I've always wondered how Luke was trapped in the carbonite chamber. Leia and Chewbacca are brought into the chamber, but when Luke goes in seconds later suddenly they all are hidden and you hear nothing of them.
Can someone explain it to me?
It's perhaps a little clearer in the original script. Luke is being herded toward the chamber through the use of locked doors and stormtrooper patrols.
Leia, Han and the ugnaughts are led out of the chamber. Leia is used as bait by the stormtroopers to tempt Luke into the 'ante-chamber' which then locks at both ends after Luke enters. While he's still puzzling this out, Luke is quite surprised that the cargo platform he's standing on starts to lift, depositing him in the carbonite chamber.
LEIA: Luke! Luke, don't - it's a trap! It's a trap!
Before she can finish, she is pulled through a doorway and disappears from sight. Luke races after the group, leaving little Artoo trailing behind.
INT. CLOUD CITY - ANTEROOM
Luke runs into an anteroom and stops to get his bearings. Leia and the others are nowhere to be seen. Behind Luke, Artoo scoots down the corridor toward the anteroom when suddenly a giant metal door comes slamming down, cutting off Luke's exit. Several more doors clang shut, echoing through the chamber.
INT. CLOUD CITY - HALLWAY LEADING TO ANTEROOM
Artoo stands with his nose pressed against the giant metal door. He whistles a long sigh of relief and, a little dazed, wanders off in the other direction.
INT. CLOUD CITY - CARBON-FREEZING CHAMBER - ANTEROOM
Luke cautiously walks forward among hissing pipes and steam. Seeing an opening above him, he stops to look up. As he does, the platform he stands on begins to move.
INT. CLOUD CITY - CARBON-FREEZING CHAMBER
Luke rises into the chamber, borne by the platform. The room is deathly quiet. Very little steam escapes the pipes and no one else seems to be in the large room. Warily, Luke walks toward the stairway.
Darth Vader tortured Luke's friends so that Luke, sensing their pain, would come to Cloud City. That's the trap. Vader needed a way to bring Luke to the Emperor so he decided to do carbon freezing. To ensure Luke would survive, the freezing was tested on Han Solo before Luke arrived, again this is before Luke arrived. Leia, Chewie, C-3PO, and Lando were all brought to the carbon freezing chamber when it was tested on Han. At this point Luke is not there yet. We even hear an imperial say during Han's freezing
OFFICER: Lord Vader, ship approaching - x-wing class
VADER: Good. Monitor Skywalker and allow him to land.
So Luke wasn't even there yet. While Luke was busy landing, everyone left the freezing chamber.
VADER: He's all yours, bounty hunter. Reset the chamber for Skywalker.
OFFICER: Skywalker has just landed, Lord.
VADER: Good. See to it that he finds his way in here. Calrissian, take the Princess and the Wookiee to my ship.
So everyone leaves the chamber but Vader, who waits in the chamber with the lights dimmed. Leia and Chewie leave with Lando (who later decides to free them instead of taking them to Vader's ship like Vader ordered). There are two main groups leaving; Leia, Chewie, and Lando etc. in one group, Fett and the now frozen Han Solo in another. Fett was taking Han to his ship when Luke, who had finally landed and entered the city, catches a glimpse of them. When Luke tries to follow them, Fett fires a few shots and they get away. Lando's group (with Leia and Chewie) are close by and hear the shots. Leia shouts to Luke that it's a trap. They also get away and Luke ends up finding his way to the carbon freezing chamber.
So, by the time Luke gets to the chamber, everyone has gone but Vader. Everyone certainly had enough time to leave the chamber while Luke was landing and disembarking.