Vanilla 1.1.9 is a product of Lussumo. More Information: Documentation, Community Support.

    •  
      CommentAuthorS_o_E
    • CommentTimeJun 24th 2012
     
    In quantum mechanics, a single equation called the wave function describes all the possible states that a quantum object can be in, and assigns each of them a certain probability. Hawking and Hartle sought a similar wave function that can generate the probability of various universes arising from the big bang. It would describe all the possible universes that could have been - including ones in which the solar system never formed, or in which life might have evolved very differently.

    Over the past 30 years, Hawking and Hartle have been forcing a positive cosmological constant into their wave function, because that was considered necessary. But that meant sacrificing precision: they just couldn't get these universes to be anything more than clunky approximations of reality.
    Tip the balance

    String theorists had also been struggling with universes with positive cosmological constants, which tend to be unstable. Building them is a bit like trying to balance a pencil on its tip: it might work for a while, but the pencil's most energetically stable state is lying flat on the table, and eventually it will fall over. The most successful versions of string theory would rather live in the Escher-verse.

    "String theory with a negative cosmological constant just goes much better," Hertog says.
    •  
      CommentAuthorS_o_E
    • CommentTimeJun 24th 2012
     
    But Hawking's latest work suggests that this supposed flaw may actually be the thing that knits string theory back to reality. In a paper posted online, Hawking and colleagues describe how they produced a plethora of universes from wave functions with negative cosmological constants, some of which are expanding and accelerating (arxiv.org/abs/1205.3807).

    "Some of those universes are accelerating, just like our universe," Hertog says. "It turns out the quantum state includes both kinds of universes, automatically." For a certain wave function, these accelerating and expanding universes even turn out to be the most likely ones.

    The key to this insight was recognising that the universes generated by the team's wave function could evolve to look a lot like a particular formulation of string theory, produced by Juan Maldacena of the Institute for Advanced Study in Princeton, New Jersey in 1997 (arxiv.org/abs/hep-th/9711200). "There was a mathematical connection, a very elegant connection," Hertog says.
    •  
      CommentAuthorS_o_E
    • CommentTimeJun 24th 2012
     
    Once they had spotted its connection to their wave function, Hawking's team decided to try to stitch the two together by writing a new wave function with a negative cosmological constant. They reasoned that this would allow them to borrow the beautifully complete mathematical picture of the universe provided by string theory and produce universes that accelerate outwards.

    What about the observations suggesting that our universe is flat? Similar to how Newton's laws of motion work for everyday objects but give way to the more comprehensive laws of Einstein on cosmological scales, Hawking's team thinks that the universe's apparent flatness may describe it well as far as we can see but ultimately gives way to an underlying Escher-like geometry.

    It is too soon to declare the universe solved. Maldacena says the Hawking team's model leaves out aspects of complete versions of string theory, such as provisions for the stability of some particles. "It would be wonderful if it was all we need to do," he says. "But I think it's too simplified. It's hard to see how it can be expanded to a more complete theory."

    Hertog agrees that their work isn't finished - but thinks that the negative cosmological constant will eventually lead to a complete, description of the universe we observe. "It's an avenue that is opening up now," he says, "not something we have yet."
    •  
      CommentAuthorS_o_E
    • CommentTimeJun 24th 2012 edited
     
    ;-)

    - Had forgotten about that!

    Ahhh, dear.. Hilarious. Now my cheeks hurt. Thankyou loreman.

    I'm 6ft 3.
    • CommentAuthorloreman
    • CommentTimeJun 24th 2012
     
    Posted By: S_o_E;-)

    - Had forgotten aboutthat!

    Ahhh, dear.. Hilarious. Now my cheeks hurt. Thankyou loreman.

    I'm 6ft 3.


    A shorty eh? I'm 9' 8" meself, but I look less like Darryl Hannah than something from Hanna Barbera.
    •  
      CommentAuthorTrim
    • CommentTimeJul 6th 2012 edited
     
    NS

    Dark matter underpinnings of cosmic web found

    The rest must be made of dark matter.
  1.  
    Posted By: loreman
    Posted By: S_o_E;-)

    - Had forgotten aboutthat!

    Ahhh, dear.. Hilarious. Now my cheeks hurt. Thankyou loreman.

    I'm 6ft 3.


    A shorty eh? I'm 9' 8" meself, but I look less like Darryl Hannah than something from Hanna Barbera.


    Hey, don't knock it. That Betty Rubble was one hot stone-age babe. I'll bet she was a good cook too. Pris--- a standard pleasure model, nice, but they don't have much kitchen programming.
  2.  
    I have a question: if the universe is expanding in all directions then why is the Andromeda galaxy going to crash into the Milky Way?
    • CommentAuthortinker
    • CommentTimeJul 20th 2012
     
    Precisely because of that. If it was only expanding in one direction nothing would change.
  3.  
    Posted By: tinkerPrecisely because of that. If it was only expanding in one direction nothing would change.


    Hmm, but if all galaxies are ostensibly moving away from each other how can we be on a collision course? I mean from our perspective Andromeda should be moving away from us if the expanding universe holds true for all celestial bodies.
    •  
      CommentAuthorAngus
    • CommentTimeJul 20th 2012
     
    The universe is expanding.
    Galaxies are travelling through the universe.

    What's the problem?
    • CommentAuthorenginerd
    • CommentTimeJul 20th 2012
     
    And of course the galaxies, being part of the universe, are expanding also.

    Now, the galaxies are moving around inside the expanding galaxy. Why are they moving at their current vectors.

    I think we should go back to my billiard table analogy.
    •  
      CommentAuthorTrim
    • CommentTimeJul 20th 2012
     
    •  
      CommentAuthorAngus
    • CommentTimeJul 20th 2012
     
    Posted By: enginerdAnd of course the galaxies, being part of the universe, are expanding also.

    Now, the galaxies are moving around inside the expanding galaxy. Why are they moving at their current vectors.

    I think we should go back to my billiard table analogy.




    Diameter of Galaxy 30 kpc = (3.09*10^16 km)

    Hubble Constant 65 km/s/Mpc

    Expansion rate 65* 0.03 = 1.95 km/s

    Proportional expansion per year = 1.95*3600*24*365/(3.09*10^16)=2*10^-12

    In percentage 2*10^-10%
  4.  
    Posted By: Anguse universe is expanding.
    Galaxies are travelling through the universe.

    What's the problem?


    The problem is that by definition of all galaxies expanding away from each other it precludes them from crashing into each other.
    •  
      CommentAuthoroak
    • CommentTimeJul 20th 2012
     
    Here in the local group we do whatever we want.
    •  
      CommentAuthorAngus
    • CommentTimeJul 20th 2012 edited
     
    Posted By: Knuckles OToole
    Posted By: Anguse universe is expanding.
    Galaxies are travelling through the universe.

    What's the problem?


    The problem is that by definition of all galaxies expanding away from each other it precludes them from crashing into each other.


    Why do you figure that? Space is expanding at such and such a rate. Some galaxies are travelling THROUGH space faster than that, so they can hit each other.
    •  
      CommentAuthoraber0der
    • CommentTimeJul 20th 2012
     
    Posted By: AngusSome galaxies are travelling THROUGH space faster than that, so they can hit each other.

    Like cars? I hope our galaxillery is not a Yugo.
  5.  
    Yes... but are we there yet?
    •  
      CommentAuthorAngus
    • CommentTimeJul 21st 2012
     
    Posted By: alsetalokinYes... but are we there yet?


    We're always there. It's just that there keeps moving.