It is well known that if two perfectly smooth plates are held very close together in a vacuum, quantum effects between the plates will have a net repulsive (or attractive, depending on the plate configuration) effect between the two. This is caused by waves of energy being too large to fit between the plates, causing a net negative energy between the plates when compared with the surrounding "normal" space.
As realized by Thorne and his Caltech team, this Casimir energy could be applied to the neck of a wormhole, potentially holding it open long enough for something to pass through.
NEWS: Time Travel? Don't Forget to Pack Your Wormhole
Alas, we are talking about quantum-sized wormhole throats, meaning Marty McFly's speeding DeLorean will be left revving in the 1985 parking lot, unable to squeeze through. But even if some quantum-sized traveler could pass through the wormhole's neck, the wormhole would still likely collapse very quickly.
On reevaluating this scenario, Butcher has identified some more stable wormhole configurations and, in certain situations, the wormhole collapse could be prevented for an "arbitrarily long time." But for this to happen, the wormhole needs to be very long and have a very narrow throat. In this case it seems possible that photons could traverse the wormhole.