LoopyMama wrote...
I'm seriously starting to come round to N7Gold's theory on Synth ending.
N7Gold says..
The Catalyst decided that the only way to stop the conflict is to make
peace between the organics and their creations, while at the same time,
"ESTABLISHING A CONNECTION" between them and the Leviathans so the
Leviathans will have a new way of controlling organics, rendering their
crystal balls obsolete. Synthetics will also be controllable to the
Leviathans.
That is what Synthesis does. It connects all organic
and synthetics in the galaxy with a special DNA, turning them into
living "Quantum Entanglement Communicator" devices for the Leviathans to
use. In this way, they will have full control of the galaxy again, a galaxy with billions of worlds in one fell swoop.
Since Mass Effect has already established that organic Quantum Entanglement is used by Rachini as a means of communication and by the Leviathan to enthrall the 'lower races' without eroding the mind, then it stands to reason that the Synth beam would be an amplification signal that perminently stimulates the 'reception' part of out brains, allowing us to be controlled. It creates the 'connection' and puts us in an natural state of indoctrination as opposed to a forced state from the reapers. This could be seen as the enevitable evolution that the Catalyst refered to while describing Synthesis as an organic race has already developed this. No more space magic, instead an explanation that doesn't break the laws of the ME universe. 
Thank you N7Gold. You have changed my endings.
But I'm now very scared of the people who picked the Synth option....
I am in tears, man...

you're welcome...

I can't just let these endings ruin BioWare's rep, the extended cut and Leviathan DLC gave us more puzzle pieces to put together, and I just had to put my thoughts in here to see what other people would think.
Your post touched me the most. I'm surprised you remember that the Leviathan DLC revealed that the ability to entangle particles in the brain to communicate is something the Rachni Queen and the Leviathans can do. Also, that woman, Ann said that the Leviathans use those crystal ball looking things to "
establish a connection" to anyone near the balls so they can control them from wherever they are hiding. And the Catalyst said that he was created to oversee the relations of synthetic and organic life, and also to "
establish a connection". That isn't coincidence, is it???