Can creatures inside the Rope Trick hear the sounds from outside?

Question

The text of Rope Trick (PHB pg. 273) quotes

Those in the extradimensional space can see out of it as if a 3-foot-by- 5- foot window were centered on the rope.

and

...creatures that can see the window can’t see through it.

Like a one-way-mirror. The description makes no mention of sounds though. Do you think sound would also work in one direction, or is the window not an opening in the conventional sense like "inside/outside" but a portal to the extradimensional space, segregated at the 2 dimensional entrance and every aspect of one side ends and begins at that line (ie. temperature)?

Answer 1

Probably yes, in the end up to the DM

The full quote for what is crossing the entrance is:

Spells cannot be cast across the extradimensional interface, nor can area effects cross it. Those in the extradimensional space can see out of it as if a 3-foot by 5-foot window were centered on the rope. The window is present on the Material Plane, but it’s invisible, and even creatures that can see the window can’t see through it.

So the only thing explicitly excluded from passing in or out are spells and area effects. However, if it behaved just like a normal opening in all other ways, then it would have been sufficient to just state the dimensions. As the spell does not say if it block sound or not, in the end the DM will have to decide so.

In our case, we play it to allow sound, and that has not caused issues. The main point I think for not allowing sound is that it becomes harder to co-ordinate actions between party members on the inside and on the outside. For example, a spotter outside you cannot just shout when the right time has come for the rest of the party to spill out and ambush a foe -- that spotter then would have to be visible from the entrance, and give some visual sign. It may also have some advantages, for example you can cast spells inside, without some enemies outside hearing you and possibly detecting your hideout.

Answer 2

As the spell does not say if it block sound or not, in the end the DM will have to decide so.

It's for that reason that we also left it up to our DM. Our DM noted that the Rope Trick spell description specifically mentions what it does not allow (pertaining to spells), and very specifically what it allows (sight out of but not into the extradimensional space). If Rope Trick was intended to permit sound then it would have been mentioned, ie. "Those in the extradimensional space can see and hear out of it..."

The same argument could be used if it wasn't permitted, it would have said so, ie. "Those in the extradimensional space can see but not hear out of it..."

In our campaign, sound did not travel across the window. Our DM intentionally asked us if anyone kept watch, and since we said no, the charmed dinosaur outside had 2 random encounters that night that went unnoticed by the party. In the morning, the dinosaur was gone, and all eyes turned to the sorceress. It was her first time using the spell, how was she to know!