Approaches to Quantum Gravity

By cjohnson | September 1, 2005 2:06 pm

Over on Musings, Jacques has given a rather nice (technical) description of some of the motivations for looking beyond quantum field theory for an approach to formulating quantum gravity, and why the stringy approach is so promising. It supplements nicely some of the discussion we’ve had over here in posts such as this, this, and this.



  • bittergradstudent

    I always was kinda annoyed by the comparisons of general relativity to the Fermi theory of the weak interaction. The former is motivated by clear physical principles, from which arise a theory. The latter was an empirical attempt to construct a theory that failed because energies capapble of weeing the W and Z bosons were not accessible at the time.

    Also, the loop quantium gravity crowd, to my understanding, are assuming that the R-squared terms do not exist, beyond the Holst term, which is coupled at a value fixed by matching LQG’s prediction of Hawking Radiation with the QFT result derived by Hawking. I don’t see where Distler is claiming that the “infinite number of independetnly adjustable couplings” is coming from…

  • Arun

    I missed how string theory enables us to take into account the back-reaction of the matter system on the metric in a purely quantum mechanical way.

    I also wonder whether the argument that we cannot construct a quantum mechanical theory of gravity without knowing all about the matter content , namely the one that begins with:

    Unless we know all particle physics interactions all the way from accessible energy up to the Planck scale, we can never hope to extract any quantitative predictions about quantum gravitational effects.

    can be elevated to the status of a theorem, because either the argument has holes in it or else we can save a lot of people a lot of time.

  • Plato

    I understand the pressing concerns of Katrina and the population, but I also see the importance of continuing with the advancement of the Quantum Gravity issue.

    Imagine, if you were to encapsulate “the effect” of this action (Time varible distinction) on a wider scope, and field of vision. Could humanities struggle for survival, have found “value” as part of the natural world new perspective, as we encountered such events as Katrina?

    Layman, are human too:)Be kind.

  • Clifford

    Plato. No. Please don’t -even in jest- trivialize the humanitarian issue by conflating it with research on quantum gravity. I appreciate you carrying on discussion in the physics (and other) threads if you wish, but please be respectful of the other concerns and issues (currently upsetting an devastating a lot of people) when you’re on this blog.



  • Plato

    I do not trivialize at all Clifford. I see the devastation as very real. This might be a oversight and first impression of senses does not serve me well with your response, but I let it rest then until you come back to it, while others continue to debate the political ramificatins. Might we put these aside too?

    Oil companies are profiteering from the misfortune. How would you respond here?

    You have to trust that my compassion is very real. Thanks

  • Clifford


    I’m not questioning your compassion. Sorry if I gave that impression. I was just suggesting that sentences like:

    I understand the pressing concerns of Katrina and the population, but I also see the importance of continuing with the advancement of the Quantum Gravity issue.

    might be better phrased.

    Please don’t think I’m asking you or anyone stop doing your physics and having discussions about it here while there is talk of other things on other threads…we can have all discussions in parallel as usual. Carry on.



  • Plato

    Yes Thank you Clifford,

    Launched in 2002, a pair of identical satellites that make up NASA’s Gravity Recovery And Climate Experiment (GRACE) are tackling the problem in an unexpected way: they are weighing Earth’s fresh water from space. Serving as a sort of “divining rod” in space that moves in response to a powerful, fundamental force of nature—gravity—the satellites respond to changes in Earth’s gravitation field that signal shifts in the movement of water across and under Earth’s surface.

    A Thalean approach maybe, to seeing the events before they happen?

  • Plato

    I thought I would draw the resources together here and link them to give further comments and approaches of opinion to the issue of Quantum Gravity.

    John Baez and Lee Smolin give introspective views on this issue, as well as linked posts to Lubos and Peter Woit respectively.

    I demystify the Thalean approach as well.

    My imput can be quickly disregarded, and hopefully bring further comments in relation furthering views on this topic.

    I have a link on the right side of my menu that has further links on the issues of Quantum Gravity that I had been collecting.


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