spacetime must organise itself in a way that maximises entropy

April 1, 2010 8:18 PM

Gravity from Quantum Information
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. (via mr)
posted by kliuless (33 comments total)

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.

Wait... so "The Secret" was actually right?
posted by Xezlec at 8:26 PM on April 1, 2010

Double?
posted by hippybear at 8:37 PM on April 1, 2010

Holy crap the comments page on that article is like Time Cube X 1000

What a bunch of loons.
posted by empath at 8:38 PM on April 1, 2010

Not a double, btw, this is a new paper.
posted by empath at 8:39 PM on April 1, 2010

Holy crap the comments page on that article is like Time Cube X 1000

Yeah, that tends to happen for science articles. My favorite science magazine, Science News, has this problem particularly badly.
posted by Xezlec at 8:44 PM on April 1, 2010

Worth it for the comments alone.
posted by KokuRyu at 8:44 PM on April 1, 2010

Materialist Analysis of Theoretical Astrophysics

The Capitalist Dictatorship Falsifies Basic Science!
Michio Kaku, Wendy Freedman, Dennis Overbye, Nicholas
Wade, Brian Greene, etc. Are Exposed as Liars!

It seems like the North Koreans are big fans of Technology Review...

The Capitalist Dictatorship’s Attempt to Falsify the
Age of the Universe to Help Provide False Belief in “god”

The capitalists have tried to falsify the actual age of the Universe and the infinite cycle of a Big Bang followed by a Big Crunch, meaning a closed rather than an open Universe, because the reality of a closed Universe does not fit with the religious brainwash of a single creation and belief in a supernatural fictitious “god.” (The statecraft of capitalism’s alliance with religion and belief in “god” and other superstition is exposed further below.) The reality is that the process of contraction of the Universe began soon after the Big Bang, which began the process of expansion. The process of contraction began with the first condensations of gas after the Big Bang. At first the process of expansion was dominant, but the processes of expansion and contraction exist simultaneously from shortly after the Big Bang until finally the process of contraction becomes dominant and all galactic matter is finally drawn into Supermassive Black Holes, which today form the centers of all spiral galaxies and elliptical galaxies in the process of becoming spiral galaxies. These Supermassive Black Holes, which are growing larger continuously, finally link up all existing matter of the Universe at one spot, one huge super-maximal Black Hole known as the Singularity in the Big Crunch, at which time critical mass in the true and ultimate sense is reached for another Big Bang Cycle and the beginning of another Universe.

posted by ennui.bz at 9:00 PM on April 1, 2010

okay, so i've actually read the paper now, and I understand a tiny, tiny portion of it.

I feel like both Verlinde and these guys are using circular reasoning (their entire argument seems to be about rearranging space time so as to maximize entropy at the event horizon of the black hole, which causes gravitational effects around the black hole. But doesn't the existence of the black hole and the event horizon itself pre-suppose that gravity exists? And what about all the gravity that exists with out black holes being involved at all?

I am not a theoretical physicist, though, I've just read a few books on black holes recently. Are there any around that can better explain what's going on here?

Actually their earlier paper which they reference is pretty interesting, as well. They propose that since the boundary of the observable universe can be described as a causal horizon, which functions similarly to the event horizon of a black hole, that 'dark energy' might be nothing more than the equivalent of Hawking radiation, except for the observable universe as a whole, rather than a single back hole.
posted by empath at 9:16 PM on April 1, 2010

So the Universe is an ever-expanding inside-out black hole? Huh.
posted by Slap*Happy at 9:32 PM on April 1, 2010

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.

I don't understand. Isn't information the emergent phenomenon? How can information be the "bedrock"? Is this related to the "universe is a hologram" theory?
posted by stbalbach at 9:52 PM on April 1, 2010

I thought Hawking lost a bet by arguing that information is destroyed in black holes.
posted by klangklangston at 10:21 PM on April 1, 2010

Isn't information the emergent phenomenon? How can information be the "bedrock"?

Please take what I'm saying with a grain of salt, because i'm not entirely sure that I understand this myself.

Information is physical.

We can theoretically know certain things about every particle in the universe -- it's location, spin, velocity, mass, etc. All of those things can be considered information. For the purposes of doing physics, the information about the particle is indistinguishable from the particle itself.

For a real world example of this, consider the case of a photon whose wave length is the size of the diameter of the event horizon of the black hole. This can be considered 1 bit of information striking the black hole -- basically the information is the photon itself. Shorter wavelength particles would also include information about where it hit the black hole, other particles would include even more bits of data.

When the photon crosses the event horizon, the photon contributes a certain amount of energy/mass to the black hole, which then increases the surface area of the event horizon by a certain amount. In the case of a single photon, I believe that the amount of the surface area that it's increased by is one Planck area (a standard unit of measurement in physics). It can be shown that the surface area of the event horizon of the black hole will increase in direct proportion to amount of information carried by any particle passing through it. It can also be shown that the entropy of a black hole is proportional to its surface area. In fact, the volume contained within the event horizon of a black hole contains the maximum amount of entropy possible.

This is where the holographic principle comes from. Essentially all of the information that passes into a black hole is somehow encoded on the 2 dimensional surface area of its event horizon, and since the black hole contains more information/entropy than any other volume, then any 2 dimensional surface surrounding a 3 dimensional volume somehow contains all of the information
which is within the surface.

Something like that, anyway. Please read Susskind's book (Black Hole War) for a more detailed explanation.

Is this related to the "universe is a hologram" theory?

Yes.

Is this related to the "universe is a hologram" theory?

He conceded his part of the bet to Leonard Susskind, but Susskind isn't sure that he rightfully won the bet, and Kip Thornley still isn't willing to concede the bet.
posted by empath at 10:38 PM on April 1, 2010 [5 favorites]

err, the last sentence was meant to answer klangklangstons' question about the bet.
posted by empath at 10:41 PM on April 1, 2010

any 2 dimensional surface surrounding a 3 dimensional volume somehow contains all of the information which is within the surface.

I can imagine that as a sphere. MRI medical scanners read the interior spatial volume from a cylindrical envelope. You'd think that a spherical arrangement, only at infinite resolution, should be able to image the interior.
posted by StickyCarpet at 1:48 AM on April 2, 2010

Maybe CAT scan would have been a better metaphor than MRI.
posted by StickyCarpet at 1:49 AM on April 2, 2010

ok, if I've understood empath correctly (and I dropped out of physics as a major in 1983) then what does this phenomena actually mean in the context of the "real world" we live in ?
posted by infini at 2:11 AM on April 2, 2010

oh man, please don't assume that i know what i'm talking about here. i'm just regurgitating what i recall from pop-sci books that i barely understood. I was kind of hoping an Actual Scientist would pop in.

The only practical application for this kind of thing that I can think of would be quantum computing.
posted by empath at 2:27 AM on April 2, 2010

that's kind of what I thought. does anyone know who is working on quantum computing out there in the 'real world' ?
posted by infini at 2:36 AM on April 2, 2010

Lots and lots of people. Billions of dollars are being thrown at it right now.
posted by empath at 2:47 AM on April 2, 2010

ah, and so this fpp may affect all that work? must go google mebbe
posted by infini at 2:59 AM on April 2, 2010

This video posted in the old thread explains a lot of this and is very interesting.
posted by delmoi at 3:35 AM on April 2, 2010 [2 favorites]

Maybe CAT scan would have been a better metaphor than MRI.

Only if done by Schrödingers Cat.
posted by DreamerFi at 5:20 AM on April 2, 2010 [1 favorite]

I guess I could walk up to the Perimeter Institute and buttonhole some of the dude that hang out there in their madras shorts, flip-flops, horn-rims and tousled hair, except this time of day they'll still be hung over from the Italian Spiderman party/event held last night in the Black Hole Bistro. The most I'd get out of them re information density would be how many shots a post-doc resident can hold, and the most I'd get out of them re black holes would be a vacant stare and then a screamed BANGARANGARANGARANG.
posted by seanmpuckett at 5:42 AM on April 2, 2010

...the information about the particle is indistinguishable from the particle itself.

The more I think about this, the more I think about this.
posted by Splunge at 7:15 AM on April 2, 2010

I was kind of hoping an Actual Scientist would pop in.

I am a scientist and I'll tell you what this means. Time travel, flying cars, warp drives, and transporters are only years away! (By the way, did I mention I'm a biologist?)
posted by batou_ at 7:26 AM on April 2, 2010 [3 favorites]

I'm not sure this would have much impact on quantum computing. I suspect the challenges there are a little more practical, in maintaining states long enough to do useful things.

I'm not sure I get much of this, and I've never found a clear enough explanation of Verlinde's stuff to understand it, but my impression is that it's really not catching on in the way you might think from pop sci articles.

I've other concerns about some of the claims (like the one where it's suggested they have a prediction for the value of the dark energy density, which I'm quite unconvinced by on reading the papers).

I'd wait and see a bit longer if this gravity-is-entropy thing catches on before getting too excited.
posted by edd at 7:31 AM on April 2, 2010 [1 favorite]

This has no implications for quantum computing (at least not in our lifetimes) because all computing is done with electricity and magnetism, forces that are vastly more powerful than gravity (and are currently well-understood). The problems with quantum computing are practical, as edd said ---forming altering entangled states, preserving them in the presence of high temperatures, etc.

In fact, this is unlikely to have practical consequences in the immediate future, since we don't possess technology that really manipulates gravity, and understanding Newtonian gravity is enough to allow the vast majority of our technology to operate correctly (interstingly, GPS really needs general relativity to be accurate). Any corrections to general relativity resulting from this sort of theory (or string theory for that matter) are so tremendously fine-grained that they will be difficult to observe with deliberately constructed scientific instruments. It's difficult to predict the practical implications of a theory that doesn't exist, but we have an okay understanding of gravity now, and we know that it's a)very weak, and b)completely indiscriminate in terms of what particles it interacts with. So I think the primary implications of this sort of work are theoretical and philosophical. By understanding gravity better, we can better understand the past, present, and future of the universe.
posted by Humanzee at 8:20 AM on April 2, 2010

Captain! The Landauer cells are discharging anti-protons into our causality chamber causing quantum fluctuations in our gravity radiator!
posted by fuq at 8:33 AM on April 2, 2010

They think that information itself is the ghostly bedrock on which our universe is built.

Would that information be "how to be organized and self-replicate"? 'cause it seems to me that self-replication, and from that, life, is pretty much an inevitable and fundamental aspect of this universe.
posted by five fresh fish at 9:24 AM on April 2, 2010

I'd wait and see a bit longer if this gravity-is-entropy thing catches on before getting too excited.

I am a real scientist (I guess, I'm a physics postdoc).. .and edd's got it right.
Verlinde's paper has generated a bunch of interest (both popular and scientific; he's got more than 50 cites since January)-- but interest is not the same thing as "has become accepted". It's interesting, worth exploring, and is being explored; but one can't really be drawing conclusions just yet. This is one of the issues with popular articles; it's cool, but the articles present it as a lot more formulated/accepted/etc than it really is. (Also there's a fair criticism that the original paper is pretty philosophical and doesn't provide a coherent mathematical background; I haven't looked at most of the followups so I don't know how precise that's gotten, but i'm sure people are working on it in any case.)

I also agree totally with Humanzee, really the issues with QC are maintaining entanglement at large enough size to do anything, and error correction. And I more or less agree regarding understanding gravity better in a general sense, too. There are pretty strong restrictions on what a good understanding of quantum gravity can do for you in our day-to-day world, mostly because Newton (+GR when needed) gives you everything you need. But that doesn't mean that someday there might be a practical application; that "someday" however is pretty far off and probably technologically hard to reach in any case, though.

Oh, and one point for StickyCarpet: It's not just that you can get all all the info from the surface. It's about how much information there is inside a surface. Normally, if we think about atoms hanging out in a box in flat space, if we make the box bigger the amount of info we need to describe the atoms scales like the *volume* of the box.

The weird thing that seems to be true about quantum gravities (string theory gives a set of examples here, but it appears likely to be true for any attempt to build a quantum gravity) is that the amount of information you need to describe what's inside the box-- -goes as the *surface area* of the box. (Basically because black holes are the most information you can have in a given region, and their entropy scales as their surface area).

It's kind of surprising that gravity should behave that way, really.
posted by nat at 11:29 AM on April 2, 2010 [1 favorite]

What ever became of the surfer dude with the 11D mandala?
posted by Mei's lost sandal at 1:04 PM on April 2, 2010

Oh, i didn't meant to say that quantum gravity was going to help with quantum computing. Only that quantum information theory in general has applications for that.
posted by empath at 3:07 PM on April 2, 2010

What ever became of the surfer dude with the 11D mandala?

Still getting paid, apparently. Having read his various arguments with Jacques Distler, though, I suspect that (1) he's not likely to be right, and may not entirely understand his subject matter, and (2) Jacques Distler is a colossal dick.
posted by Xezlec at 7:12 PM on April 2, 2010