(Audio version of this post for those who can’t be bothered to read it all.)
If you watch any pop-sci YouTube channel, you have probably heard the old story: physicists used to believe in this silly thing called the aether, but then the Michelson-Morley experiment disproved it in 1887, and Einstein replaced it with his theory of special relativity in 1905, which is “the most tested theory of all time.”
But this is historical revisionism and does not accurately reflect the reality of what actually happened.
The 1887 experiment was only intended to test aether models where the aether is directly detectable. Its negative result could imply the aether doesn’t exist, or it could imply it is only indirectly detectable.
Indeed, in 1904, the physicist Hendrik Lorentz put forward an aether model whereby the aether is not directly detectable, and thus was consistent with the Michelson-Morley result.
This model is mathematically equivalent to special relativity, and in fact Einstein’s 1905 paper was explicitly in response to Lorentz’s paper.
Since they are mathematically equivalent, the claim that “special relativity is the most tested theory of all time” makes no sense because no experiment can directly distinguish between Lorentz’s 1904 model and Einstein’s 1905. If you were to experimentally confirm time dilation, for example, well, both Lorentz’s and Einstein’s models predict that, so you didn’t distinguish them.
Einstein’s theory thus won out on philosophical grounds, not empirical grounds. Einstein had, at the time, the stronger philosophical argument: if the aether is not directly detectable, then maybe it doesn’t exist, so maybe we should try constructing a model which makes the same empirical predictions as Lorentz’s theory but without the aether.
And that is precisely what Einstein’s 1905 paper achieves. This convinced basically every physicist to abandon Lorentz’s ideas and adopt Einstein’s ideas.
So, if Einstein’s 1905 paper showed that the undetectable aether is not necessary to make the right predictions, what’s the issue? Why do I even bring it up? Seems like all of this is completely reasonable.
I bring it up because of a caveat Einstein was well aware of himself: Lorentz’s theory only renders the aether directly undetectable. It does offer a path under which its existence can be indirectly verified, and this bothered Einstein significantly, since he knew it would rule out his special relativity.
What is this indirect verification? The existence of Lorentz’s aether can be indirectly verified if we can provide any experimental evidence, at all, that nature contains, anywhere, in any empirical observation, non-local effects.
Why?
Well, if two events occur so far apart and in such quick succession that not even light can traverse the gap, then special relativity predicts that different observers can disagree as to the temporal ordering of the events, measured on their clocks.
If no effect can travel faster than light, then these disagreements about the temporal ordering of events are always causally disconnected, and so it has no real implications.
If an effect can travel faster than light, then the causal sequence can become out-of-order in some perspectives, leading to causal paradoxes and logical inconsistencies in the theory.
This is only true for special relativity, however, because Einstein’s theory treats the time-readings on clocks as equivalent to true, ontological time. Lorentz’s theory treats the time-readings on clocks as an emergent feature and not fundamental, and so it is perfectly consistent for two observers to disagree about what event happened first without there being a paradox, because one of them can just be wrong and the other correct.
Why is all this relevant?
Newton’s theory of gravity is unambiguously a non-local action-at-a-distance theory. Einstein knew that if he wanted his theory of special relativity to make sense, he needed to replace Newton’s theory with a local theory of gravity, and so he did precisely that: developing the theory of general relativity.
However, Einstein also realized quantum mechanics is a non-local theory, and tried for the rest of his career to replace it with a local field theory, but never succeeded.
In fact, in 1964, the physicist John Bell proved it is impossible to replace it with a local theory without contradicting its empirical predictions. As Bell concludes at the end of his 1964 paper, either quantum mechanics is wrong, or the states of particles cannot be Lorentz invariant.
If they cannot be Lorentz invariant, they must be Galilean invariant, which then returns us to Lorentz’s theory, as there is no absolute reference point in Einstein’s theory, so Einstein’s theory is incompatible with the requirement of Galilean invariance.
In 2022, the Nobel Prize was awarded for experimentally testing quantum mechanics and verifying that quantum mechanics is indeed not wrong, and, by extension, Lorentz’s theory must necessarily be the correct theory, as the existence of the rest frame of the universe has been confirmed indirectly through proving the existence of non-local effects.
Did physicists respond to this by revisiting Lorentz’s ideas? No! Because to do so would contradict the last century of ideology centered around the “revolution” that is special relativity.
So, instead, physicists took a different approach. Rather than agreeing with Bell’s own conclusion that his 1964 theorem shows that nature is non-local and therefore rules out “locality,” they instead claim that Bell’s theorem rules out “local realism.”
The implication here is that you could deny locality, but you could also deny realism.
“Reality doesn’t exist, but thank God it is local!”
Despite a weird common misconception I’ve seen thrown about, “realism” has nothing to do at all with determinism or randomness. It is about object permanence, the idea that observable objects with observable properties continue to possess observable properties even when they are not being observed in the instantaneous moment of observation.
Bell’s theorem does not assume determinism; it assumes merely that at least one of the particle’s observable properties still contains definite values even when not being observed, regardless of whether or not those values evolve randomly or deterministically.
The denial of realism leads directly to the “measurement problem,” because it creates a disconnect between the fact that you are claiming particles possess no observable (measurable) properties when not being observed (measured), but then this fails to explain why, when we try to observe (measure) them, they always empirically possess those properties.
This has led to a deluge of incoherent, incomprehensible papers on “interpretations” of quantum mechanics which all start with the premise that particles do not possess any observable properties at all when you are not looking at them and then work backwards from this conclusion to try and desperately make it coherent.
None of them succeed in this, and they readily admit they do not succeed in this. The popularization of statements like, “no one understands quantum mechanics” are all just passive admissions that these attempts to make sense of it in a non-realist framework are simply incomprehensible and nobody even knows what is being talked about anymore.
People use these kinds of phrases in an incredibly dishonest fashion. It gives the implication that quantum mechanics is objectively incomprehensible, and that is just a fact of life. But it’s not true at all.
As Bell pointed out in 1982…
[T]he subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated…that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice
That is to say, the supposed “incomprehensibility” of quantum mechanics, the insistence that it is impossible to understand, the hyper-focus on the observer, measuring apparatus, stemming from its non-realist premises, are not fundamental features of the theory, but are explicit theoretical choices made by physicists.
These explicit theoretical choices all arise from a desperate attempt to preserve locality. The 2022 Nobel Prize shows empirically that, if the particles possess observable properties when not being observed (realism), the experimental results are impossible to explain unless those properties influence each other in a non-local fashion.
That directly renders special relativity non-viable. But, physicists use a loophole where they just argue the particles possess no properties when you’re not looking at them.
You see, if you deny that anything exists when you’re not looking at it, then the only possible way to prove non-locality is to prove non-locality precisely in what you are directly observing, which requires you to send a direct signal, i.e., superluminal communication.
Under a non-realist framework, you can’t prove non-locality indirectly by showing merely that the results are impossible to explain without non-local influences if you did not directly observe those non-local influences. A non-realist framework only allows for the proof of non-locality if you can directly signal with it.
Of course, it has been proven for decades that quantum mechanics does not allow for signaling, so this loophole allows you to continue to claim quantum mechanics is local, but at the cost of denying that particles have real properties in the real physical world independently of you looking at them.
This denial of object permanence, the very basis of realism, then leads to all the absurd interpretations around the theory, interpretations which its own authors admit are entirely incomprehensible by continually repeating that “quantum mechanics is impossible to understand” over and over again.
Indeed, the complete incomprehensibility of these interpretations was proved in a paper by Frauchiger and Renner in the journal Nature titled “Quantum theory cannot consistently describe the use of itself.” They proved in a simple four-qubit circuit that every major interpretation of quantum mechanics is logically inconsistent.
The only one which they analyzed that wasn’t inconsistent was a realist interpretation, but when they applied this interpretation, they point out in the paper that the time-ordering of events matters, meaning you have to introduce an absolute time-ordering of events to resolve the inconsistency… meaning you need Lorentz’s model.
All of this nonsense is just a desperate attempt to preserve the dominant philosophical paradigm for the last 100 years. As pointed out by Bell in his paper “How to Teach Special Relativity,” Lorentz’s and Einstein’s views are mathematically equivalent, so changing from Einstein’s to Lorentz’s view does not require actually even changing any of the mathematics or the empirical predictions.
It is purely a philosophical reinterpretation of the same empirical results and the same mathematics, yet the reinterpretation allows you to avoid having to deny reality to make sense of violations of Bell inequalities, and to make sense of quantum mechanics in a trivially intuitive framework.
But, of course, if the distinction is only philosophical in nature and non-empirical, a lot of physicists just don’t care, since many aren’t particularly interested in philosophy and don’t really care to know anything about the natural world. They are more pragmatic engineers and just want to build stuff, so they just want to know what the math says and can’t care much about the ontological implications of said math.
If a person is a pure pragmatist, they wouldn’t care about this debate anyway, one way or the other. So this rant is largely on the side of people who do care.