# Gamma-ray Bursts: 50 Years and Counting!
## 12 Conclusions and Open Questions  
GRBs are extreme phenomena, pushing the limits of our physical theories. Even 50 years after the first publication about their discovery, they continue to surprise us and elude our complete understanding. Given their extreme nature, GRBs are (almost) unique in astrophysics in their multi-disciplinary nature. As discussed in [233], the study of GRBs has connections with many other major branches of astrophysics, with important consequences for stellar astronomy, the study of the interstellar medium, galactic astronomy, and cosmology. The connections do not end here, and indeed, the study of the GRB phenomenon has connections with various branches of physics (and not only). These connections go far beyond just physics; e.g., some groups have studied the possible links between GRBs and mass-extinction phenomena. Focusing more precisely on the study of the basic mechanisms of these phenomena, it is evident that every step forward in our understanding has been intimately linked to a technical-scientific advancement, which, through the conception and implementation of increasingly targeted measures, has allowed, from time to time, the discovery of more and more details of these fascinating and varied phenomena. Without any pretense of completeness, we can summarize the open questions and the lines of research to follow as follows:  
* The Standard Model:
* The standard fireball (plus internal/external shocks) model can explain many features observed in prompt GRBs and afterglows... before the _Swift_, HE, and VHE eras. More realistic assumptions are needed (ejecta, environment). * What is the nature of GRB jets? * Long GRBs:
* Collapsar vs. magnetar: which is dominant? * Where are the GRB remnants? * The nature of subluminous vs. ultraluminous GRBs: what determines the difference? * Short GRBs:
* Are all short-hard GRBs compact binary mergers? NS-NS or NS-BH mergers? * How can hard long GRB \"spikes\" be distinguished from short GRBs? * GRBs as probes of the Early Universe:
* What is reionizing the IGM? * Did the reionization begin at \(z\sim 12\)? * Do Pop III stars make luminous GRBs? * GRB221009A and other extreme events:
* How are \(\geq\)10 TeV photons produced? * Are UHECRs accelerated in high numbers in GRBs? Why are there still no associated detections of GRBs and neutrinos (only upper limits)? * How is it possible that \(\geq\)10 TeV photons arrived from \(z\sim 0.151\) despite the theoretically predicted EBL absorption? Is the signal of exotic or fundamental physics effects (LIV, ALPs, other)? * Does the narrow \(\sim\)10 MeV emission component seen in GRB221009A really exist? Is this a characteristic of this burst only or of all GRBs? * Experimental development: how can we develop new instruments to make new and better observations? * Large sky coverage with high localization capabilities/better angular resolutions to observe more signals (better statistics). Large-single-satellite missions vs. distributed geometries? * Better spectroscopic capabilities over wider energy ranges. * Better timing capabilities to characterize the light curves. * Ability to measure gamma-ray polarization to distinguish emission mechanisms. * Better follow-up strategies (and collaborations) for reliable multi-messenger observations. After 50 years of research on GRBs, enormous progress has been made in the study of these phenomena. However, we are still far from a complete understanding of them. There is no doubt that this research area is one of the liveliest at the moment and that, thanks to the enormous effort of experimental improvement and theoretical understanding of the scientific community, it will still yield great surprises and lessons in the future. Writing, A.A.V. ; review and editing, F.L. and A.A.V. ; supervision, F.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding. No new data were created or analyzed in this study. Data sharing is not applicable to this article.