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\lhead{Retrocausal Objections Are Disallowed for the Photon}
\rhead{John C. W. McKinley}
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\title{Retrocausal Objections Are Disallowed for the Photon}
\author{John C. W. McKinley \orcidlink{0009-0005-7097-5035}}
\date{April 18, 2026}
\begin{document}
\maketitle
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\blfootnote{\scriptsize This version published at \url{https://doi.org/10.5281/zenodo.19648209}.}
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\begin{abstract}
There is no time factor for the photon. Therefore retrocausal objections regarding
the photon are disallowed. Such objections require a timed intermediate subject on
which backward influence, endpoint foreknowledge, or route-coordination problems
could be built. But the photon has no such time-bearing middle. What remains is a
lawful state change, while duration, delay, and geometric order belong to spacetime
description. The result is not new physics. It is the direct consequence of taking
the null case literally.
\end{abstract}
\section{Introduction}
A familiar objection to non-transit accounts of the photon is that they seem to
invite retrocausality. If the photon does not possess an internally timed middle,
then how can emission and absorption be lawfully related without the destination
already being built in from the future?
This paper makes a narrow no-go claim. There is no time factor for the photon.
Therefore retrocausal objections regarding the photon are disallowed.
The reason is simple. A retrocausal objection requires a timed intermediate
subject on which one may place backward influence, endpoint foreknowledge,
route-finding, waiting, updating, or other coordination across moments. But the
photon has no such timed middle. The objection therefore has no licensed target
in the photon case.
This paper does not re-prove established restrictions. It draws the next
consequence from them.
\section{Prior Restrictions Presupposed}
\begin{proposition}[Prior restrictions]
Within the present sequence, the following restrictions are presupposed:
\begin{enumerate}
\item null proper time withholds an internal photon duration~\citep{McKinleyNullProper2025};
\item the absence of a rest frame withholds the ordinary persistence template~\citep{McKinleyNoRest2025};
\item null curves do not by themselves supply carrier histories~\citep{McKinleyNullCurves2025};
\item wavefunction prediction does not license an intermediate photon path~\citep{McKinleyWaveNoPath2026}.
\end{enumerate}
\end{proposition}
\begin{remark}
These restrictions are not established anew here. They serve as the fixed
starting point for the present no-go.
\end{remark}
\section{The No-Go}
\begin{definition}[Retrocausal objection regarding the photon]
A retrocausal objection regarding the photon is an objection that presupposes a
timed photon middle and then attributes to it backward influence, endpoint
foreknowledge, route coordination, or timed adjustment across an intermediate span.
\end{definition}
\begin{proposition}[No-go]
There is no time factor for the photon. Therefore retrocausal objections
regarding the photon are disallowed.
\end{proposition}
\begin{proof}
A retrocausal objection requires a timed intermediate subject on which one may
place backward influence, endpoint foreknowledge, route-finding, waiting,
updating, or other coordination across moments. The photon has no time factor and
therefore no such timed middle. Hence no retrocausal objection regarding the
photon has a licensed target.
\end{proof}
\section{Spacetime as the Domain of Duration}
The no-go does not remove time from physics. It localizes duration to the correct
domain. Spacetime remains the domain of duration, delay, geometry, interval
structure, and observer-side order~\citep{McKinleyBedrock2026}.
\begin{definition}[Localization of duration]
Duration, delay, temporal order, and geometric separation belong to spacetime
description rather than to the defining photon relation itself.
\end{definition}
Thus when a source emits and an observer later detects, the interval may be vast
for clocks and geometry in spacetime. That does not imply a photon-side internally
lived duration. The long interval belongs to spacetime description. The photon
does not carry an internal timeline across it.
\section{Lawful Admissibility Without In-Flight Knowledge}
The disappearance of the retrocausal objection does not make photon appearance
arbitrary. There are no unlawful photons. Standard physics already contains the
structure governing admissible outcomes: amplitudes, coupling structure,
conservation laws, symmetry restrictions, boundary conditions, and final-state
availability. The present claim denies only that these should be narrated as the
internal itinerary of a persisting photon-object.
\begin{remark}
The retrocausal objection often assumes a false dilemma: either the photon travels and
learns where to go as it proceeds, or the future endpoint reaches backward to
constrain it. The present reading rejects both horns. It does not preserve an
internally timed photon middle and then add a backward influence to repair it. It
denies the internally timed middle itself.
\end{remark}
\begin{remark}
Wavefunction language remains fully available in this reading, but not as a
description of an internally traveling photon body. The wavefunction belongs to
the lawful admissibility of observable spacetime outcomes, not to a photon-side
middle.
\end{remark}
\begin{figure}[H]
\centering
\begin{tikzpicture}[scale=1.0]
\draw[->] (0,0) -- (0,5.5) node[above] {$t$};
\draw[->] (0,0) -- (7,0) node[right] {$x$};
\fill (1.2,1.2) circle (2pt) node[left] {$E$};
\fill (5,4) circle (2pt) node[right] {$A$};
\draw[dashed] (1.2,1.2) -- (5,4);
\node at (2.5,3.0) {$ds^2=0$};
\node[anchor=west] at (4.5,2.5) {\footnotesize lightlike relation only};
\node[anchor=west] at (4.5,2.0) {\footnotesize not an occupied history};
\node[anchor=west] at (4.5,1.5) {\footnotesize not a persisting traveler};
\node[anchor=west] at (0.2,5.0) {\footnotesize Photon relation:};
\node[anchor=west] at (0.2,4.55) {\footnotesize no internal time-bearing middle};
\node[anchor=west] at (0.2,0.65) {\footnotesize Spacetime description:};
\node[anchor=west] at (0.2,0.25) {\footnotesize endpoint order and measured delay};
\end{tikzpicture}
\caption{The emission and absorption events are lightlike-related in spacetime
description, but the dashed segment is not to be read as an occupied intermediate
history of a persisting photon. The measured interval belongs to spacetime
description. The photon relation itself is not defined by an internal timeline.}
\end{figure}
\section{Conclusion}
There is no time factor for the photon. Therefore retrocausal objections regarding
the photon are disallowed.
Spacetime remains the domain of duration, delay, geometry, and observer-side
order. The photon relation itself is not defined by an internal timeline. The
long interval between source and observer is therefore a fact of spacetime
description, not evidence for a photon-side middle that must be coordinated from
the future.
The result is not new physics. It is the direct consequence of taking the null
case literally.
\begin{thebibliography}{9}
\bibitem[McKinley(2025a)]{McKinleyNullProper2025}
J. C. W. McKinley,
\emph{Taking Null Proper Time Seriously: An Interpretive Clarification of Null Proper Time},
Zenodo (2025).
DOI:\,\href{https://doi.org/10.5281/zenodo.18004632}{10.5281/zenodo.18004632}.
\bibitem[McKinley(2025b)]{McKinleyNoRest2025}
J. C. W. McKinley,
\emph{No Rest Frame, No Persistence: A Kinematic Constraint on Photon Interpretation},
Zenodo (2025).
DOI:\,\href{https://doi.org/10.5281/zenodo.18005884}{10.5281/zenodo.18005884}.
\bibitem[McKinley(2025c)]{McKinleyNullCurves2025}
J. C. W. McKinley,
\emph{Null Curves Without Carriers: Resolving an Ontological Tension in Relativistic Geometry},
Zenodo (2025).
DOI:\,\href{https://doi.org/10.5281/zenodo.18028886}{10.5281/zenodo.18028886}.
\bibitem[McKinley(2026b)]{McKinleyWaveNoPath2026}
J. C. W. McKinley,
\emph{Wavefunction Prediction Does Not License a Photon Path},
Zenodo (2026).
DOI:\,\href{https://doi.org/10.5281/zenodo.19504771}{10.5281/zenodo.19504771}.
\bibitem{McKinleyBedrock2026}
J. C. W. McKinley,
\emph{A Minimal Structural Statement of the Timeless Light Model},
Zenodo (2026).
DOI:\,\href{https://doi.org/10.5281/zenodo.19167403}{10.5281/zenodo.19167403}.
\end{thebibliography}
\end{document}