Posted on 03/27/2010 11:06:22 AM PDT by LibWhacker
The new role that quantum information plays in gravity sets the scene for a dramatic unification of ideas in physics
One of the hottest new ideas in physics is that gravity is an emergent phenomena; that it somehow arises from the complex interaction of simpler things.
A few month's ago, Erik Verlinde at the the University of Amsterdam put forward one such idea which has taken the world of physics by storm. Verlinde suggested that gravity is merely a manifestation of entropy in the Universe. His idea is based on the second law of thermodynamics, that entropy always increases over time. It suggests that differences in entropy between parts of the Universe generates a force that redistributes matter in a way that maximises entropy. This is the force we call gravity.
What's exciting about the approach is that it dramatically simplifies the theoretical scaffolding that supports modern physics. And while it has its limitations--for example, it generates Newton's laws of gravity rather than Einstein's--it has some advantages too, such as the ability to account for the magnitude of dark energy which conventional theories of gravity struggle with.
But perhaps the most powerful idea to emerge from Verlinde's approach is that gravity is essentially a phenomenon of information.
Today, this idea gets a useful boost from Jae-Weon Lee at Jungwon University in South Korea and a couple of buddies. They use the idea of quantum information to derive a theory of gravity and they do it taking a slightly different tack to Verlinde.
At the heart of their idea is the tricky question of what happens to information when it enters a black hole. Physicists have puzzled over this for decades with little consensus. But one thing they agree on is Landauer's principle: that erasing a bit of quantum information always increases the entropy of the Universe by a certain small amount and requires a specific amount of energy.
Jae-Weon and co assume that this erasure process must occur at the black hole horizon. And if so, spacetime must organise itself in a way that maximises entropy at these horizons. In other words, it generates a gravity-like force.
That's intriguing for several reasons. First, Jae-Weon and co assume the existence of spacetime and its geometry and simply ask what form it must take if information is being erased at horizons in this way.
It also relates gravity to quantum information for the first time. Over recent years many results in quantum mechanics have pointed to the increasingly important role that information appears to play in the Universe.
Some physicists are convinced that the properties of information do not come from the behaviour of information carriers such as photons and electrons but the other way round. They think that information itself is the ghostly bedrock on which our universe is built.
Gravity has always been a fly in this ointment. But the growing realisation that information plays a fundamental role here too, could open the way to the kind of unification between the quantum mechanics and relativity that physicists have dreamed of.
Ref: arxiv.org/abs/1001.5445: Gravity from Quantum Information
BTTT
I don’t get it.
If gravity is a force of entropy, why does gravity cause things to be attracted to each other - that seems less entropic rather than more.
I don't think attraction is the correct term. I think in terms of "weight". The earth is not pulling you towards it but rather space is pushing you down towards its cog.
universe starts as singularity - more entropy - less gravity - things move apart - universe expands.
Why did the phrase, "In the beginning was the Word - - -", suddenly come to mind?
I would love to see and hear these physicists debate global warming with Al Gore, just to see himself sputter into the pool of his noninformation and inconvenience.
Agreed. Pardon my illiteracy, but, what is meant by “information”?
Which brings up the potential to "hack into" the transmission of the information and by definition control everything.
I'm not entirely sure this would be a good thing. I can think of a number of people who I don't want to have such control.
I think the universe still is a singularity.
It only appears not to be so by those who are in it.
That is why every particle is at the center of the Big Bang,just as they were at the Big Bang.
They are separated by time and momentum but have never reall moved relative to the universe’s event horizon.
That explanation is not based on physics. Gravity is an acceleration: the rate of distance per time squared. The only way an object can accelerate is by a force acting upon it such as gravity.
An object moving through space at a constant velocity has no acceleration. Therefore no force is acting upon it. To change its velocity, there must be an acceleration. To get that acceleration, a force must act upon the moving object.
The velocity at which the universe is expanding is increasing. That means there is an increase in acceleration. That increase can only come about due to a force.
I thought Einstein’s General Theory of Relativity proposed that gravity isn’t a force but a distortion of space-time caused by the mass of an object that resides in space-time.
I thought Einstein’s General Theory of Relativity proposed that gravity isn’t a force but a distortion of space-time caused by the mass of an object that resides in space-time.
Gore can't even understand the simple concept of equilibrium, he would blow a fuse trying to understand entropy.
You are assuming that the expansion of the universe consists in matter moving further apart in pre-existing empty space.
Rather it consists in the volume of space increasing over time. It’s hard to imagine it with space being three-dimensional, but down a dimension, space should be thought of not as 3-dimensional analog of an infinite plane, but of a closed surface (for simplicity, the surface of a sphere, say), which is increasing in area (volume in the 3D case) over time (like a balloon being blown up). What you say about accelerations and forces is about dynamics of matter within space (on the surface of the sphere in the dimension reduced analog) not about the dynamics of space itself.
In the beginning was Will and Idea.
The geometry of space due to gravity still results in an acceleration of mass. You can still use the formula for convenience: F = mg, where the force is F, the mass is m, and the acceleration g is gravity.
But let's not loose sight of the big picture. The universe is expanding at an increasing velocity. That means some force is accelerating it.
Quantum physics is the obstacle to the theory of everything. It’s sort of like a modern day flat Earth.
That is an inference you made. Conceive of space however you want. That doesn't change the facts of observation. The universe is expanding at an increasing velocity. That means a force is accelerating it. Hence the need to theorize the existence of dark matter and dark energy.
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