1) What the heck do they mean by a hologram? The analogy here baffles me. Is this just a layman's analogy, or does this actually mean something scientific?
2) Anybody have any suggestions on a high-quality layman's explanation? I finished reading Feynman's QED the other week, and loved it, and was wondering what the closest might be for string theory.
"The holographic principle is a property of quantum gravity and string theories that states that the description of a volume of space can be thought of as encoded on a boundary to the region—preferably a light-like boundary like a gravitational horizon. First proposed by Gerard 't Hooft, it was given a precise string-theory interpretation by Leonard Susskind[1] who combined his ideas with previous ones of 't Hooft and Charles Thorn.[1][2] As pointed out by Raphael Bousso,[3] Thorn observed in 1978 that string theory admits a lower-dimensional description in which gravity emerges from it in what would now be called a holographic way.
In a larger sense, the theory suggests that the entire universe can be seen as a two-dimensional information structure "painted" on the cosmological horizon, such that the three dimensions we observe are only an effective description at macroscopic scales and at low energies."
So the analogy is that the field inside the volume can be completely described by some function over the bounding surface of the volume, similar to how the light field captured by a hologram is projected and recorded on a flat glass or film plane. I can visualize that pretty easily, but I don't know enough to tie that to some concrete relationship to the fundamental physical forces of the universe.
"In mathematics, Cauchy's integral formula, named after Augustin-Louis Cauchy, is a central statement in complex analysis. It expresses the fact that a holomorphic function defined on a disk is completely determined by its values on the boundary of the disk, and it provides integral formulas for all derivatives of a holomorphic function. Cauchy's formula shows that, in complex analysis, "differentiation is equivalent to integration": complex differentiation, like integration, behaves well under uniform limits – a result denied in real analysis."
Does anyone who knows this stuff better than me know if there's any meaningful connection?
It's similar to Green's Theorem, a special case of Stokes' Theorem. The latter is probably very closely related to the ideas underpinning the holographic principal (just guessing; my background is more math than physics, though I love both).
Short version: The bulk is encoded in the boundary.
Imagine a special circle. The border of this circle contains all the information of everything inside the circle, so the inside of the circle is a "holographic projection" of the information in the boundary.
In the same way that a holographic projection is physically two-dimensional, but contains enough data to appear three-dimensional from many different angles? (I'm guessing here, I don't really get holograms.)
A regular photograph captures the intensity pattern of light at a particular location at a particular time.
Holograms recreate the interference pattern of light in a volume of space. By interfering two coherent sources using a film that has the interference pattern captured, you recreate the interference pattern. Hence it exists in 3-D.
It means in essence, that we live in the two-dimensional space, which contains just enough information (thanks to interference patterns), to be projectable to the 3rd dimension. In holographic duality, this is a way to derive a more complex dimension from the next lowest dimension. It is thought that the four-dimensional space, which you may have just been thinking about, exists due to distant entangled quarks and may be the thing we call space-time. The holy grail every physicist is searching for is "gravity". Nobody on earth knows for sure what gravity exactly is. But it is thought to exist in the fifth-dimension "bends & shapes the our space-time.
Don't confuse this with the simulated universe theory, as I initially did. That's a whole nother story.
Time is believed to not exist as a separate dimension, but as a byproduct of gravity.
"Time is believed to not exist as a separate dimension, but as a byproduct of gravity."
I love this comment because I hadn't heard ^^ perspective before. Do you know what particular schools / models treat time this way, or are you inferring that this is the general conclusion of the field?
No, that is not what's believed in general, but gains in attractivity as a possible solution. That's because, it's simpler. I have read about it on various blogs and have also seen an inspiring TED talk about it, before it got removed.
i think its quite well established that space and time break down as approximations at the small scale.
i also think that gravity is interesting because in GR there really isn't such a thing - its an artefact of the geometry of space and time - because of how we perceive the passing of time.
i'm not sure exactly how time would fall out of gravity... afaik the quantum mechanical descriptions usually break the magic trick of GR and make it into a graviton field, which depends on some background time.
i do wonder why we pursue theories which our existing theories show to be unlikely to be fundamental... thinking about the limits, near the planck scale we find that it is impossible to tell if an event is before or after, or if a thing is one or two things, or if its seperated in x or y... the simple conclusion imo is that space and time are approximations that are useful at everyday scales, but have no physical reality.
> we live in the two-dimensional space, which contains just enough information
I would change "just enough information" to "much more than enough". If it was just enough, then the universe would be an enormous black hole. Note that I'm not an expert, and I could be wrong, but this is my interpretation.
Thinking about the universe as a massive black hole, whereas black holes are a concept that is still not entirely known makes thinking about this subject highly speculative. This list only adds salt to that wound: http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_ph...
But to me Black Holes are spinning L-Systems which distribute information in the universe instantly by quantum teleportation. This is much simpler than other existing theories which leave open question like: http://en.wikipedia.org/wiki/Black_hole#Open_questions
Take this information with caution, but these paper supports such possibility:
When reading that article, while I don't have the background for all of it, I find that most of it sounds fairly plausible, until I get to this: "In 1995, Susskind, along with collaborators Tom Banks, Willy Fischler, and Stephen Shenker, presented a formulation of the new M-theory using a holographic description in terms of charged point black holes, the D0 branes of type IIA string theory. The Matrix theory they proposed was first suggested as a description of two branes in 11-dimensional supergravity by Bernard de Wit, Jens Hoppe, and Hermann Nicolai" at which point I start to suspect that this is all just made up technobabble.
"In a larger sense, the theory suggests that the entire universe can be seen as a two-dimensional information structure "painted" on the cosmological horizon"
True for an anti de Sitter space (thus ADS/CFT) but not for the one we live in which is a de Sitter space and lacks the requisite boundry. I wish someone could explain the relevance of ADS/CFT to this universe.
I once had the opportunity of being in a car alone with Juan Maldacena for an hour and asked him. He pretty much shrugged (probably meaning any attempt to explain that to me, a layman physics junkie, would be futile.) He's a really, really nice and personable guy so I'm sure that if there was anything I could have understood he would have tried.
Think of it this way de Sitter space is essentially analogous to living on a sphere. In that space any triangle on the sphere's surface has more than 180 degrees.
http://en.wikipedia.org/wiki/Spherical_geometry
In hyperbolic space any triangle on the hyperbolic surface has less than 180 degrees.
A sphere has no boundary (think invisible walls in video games). You can move over it for infinite time without encountering an invisible wall that says, you can't go further. Because it closes on itself. Contrast this with hyperbolic space, which must has such boundary, because it can't close on itself without becoming some other kind of space.
1) The gist is this: Hologram is a 2D picture that encodes a 3D object using light interference.
Holographic principle states that information encodes reality into matter/energy and gravity. Basically gravity, matter and energy are sideffects of information. They are its projections.
How does this relate to hologram? Well dots that might appear like two separated dots on the 3D model, could be encoded on the 2D surface as very close. What this explains is "spooky action at a distance". We perceive two entangled electrons as being far away on a reality hologram, when in reality they are close on the fundamental 2D picture of the world.
Summary: What we perceive and measure as reality is not what reality fundamentally is.
NOTE: This is extremely layman termish and don't be too surprised if it's wrong. I last read UiaN years ago. There are also some other interesting properties, like that the any part of hologram contains whole picture of hologram but of lousier quality, etc.
2) I think Universe in a Nutshell covers most of this theory pretty well.
The same reason you don't see each dot on your monitor as separate light source, unless you take a magnifying glass.
Or that you don't experience theory of relativity when accelerating.
Senses are imperfect and the information such as those aren't vital to our survival. And their effect is tiny, tiny, tiny. I'm pretty sure spooky action (iirc quantum tunneling) at a distance keeps our sun running, or at least computers.
i think you're missing the point? the original question was making the argument, i think, that if the universe is fundamentally non-local, why is almost all physics local?
using an optical analogy: if fourier space is "the real thing", why do we live in a world where point sources are much more common, useful, and interesting, than diffraction patterns?
you seem to be saying in reply "because non-local stuff is difficult to observe". but that's not an explanation; that's the problem.
[although tbh i think you could make this argument against any unified theory - it's effectively the same as "why do we get quantum decoherence?" except that now the idea that it's caused by complexity seems less intuitively right]
TL;DR. Theory of evolution meets anthropic principle
I think you are missing my point as well. Reality IS non-local, we just PERCEIVE it as local. No triangle on Earth surface has sum of angles 180, but we say - well it's close enough to 180 so lets say it's 180.
We perceive causality because it's an easier approximation than calculating probability distribution of each molecule. It's like a Russian doll, we perceive the outer doll as whole because we don't look close enough.
Because we don't need to. Evolution didn't specialize us to notice the subtle effect of quantum reality, when a good enough approximation allows us to survive and thrive. We perceive things we perceive, because of their importance for our survival. True nature of reality isn't important to our survival. Thus we don't perceive it.
Reality requires infinite amount of data to process. So we approximate it to stop being overwhelmed.
E.g. geocentric or heliocentric model of solar system are both equally valid. We just choose Heliocentric because its orbits are easier to calculate. Or earth is essentially flat even though it's a sphere etc.
> We perceive causality because it's an easier approximation than calculating probability distribution of each molecule.
That's not true. Causality is the very mode of operation of the world and it is a requirement for anything to exist at all. Without causality there would be no change and no change means no existence.
Probabilistic models only indicate the degree to which the system is not understood by the observer before his/her confirmation of the system state.
Ok, gonna be more specific, but I meant the classical notion of causality. Ball A hits ball B that hits ball C, where each effect occurred in respective chronological order that was given.
Quantuum theory proves that ball A can hit ball B that will travel back in time and hit ball C before ball B was hit. The causality isn't as narrow as in classical physics.
Also another thing to note - that all molecules in any matter move in random direction all the time, as so much their bounds allow them. It is not inconceivable that all molecules of a gold coin could simply move in the same direction and flip the coin by themselves. Chances of gold coins flipping on their own aren't impossible, just very very very very... improbable.
Sean Carroll talks a bit about this kind of problem here, (albeit when discussing the distinction between "coordinate space" and "momentum space") where we perceive the world in one way, but a lot of physics seems gears towards either one of the worldviews, and the question then is "why the hell?"
that's a good point - this is a more general issue than qm. ugh. slideshare is awful [oh; advice to expand to fullscreen makes all the difference. good slides; wish i understood more]
Well, a universe with constants that make non-local/relativistic effects common doesn't seem like it would be very good at hosting intelligent observers.
That explanation would be hidden in the formulations that describe the 10 dimensions they found.
Even though shadows in usually are short and sort of shaped like we are, though a 2d projection on the ground. When the 3d objects are in weird relations to each other the shadows can be large and deformed (spooky).
i thought every action was spooky and at a distance?
if you drop down to the smallest scales you can't tell if two things are in contact. i'm inclined to think that an infinitesemally continuous universe is an approximation we use to make the math 'easier' - in fact so are space and time - and even countability.
our best theories indicate that at small scales you can't actually tell if things are separated or not - or even if there are one or two - or even if events happen first or second.
thinking about a tiny 'almost a black hole' clock on the planck scale can reveal this very quickly with only the most basic of QM, SR and GR relations... below a certain tick rate it will collapse into a black hole and stop working, or the uncertainty effects will smear out the results so that you can't tell which tick comes first, or the error in the ticks exceeds the length of the ticks. in essense space and time are unmeasurable in the context of semi-classical QFT + GR theories
"Spooky action at a distance" implies some kind of faster-than-light phenomenon. Regular things that interact while separated by space aren't considered to have "spooky action at a distance."
Hmm.. does that mean that E=mc² is only correct for our dimension? Because, if you say that matter is a side-effect and not something like "higgs particle", then this doesn't hold up anymore. I mean not everything we don't know must exist as a particle.
I mean I believed the holographic universe theory a long time ago already, but taking it really serious, like considering it's implications to all existing findings and formulas is ripping apart my whole worldview (into a flat shape, with a lot of meta-data).
Dimension as in - three spatial dimensions we navigate every day. There is no other reality, ergo there is no our dimension.
Don't take it too literally, it's like saying information gives rise or causes energy, as in - information of the holographic universe causes energy to behave in the world we experience, probably with some other descriptions how it behaves in spaces where lower or higher dimensions are flatter than our own.
Yeah, this is trouble, because the common understanding of "hologram" is very different from the actual definition.
As far as I understand it (and another person has explained it better below), the indication is that the way we perceive the universe indicates that the "data" producing those perceptions is not stored in the same structures we see or detect - instead, those structures (space, mass) are sort of "implied" by a more fundamental way of "storing" that data, which we interpret secondhand because we can't perceive the original. Not sure if this is clear or accurate, but that's what I've taken away from previous articles on a holographic universe.
If I get this right, then the irony here is, that everybody is correct and wrong at the same time. Just draw some dots, circles etc. on paper and it could be that one day that non-local representation of the holographic universe holds true.
From a few long Youtube videos I just watched, the amount of information in the Universe is limited and based on the total surface area, not the volume.
Others can hopefully chime in with more, but when I first was learning about it, my reaction to the word "hologram" was the same as your (1). My understanding is that when they say "hologram", they're simply meaning an n dimensional object that's encoded in n-1 dimensional space.
"But Jacob Bekenstein noted that this leads to a violation of the second law of thermodynamics. If one throws a hot gas with entropy into a black hole, once it crosses the event horizon, the entropy would disappear. The random properties of the gas would no longer be seen once the black hole had absorbed the gas and settled down. The second law can only be salvaged if black holes are in fact random objects, with an enormous entropy whose increase is greater than the entropy carried by the gas.
Bekenstein argued that black holes are maximum entropy objects—that they have more entropy than anything else in the same volume. In a sphere of radius R, the entropy in a relativistic gas increases as the energy increases. The only limit is gravitational; when there is too much energy the gas collapses into a black hole. Bekenstein used this to put an upper bound on the entropy in a region of space, and the bound was proportional to the area of the region. He concluded that the black hole entropy is directly proportional to the __area__ of the event horizon."
>>My understanding is that when they say "hologram", they're simply meaning an n dimensional object that's encoded in n-1 dimensional space.
If you apply that definition recursively. i.e, n in n - 1 , n - 1 in n - 2 and so on. You can ideally represent every thing in the very first dimension itself.
Unless we figure how to tunnel to the other side of the universe. Because quantum tunneling would allow us to move faster than light which is necessary to escape.
wow, this thread gets more and more interesting. I think the discovery of the holographic universe just broke all norms and worldviews of physics for the most of us.
Is there any issue here about fundamental stability? I'm struggling with how the universe can be at once expanding and some form of dimensionalized representation. Unless the other half of the relation is also in some sort of dynamic transition. Which might be true but suggest (perhaps as you do) there are things outside our perception that we can never perceive, not to mention measure or experience (ie travel too) because they are outside the space of our cognitive faculties. Or like you say, we are in a black hole and can't see out.
A piece of hologram film doesn't look anything like the image, but it does have a certain distinct "look" to it. Much like the famous quote about not being able to define pr0n but I know it when I see it. Holograms have a certain "look" to them. It's what happens when you project a 3-D image onto a 2-D piece of film using all manner of weird wave interactions from a coherent source blah blah blah science talk blah.
So the terrible awful analogy is they're saying their simulation of a projection of some weirdness into normal space looks like our gravity and space and mom and apple pie.
The awful analogy being that the squigglies on holographic film are to the actual object, as their weird theory is to something vaguely like the space we live in, at least in some aspects. Take two things and there's a certain look to them and a certain transform in between and thats pretty much kinda whats going on in both cases.
This post exceeds the US recommended daily allowance of "kinda" "sorta" "mostly" so take it with a death star sized grain of salt. I'll laugh at anyone flaming me for not getting it exactly right cause this is simplified almost to not meaning much.
There is nothing else I've ever seen like Feynman's QED, not for any field of physics. It's spectacular: a "popular" level book for a general audience that doesn't tell a single fib (even by omission), and that captures the essence of the subject without delving into the math required for serious calculations. I dream of writing a book like this (about string theory or anything else).
I am not entirely sure either, what they mean by hologram. The problem is, that holographic principle ( or similar) can mean different things depending on the context. But in string theories, it is sometimes the case that lower dimensional theories can encode the same information as the full string theory. Just as illustration, if the endpoints of your strings are stuck on a two dimensional plane, but the strings can vibrate in three dimensions, then you can potentially describe the system as a theory of the endpoints in two dimensions ( and the vibration mode of the string would potentially be encoded as the type of particle), or you can describe how the strings move through three dimensions.
As for recommended reading, I liked Brian Green's The Elegant Universe.
If you can accept some tiny bits of math, I'd suggest Susskind's lectures. As close to the real thing as it can get, and almost effortless on your part.
2) Anybody have any suggestions on a high-quality layman's explanation? I finished reading Feynman's QED the other week, and loved it, and was wondering what the closest might be for string theory.