Okay this is kind of a jumble - let me see if I can untangle some of this:
- special relativity is the bedrock of general relativity: general relativity utilizes the spacetime geometry of special relativity, and simply extends it from the special case of a flat Minkowski spacetime, to a curved Reimannian manifold. So SR is embedded into general relativity - they work in concert in GR.
- I don't deny any credible theoretical physics; I don't know where you got that idea.
- Wikipedia can be useful, but you have to be careful with it: the editors there often express their dogmatic bias against anything even slightly outside the mainstream, including at times even valid avenues of on-going academic research.
- You didn't specify which theory of relativity you thought was broken, so I had to defend both, because neither are broken, though GR is incomplete because it doesn't incorporate quantum phenomena.
- There's almost certainly a grand unified theory that will tie all fundamental physics together - we just haven't found it yet. I think it's vital to do so, however, because I expect that once we unify GR and QFT, we should be able to figure out how to technologically manipulate gravitation.
Same here, and thank you. I endeavor to be as accurate as possible when talking about physics, and I'll always be very clear when I'm speculating. Hopefully that will help to avert any confusion or contention.
Yes. I recently spent some time studying photonic metamaterials with an eye to spacetime engineering applications, because of the AATIP story and the materials mentioned recently in that regard. It's not my area of specialty but the literature was very clear.
After years of debate about the correct stress-energy tensor to apply for photonic metamaterials, a team of researchers recently found that the Helmholtz stress tensor yields very accurate results. And this stress tensor contains two terms, electrostriction and magnetostriction, which provide a mechanism for producing tension (negative pressure) within such materials when their microstructure is arranged in a triangular lattice. When the miscrostructure is arranged in a square grid, these terms have a positive value. So, to a minuscule degree at least, we now have a mechanism for producing negative and positive components in the stress-energy tensor within the material when it's activated with the right frequency of electromagnetic radiation, which means that we can produce positive and negative terms within the Einstein stress tensor as well (which produces negative and positive mass modulation), using photonic metamaterials. We don't know the upper limits on the magnitude of these effects yet. It's hard to imagine a way to produce any detectable mass change in this manner, but it does appear to be a promising proof-of-principle that it might be possible.
Like I said before, I don't think that backwards time travel is possible, without some new and unexpected revolution in physics. Changing
the rate that one moves into the future does appear to be possible though, and it's certainly possible to travel faster into the future within a gravitational field, or by accelerating to a higher relative velocity. If substantial negative energies become available, then one could also slow one's motion into the future.
In any case, such effects would be immediate. Let's say that you turn on your gravitational time machine and accelerate into the future - if the machine breaks or whatever, you'll have traveled some distance into the future, so that's where you'll end up. I don't see any reason to expect that a traveler would get thrown back to the starting point; time dilation just doesn't work like that.
All cogent and viable models in physics are called theories: they're never called facts. The term "fact" is reserved for undisputed empirical observations. So don't get hung up on the word "theory," so far both theories of relativity have made all the correct predictions in every regime that we can rigorously test them. Clifford Will wrote a brilliant review paper about the experimental status of general relativity - I highly recommend having a look through it:
“The Confrontation between General Relativity and Experiment,” Clifford M. Will, 2014
https://arxiv.org/pdf/1403.7377.pdf