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Old 22nd July 2010, 10:07 AM   #62
Tim Thompson
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Join Date: Dec 2008
Posts: 969
Lightbulb String Theory IV

Originally Posted by sol invictus View Post
If you're familiar with Feynman's path integral, the issue is whether one integrates over all field configurations and all metrics (that's quantum gravity) or merely over all field configurations with fixed metric (that's quantum field theory).
That's the secret handshake that clarifies the key point. I didn't realize the real difference between gravity and quantum field theory.
Originally Posted by arthwollipot View Post
Okay, now we're way beyond my level of graspingness.
At some point this always happens to everyone, we just have different levels of graspingness. The closer we get to the frontiers of physics, the farther we get from things that can be readily explained to non-physicists. Popular level explanations, in order to avoid complication, usually imply that physicists actually know things that are in reality not necessarily well known.

String theory is as far out on the frontiers of physics as you are going to get. Most people who have opinions about whether or not string theory is worth pursuing are far short of the level of graspingness required to actually know what they are talking about. This is true even for people with a physics background, if they have not studied string theory in considerable detail. My own expertise is in physics, but mostly atmospheric physics. I have no direct experience with quantum field theory, quantum gravity or string theory. I am dealing with my own level of graspingness here and myself learning things as I go.

So welcome to the "limited level of graspingness" crowd.
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell
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