[torginus]

Unfortunately my understanding of physics stops at general relativity and quantum mechnics (which I did study both at uni, with some mathematical framework of understanding).

How would I advance from this point, what should I read to get a grip on string theory, including the concepts and maths involved? Could you recommend some resources?

Like why did they come up with the concepts they came up with, how does that help explain established theories and experimental phenomena on a deeper level, etc.

Also I've noticed there are several competing theories in this domain (like Quantum Gravity, String Theory, hope I'm not wrong), what are the odds that these theories end up being equivalent?

As others have pointed out, compared to classical physics, quantum mechanics describes the world of tiny distances and energies in greater detail while relativity becomes useful at the opposite end.

How would one construct an experiment whose results depend on both phenomena?

[superjan]

I would argue that you don’t need to learn string theory as it currently does not predict anything we can realistically observe (as you need energies that occurred only at the big bang). If string theory is correct we could observe a “supersymmetric” twin of all known particles, however we haven’t seen these, and they could exist even if string theory is false.

String theory aims to explain all physics as manifestations of a mathematical concept best understood as a vibrating string.

Initially, the hope was that string theory could predict the particle masses we observe, but that hasn’t worked as it turns out there were many different predictions possible. String theory has also struggled to develop a version of the theory that does not contradict known properties of our actual universe.

Loop quantum gravity is not equivalent to string theory, except that it also tries to unify gravity and quantum physics.

As things stand, string theory is not falsifiable, while that is the case, you could argue it does not count as physics.

But, by multiple accounts, it is interesting math, which can be worth doing for its own sake, and it’s happened often enough that interesting math turned out to be useful somewhere. Just not for explaining physics.

[_bypa]

The easiest book that's not popsci but actual physics is Barton Zwiebach's "A First Course in String Theory".

It does not presuppose a background in QFT. It does require you to know quantum mechanics. Mind you, it's not as deep as the standard texts (Polchinski et al. or Kaku's work prior to going off the rails) or my favourite which is the two-volume "Quantum Fields and Strings: A Course for Mathematicians". But it makes reading the others possible.

[keithnz]

I’m no expert in string theory but with all the bagging on string theory I tried to get to the guts of what's going on without as much "opinion". I did watch this great video which interviewed a bunch of scientists working on various aspects of string theory, and overwhelmingly it seems there's still a lot of interesting questions to be answered (even if string theory doesn't describe this universe), unfortunately I can't seem to find it at the moment.

I think the main thing is, even if string theory turns out not to describe reality, it shows that quantum mechanics and general relativity can be reconciled within a single, mathematically consistent framework. The tension between the two is gone and it's actually needed for physical correctness. Simply knowing that such a reconciliation is possible is already a meaningful result.

String theory emerged from attempts to quantize gravity. I think the most interesting thing is that when a relativistic string is quantized, a massless spin-2 particle inevitably appears in the spectrum. This particle behaves exactly like a graviton, meaning that gravity is not introduced by hand but instead arises naturally from the theory.

Competing approaches may possibly be all compatible, much like different interpretations of Quantum Physics.

The main difficulty with experimental tests is that the relevant energy scales and distances are far beyond what we can currently probe in the laboratory. This is not a weakness unique to string theory, but a general problem for any theory of quantum gravity. The Planck scale is simply too extreme to access directly with present technology.

As for experiments that depend on both quantum mechanics and general relativity, in principle these would involve situations where quantum coherence and strong gravitational effects are both important. Examples include black hole evaporation, aspects of early-universe cosmology, and possible quantum effects in curved spacetime. These are extraordinarily difficult to study experimentally, but they are what motivates the search for a theory of quantum gravity in the first place.