– http://www.youtube.com/watch?v=GFMfW1jY1xE

Less crazy than I thought – but he doesn’t really present or consider alternatives to the “baby universe” hypothesis – which seems to make little sense considering what wild speculation it is.

‘The Entropy Force’ (New Scientist)

The Entropy Force

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Verlinde’s work offers an alternative way of looking at the problem. “I am convinced now, gravity is a phenomenon emerging from the fundamental properties of space and time,” he says.

To understand what Verlinde is proposing, consider the concept of fluidity in water. Individual molecules have no fluidity, but collectively they do. Similarly, the force of gravity is not something ingrained in matter itself. It is an extra physical effect, emerging from the interplay of mass, time and space, says Verlinde. His idea of gravity as an “entropic force” is based on these first principles of thermodynamics – but works within an exotic description of space-time called holography.

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There is an arrow of time problem regarding why thermodynamics predicts future evolution but not past evolution, as Hanson and Tyrrell both correctly explained.

I’m sticking to my guns and saying its got something do with Occam’s razor and complexity. Hanson and you both rebutted me in the earlier thread by stating that Occam can’t be the solution because high entropy states can be very simply spcified, but I don’t buy it. It all depends on exactly how your complexity meausre is defined.

It’s Occam I’m telling you all. Universal priors are the answer. Of course, pinning down exactly why and how is where I’m running into a spot of bother

For every trajectory through state-space moving from high entropy to low entropy, there’s a trajectory moving from low entropy to high entropy. Why is ours one of the former rather than the latter?

Ignore this point; it is incoherent. We just define the direction of time on a trajectory to point in the direction of lower entropy. My second point above is the real one. By the 2nd Law, we would expect the present to be a local maximum with respect to both “temporal sides”. That is, we would expect both temporal directions on our trajectory to be “thermodynamic futures”.

That seems pretty trivial to me: you get analogs of the second law in practically any reversible cellular automaton that exhibits complex behaviour.

The issue isn’t the 2nd Law. It’s making the connection to an arrow of time. For every trajectory through state-space moving from high entropy to low entropy, there’s a trajectory moving from low entropy to high entropy. Why is ours one of the former rather than the latter? Or, rather, what justifies our belief that it is?

Given a state on a trajectory, the 2nd law says that its future is very likely to be high entropy. But the 2nd law also says that its past is very likely to be high entropy. For some reason, we think that there is countervailing evidence showing that our past was actually low entropy. But we also think that this evidence doesn’t imply that the future is low entropy.

What justifies this asymmetry? That’s the problem of the thermodynamic arrow of time.

That seems pretty trivial to me: you get analogs of the second law in practically any reversible cellular automaton that exhibits complex behaviour.

There is no “arrow of time problem”. Those who think there is are just in a muddle about the issue. The reason the psychological arrow of time and the thermodynamic arrow of time are linked is rather well understood.

But that’s not the really hard part of the arrow-of-time problem. Given a thermodynamic arrow, you can probably derive a psychological arrow. (This 12.5 minute BloggingHeads segment makes the case that it’s not as straightforward as many think, though.) The hard problem is closer to what salacious described—it’s showing why there’s a thermodynamic arrow in the first place.