Alphanumeric, you said once to Terry:

''Thus KK methods provide a way to unify classical gravity and classical electromagnetism, but it costs you a scalar field whose presence is not seen in experiments on the levels predicted by the theory. These methods are used in string theory which also recasts what is and means that its not experimentally disproven.''

I have some questions.

What is the nature of the scalar field? What does it represent by definition? And what is the reason why we cannot detect it? What are they looking for to detect this scalar field?

The scalar field would couple to matter in the same way as gravity--i.e., to everything. Scalars coupling to matter give an attractive force, which is easy to prove with QFT. So all you have to do is look for a fifth force, which we don't see in experiments (google fifth force experiments).

The scalar field would couple to matter in the same way as gravity--i.e., to everything. Scalars coupling to matter give an attractive force, which is easy to prove with QFT. So all you have to do is look for a fifth force, which we don't see in experiments (google fifth force experiments).

A fifth force which couples to matter. It gets even juicer.

Thanks, I'll look it up.