I Does String Theory Justifiably Extend Gravitational Laws to Sub-Planck Lengths?

[john t]

I posted this earlier, but the thread has been closed.

String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the theorists are assuming the gravitational laws extend to the sub-Planck length and are trying to force the conclusions along those lines. Is this considered justifiable by physicists/mathematicians?

I got an unhelpful reply from wierdoguy, who discounted the question because it was prompted by my reading of a well-footnoted but non-textbook category book, he derided as pop science. This repliy strikes me as contemptuous of books written by experts who are striving to bring complex subjects into an accessable form for people outside their field. I would welcome further comment if purposeful.

 

[Nugatory]

First, a quick public service announcement: Restarting a closed thread is specifically prohibited by the forum rules. If you believe that a thread was closed prematurely, you can ask that it be reopened: report the post announcing the closure and explain why you want the thread reopened. Just restarting the thread comes across as contempt for both the forum rules and the unpaid volunteers who make it work.
With that said...

A thread that starts with the premise "It seems to me the theorists are assuming the gravitational laws extend to the sub-Planck length and are trying to force the conclusions along those lines" based on a Brian Greene book isn't going to be reopened. We have close on two decades of experience to show that an "it seems to be me [that there's a fallacy here]" drawn from a popularization isn't going to lead to a productive discussion - there are too many ways that the popularization, although well-intended, will be an inadequate representation of the actual thinking. This is (one of the reasons) why we have the acceptable sources rule.

It may be that you're actually trying to ask a different question: Why do we expect the gravitational constant to to be relevant to string theory even though we know perfectly well that classical general relativity won't work unmodified at the length scales where string theory is relevant? If that's what you're trying to ask, it's a better question (and the fact that the answer is not apparent to you from Greene's book just goes to show the limitations of the popularization). Let me know by PM if that's closer to your question.

This thread is closed, and the other one will reman closed, pending further discussion.