This post is a reaction to recent article On the Origin of Gravity and the Laws of Newton of dutch theorist Erik P. Verlinde. Albeit Verlinde is string theorist, his finding has basically nothing to do with string theory and it's logical connection to holographic model proposed is extremely vague here. When random gas exhibits entropic behavior, it still doesn't make it a hologram, some memory the less and it requires a huge portion of fantasy to interpret it in such a way.
Maybe string theory or holographic theory are related to entropy quantity in some abstract way (albeit I can see nothing entropic in their postulates with exception of vagueness) - but the connection of Aether gas concept to entropy is still much more straightforward and transparent (entropy quantity original derivation was based on Boltzmann gas concept). This is simply how analogy differs from vague homologies: by absence of additional manifolds in causal space.
"Starting from first principles and general assumptions Newton's law of gravitation is shown to arise naturally and unavoidably in a theory in which space is emergent through a holographic scenario. Gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations. When space is emergent even Newton's law of inertia needs to be explained. The equivalence principle leads us to conclude that it is actually this law of inertia whose origin is entropic".
If it smells like entropy, and it behaves like entropy, it's probably a Boltzmann gas...;-) We simply cannot have an abstract entropy quantity existing as such without underlying physical system (usually inertial particle gas or fluid), which maintains the laws of statistics. Emergence is just another postmodern word for ancient Aether model, described by gas (thermodynamics) or by fluid (hydrodynamics) models. Eric expressed it unvillingly in interview with the newspaper de Volkskrant:
"On the smallest level Newton's laws don't apply, but they do for apples and planets. You can compare this to pressure of gas. Molecules themselves don't have any pressure, but a barrel of gas has."
The same, just more vague conclusion former string theorist Lubos Motl got on his blog:
"I find it somewhat unlikely that "bulk physics" may be really derived without any "bulk physics".
While Motl's intuition was exceptionally right in this particular case, the above approach is exactly, what the string theory or quantum gravity did all the time (the formal strings or quantum loops, i.e. Aether density fluctuations are the same temporal aspect of dense gas behavior, like entropic character of energy shielding, i.e. the gravity). We should realize, comments of Mr. Motl aren't Aether theory motivated in any way - but by fact, Verlinde's rather insightful work has nothing to do with string theory. Mr. Motl just feels some competition of his pet string theory in the air. But the true insights concerning formal entropy models of elementary particles were achieved before few years in GUITAR theory of Quantoken.
Concerning "Newtonian physics", Newton believed, gravity force is indirectly proportional to distance with compare to R. Hooke, who claimed the inverse square law on background of former Alhacen's work. Just the Aether model of Newton's friend Nicolas Fatio de Duillier convicted Newton to change his opinion on behalf to inverse square law - we can see, Newton's physical intuition was far not so brilliant, as it's believed usually. Duillier's model was later extended by Le Sage and so far we have no other working theory of gravity based on physical, i.e. not completely abstract ad-hoced model, separated from observable reality.
The apparent inability of physicists to distinguish trivial particle system beneath all these noble abstract ideas about thermodynamics, entropy and emergent holographic scenarios is striking. Even worse, it's a sort of modern religion or political decision - supposedly the both. Other extrapolations of this work assigned to Verlinde (?):
"Gravity does not exist. The whole universe is a giant holographic memory that gets more and more filled with data as time evolves. This filling of the cosmic memory we interpret as gravity. What if the memory gets full? Than you find yourself in a black hole."
are bringing logical questions, whether these ideas are really consistent with present model of black hole as a physical singularity or whether gravity doesn't apply to interior of black hole, or whether it can not exist something, which we can measure reliably. After all, such naively abstract ideas separated from reality are typical for both many formal theorists of present era, both their layman interpreters.