We do know that "spontaneous emission" and other fundamental things are not completely physically independent. For example, we know that they can change their rate when mass is moving.
But there is no agreed-on conception in physics of what is happening at the quantum level, although there are a variety of competing heuristics, and each time one side thinks it has staked the other through the heart and nailed the coffin lid down, the lid flings off and the creature lurches back out grinning - and thus it has been since the first half of the 20th century.
Not a great deal of progress has been made since, mainly because many physicists have tried to stop talking about it, or have even contended that they don't need to talk about it, and a generation of physicists have spent careers in an environment that attempts to suppress such discussion (or, when it involves the most prominent physicists, to disown it as obiter dicta and personal musings on "philosophy", rather than serious work in the field of theoretical physics, whether it be correct or not).
EDIT: to anyone who disagrees with any aspect of this post, it would be helpful (for all our sakes) if you were to review the further discussion that was had on it, and to leave such further remarks as you may feel justify its contradiction.
Right of Reply: @EmilioPisanty makes some forceful points about the clarity of my assertions.
He makes the point that work in "quantum foundations" is ongoing in the field even if a settled resolution of the multiple QM interpretations has not been achieved. He differentiates between "progress" defined in terms of furtherance toward a resolution of a question, with "progress" defined in terms of the achievement of a resolution and a moving-on from the question. I should be clear that I use the word in my answer here in the latter sense. 800
He argues that, otherwise, the reader may well think no useful work is being done on the question at all!
He also argues that work was never totally halted in the field - a point on which I agree with him - whereas my original words are capable of implying that it stopped completely. On the contrary, it is only my position that work on "quantum foundations" was widely devalued in physics, and that therefore fewer physicists turned their time and attention to it than otherwise would have if it had instead been lauded as an important outstanding question in physics.
<PERSON> acknowledges that this "attempt to suppress" was made, but denies that it was successful, and denies that the attempt had any appreciable effects on the progress in this area of physics. Therefore, if the long-standing controversy over QM interpretations remains outstanding in physics, he argues is wrong for me to attribute this to "suppression". This remains a matter of difference between us upon which the reader would have to adjudicate.
EDIT: I'd also like to offer the following, from authors on either side of the issue, as particularly enjoyable reads:
<PERSON>, On Quantum Theory:
https://arxiv.org/abs/1308.5290
<PERSON>, Shut up and let me think. Or why you should work on the foundations of quantum mechanics as much as you please:
https://arxiv.org/abs/1308.5619 682