A final theory and the Omniverse
I just read “The Cosmic Landscape” by Leonard Susskind. Susskind believes that the small magnitude of the cosmological constant (119 zero digits after the decimal) compared to a randomly generated constant (which is likely to be close to to unity) leads to a multiple universe explanation. The actual choice of universe in which we live is constrained (and enabled) by the Anthropic Principle (AP). We exist in a habitable universe (where the constant is within a range consistent with life). Other universes exist in the Multiverse where things are not fine tuned, but nobody is there to notice.
Susskind further makes a distinction between the Landscape (set of possible universes) and Multiverse (set of actual universes). Universes can actually be born from other ones through quantum fluctuations and it seems that Susskind thinks that only those Universes born from others are “real”.
However, that seems arbitrary. What is the reason that only some of the universes in the Landscape exist, assuming they are all consistent? There is no “prime motive”, so no set of universes is preferred over any other set. Just because a Universe can arise from another, doesn’t seem to give its existence additional justification. For example, assume Universe A can give rise to B and C. Then on the other hand we have D that can give rise to E and F. If we say B exists (is in the multiverse) and E does not (in the Landscape but not in the Multiverse), what is the reason for that?
Additionally, Susskind speaks of the Landscape as being created by varying parameters of String Theory. The question here is what are the limits? All theories can be embelished or modified with additional rules and constructs. Different Landscapes can be created. Why choose one Landscape over another?
I would like to propose an extension to these ideas. Here is what I propose:
- The Landscape includes all self-consistent mathematical constructs (the Omniverse)
- The Multiverse and Landscape are identical
Some corollaries:
- Every self-consistent mathematical construct exists as an independent universe
- We exist in such a universe (but we have to find out which one)
- Every perturbation of a self-consistent mathematical construct also exists
Note that a mathematical construct is not just what humans can conceive of – it’s the class of all possible ones.
Some speculations:
- Quantum mechanics has a random nature at small scales because every perturbation exists
- Our particular universe is a machine that is good at hiding the perturbations. In particular, at the macroscopic level the perturbations are smoothed out. This is another application of the AP – life could not exist in a fatally chaotic and/or unpredictable universe.
- The Universe is quantized and finite in all dimensions and magnitudes (although unboundedness may be okay). Otherwise we get into the measure problem.
I found a few other mentions of similar ideas. The canonical references seems to be Max Tegmark:
http://space.mit.edu/home/tegmark/toe_frames.html
I believe a couple of additional features apply that I haven’t seen in other people’s theories: 1. randomness is a given at the bottom, because all perturbation exist, and universe must smooth it out 2. the measure problem means that the universe must be quantized and finite.
About the prospect of a gazillion universes, what about the idea: “extraordinary claims require extraordinary evidence”?
Carol,
[ Sorry your comment too so long to appear. The moderation queue for the blog has been inundated with spam, so I didn’t see your post. I tried Akismet today and managed to clear the spam and dig the real comments out.]
To the actual topic – I’m not sure it’s more “extraordinary” to have all alot of universes or to have just one arbitrary universe.
Here’s another way of looking at it: Imagine we had a permanent cloud cover and couldn’t see other stars. Would a claim that there must be many stars out there be ordinary? I think it would, if plausible evolutionary scenarios of the universe are taken into account. Otherwise, we would have to assume that our solar system configuration came into being in an arbitrary fashion.
Similarly, it would seem that our universe came into being in an arbitrary way if we claim it is the only one. That seems extraordinary.
Another way of looking at it is by Occam’s Razor. The explanation we should accept is the simplest that fits the facts. A universe has quite a few arbitrarily chosen variable values. It would be quite a long description (“Our universe is such that X, Y, Z… and it is the only one that exists”). In contrast, “All Universes Exist” is a very compact explanation (possibly also the most compact explanation possible).