Our understanding of gravity might be completely wrong. If 85% of the gravity is unexplainable that seems like a pretty safe bet. Maybe it just behaves very differently at galactic scale.
Much like the aether, it seemed most likely that light traveled through a medium until it turned out that it probably doesn't.
The aether stuff confuses me. We replaced light traveling through some medium, the aether, with light traveling through a photon field which permeates all of space, among many other fields. That sounds like an aether by another name. Yet now we say aether theories of the turn of the 20th century types are debunked and everyone then was wrong. Yes the medium of a field is very different in nature than any classical ones (it's quantum after all), but the concept overall seems similar. Even when aether theory was in vogue it was known that the light medium would have to be very different than that of a gas or liquid (waves traveling without resistance).
So maybe this is being pedantic, but I just don't see how a field is not a medium. It seems like we found the medium and described it, then gave it a new name and turned around and laughed at our physics forebearers like they were ignorant geocentrists (slight exaggeration).
You are almost correct. The problem is that most of the people that laugh at aether only studied just a little of special relativity and wants to sound smart in the Internet.
The aether was a good idea, it was wrong, but it was a good idea anyway. Perhaps they exaggerated trying to model it like a solid/liquid and deduce the properties, so they got weird results, but it was common those days. For example, the first model of Maxwell used some weird mechanical elements. The mechanical part was useful to deduce the equations. A few years later he dropped the mechanical part and keep only the equations. https://en.wikipedia.org/wiki/History_of_Maxwell%27s_equatio...
The main difference between aether and a modern field theory is that with aether you have a preferred reference frame. Some things are not moving and other things are moving. Like in a lake with still water, the buoys are not moving, a moving boat is moving, and you can make some experiments to measure your speed of the boat relative to the water.
In the field that is used currently for photons (and other elementary particles) is different. You don't have a preferred reference frame. Any object that is not accelerating can be selected as a not moving object. But any other object that is moving at a constant speed can be also selected as a not moving object too. Any of them can be selected as not moving! But to compare the measurements in one of the object with the measurements in another object you must make some corrections. And the most important property is that there is no experiment that you can do to measure your speed relative to the field. This is related to the fact that light goes at the same speed for every "boat" here, even when they are moving at a constant relative speed.
So the field is like a magical fluid, even more magical than the aether. The important part is that there are accurate equations to describe all this handwaving and all the magical properties of both. The equations for the aether doesn't agree with the measurements in experiments, the equations of the field agree.
A medium can have independent dynamics (consider waves in a bathtub: you can pull the plug, or move the whole thing around; you can't do that with a fundamental field).
It is true that from a slightly different perspective, modern physics has arguably resurrected a kind of aether (think condensates in quantum chromodynamics) - it's just that said aether is Lorentz-invariant...
okay i'm not a physicist myself, but this is how i understand it. sound (ie pressure) waves require a medium to propagate through. the wave itself can travel over a long distance, but the actual particles involved are displaced only locally. now if you have a light and point it in a particular direction, the EM waves will propagate even through a vacuum. rather than local displacement of a medium, the photons themselves actually travel.
> Why do you think this hypothesis is simpler than the existence of matter we haven’t detected yet?
Scientifically speaking, if you can't detect 85% of something that you think is there, then you have to admit to the possibility that it does not exist.
For example, the original article has this poorly-phrased sentence - "Not finding dark matter in an experiment is not evidence that dark matter doesn’t exist". Clearly the writer does not literally mean what they wrote, because not finding something in an experiment _is_ evidence it does not exist.
It is pretty obvious something is going on, we have lots of highly suggestive data. As you point out there are lots of extremely plausible explanations. But until we have some direct evidence, then we are in a situation where there is no direct evidence that it exists. Therefore, it might not. That remains a very simple explanation.
As I was alluding to when comparing this situation to the aether, and as other commenters have pointed out, working on the question of what light was turned out to break time. Same thing might happen with gravity.
Much like the aether, it seemed most likely that light traveled through a medium until it turned out that it probably doesn't.