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Only Pure Moment

  1. Mar 25, 2005 #1
    Let me begin by stating that I am a very very new reader of Quantum Mechanics. I have been reading lay-person versions of all these exciting ideas. Mine is this. I think I understand the bit about even observation changes the subject, and I got to thinking about the big bang and how I read that we have observed, through space all time leading back to the "big bang" all up to only a microsecond before the moment. What does that say about that moment in time? That it doesn't exist? Is this the only moment not observed by someone and therefore PURE??
    Please forgive my foggy thinking on this, but as I said.. i am only just beginning my knowlege...
  2. jcsd
  3. Mar 26, 2005 #2
    Our theories cannot account indeed for the moment of Big Bang itself (the density was infinite, this at least according to GR; anyway temperature and pressure were huge). Yet this does not mean that we cannot talk meaningfully about the time of Big Bang or even about what happened before Big Bang. The old positivst view that is futile to ask what was before Big Bang is no more 'en vogue', at least among cosmologists.

    Indeed Hawking's hypothesis is very speculative (time 'freezes' the closer we approach the Big Bang, being not well defined; so in this view it is futile to ask what was before Big Bang, netiher was there a precise time of Big Bang). The same is valid for Vilenkin's proposal that the universe could have appeared out of pure nothingess (not even a spacetime structure).

    Currently the main focus of the scientific community in the cosmology field is on the 'infinite bubbles' inflationary universe (here there was a 'time' even before the 'Big Bang' of our universe). The main advantage of the Multiverse theory, apart from being a 'natural' extension of the standard inflationary theory, is that it is (still) our best candidate to solve the so called 'fine tuning' of the universe problem.

    But from what I see you need rather an introductory approach in the topic:



    If you want more then Guth's book 'The inflationary universe' is perfectly suited for this topic (it is written for a wide audience, with many details however).

    As a digression here I think it's worth saying few words about Vilenkin's proposal, as presented in Guth's book (upon him it seems that not even the Multiverse can avoid having a beginning-but this is still debatable-though it extends infinitely toward the positive axis of time, the future). Well it's one to say that the Multiverse appeared out of 'nothing' (meaning from 'something' beyond Multiverses' spacetime) and totally another thing to say that it appeared from 'absolutely nothing' (not even a 'spacetime').

    In Tryon's proposal for example the Universe appears 'out of nothing' due to the fact that the total energy of the universe is 0, the negative energy of the gravitational field cancels exactly the positive energy of matter. There is still assumed, implied indirectly, the existence of 'something' in the form at least of a spacetime structure.

    But Vilenkin's proposal sees 'nothingness' in mathematical terms, there we can define the null set. His 'nothingness' involves not only the absence of any form of matter and energy but also the absence of a spacetime structure at the most fundamental level possible.

    From GR he took the idea that that the geometry of spacetime is not fixed,being capable of distorsions. Different geometries are possible then, even in the total absence of matter and energy. Well one of these possible geometries is the empty set, no geometry at all.

    We are dealing with quantum systems here or quantum systems can make transitions from one configuration to another configuration, as much as no conservation laws are broken. Thus in his view we can imagine that the Multiverse itself appeared from a configuration with a total empty geometry (additional to the total absence of matter/energy); from 'absolute nothingness' to use Guth's words.

    This could be easily identified with the 'absolute nothingness' of philosophers. My impression is that this is exactly what Vilenkin's meant. If not, then it's clear that he left things too open to interpretations. But how on Earth could we talk of a physical 'something' since even spacetime is postulated to not exist initially?
    Last edited: Mar 26, 2005
  4. Mar 26, 2005 #3


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    There is also the now famous paper of Ambjorn, Jurlevich, and Loll, http://www.arxiv.org/abs/hep-th/0404156, which shows that 4-D spacetime can arise from prespace "causal triangulations". They use a montecarlo simulation to generate the effects of summing causal path integrals.
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