Experiments Show Gravity Is Not an Emergent Phenomenon

[AcesHigh]

http://www.technologyreview.com/blog/ar ... 2/?ref=rss

Experiments Show Gravity Is Not an Emergent Phenomenon

The way gravity effects quantum particles proves that it cannot be an emergent phenomenon, says physicist.

One of the most exciting ideas in modern physics is that gravity is not a traditional force, like electromagnetic or nuclear forces. Instead, it is an emergent phenomenon that merely looks like a traditional force.

This approach has been championed by Erik Verlinde at the University of Amsterdam who put forward the idea in 2010. He suggested that gravity is merely a manifestation of entropy in the Universe, which always increases according to the second law of thermodynamics. This causes matter distribute itself in a way that maximises entropy. And the effect of this redistribution looks like a force which we call gravity.

Much of the excitement over Verlinde's idea is that it provides a way to reconcile the contradictions between gravity, which works on a large scale, and quantum mechanics, which works on a tiny scale.

The key idea is that gravity is essentially a statistical effect. As long as each particle is influenced by a statistically large number of other particles, gravity emerges. That's why it's a large-scale phenomenon.

But today, Archil Kobakhidze at The University of Melbourne in Australia points to a serious problem with this approach. He naturally asks how gravity can influence quantum particles.

Kobakhidze argues that since each quantum particle must be described by a large number of other particles, this leads to a particular equation that describes the effect of gravity.

But here's the thing: the conventional view of gravity leads to a different equation.

In other words, the emergent and traditional views of gravity make different predictions about the gravitational force a quantum particle ought to experience. And that opens the way for an experimental test.

As it happens, physicists have been measuring the force of gravity on neutrons for ten yeas or so. And...wait for the drum roll... the results exactly match the predictions of traditional gravitational theory, says Kobakhidze.

"Experiments on gravitational bound states of neutrons unambiguously disprove the entropic origin of gravitation," he says.

That's an impressive piece of physics. It'll be interesting to see how Verlinde and his supporters respond.

[Giorgio]

The whole idea of gravity as an emergent phenomena is contrary to our observations and Verlinde theory is derived by a twist of logic that does not hold once carefully analyzed.

It is well observed that gravitational interaction between bodies is related to the mass of the bodies. On the other hand an entropic force depends on the system property and not on the mass of the bodies that are part of the system.
It comes immediately clear that the idea of gravity as an entropic force is not supported by our actual observations.

Additionally, we can remember the connection between energy increase and entropy increase.
If we have energy increase than we can have an entropy increase, but a "spontaneous" entropy increase does not produce an energy increase.

So, the entropy increase of the system is caused by its energy increase and not from a tendency of the bodies to redistribute themselves so as to increase entropy. If this tendency does not exist than one cannot theorize the existence of an entropic force (no cause=no effect) and so gravity is not an entropic force.

Sorry for the long rant. Is 3:30 AM and I am suffering from insomnia.

[Giorgio]

Link to the original Verlinde paper for the one interested:
http://arxiv.org/pdf/1001.0785

[Tom Ligon]

There is a fond hope (not to be confused with a theory) that gravity is an emergent force, essentially a little leftover effect, of electromagnetism. This leads to ideas of anti-gravity boots and space propulsion systems which don't require rocket thrust. Cue the funny spinning disks.

I'll stand by while the scientific method sorts all this out, but I lean the other way. I personally believe gravity refuses to unify with the other fundamental forces because it is fundamentally different in kind. My own fond hope (not to be confused with a theory) is that gravity is the result of a level of physics we don't even suspect exists.

In fiction, I can weave a pretty good yarn that gravity is part of c-prime physics, which allows faster than light travel. In reality, I'd rather readers not analyze that too deeply. But I do like any theory that keeps gravity apart from the rest of the forces, and from being emergent from something mundane, because it keeps my particular fond hope alive.

I will point out that we're now dealing with two totally mysterious but otherwise well-accepted phenomena: dark matter and dark energy. We have no idea what they are, yet physics has pretty well bought into the idea that they are real. The first one makes gravity, and the second is essentially anti-gravity. Yet, we have not identified any demonstrable physics from which these arise. And I think we can say we really don't know what gravity is, either. Also, cosmologists almost universally accept that the birth of the Universe involved an instant of "inflation", the expansion of space FTL. A bit of handwavium follows saying it is OK for space to expand FTL, but within space nothing can travel FTL. This, for all the kids studying science today, is marvelous news ... there are still discoveries to be made in science, and they cover 95% of everything. At least!

One more little myth of modern physics bugs me. Because "action at a distance is spooky", we have an article of faith that forces must have a mediating particle. Thus, there must be a graviton. Yet, with the galaxy, and and our local group, and our supercluster all held together by gravity, I am expected to believe every particle of matter is exchanging gravitons with every other particle of matter in the Universe. Maybe the poor things run out of steam over 7 billion LY or so, and hence we have apparent Dark Energy. But if gravity is a distortion of space per Einstein's vision, why would we need mediating gravitons? Matter itself would be the mediator that distorts space. Gravitons are a tough sell for me. I'm OK with spooky.

[ladajo]

Sorry for the long rant. Is 3:30 AM and I am suffering from insomnia.

Stop talking to Joeseph. This obsession could be the root of your insomnia.

[Torulf2]

Some of the idea of emerges may have roots in the works of Ilya Prigogine. Prigogine mention the second law of thermodynamics as the arrow of time. In Relativity and quantum theory there is no preferred direction of time. But if the speed of light is insuperable this prevents information to travel back in time. For example, if you send high entropic mater back in time the entropy would decrees. A time machine contradicts the second law in same way as a perpetum mobile do. Also, if the event horizon of a bh dos not leak information you can decrees the entropy from putting entropic mater in a bh. But the second law is saved by the hawking radiation. Or as thermodynamics seen it, bh,s is saved by hawking radiation.
Threw relativity, time and gravity is connected and also time and the second law is connected. Its may have been natural for some people to try draw gravity from the second law.

[Skipjack]

Ilya Prigogine

Good man that!

[Giorgio]

Sorry for the long rant. Is 3:30 AM and I am suffering from insomnia.

Stop talking to Joeseph. This obsession could be the root of your insomnia.

Uhm.... I did talk less to him yesterday and actually slept more......
This might be the first experimental evidence of what can now be described as the "Ladajo theorem!"

[tomclarke]

One more little myth of modern physics bugs me. Because "action at a distance is spooky", we have an article of faith that forces must have a mediating particle. Thus, there must be a graviton. Yet, with the galaxy, and and our local group, and our supercluster all held together by gravity, I am expected to believe every particle of matter is exchanging gravitons with every other particle of matter in the Universe. Maybe the poor things run out of steam over 7 billion LY or so, and hence we have apparent Dark Energy. But if gravity is a distortion of space per Einstein's vision, why would we need mediating gravitons? Matter itself would be the mediator that distorts space. Gravitons are a tough sell for me. I'm OK with spooky.

While we are on personal casts on physics.

I am firmly of the belief that we still anthropomorphise physics too much. What I mean is that things which make sense to us macroscopically and are integral to our conscious view of the world, are thought to be somehow privileged, and stuff that behaves differently is therefore looked at with suspicion.

QM is the obvious much cited example of where our macroscopic ideas clearly do not hold.

But it is more fundamental. Many ideas current, from Cramer's Transactional Interpretation, brane theories, etc, cast doubt on whether spacetime as envisaged by GR has any prime mover existence.

If, as seems fairly clear, it does not, then a number of loved concepts become likely emergent properties and therefore broken in some situations:
existence of spacetime (as a way to measure stuff)
causality
locality
time
single reality

Of course some of these are now almost accepted broken (MWT QM now is I guess predominant). And theories breaking others are now mainstream.

But as far as particles go: Differential equations seem to me a very unlikely "prime mover" in all this. In which case action at a distance from classical fields seems equally dubious.

Particles obviously can be reinterpreted as some kind of discrete interaction, rather than a reality apart from their interactions. (Mead C.E. does this perhaps for photons - have not read it).

Gravity different from other stuff, fine. Could be. But gravity coming from differential equations?

My money is on gravity an emergent property from interactions of some sort which could (probably though not necessarily) be identified with particles.

Best wishes, Tom

[happyjack27]

random noise from the variances in the quantum interference patterns produced by a pair of "particles" in proximity will differ statistically in things such as amplitude and color at different points along the space surrounding and between them. this difference will be most pronounced in comparing the space between them versus outside them. in between them the probability of coherent -- if ephemereal -- (canceling or resonating) interference is higher than outside of them.

"mass" may simply be a measure of how noisy and/or sensitive to noise particles are. a sort of "bandwidth" if you will; one may be able to represent "mass" in units of bits-per-second.

[happyjack27]

"particles", through their position and momentum, carry information about where other "particles" are -- or, rather -- were.

the rate of decay of this information (as it's displaced by new information it recieves from other particles), as well as the rate at which it's communicated, is directly proportional the particles "mass".

indeed, the precision to which a particle's position and velocity (<-not momentum!) can be measured is -- quite simply -- it's mass.

delta(x)*delta(p) >= h/2
delta(p) = delta(v*m) = m*delta(v) (since m is constant)
delta(x)*m*delta(v) >= h/2
delta(x)*delta(v) >= h/(2m)

[Giorgio]

I am firmly of the belief that we still anthropomorphise physics too much.

What a beautiful way of expressing the egocentric plague that is infecting our race since the dawn of reason.
I fully agree with your post and I am also convinced that the day we will loose this attitude we will probably make a leap in understanding this universe we are living in.

[Betruger]

IMHO, intelligence enhancers (ie "transhumanist" type) can't come soon enough. We are struggling too hard with just what we have on our scientific plate already. And nowadays that's mostly within each field and sub/sub-sub fields. There's all the interdisciplinary wisdom IMHO mostly yet to be reaped in earnest.

[djolds1]

I am firmly of the belief that we still anthropomorphise physics too much.

What a beautiful way of expressing the egocentric plague that is infecting our race since the dawn of reason.
I fully agree with your post and I am also convinced that the day we will loose this attitude we will probably make a leap in understanding this universe we are living in.

You are wishing for the day we become gods. A fine metaphysical ambition, but don't confuse that with concrete reality.

IMHO, intelligence enhancers (ie "transhumanist" type) can't come soon enough. We are struggling too hard with just what we have on our scientific plate already. And nowadays that's mostly within each field and sub/sub-sub fields. There's all the interdisciplinary wisdom IMHO mostly yet to be reaped in earnest.

Plenty of nootropics available today as off-label uses of other pharmaceuticals. Get the scripts, or roll the dice with drug laws.

And wrt specialization, I think its the explosion of specialization that is both featherbedding and delusional. Its the profound simplicities that underlie physical and human reality, not the illusory and emergent complexities.

[Giorgio]

You are wishing for the day we become gods. A fine metaphysical ambition, but don't confuse that with concrete reality.

It couldn't be further from my thoughts, as I am wishing quite the opposite.

I am wishing for the day we will be able to look upon ourselves and the universe we live into and realize what our importance really is in respect of it.
I wish for the time when we will start to look at the universe for the way it really is and not for the way we like it to be.
I wish for the time when humility will be placed in front of the arrogant thought that we are enough smart to bend this universe at our will, while in fact we are still striving to survive on the crust of a single dust of sand lost in the vastness of what we call the milky way.

My belief is that the more we detach ourselves from the idea that we can become gods the more easy will be for us to improve our understanding.

And I also agree with Betruger on the point that we are starting already to struggle with a knowledge that is growing exponentially but randomly.
It seems like there are fewer and fewer people nowadays that are able to connect together all these interdisciplinary discoveries and to transform them in useful applications.