I prepared a MWE with your rar given informations.
Please see the following code:
\RequirePackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@booklet{Reference1,
Author = {B. Cook},
Title = {An alternative Model of Cosmology},
Year = {2010},
}
@book{Reference2,
Author = {P. Coles},
Title = {Cosmology: A very short introduction},
Publisher = {UOP Oxford},
Year = {2001},
}
@book{Reference3,
Author = {V.H. Ironside},
Title = {Behold! I Teach You Superman},
Publisher = {Malleus Maleficus},
Year = {2010},
}
@mastersthesis{Reference4,
Author = {S. Bhargava},
Title = {Type Ia Supernovae and Testing Inhomogenious Models of Cosmology},
School = {University College London},
Year = {2016},
}
@article{einstein,
author = "Albert Einstein",
title = "{Zur Elektrodynamik bewegter K{\"o}rper}. ({German})
[{On} the electrodynamics of moving bodies]",
journal = "Annalen der Physik",
volume = "322",
number = "10",
pages = "891--921",
year = "1905",
DOI = "http://dx.doi.org/10.1002/andp.19053221004",
keywords = "physics",
}
@book{dirac,
title={The Principles of Quantum Mechanics},
author={Paul Adrien Maurice Dirac},
isbn={9780198520115},
series={International series of monographs on physics},
year={1981},
publisher={Clarendon Press},
keywords = {physics},
}
\end{filecontents*}
\documentclass{article}
\usepackage[%
backend=biber,
style=authoryear,
natbib=true
]{biblatex}
\addbibresource{\jobname.bib}
\begin{document}
Some \autocite{Reference4} text \cite{Reference4}.
\nocite{*} % <========== to call all uncited bib entrys to be added to bibliography
\printbibliography[heading=bibintoc]
\end{document}
To get a proper sorting you need to divide firstnames and lastnames of authors with an blank. I added that to your given bib entrys. See for example:
@booklet{Reference1,
Author = {B. Cook},
% ^ added blank!
Title = {An alternative Model of Cosmology},
Year = {2010},
}
The environment thebibliography is created by biblatex and biber in the resulting bbl file, do not use it by your own in your code.
Command \nocites{*} adds all uncited bib entrys to the printed bibliography and that is that what you want and need ...
Package filecontents is only used here to have BiB file and TeX code concatenated into one compiling MWE. Please do not use it in your real code!
With my given MWE you get after compiling with pdflatex, biber,pdflatex and pdflatex the following result:

\documentclasscommand, have a minimal preamble and then\begin{document}...\end{document}. The code should compile and be as small as possible to demonstrate your problem. Cutting your code down to a MWE may well reveal what your problem actually is. – Oct 24 '16 at 12:46authorfield. And you should not use thethebibliographyenvironment for that data. It should be in an external file. – egreg Oct 24 '16 at 13:07\nocite{*}if you want everything in the bib file to be in the bibliography. – StrongBad Oct 24 '16 at 15:45biblatex/biberworks with thethebibliographyenvironment). This does not seem like one of those "good" duplicates. – StrongBad Oct 24 '16 at 17:47\nociteing the relevant references after all) instead of closing right away as a 'good' duplicate. – moewe Oct 24 '16 at 19:21