Gravity, it's not a force!

[Ali Quadir]

GRAVITY IS NOT A FORCE

The last few weeks he's had moments of cycling through Amsterdam with a grin on his face the theoretical phycisist, Erik Verlinde (47) international expert in string theory, admits. Inside was the mixture of disbelief and euphoria. After all, how often as a physicist do you get the idea that you really discovered something no man has ever seen? And this with only a ridiculously little amount of calculus.
The only thing that's now becoming scary is the idea that someone else could beat me to publishing it, he says slightly nervous. "My friends tell me I should hurry up. But I have to be precise. I'm sticking my neck out pretty far."
Last wednesday Verlinde gave his first complete review to his dutch colleagues on a meeting at the Spinoza-institute for theoretical physics in Utrecht. The lions den, home base of nobel price winner Gerard 't Hooft, who is Verlinde's old Promotor.
In certain ways a baptism by fire for a potentially revolutionary new insight, Verlinde says. Especially because he partly bases himself on ideas by his Promotor about space, time and black holes.
On the blackboard in his study on the Roetersisland in Amsterdam Verlinde with chalk in hand told us the story in 10 minutes with an astonishing punch line in the form of a very well known formula: Newton's law of gravity. The formula states that the mass between two masses is equal to the product of both masses divided by the square root of their distance.
Isaac Newton wrote down the formula in 1687 for the first time, together with two other fundamental laws for force and motion. He based himself on planetary orbits like Johannes Kepler described them in 1609 for the first time.
Since that moment all school kids over the whole world learn to use it for calculations. Only in 1916 Albert Einstein added the relativistic dimension to it, where gravity is described in terms of a curvature of space and time.
Beautifull physics, Verlinde says, but with one fundamental problem: Physicists can completely describe gravity, but no one knows what this attraction really is. How it works is known, but why do two masses attract each other? And why does this force refuse to be described by the theory for the other forces between particles? Verlinde's revolutionary claim is that this because gravity is not a basic element of the universe.
According to his theory force exists because of a concentration differential in information in the empty space between two masses and outside of them. Verlinde: "I don't see gravity as something fundamental. It is an emergent property that arises from a deeper microscopic reality. On the tiniest level the laws of Newton play no part, but they do for apples and planets. Compare this to the pressure of a gas: molecules themselves have no pressure, but a container full of gass does. Or water. Watermolecules are not wet, yet a drop or a glass of them is.
Verlines derivation of this insight is not easy to follow for a laymen, but for colleague theoretical phyisicists it is almost ridiculously simple. With only a few basic insights from quantum physics and ideas about black holes, and without any serious math, Newtons formulas just show up.
"People who I show, in the first instance become a little giddy", Verlinde tells, "as if I'm pulling a phrank on them."
But this isn't true, he is convinced of this after months of thought and reexamining, among others in discussions with his twin Herman, also a prominent physicist and connected to Princeton University.
Now that he's putting the last hand to an as elegant as possible explanation and a quick publication, his thoughts also head out towards the large problems surrounding physics, which physics still knows.

Big bang.
Hopefully, Verlinde says, his interpretation of gravity can give us a more acceptable image of the big bang. Right now the supposition that the whole galagy started with infinite density in a single point. For a theorist this is an uneasy fact, Verlinde says. We don't calculate well with infinity. He has not figured out an alternative yet.
Another matter is the so called dark energy, a kind of anti gravity which seems to cause the universe to rapidly expand, but of which no one knows what it is. The information theory of gravity must also be examined in this light he expects.
"If it will yield results I do not know", verlinde says. It's certain that physics with the current insights had not come closer to a real solution for this cosmological riddle.
Interesting, but especially ironic, is that the laws of gravity turn out not being a fundamental theory, but rather a statistical theory about the behavior of a collective of individual parts, like thermodynamics or quantum theory. Verlinde: "I think einstein will roll over in his grave. God does not play dice he said. And now even his beloved gravity turns out to be a statistical representation of something deeper.
It is big insights with complicated consequences, twin brother Herman states from Princeton. "But this certainly is a very deep idea."
Theorist and KNAW-president Robbert Dijkgraaf: "Erik puts the world upside down. Known formulas are derrived from new physics. But that is exactly what you need for a breakthrough."
Last news is that 't Hooft called the work intriguing. Verlinde is clearly relieved about this.

TAKE ONE BLACK HOLE AND ONE HOLOGRAM
Erik Verlindes derivation of Newtons classical mechanics depends on an older idea of his tutor and Nobel price winner (1999) Gerard 't Hooft: All information about all parts in a physical system are as it were stored in a hologram in a ball around it. This prediction touches the theories of Stephen Hawking about the surface of black holes.
Take a black hole, a mass so big that even light cannot escape from it if it crosses a certain horizon. According to the theories of Hawking this spherical horizon has a surface which is equal to the amount of information that vanished into the black hole. This horzion is not mathematically smooth; there is a minimal uncertainty about where it is. This is because in the quantum world nothing is exactly certain. This uncertainty, Hawking explained in a famous claim that black holes have a temperature and therefore radiate energy.
According to 't Hooft in the same way around each mass M a kind of hologram can be envisioned, a screen on which all the information about it's content is stored in the shape of bits. The energy inside the sphere is neatly divided across the bits on the screen. For this reason even the imaginary holographic screen has a temperature. This imaginary temperature is, according to Erik Verlinde, the key to gravity that a mass m experiences from a mass M.
If a particle with mass m moves from one side of the imaginary screen to the other side, the infomration-content of the sphere changes with one bit. This change times the temperature of the screen according to Verlinde is the energy transfer of the system. This energy change must be created during transfer. He who wants to move the particle, always feels this as a force towards mass M.
So far the conceptual story, which completely depends on thoughts about information and energy within a physical system and what changes mean in such a system. The crucial fact is that transfer of mass causes information change which costs energy, and this expresses itself in gravity.
Verlinde combines some simple formulas for energy, information-content, temperature, surface and bitcounts, and discovers almost immediately two classical laws by Newton.
The first is the law of acceleration F=ma: force equals mass times acceleration of a particle with mass m.
The second is Newtons gravity law which states that masses M and m attract each other on a distance R with a force related to the masses and inversely related to the square of the distance.

M. van Calmthout

A quick translation, I think I stayed true to the information. But I may have made some specific field related translation errors here and there. This is an article from a dutch newspaper as it appears on Verlinde's site.