Which features of the Morris-Thorne wormhole require exotic matter?

Question

This particular solution has some features that make gives it more utility for humans, such as time stability, enough size for someone to transverse it and other things made for humans. Could an advanced civilization abandon some of these to just test wormholes using particles to achieve the goal of not requiring exotic matter?

Answer 1

What you are looking for is the Raychaudhuri Theorem concerning exotic matter. Basically it states that for any wormhole to be traversable for even lightspeed particles, a negative stress-energy is required. Consider, as light passes through a wormhole, parallel lines exiting the wormhole diverge. This divergence is the opposite of how energy usually results in curved spacetime, hence the need for negative stress-energy or exotic matter.

Answer 2

There's modified theories of gravity that are completely nonsensical that don't have a proper initial data problem that allow you to make wormholes and stuff, like $f(R/T/Q)$ theories that everyone is spamming the gr-qc arXiv with, but in Morris-Thorne solutions, which are classical GR solutions, you do need at least an infinitesimal amount of exotic matter. These are still not traversable per se, but a lot of people argue that these might be stabilised somehow. But none of these are physically viable arguments as far as real physics is concerned.