Can a photon get emitted without a receiver?
Richard Feynman's PhD thesis was about just this topic, if I am understanding your question rightly. Here is an earlier question about Feynman's thesis that addresses some of the fascinating issues involved with this.
At the suggestion of his thesis adviser John Wheeler, Feynman explained photon emission as a two-way interaction in which the regular photon is emitted and follows the "retarded" solutions to Maxwell's equations. "Meanwhile" (in some rather abstract sense of the word indeed) a target atom or particle in the distant future emits its own photon, but a very special one that travels backwards in time -- a type of solution to Maxwell's equations that had been recognized since Maxwell's time but had been ignored. These solutions were called the "advanced" solutions. This advanced photon travels back in time and "just happens" to arrive at the source at the exact instant when the regular photon is emitted, causing the emitting atom to be kicked backwards a tiny bit.
Amazingly, Wheeler and Feynman were able to write a series of papers showing that despite how mind-boggling this scenario sounded, it did not result in violations of causality, and it did provide a highly effective model of electron-photon interactions. From this start, and with some important changes, Feynman eventually produced his Feynman-diagram explanation of quantum electrodynamics, or QED. The curious time relationship continue in Feynman's QED, where for example a positron or anti-electron simply become an ordinary electron traveling backwards in time.
Staying fully consistent with his own ideas, Feynman himself described photon interactions as always having an emission and a reception event, no matter how far apart those events occur in ordinary time. In his view, if you shone a flashlight into deep space, the photons could not even be emitted until they found their "partner" advanced photon emission events somewhere in the distant future. The proof of it is in the very slight push back on your hand that happens when you shine the light, that kick coming from the advanced photons arriving from that distant point in the future and nudging the electrons in your flashlight filament.
You clarify in the comments to @FredericBrünner 's answer:
The question is Can a photon get emitted without a receiver?
Yes. An atom in an excited state will emit a photon into space, vacuum, whatever
And it seems like photons that don't hit a receiver never can be measured,
Wrong. If you set up an experiment with atoms at an excited state you know that a photon has been released by finding it at the ground state. That is a definite measurement.
so its hard to test if they are there.
If you want to test for the existence of photons you have to have something that can interact with them, yes. It is not hard.
But the energy input of a light bulb in space will produce a certain amount of photons,
Whether in space or not this is true. The sun is a huge light bulb in space
and if we have a connected receiver we would expect a rise in measured radiation,
our eyes connect with sunlight and they do measure the electromagnetic radiation . Different detectors are needed if the radiation is absorbed and turned into heat.
if all photons must be connected to a receiver.
No. This is a wrong premise. The flux of light/em-waves from the sun can be calculated accurately and we know it disperses the same photons per unit area at the same distance from it whether there exists an absorbing or reflecting body or not.
Its a observational experiment which might fully dismiss or confirm the hypothetical question.
certainly the hypothesis that a photon has to have a receptor is dismissed from the experiment with the sun.
Do you mean that the emitter, the electrically charged particle, is the only particle in the universe? If that is how you mean your question, then here is a possible answer.
Since the question is about a very hypothetical situation, one must start with a hypothetical scenario, and then build from that position.
Let us imagine there is an electron in space all by itself. The question is:
Can this completely isolated electron emit a photon?
We assume the laws of physics hold in this case as normal.
Some of the facts we do know about the electron
(i) According to classical electrodynamics an electrically charged particle radiates electromagnetic waves only when it is subjected to acceleration, or for some reason it lowers its energy.
(ii) From quantum mechanics point of view the electron cannot be in a state of absolute rest, because then its momentum will increase in unpredictable ways by quantum fluctuations of the vacuum.
(iii) If the electron is moving with constant momentum, then according to the uncertainty principle its position will be totally undetermined, i.e. the electron will be spread all over the space available to it.
(iv) The vacuum has a Lorentz invariant structure, which requires the presence of a positron. This is a result of Dirac’s theory.
ANALYSIS:
According to (i): the electron will not be able to emit a photon. The emission of a photon by an atom, as mentioned in another answer, assumes the electron has absorbed some amount of energy at an earlier time, so it will have to re-emit it, as there is a lower energy level below it. Anyway, in this case the electron is not an isolated particle in an “empty” space as hypothesised.
According to (ii): the electron will accelerate and therefore will emit photons, and it is even possible it will reabsorb them (self energy diagrams).
According to (iii): the energy of the electron would be well defined and constant, hence it would not be able to emit any energy, so no photon emission. If the electron kept emitting photons from that state, it would soon lose all its energy and would end up a massless electrically charged particle!!
According to (iv): the electron cannot be on its own, without the positron. This is necessary by Lorentz invariance of the vacuum. So the electron will exchange photons with the positron, and might even suffer pair annihilation.
Since Lorentz invariance is an inherent property of nature, in my opinion, scenario (iv) is the most likely than any of the others.