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.
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.
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Please correct me, if I'm wrong on something.
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.
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:
http://arxiv.org/abs/quant-ph/0310003
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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?
Here's a similar video: The Origin of the Universe and the Arrow of Time by Sean Carroll: http://www.youtube.com/watch?v=r_QMnG232Js
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.
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.
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.
"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?
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.
Anti de Sitter space is essentially living on a boundary of a black holes like curvature. Like this one: http://en.wikipedia.org/wiki/File:HyperboloidOfOneSheet.png
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.
Note: it's an analogy, don't be too nitpicky.
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.
So what's the explanation for why almost all interactions that we perceive seem to not be spooky or at a distance?
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.
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]
http://www.preposterousuniverse.com/blog/2010/11/10/against-...
Do we know that it is? Clearly we are experiencing major observation bias.
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.
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.
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.
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).
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
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).
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.
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.
Isn't the universe infinite? Where does this leave entropy?
If you're not familiar with the basics of the Holographic Principle, start here: https://en.wikipedia.org/wiki/Holographic_principle
It's been a while since I've watched these, but IIRC these are very good videos to start with:
- http://www.youtube.com/watch?v=2DIl3Hfh9tY
- http://www.youtube.com/watch?v=GHgi6E1ECgo
EDIT:
Key clippings from the wikipedia article-
"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."
(__'s mine)
So would it follow that the equilibrium state of the universe is one gigantic black hole?
As our cosmos expands faster than speed of light, we can't ever escape this cosmos. Our light cone is similar to one that sits in a giant black hole.
Unless we figure out how to emit ourselves as Hawking Radiation in the outer universe?
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.
Makes me wonder what it actually means to say a system is n-dimensional, if you can equally well "implement" it for any n.
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.
As for recommended reading, I liked Brian Green's The Elegant Universe.