6 Feb 2010 20:22:47 UTC

Topic 194763

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I have a hard time getting my head around this...

Maybe somebody can give a little enlightenment..

There are some who can live without wild things and some who cannot. - Aldo Leopold

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## New look at gravity..

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That looks to be a nice thought game that is trying to turn around the presently accepted cause, effect, and association for the "force of gravity".

It does give a very good question of: What if gravity is not a fundamental force of nature, but is instead merely something that we observe as a consequence of, or is associated with, other effects?

Could there be a 'force' associated due to the arrow of time of change of entropy?

Note also that Terry Pratchett gives a convincing argument that the entropy described for the state of a gas in a volume is NOT the same entropy presumed for matter in the universe, just as that is not the same entropy as formulated for data bits in information theory. The formulae may share the same pattern of terms. However, the physics is very different!

Keep searchin',

Martin

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## I've read that it was John

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I've read that it was John von Neumann who suggested to Claude Shannon the term "entropy" for a quantity in his theory of communication. But this does not mean that it can be identified with thermodynamic entropy (modulus a minus sign).

Tullio

## Hi! If I understand all

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Hi!

If I understand all this correctly (which I'm not certain of at all...) then already Ralativity (as opposed to Newtonian physics) indicated that gravity is in fact indistinguishable from a pseudo force (forces like Coriolis force that depend on the coordinate system you choose) if you just pick the right geometry to describe space (or rather space-time). At least that's what I think the last part of chapter 12-5 of the "Feynman Lectures on Physics" is about, so the idea itself that gravitation isn't a "fundamental force" is not new. I guess the link to thermodynamics is.

Right?

CU

HBE

## RE: ... already Ralativity

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If you were to be inside say, an elevator, what you feel whilst standing inside the box for your body weight would be indistinguishable from whether the elevator was static at the surface of the earth, or whether it was onboard a spaceship in deep space accelerating at 9.8m/s2.

So indeed, the 'force' of gravity is indistinguishable from the same force experienced due to acceleration.

Are those two examples actually one and the same phenomenon, or a game of pseudo forces?

Also note that we have:

force = mass * acceleration

energy = mass * (speed of light)^2

and mass (energy) 'distorts' space-time that we also observe as 'gravitation'.

Regards,

Martin

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## Well, he's my try at

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Well, he's my try at interpreting the paper:

- you have entropy and it's tendency to globally increase.

- anarchy rules. If something can happen it will.

- this makes the universe more messy, a greater occupation of states, with time. [ So an atom with an electron in an excited state is simpler than an atom in ground state plus emitted photon. Take care with defining the system boundary. ]

- any given system has a ( macro ) state to which it tends with time.

- to keep the system off this state you have to supply energy, which you can envision as a force to be applied over a distance(s). Pull things apart to stop them collapsing ....

- a force ( whatever it is actually ) can be summarised as 'entropic' if it opposes your attempt to separate things.

- ergo if we keep systems away from their entropic maxima then we are applying/opposing a force to achieve that.

- one assumes a holographic principle, that a volume's information can be stored on it's bounding area.

- then all distance changes b/w contained objects is reflected as an entropic change on the bounding area.

- black hole horizons ( from afar ) behave like holographic screens.

- black holes are caused by gravity.

- the force opposing ( negative ) entropy changes is gravity.

- ergo gravity is an 'entropic force'.

The Newton's Law of Gravity comes out of the maths simply because in flat space, for a sphere, the rate of change of volume with radius is the surface area! [ V = (4/3)*PI*r^3 and A = 4*PI*r^2 so dV/dr = A ]

from memory ( Berkenstein? ) derived the black hole horizon area + entropy thing by applying that logic in reverse. So I guess this guy has cranked the logic the other way, showing that the implications are two-way.

Could one explain electromagnetism this way? The inverse square of Coulomb's Law seems ripe to pluck, just by coping with the direction of lower energy according to charge types ( apart from the sign, dV/dr = A is still true ).

As it stands I don't see anything 'new', and like many propositional systems one can invert what are axioms vs what are derived.

The entropy/information link is that one has to choose a representation for any data. That representation must have physical differences ( at the basic level storing 0's and 1's ) to distinguish. There is an energy cost to transit between the states ( otherwise they'd be degenerate and you couldn't tell the difference ). So you interact by putting-in/taking-out energy ie. using a force .... etc

Cheers, Mike.

( edit ) So the squirrely bit becomes, say, the nuclear force. It ain't inverse square for sure, at least not in a Euclidean Universe. What geometry would respect dV/dr = A for that context? I'm allowed to be cheeky by asking that as the bulk of the author's logic is not gravity specific ...... can I predict ultra small scale spacetime structure on or about nuclei by starting with a force that is virtually constant with distance? [ fully specifying dV/dr is another way of stating the geometry ] Or does the radioactive decay of a nucleus have no effect on the entropy of the bounding volume? If it doesn't then we are going to trip over and get fully reversible perpetual motion engines ...... :-)

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## Is a black hole considered a

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Is a black hole considered a 2D Object?

There are some who can live without wild things and some who cannot. - Aldo Leopold

## RE: Is a black hole

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Not the black hole, the event horizon. It's the surface of a sphere, and so has two dimensions.

GruÃŸ,

Gundolf

Computer sind nicht alles im Leben. (Kleiner Scherz)

## Note also that even though

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Note also that even though all the 'information' inside a sphere can be 'holographically imaged' on the surface of that sphere, that is merely an abstraction. It might let us gain an alternate insight to describe some effects holographically or in terms of 'information theory'. However, the real test is whether we can make new predictions of reality from that.

Reality for us is still just as real.

Another question for gravity (and time): Is it quantised?

And even if it appears to be quantised, is it really quantised or is the apparent quantisation just an artefact of our methods of observation?

Would not the holographic view require that everything inside the sphere is quantised due to the quantum limits of the holography...?

Regards,

Martin

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## RE: Note also that even

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I think I remember reading that it places a cap on the maximum density of a black hole - the event horizon 'shows' all the information contained inside, and it can't be packed anymore densely than the planck length. Is that right?

## A Planck length long by a

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A Planck length long by a Planck length wide get's you a Planck area. As thick as two short Planck's .... :-)

With or without a factor of PI, 2 or 4 or even G ( depending on who you ask ) gives you a bit's worth of information/entropy.

But, as Martin says, this is an abstraction. The idea of reconstructing the state of the interior of a volume from it's bounding surface is a derivation. It's a bit like a magic square, or the inversion of a matrix as per computerised tomography. It's sounds like a cheat in that one can 'compress' volume information to an area, but it is important to understand that you have to have an algorithm to do that. So :

Volume information = Area information + algorithm

thus you've 'hidden' information in the presence/complexity/need for an algorithm. As programmers know one can often trade executable size for data file size ( thus speed for memory generally ). Take zip/unzip technology for instance ....

Cheers, Mike.

( edit ) And when Mr Kaku wants to represent a Theory Of Everything by an equation 'a few inches long', he is hiding a huge interpretative machinery to unwrap the content for a given application. It's like saying everyone's phone number is actually just one number :-> directory assistance!!!!

Hence my earlier comment about system boundaries, which applies also to the 'intellectual volume' to operate a theory within. Adding an arm's length, or three, of de-referencing doesn't alter the physical content one wit. So we still need engineers to build our actual bridges. :-)

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal