Can a photon get emitted without a receiver?

Question

It is generally agreed upon that electromagnetic waves from an emitter do not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non-received EM-Waves, because if we observe them the instrument of observation becomes a receiver.

Electromagnetic waves have changing electric and magnetic fields and are both electric and magnetic. Electric current connects like from an anode to a cathode. Magnetic fields illustrated by flux lines connect from one magnetic pole to another, and no non-connecting flux lines are observed.

So electric currents connect and magnetic fields connect, so why doesn’t the electromagnetic wave also always connect to a receiver? A receiver which could be a plasma particle, a planet, a star and anything else which can absorb EM-radiation.

There is one big problem. If a photon has to be emitted in the direction of a future receiver, the photon must know where a future receiver will be. So this conflicts with our view on causality, or a cause creating an effect. And as the emitter doesn’t know where the receiver will be some time in the future, it can't emit an EM-wave against it.

But how can we know that the causality principle is always valid without exceptions? There seems to be reasons for questioning the universal validity of the causality principle:

• Information does not have a mass and may then not be restricted by the speed of light, so the causality principle may not always hold for massless particles/waves.

• When something travels with the speed of light, it will experience that distance become zero. If there is no distance, there is a full connection and a continuous electromagnetic wave between the emitter and receiver. Again, using the photon as a reference frame is not something relativistic physicists seem to like.

• Maxwell's electromagnetic wave equation has a simple and an advanced solution. The advanced solution is usually discarded because the effect happens before the cause. But in Wheeler–Feynman absorber theory the advanced solution is used because it works. See this link for more information: http://en.wikipedia.org/wiki/Wheeler%E2%80%93Feynman_absorber_theory

• The field of quantum mechanics is discussing many different causality problems. Like the observation of a particle might decide where the particle will be in time and space. Relevant to this discussion is the question of what triggers the atom to emit light:

Over the last hundred years, physicists have discovered systems that change from one state to another without any apparent physical “trigger.” These systems are described by quantum mechanics.

The simplest such system is the hydrogen atom. It’s just an electron bound to a proton. Two particles – that’s about as simple as you can get. According to QM, the electron can occupy one of a discrete set of energy levels. The electron can be excited to a higher energy level by absorbing a photon…

When the electron drops from a higher energy level to a lower level, it emits a photon: a quantum of light…

Quantum mechanics describes this process beautifully, but it only predicts the average time the electron will stay in the higher energy level. It doesn’t give any clue as to the specific time the electron will drop to the lower level. More precisely, the transition rate (the probability of a transition per unit time) is constant: it doesn’t matter how long it has been since the atom was excited, the transition rate stays the same…

When you first encounter this, you can’t quite wrap your brain around it. Surely there must be some internal mechanism, some kind of clock, that ticks along and finally “goes off,” causing the transition!

But no such mechanism has ever been found. QM has had an unexcelled record of accurate predictions, without any need for such a mechanism…” -George Mason University physicist, Robert Oerter

So is the excited atom a random generator or is it something external that triggers the release of a photon? It seems like it’s something external, and this external trigger might be the unphysical connection to a future receiver described by the advanced solution to Maxwell’s equation of electromagnetic radiation.

So it seems to me like we currently can’t be sure if a photon is always emitted against a receiver, or it is emitted randomly in any direction into space. But this question might be one of the most important questions ever asked, because if an electromagnetic wave is always connected to a receiver the implications are vast. It could shed light on the discussion of many topics. It might change our view on time and space. It might not only be the past pushing the present forward, but the future pulling on the present, making a syntropy which will create order out of chaos, and describe the marvelous universe we live in. Even the view of the present itself as a sharp line between the past and the future could be questioned. Time itself might not be totally linear, and the future may change the past. To avoid paradoxes with time travel we have to allow a number of parallel universes, as suggested by American physicist Hugh Everett who formulated the idea of their existence to explain the theory that every possible outcome of every choice we have actually does happen.

But before we can fully dive into all these fascinating questions, we have to solve this question:

Does an electromagnetic wave always have to connect to a receiver?

This hypothetical question might seem purely philosophical, but it is not. And it might even be confirmed by observations. We can’t directly observe non-received photons, but we might indirectly observe the existence or nonexistence of these photons. Any answer or suggestions are most welcome.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

The Cosmic Microwave Background includes photons that will not be absorbed before the universe inflates to the point where there is nothing to hit ever again. If parts of the last scattering were somehow barred from releasing that energy, I think we would notice.

The photon carries energy. Particles do that. How is it any different from the electron, which is allowed to exist without complaint? If a flashlight (or photon rocket) emits particles bearing momentum, it recoils without any regard to what happens to the exhaust later elsewhere. I wonder if the problem is getting confused with non-radiative energy-bearing fields and so-called "virtual photons"? A charged object won't react without another charged object exchanging virtual photons with it.

Answer 5

First of all, the "point of view" of a photon is not well defined. One can not use a Lorentz transformation in order to get to the rest frame of a photon.

Furthermore, a photon is a physical entity of its own which can exist independently of any receiver. In principle, it can go on "forever" without ever being absorbed by something.

Regarding the tree in the forest: Suppose I throw a baseball as far as I can into empty space. Even if I never hear about it again and even if nobody catches it, it is nevertheless real.

Answer 6

yes this is how things are... on the other hand the QED makes it more clear (having Feynman started from the absorber theory to get into QED). However, in this regard, I can suggest two experiments that indicate that this is actually the correct direction of interpretation: the Purcell effect (I have a paper entitled <>) and <>