# B Proof photons exist?

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1. Dec 4, 2015

### entropy1

This may seem an odd question, but I'd really like to find out: is there proof that photons actually exist?

2. Dec 4, 2015

### newjerseyrunner

Well, we can produce and detect individual photons. Google the double slit experiment, light always shows up in packets.

3. Dec 4, 2015

### entropy1

Yes, I know. But I was wondering if that could be explained by the packets being an artefact of decoherence in the measurement apparatus that 'flips' to a certain measured value...

4. Dec 4, 2015

Staff Emeritus
No. Proof is a mathematical term, not a scientific one.

5. Dec 4, 2015

### entropy1

So the existence of photons is an assumption or something? (can't find the right word. )

6. Dec 4, 2015

7. Dec 4, 2015

### Staff: Mentor

It is an assumption that has an extremely high probability of being correct.

We have experimental results that suggest that electromagnetic radiation always delivers its energy and momentum in discrete lumps at a single point when it interacts with matter. These results might be "an artifact of decoherence" if different detection technologies all happened to have different artifacts that somehow ended up yielding the same $E=h\nu$ relationship between frequency and energy delivered per chunk. However, we wouldn't have artifacts of decoherence unless we have decoherence, and we wouldn't have decoherence if we weren't using QM, so we're accepting at least parts of QM. And if we just apply QM to electromagnetic fields, we find that QM predicts the existence of quantized disturbances of the field that interact with matter, including our measurement apparatus, in exactly the way that we have observed.

So there are two interpretations of these facts:
1) QM is right enough to produce these "artifacts of decoherence" AND these artifacts exist (although no has presented a rigorous description of them that predicts any experimental results) AND there's something wrong with QM when we apply it to electromagnetic fields, such that the prediction that photons exist is wrong AND no one has noticed the error in the math in the past 75 years AND all of the many different experiments and detectors that we use to study the exchange of energy and momentum between matter are all flawed in different ways AND despite the different mechanisms the flawed results all happen to be consistent with the quantum electrodynamical prediction.

2) The things our instruments are detecting are the photons that QED predicts.

I can assume that #1 is correct, or I can assume that #2 is correct. I can't prove anything.... But I know which way I'm betting.

8. Dec 4, 2015

### entropy1

I get that! Has there ever been considered that photons may be artefacts of decoherence though? (wondering... )

9. Dec 4, 2015

### Staff: Mentor

Yes. You just did.

Now, if anyone were to go from "consider" to a quantitative calculation that matches the existing experimental support for quantum electrodynamics, and makes at least one testable prediction that QED does not... Then it would be part of the empirical science of physics. Until then, this thread is closed.