The Return of the luminiferous Aether
I think “aether” is one of those words that became socially radioactive in parts of the physics internet.
Not because the underlying idea is automatically foolish — but because a very specific version of it (a mechanical, wind-like medium you move through) ran into brutal experimental reality, and the word never really recovered.
What people originally meant by “aether”
The original intuition was almost unavoidable:
- Light behaves like a wave.
- Every inquisitive person knew sound, water waves, vibrations in solids needed a medium.
- So they asked: what is waving when light travels through “empty” space?
That “something” was called aether (or ether), from the ancient Greek aithēr — the “upper air” or “pure bright sky” that Aristotle thought filled the heavens.
The idea long predates modern physics, but it became scientific when optics became wave-based.
Huygens (1690) used an aether idea to describe light as a wave. Newton didn’t love wave optics, but even he entertained “aether” in different forms to explain forces at a distance. By the 1800s, once interference and diffraction nailed down that light really does behave like a wave, aether stopped being optional and became the default assumption.
The famous physicists who argued about it
This wasn’t fringe stuff — this was the centre of physics:
- Fresnel proposed a mostly stationary aether with partial “drag.”
- Fizeau tested that drag idea experimentally – a surprisingly modern piece of work.
- Maxwell built electromagnetic theory and initially pictured fields in a mechanical “sea” with vortices.
- Lorentz developed the most sophisticated aether theory: a totally undetectable stationary aether, with moving matter undergoing contraction and time effects.
- Poincaré sharpened the relativity principle, still sometimes speaking as if an undetectable aether might exist.
- Einstein rejected aether as a required mechanical medium in 1905… and then later did something that surprises many people: in 1920 he said you can speak of an “ether” again, provided it has no mechanical motion and no “wind,” and is essentially the physical character of spacetime itself.
That last point is one of the best historical jewels: Einstein didn’t treat the word as forbidden — he treated the old meaning as wrong.
Why the aether went out of fashion
The classical aether collapsed because its required properties became mutually contradictory.
To fit all the data, it had to be:
- rigid enough to transmit transverse light waves at enormous speed,
- yet offer almost zero resistance to planets moving through it,
- yet somehow allow no detectable wind,
- yet still be a real physical substance.
Then came the famous experimental blow:
Michelson–Morley (1887): the aether wind that never showed up
If Earth moves through a stationary medium, you should measure a direction-dependent light speed.
Michelson and Morley built an interferometer to detect that. The result was essentially null – no significant “aether wind.”
Physicists didn’t instantly abandon the idea. They tried increasingly elaborate fixes:
- FitzGerald–Lorentz contraction of moving bodies,
- Fresnel drag models,
- Lorentz’s full transformation theory.
Einstein’s 1905 move was to stop patching the medium and instead elevate the symmetry principle itself: the laws of physics are the same for all inertial observers, and the speed of light is invariant.
Once that worked spectacularly well, the mechanical aether stopped being necessary.
Why the word itself is treated so harshly online
In some corners of the internet, “aether” has become almost a swear word — a red-flag term that signals to many readers:
- a hidden preferred rest frame,
- a flowing medium already excluded by experiment,
- or a rejection of relativity without new quantitative predictions.
That reaction is cultural as much as scientific: people associate the word with a historical failure, so even modern discussions of structured vacuum fields get lumped in unfairly.
Ether vs aether: why the spelling differs
This is mostly linguistics and history:
- Aether is the classical Greek-derived spelling.
- Ether is the later simplified English form, and also refers to a chemical compound, which adds confusion.
Physicists usually say “aether” when discussing the historical concept.
What about neutrinos as an “aether” — wouldn’t Earth heat up?
Neutrinos provide a useful reality check.
They stream through Earth in enormous numbers — tens of billions per square centimetre per second from the Sun alone – yet hardly interact at all. Detectors have to be buried underground and made gigantic to catch even a few.
Because their interaction cross-sections are tiny, neutrinos pass through the planet with negligible heating. Energy transfer requires collisions, and neutrinos almost never collide.
But this highlights a deeper issue:
If something interacts so weakly that it does not heat Earth, it also cannot easily behave like the old-style aether – a medium stiff enough to transmit electromagnetic waves mechanically.
Neutrinos are ghostly particles, not an elastic substrate.
The modern “aether” that physics actually accepts: fields
What people often overlook is that modern physics already embraces universe-filling entities.
The Higgs field
The Standard Model contains a scalar field that fills all of space: the Higgs field.
Particles couple to it and acquire mass through symmetry breaking. The Higgs boson discovered in 2012 is the excitation of that field.
That’s about as close to a universal medium as one can get – but it does not define a rest frame or generate drag.
Vacuum energy
Quantum field theory also says the vacuum is not empty: every field has zero-point fluctuations.
In cosmology this leads to one of the deepest puzzles in physics: naïve estimates of vacuum energy differ wildly from the observed cosmological constant.
Again, the vacuum behaves like a physical object – but not a Victorian fluid.
Is there any serious argument for reviving “aether”?
Only in a very restricted, modern sense.
If “aether” simply means the vacuum has physical structure, then:
- quantum fields already do that,
- general relativity already gives spacetime dynamical properties,
- and Einstein himself said the term could be used carefully for spacetime in GR, stripped of any notion of motion.
The only revival that would matter scientifically is one that comes with:
- new testable predictions,
- consistency with Lorentz-invariance experiments,
- and a precise mathematical formulation.
Otherwise it is just renaming “fields.”
My bottom line
- The classical mechanical aether is gone for very good experimental reasons.
- The modern idea that “empty space” has structure is not fringe – it is mainstream physics.
- The hostility toward the word comes from history and internet culture more than from the concept itself.
And finally: Occam’s razor, Aristotle, and whether the word should retire
There’s a deeper philosophical reason the word “aether” keeps getting people into trouble.
Long before modern physics, Aristotle argued that nature should be described in the simplest adequate way — not cluttered with unnecessary entities. (Later medieval philosophers formalised this instinct into what became known as Occam’s razor: do not multiply assumptions beyond necessity.)
The classical luminiferous aether violated that rule in hindsight. Once Einstein showed you could explain optics, electromagnetism, and time dilation without a mechanical medium, the aether stopped being the simplest description. It became an extra, invisible structure doing no additional explanatory work.
But there’s an irony here.
We don’t actually deride the word because the idea of a physical vacuum is absurd.
We deride it because, historically, people tried very hard to say what the ether was – gears, vortices, elastic solids, drag models, partial entrainment – and every concrete version they proposed turned out to be wrong, mainly because they couldn’t really figure out the mechanics of it.
Each failure poisoned the word a little more.
So perhaps the sensible lesson is not “never talk about a substrate,” but:
be extremely careful about naming the substrate before you understand it.
That leads to an uncomfortable possibility.
It may be that the ultimate carrier of light is not literally “nothing,” and not a Victorian mechanical jelly, but some deeper quantum or geometric structure we haven’t finished uncovering yet. In that case, history might repeat in a subtler way: not by resurrecting Fresnel’s medium, but by discovering that the vacuum itself has microstructure we’ve only just begun to glimpse.
Which is why I sometimes think the word aether might need to be retired entirely – not because the underlying question is foolish, but because the word now comes with centuries of incorrect baggage.
The chance that there is something underlying the propagation of light – some field, some causal substrate, some structure of spacetime itself – has never really gone away.
We just learned, the hard way, that guessing too early what that “something” is can mislead you for a very long time.