This contains a bunch of spoilers if you’ve yet to see Inception.
I’ve seen a lot of arguments going back and forth about how Ariadne and Cobb may actually just be going to a fourth level rather than Limbo when they rescue Fischer. I felt the same way, for the following reasons:
1) Ariadne says “Mal killed Fischer,” and Cobb doesn’t check. If she’s trying to pull a fast one on him to get him down one level, this might be the way she gets him to do it.
2) Ariadne is the one who suggests they go down, Cobb agrees, but she’s the one with the idea.
3) Cobb hasn’t seen any of the designs they worked on, because he’s afraid of Mal compromising the mission, so Ariadne would have been able to design another level without his knowledge.
However, there are many reasons why this might not be the case.
1) They “wash up” like you do in Limbo.
2) All of Cobb’s stuff is there, he’s the tour guide. If Ariadne designed it, she’s doing a good job of both playing dumb and guessing what Cobb made there.
3) Shocking Fischer causes the “lightning flash” in the sky even though he’s not hooked up to the machine.
So how do you resolve these things? I started doing the math, and I realized that when Mal and Cobb accidentally ended up in Limbo, they might very well have been four levels down.
From the shooting script:
ARIADNE: This is not just about Fischer, it’s about you. Tell me what happened to you and Mal. Trapped in Limbo.
Cobb looks at her. Thinking it through.
COBB: We were on a job. Exploring dreams within dreams. But we didn’t understand how your mind can get trapped. Trapped so deep that when you wash up on the shore of your subconscious…
Insert Cut: Mal lies on the sand, staring up at a cloudless sky, waves washing over her…
COBB: You can lose track of what’s real.
ARIADNE: How long were you stuck?
Cobb pauses before he answers. Looks at Ariadne.
COBB: Fifty years.
Fifty years is roughly 438,000 hours.
Without a sedative, as Arthur explains to Ariadne, Five minutes in the real world gives you an hour in the dream.
So for one dream level:
300 seconds = 3600 Seconds
Or 1 second = 12 seconds
Or 1 hour real time = 12 hours at dream level one
If nesting dreams work the same way as they do with Yusuf’s compound, with time getting stacked exponentially:
1 hour real time = Six days at dream level two (144 hours)
1 hour real time = Around two and a half months at dream level three (1728 hours)
1 hour real time = Around two and a half years at dream level four. (20,736 hours)
1 hour real time = Around 30 years at dream level five. (248,832 hours)
1 hour real time = More than 340 years at dream level six. (2,985,984 hours)
To get to 50 years, they’d have to spend:
Level 1: Over four years.
Level 2: Over four months.
Level 3: Around ten and a half days.
Level 4: Less than a day, around 21 hours.
Level 5: Around two hours.
Level 6: Less than ten minutes.
Now, it’s made clear by Cobb’s conversation with Yusuf that without sedatives, a dream within a dream at level three would collapse. Yusuf’s sedatives give time dilation a factor of 20, rather than twelve.
1 hour real time = 20 hours at dream level one
1 hour real time = 16 days at dream level two. (400 hours)
1 hour real time = Almost a year at dream level three (8000 hours)
1 hour real time = About 18 years at dream level four (160000 hours)
1 hour real time = About 365 years at dream level five (3,200,000 hours)
1 hour real time = Over 7,000 years at dream level six (64,000,000 hours)
With that in mind, to get 50 years it would be:
Level 1: About two and a half years
Level 2: About a month and a half
Level 3: A little over two days
Level 4: A little less than three hours
Level 5: About eight minutes
Level 6: Around 24 seconds
Yusuf’s sedatives are very powerful, so they may be more powerful than what Mal and Cobb were using. Therefore, we can figure that they were using something in between straight-up dreaming and Yusuf’s sedatives.
With this in mind, my guess is that they ended up at least four levels deep, because of these two bits of dialogue:
ARTHUR: This can’t be done.
COBB: It can. You just have to go deep enough.
ARTHUR: You don’t know that!
COBB: I’ve done it before.
COBB: We need you there to tailor compounds to our particular requirements.
YUSUF: Which are?
COBB: Great depth.
YUSUF: A dream within a dream? Two levels?
YUSUF: Not possible. That many dreams within dreams would be too unstable.
COBB: I’ve done it before. You just have to add a sedative.
Cobb isn’t planning to visit Limbo with his team, but he is trying to go as deep as he can to implant the idea. My guess is that means he stops short of where he and Mal went when they reached Limbo.
It also makes sense time-wise.
If they only went to level three (depending on what sedative they used) they’d be out anywhere for two to 10-and-a-half days. Maybe grandma was watching the kids, but that’s still a *really* long time.
With level four, they’d be out for three hours to almost a full day, much more believable.
Then, there’s Yusuf’s statement, “That many dreams within dreams would be too unstable.”
What happens when a dream collapses?
So far, the ultimate bad thing that can happen when you’re in a dream is that you’d end up in limbo.
My current thought is that it’s not so clear-cut that it’s either “Level Four” or it’s “Limbo.”
I think that going down one more level from three would be enough for them to end up in Limbo, even if there were something constructed there.