How was this possible? *spoilers*

[Eldrick4221]

I can accept the fact that Nynaeve was able to make an A'dam in Tel'aran'rhiod and capture Moghedien. It's explained in detail the abilities the unseen world has to offer.

It's also mentioned several times that nothing that happens there can affect the real world. How is it that the A'dam persisted?

 

Sorry if this has already been discussed. I couldn't find a topic about it.

[Andra]

It's not that nothing that happens in Tel'aran'rhiod can affect the real world, it's that only things that happen to people in Tel'aran'rhiod persist in the real world.

We see examples of things happening to people in the world of dreams persisting after they wake up all through the series.  It's why the Aiel Dreamers were so insistent that Egwene stay out of it unless she was with one of them.  It's why Rand killing Rahvin with balefire in TAR resulted in Mat and Aviendha coming back to life in the real Caemlyn.  Because those were all about things happening to people in TAR persisting in the waking world.

 

Regarding the a'dam that Nynaeve dreamed up - it didn't persist.  Elayne made one to use in the real world.  A different version, that could be disguised as a set of jewelry.  The reason they were able to put it on Moghedien before she could escape is because Nynaeve drugged her in TAR so she wouldn't wake up in time to get away.

And as the drugging happened to her person, the effects lasted just as they would have in real life.

[Dedicated]

I may be missing something, but I believe the reason why things that happen to people in the world of dreams happen to their waking selfves is basically because of psychosomatic effects. So Mogedien getting drugged in the world of dreams blocked her real body long enough for Elyane, Nynave and Brigette to get a read a'dam on her. 

[Eldrick4221]

My issue was I thought the a'dam somehow persisted into the waking world. I couldn't figure out how.

 

The forkroot part makes complete sense.