I suspect that gravity manifests as a force but does not stem from the same underlying drivers as other forces.
Yeah, this fact made me cringe at explanation #2: the guy keeps saying things like "gravity is the only force that is felt by all kinds of matter". Stuff doesn't "feel" gravity; it's not a force, it's just the shape of spacetime. Also, gravity doesn't just affect matter; photons are not matter, but are affected by the curvature of spacetime (i.e. gravity).
/me not a physicist; but I'm not a baby either, and I don't appreciate babytalk oversimplifications.
Here's a colloquium talk[1] and here's a recent paper[2].
Not exactly what you said but perhaps interesting.
As mentioned it's work in progress so remains to be seen if the idea pans out.
Everything we can’t explain recently has people, who I assume don’t know how to say I don’t know, proclaiming “it’s emergent”. As if that’s an answer to anything. Much less a claim to knowledge.
Might as well claim “god made it happen”.
That's the opposite of what emergent means, isn't it? Because of force on the transmission, you can say that the motion of the vehicle is emergent rather than needing its own framework or explanation.
It's not wishy washy, it has a precise meaning that can be both derived and, typically, refuted.
If you say that spacetime is emergent that is a big deal: it means that, while it can be studied on its own, it's actually composed of other, more fundamental things. But you still need to show that
a) this other fundamental thing actually exists, and
b) we can show mathematically how the spacetime works, in terms of those other fundamental thing (just like you can show how thermodynamics works in terms of statistical mechanics)
And that's where your "because you don't know how it works" thing breaks apart: one can't claim to have solved this problem without tacking b).
Then explain those things and prove they exist. Otherwise this just sounds like bullshit.
There’s a difference between observing thermodynamics (and not trying to answer why but rather how we observe it - big difference!) and writing equations we can measure and just saying “it’s emergent” to “…” things we are unable to answer “I don’t know to”.
> Lee Smolin is working on an idea where the building blocks are events where momentum is exchanged.Space, and hence position, is an emergent phenomena.
It’s perfectly OK to speculate that perhaps gravity, say, is not fundamental, but instead emerges from interactions or whatever at a lower layer that we haven’t yet identified.
What word would you use?
Yet it is very compelling bullshit that stands up to intense scientific scrutiny.[1]
[1] https://einstein.stanford.edu/content/relativity/a11332.html
[1]: https://arxiv.org/abs/1307.6167 (section 2.2)
I think looking down to the start of §6 of your [1] is even more fruitful than §2.2:
"... novel form of dynamics that can be applied to a unique system -- the universe as a whole [--] that is neither quantum mechanics nor general relativity[,] from which quantum physics and space-time emerge as approximate descriptions of systems that may be regarded to a sufficient degree of approximation as isolated subsystems."
Or, more succintly and focusing on the gravitational content, "the Einstein Field Equations may be derived for some part(s) of a universe described by our theory", with the additional constraint, "but our theory cannot be derived from General Relativity".
Compare with Newton's gravitation and its ability to be derived in the weak field, low speed limit of General Relativity (and that physically interesting generally curved spacetimes have large regions that are effectively flat).
Generalizing, a theory of gravity is emergent when its fundamental equation(s) can be derived from a different dynamical theory, and the derivation is a one-way street.
However, "emergent" gets used in a different sense only a few paragraphs later in [1]: "Time reversal invariance is amongst the symmetries that must emerge from the coarse graining that neglects the unique identity of each event. From our perspective fundamental physics is time asymmetric and the apparent time symmetry of the laws of nature is approximate and emergent."
In this case they are not strictly speaking deriving time symmetry from their dynamical theory, but rather they are claiming that averaging the behaviour of their theory across some region(s) matches observation.
I think it helps to see an easy example first.
Take a great body of water (h2o) on earth, such as the ocean. That water has waves and those waves have amplitudes, as well as other properties such as crests.
A molecule (or even a few) of water (h2o) doesn’t really have these properties. It doesn’t have crests. You could argue it has amplitudes. Crests are an emergent property of large masses of water molecules within a specific system. There’s no crest to a water molecule.
Similarly, for demonstration purposes we could say there’s no waves/crests when gravity is removed.
So when I hear emergent, I imagine properties that show up under certain conditions within a system, that were not present in individual components.
It is kind of hand-wavy and you often find the phrase 'holistic' in the same paragraph as 'emergent', which reflects that it's a kind of pushback against entirely reductive approaches, but it really just means that if you want to reconstruct a complex entity (like an automobile) you can't just count up the parts, at each stage of reduction you need to save this set of information describing the relationships between elements if you ever want to reconstruct the overall system from the most fundamental components.
It's essentially just an abstraction, I think. The justification is that you can wrap up complexity into hierarchies of little black boxes that have predictable behavior. E.g.
https://guava.physics.uiuc.edu/~nigel/courses/569/Essays_Spr...
>"The idea of emergence in physics is pervasive especially in condensed matter and cold atom physics. For example, superconductivity and superfluidity are both described by a condensate, which is an emergent state of matter with finite fraction of particles in the ground state and long range order."
The suggestion here (further developed in above paper) is that spacetime is also a kind of 'effective description' based on some other underlying microscopic organized structure, which is a theory that's likely hard to test.
Sort of like how all the parts of an engine, even when connected, do nothing if fuel isn’t being pumped through. We can not proclaim we have knowledge of the engine by simply understanding many of its parts but failing to grasp how fuel moves through it. And instead say when these parts are together motion “emerges” and believe we are profound.
We haven't stopped studying consciousness after having concluded that it's a phenomenon that emerges from brains and their neurochemical environment by studying the pieces.
I feel like your critique is fundamentally misguided.
Here we discuss a sharp definition of the narrow concept of emergence in physics; we give a mathematically precise meaning to the notion of ‘qualitative difference.’ We propose the following:
An emergent behavior of a physical system is a qualitative property that can only occur in the limit that the number of microscopic constituents tends to infinity.
Which is essentially the opposite of what you mention (vanishes when looking at the microscopic constituents).
> "Critical phenomena represent another distinct form of emergent properties."
A single water molecule won't undergo observable sharp phase changes from ice to water to steam as the temperature is increased, so the emergent property vanishes when looking at the (isolated) microscopic constituent.
Emergent properties are definitely a thing. The reason you’re hearing more about them is because we’re paying more attention to them in lots of domains, one of the most recent and date I say common around these here parts, being the study of “intelligence”.
When you think about it a wave is not so different from anything else that exists. Yesterday's rock is tomorrows top-soil, before it becomes part of a plant, after which some of its former constituents will seep back into the ground while others take to the skies. In the future, all of these components might meet again to form a new rock.
All of these things are emergent and evanescent. Their properties can hardly be predicted from the sum of their parts. When you think of it, there are many words for concepts—'liberty', 'inflation', 'boredom', 'exaggeration'—that are essential to the human experience and can even be partly made measurable, but that do not have any manner of physical reality.
That’s not true. We know when water boils, we know tension laws, we know a ton to predict and define the interactions.
We know how to add carbon to iron, we know how make glass withstand huge loads. We know material limits because we rely on those material limits to build our world.
We choose to ignore those limits, the outcomes, the effects, climate change, earth is round, smoking is bad for you, etc.
If we wanted to know that chemical reaction takes place in your body that makes you feel boredom, I am sure we could, we figured out cocaine and pain killers, there is just no profit in making a boredom pill.
The world is not as romantic as poets make it out to be. Sun goes up sun goes down never a miscommunication. Complex, sure.
https://cse-robotics.engr.tamu.edu/dshell/cs689/papers/ander...
An example would be the centrifugal force, which "emerges" from basic Newtonian inertia.
Or the skin effect in AC electrics which (like pretty much ALL of circuit theory) is just a consequence of a few electrodynamic laws (Maxwell etc.).
But just knowing the basic laws does NOT mean that we can grasp all of the emergent behavior that necessarily follows-- physics => chemistry => biology would be the same thing, otherwise :P
However if you take a look at cellular automata, which are artificial and thus completely defined, it's much clearer that complex "emergent" behavior really can result from nothing but very simple rules.
you should probably read over https://en.wikipedia.org/wiki/Emergence to convince yourself that emergence as a distinct concept is a useful abstraction to have
There's promising math behind the idea that there are multiple additional dimensions, but where are they? How can we perceive them? What do they have to do with gravity?
The unifying theory of dimensional geometry and interaction: https://youtu.be/fvqXshyuvOg
i.e. it's force and acceleration that cause it, not gravity.