, but the other party (B) can't read that same collapsed-yet property; B can only read the entangled state, which is something A didn't set. So even though the two particles might be said to be communicating with each other instantaneously, the two people who have them can't.

I'm not sure if I've got it right, but it feels good to think that I grok it.


Spherical Time said...

So, is an ansible an important aspect of one of your stories? It certainly is in mine. Thus, I'm having to come up with alternate explanations for the FTL communications that play a major role in the formation of the interstellar government.

Any ideas for yourself?

Hysteresis Monkey said...

Ah, shoot. No, sorry, I got nothin'. I don't have any work-in-progress that relies on ansibles; I just brought it up because I'm terminally curious about this stuff. When I learned about entanglement, my first thought was, "Ooh! Ansibles!" And then I saw a comment somewhere that said, "Nope, you can't use entanglement to make an ansible." But no clear explanation of why. Thus this post.

As a writer of spec-fic, though, my opinion is not that this means you can't have ansibles, but that you can't base ansibles on entanglement.

Which brings up a bigger point in SF writing. Hrmm, how do we word this. Uh...

What annoys smart readers is not when you make up stuff that's outside what we, as a civilization, currently think we understand about nature, it's when you make up stuff that directly contradicts what we, as a civilization, currently think we understand about nature.

The former suggests that you're thinking outside the box. The latter suggests that you don't even know where the box is.

The entanglement thing would be a sub-genre of this problem, which I'll call the Buzzword Problem (it probably already has a name though). For instance, you can say that in your world people can communicate faster than light, and imply that it depends on some as-yet-undiscovered loophole in relativity. That's a stretch, but if you write it right, you can make clear that it's the former thing. If, however, you do what many writers do, and say it's possible because of [insert some hot science buzzword that doesn't actually justify FTL communication], then many readers will figure that you just didn't read the Wikipedia page all the way to the end, and that it's the latter thing.

Anyway, that's my current thinking on that topic. Might change next week.

And I've never been published. So, you know, take anything I say with a grain of salt.

Spherical Time said...

I definitely agree with your second paragraph, but as spec-fic writers, we need to come up with better buzz words. Especially if we need instantaneous communication to validate certain plot points.

Perhaps something to do with teleportation?

Heh. And remember, I'm not published either, so we can hypothesize together.

Jon Peck said...

Entangled particles are still great for encryption, tho. Hey, maybe you don't need FTL communication if you cave sufficient encryption...just stretch your plot out over a few thousand years!