Parallel Universes: Everett vs M-Theory

[Boris Leykin]

I've made transcript of the whole dialog, like http://en.wikipedia.org/wiki/Laugh_track" , very funny.

Time 1:12:30

Ed Witten: "...Every quantum mechanical system has a gravitational interpretation..."
...
Lenny Susskind: "...It seems to me we have two different conjectures about the way the Landscape gets populated one of them is that bubbles nucleate in the inflating universe and simply populate every possible many many different vacuums - eternal inflation, another idea that has been along for a long time is the idea of, what is it called, eh, alternative universes, eh, the many worlds interpretation of quantum mechanics, that the wave function splits and splits and splits and that way populates all of the Landscape. My conjecture is that those two things are exactly the same, that the multiple bubbles of de Sitter space bubbling nucleating and all that stuff, pocket universes, all these words mean exactly the same thing as the many worlds interpretation of quantum mechanics. Do not expect me to explain what I've just said"

(everybody is laughing)

Moderator: "So, any reaction from the panel to?"

(laughter)

Andy Strominger: "So can we infer from that, Lenny, that you think that quantum mechanics is an absolute concept which will survive any future developments?"

Susskind: "Yes. I do think quantum mechanics will survive. But I'm not sure that this is necessarily means that time is an absolute concept. But I think that may be quantum mechanics does have something to do with eternal inflation, bubble nucleation, many many universes and that concept is not really different from the many worlds interpretation of quantum mechanics. I don't think we should have two independent and different ideas about how the landscape gets populated, so I think they are the same"

Ashoke Sen: "I just want to make a quick comment. Gh-ha-ha. [] It seems clear that if you want to make a significant impact in string theory it really helps if your last name begins with "S"?"

(laughter)

Moderator: "I think having an "S" in your name is partial... Other people in the panel want to talk about this? :)" (laughter) "Do you want to change your last names? :) Do you think that quantum mechanics and eternal inflation is the same thing?...well, in the sense that Lenny mentioned?...No comments?"

Juan Maldacena: "I think what Lenny said is probably clearly right"

(laughter)

Moderator: "Is that universal opinion of the panel? :)"

Joe Polchinski: "This is in fact the same thing as the anthropic CFT duality :)"

(laughter, Andy Strominger is laughing hysterically)

Moderator: "[] Anybody else? Do you think it's possible? I hated it when Lenny first told me about [] I can't remember why but there was a good reason."

Juan Maldacena: "I think that there's some evidence that it is right if you...Linde et al. with this eternal inflation calculated these probabilities that are the same as Hawking gets from a wavefunction of the universe, that is how you imagine it from insider's point of view, so I think that there's some evidence that it is correct. (with cunning smile)"

Moderator: "I have to confess I have a foggiest idea what he means. So, if we put Lenny in the box in place of Schroedinger's cat I would have thought we'll end it up with two worlds where we were in this part of the landscape with Lenny alive or Lenny dead, but is he claiming that we'll end up in some other part of the landscape []? What are you talking about, Lenny?"

(laughter)

Susskind: "OK. So. There's another Lenny someplace, right? Some place far far away in some other bubble universe there's another Lenny and he's doing exactly the same thing as I am now and you put me in a box, that Lenny will survive, this Lenny is not going to survive for too long, yes, decoherence. :) That's one thing which is clear in an infinite landscape that everything is replicated in this way. On the other hand I also have a suspicion that the multiple replications of things is a kind of gauge redundancy so that there really []"

"Gauge redundancy"?

 

[Demystifier]

It is really amusing to be a string theorist.

 

[Feynman diagram]

Have you seriously considered what a dimension that contains only gravity would look like?
Like! … man! … It would be the mother of all the black holes. Now!, … how does this dimension know where to find 10^80 particles in our big universe so that it can endow each of them with a little bitsy bit of gravity which can then follow the inverse square law.
Would you like to borrow my razor blade?
jal

Why should the 11th dimension only contain gravity? M-theory posits that the particles of the standard model are described in terms of open strings which are attached at their endpoints to our 4-brane. The hypothesized graviton is described by a closed string which can thus propagate in higher dimensional spaces. So if we choose a particular 11 dimensional coordinate system to describe this situation we would find that all points on our 4-brane have the same numerical value in the 11th dimension. Now M theory also says that our 4 brane moves in the 11th dimension. If it does this then we would find that our 11th spacetime coordinate would change with time, but it would take the same value at any particular time we choose to measure it all over our 4-brane. So in other words, our observable universe is perfectly capable of moving in the 11th dimension but that we are unaware of this movement owing to the fact that the observable universe is composed of open strings.
In fact this is still over-simplified because it is quite likely that if M theory is correct then our 4-brane will ripple in higher dimensional spacetime so the 11th spacetime coordinate with smoothly vary over the 4-manifold we use to describe our world. This does not in any way contradict the fact we cannot directly see or 'move' in the 11th dimension in the way that we think of moving in 3 dimensional spaces.