Wednesday, June 21, 2006

4Qs to Leonard Susskind

2004 Reply from L. Susskind to Lee Smolin. edge145

In a nutshell, here is the view of physics and cosmology:

(1) In the remote past the universe inflated to an enormous size, many orders of magnitude bigger than the observed portion that we can see. Most of the universe is behind the cosmic horizon and cannot be directly detected.
(2) The mechanism of inflation leads to a diverse universe, filled with what Alan Guth calls pocket universes. We live in one such PU. Some people call this super-universe the Multiverse. I like the term Megaverse. This growth and continuous spawning of pocket universes is called, in the trade, eternal inflation.
(3) String theory leads to a stupendously large Landscape of possibilities for the local laws of nature in a given pocket. I'll call these possibilities environments. Most environments are very different from our own, and would not permit life: at least, life as we know it.

Combining 1,2 and 3—the universe is a megaverse filled with a tremendously large number of local environments. Most of the volume of the megaverse is absolutely lethal to life. Some small fraction is more hospitable. We live somewhere in that fraction. That's it.

QUASAR9 questions to Leonard Susskind.

(1) You claim a "Megaverse" with eternal inflation, expanding or evolving in perpetuity, without one iota of proof. Since most of the Universe as you clearly point out is behind or beyond the cosmic horizon and cannot be directly detected. Would it not be more logical, realistic and factual to say that our pocket universe, may or may not have been preceded by a big bang, and this would conform to our present models, explanations and theories of the present day detectable pocket universe, from whence we carry out our observations. And even then with our current limited knowledge of the universe, it would be purely conjectural to claim that it is expanding.

(2) This again an absolutely conjectural statement or premise with no more solid foundation than a claim that the universe beyond the cosmic horizon is green, blue or purple. In fact all you are saying is that forargument sake you will make that statement, which is corroborated by fellows of stature in the field of cosmology, and it cannot be refuted. No more than the existence of a Creator God can be refuted. A Creator God who for all we know may well be planting yet more pocket universes in this 'imaginary' Megaverse, just for something to do, like a landscape gardener doing weekend gardening.

(3) We already know this to be true in the observable universe, no one has encountered any aliens or lifeforms beyond Earth. So the statement per se is most likely true for our pocket universe. But it does not proceed hence that a Maegaverse exists. It simply states your support for string theory as a theory which will or may lead to a stupenduously large landscape of local physical laws in nature or environments. Well these are evident in nature in our very own pocket universe, on our very own planet in our very own bacykard.
You try living in the bottom of the ocean, if you know what I mean.
There is whole Megaverse of lifeforms, and local laws of nature or environments which permit marine life, and lifeforms we have not yet discovered which defy most laws of physics as known.

In a nutshell does a plane fly like a bird?

Therefore combining 1, 2 and 3 have only served to explain the concept of the pocket universe as it is perceived by big bang theorists, without I add one bit of proof, and then applied these same attributes to multiple (infinite?) pocket universes to create your preferred choice or vision of Megaverse. You even go as far as to point out that Lee Smolin does in fact agree with you on these three points.

Yet when we come to point 4, ie black holes or singularities, versus Lee Smolin's preferences for black holes as the gateway to the creation of these new (or other) pocket universes, you are silent. Though from other sections on the paper not in the nutshell above, yet I deduce you are still undecided or very non-descript in giving your own version of possible events in the occurring observable phenomena denominated blackholes or singularities.

(4) what is a blackhole, and what is a "singularity", and what in your opinion is on the other side of a blackhole? supposing the black hole has another side. No I am not asking if there are black holes or singularities or do we need to go look there, the fact that it is there is enough for us to want to go look there and/or know what is there. I am asking you to define whether a black hole is a hole or a "singularity" ie: high density matter a Sun or Star compressed to the size of a marble.

Cambridge Relativity black holes
This evolution doesn't produce a blackhole
This collapse does produce a blackhole (maybe)

Labels: ,