In the past, I already wrote about Holographic Principle and Simulation Argument. I have seen both recently covered on some blogs and publications with mixed feelings about it. I suspect there are two reasons for sudden emergence of these two topics in the media:
- This week, on 21st of March, Planck data will be released. You can follow NASA update here. Planck data mat give further details about so called bubble universe or namely their collisions (or traces of their collisions). While none of these is directly tied to Holographic Principle or Simulation Argument, both multiverse theories get attention as being most bizarre of all multiverse theories out there.
- Fermilab, somewhere this year, will start with their Holometer experiment
While Holographic Principle and Simulation Argument can be even related, I will try to summarize current state of both here with current future aspects not covered in previous articles.
Holographic Principle is more scientific than Simulation Argument - no discussion there. Simulation Argument is interesting philosophical aspect that can easily poison your mind, but at the end of the day it is more religion than science. Holographic Principle is on the other side something that has been building up over the years and it is mostly based on calculations and observation done on - black holes. Black holes may look and act bizarre to usual Earth population, but they represent area where gravitational pull is so strong that nothing can escape - even light. As there is no spectrum of light coming out, we say this is a black hole. Obviously, there is a point at which if you come too close, you can return - point of no return if you want. This is called black hole horizon. Back in 70s, it was Stephen Hawking who made physics world upset with his claim that once black hole swallows something (eg. star) then all information about it is - destroyed. That really didn't fit theories of that time where information about existence of virtually anything is preserved and can be reconstructed (reverse engineering) if we would have access to each elementary particle making such object. Now, one may argue that information is still within black hole, but what Hawking showed was that black hole does evaporate during the course of time and thus is not that black after all. But by evaporating, all information is gone. This came to be known as Hawking radiation.
Then Jacob Bekenstein entered the scene and found that it was surface of horizon which contained information. Juan Malcadena in 1997 made phenomenal mathematical model and showed that Hawking radiation has impressed information about objects previously swallowed by black hole. That way, no information is lost and information paradox as such is resolved. The easy way imagine this is to think about radio waves carrying information about someone's voice or song from radio station. However information being retained on surface of black hole would indicate that 2D object would contain information about 3D objects (eg. star, planet or moon) and that's pretty much what hologram is about. Thus, we call this holographic principle.
Leonard Susskind took this further in 1990 with claim that whole Universe is one big hologram and that we can't see 2D horizon. Actually, we and everything around us are 3D representations of 2D world on horizon. This claim has sparked imagination and many theories and interpretations. Now, if for a moment we take this as valid hypothesis, how do you figure out this? How do you test your hypothesis?
Being in airplane and flying over the ocean gives you an idea that surface of ocean is smooth. However, as soon as you approach surface you start to realize this ain't true. The smoothness is lost. Scientists believe something similar is the case with space-time - more we go into quantum realm, less smooth it is. Right now, we believe our limits should be around Planck size (10 trillion trillion times smaller than typical atom). We can forget about getting at such small scale any soon (or later). However, scientists argue that graininess should be visible much before if holographic principle does hold the water. How much before is unknown though.
Back in 2008 this theory got attention again once that GEO600 experiment, looking for gravitational waves, reported to have recorded certain jitters in laser beams between its interferometers. It sounds too good to be truth and indeed it was. Later on, it was found this was a noise which has been eliminated by using different readout method. Craih Hogan at Fermilab did get excited and decided to make experiment which would be dedicated to this solely purpose. Thus Fermilab Holometer was born. What it is exactly?
A carefully prepared laser light travels to a beam splitter, which reflects about half the light toward a mirror at the end of one arm and transmits the rest to a mirror on the second arm. The light from both mirrors bounces back to the beam splitter, where half is again reflected and half transmitted. A photodiode measures the total intensity of the combined light from the two arms, which provides an extremely sensitive measure of the position difference of the beam splitter in two directions. The holometer as constructed at Fermilab will include two interferometers in evacuated 6-inch steel tubes about 40 meters long. Optical systems (not shown above) in each one "recycle" laser light to create a very steady, intense laser wave with about a kilowatt of laser power to maximize the precision of the measurement. The outputs of the two photodiodes are correlated to measure the holographic jitter of the spacetime the two machines share. The holometer will measure jitter as small as a few billionths of a billionth of a meter. If light waves will go out of phase, we have found proof of graininess. If not, well, it still doesn't necessary kill holographic principle idea, but it will define some new limits to the theory. One might think that such experiment will cost the fortune, but that's not the case - only $1 million. Compared to some other experiments, that's peanuts. And while holometer will start to run this year, no one knows how much time and work will be required for tuning. And since nothing like this has been done before, no one knows what to you as reference - it is new territory and that's what makes it even more exciting. People in scientific community seem to be split regarding opinion on this experiment; some support it regardless of result and some do not. Nevertheless, it is done deal and we might get some updates on this even this year.
With that in mind, let me add that recent analysis shows that space at least is smoother than originally thought. This observations comes by checking X-rays and here is why. Einstein described space and time as smooth, deforming only under the weight of matter and energy. But according to some theories of quantum gravity, which deal with matter and energy at the smallest scale, spacetime is made up of a froth of particles and possibly even black holes that pop in and out of existence over infinitesimally small moments at the Planck-length. The "bubbles" in this foam - should they exist - are so small as to be almost undetectable. However, scientists have theorized that photons from gamma-ray bursts should be able to track down the bubbles' signature. The wavelengths of gamma-ray burst photons are some of the shortest distances known to science - so short they should interact with the even smaller bubbles of quantum foam. And if they interact, the photons should be dispersed - scattered - on their trek through frothy space-time. In particular, they should disperse in different ways if their wavelengths differ, as in the case of three photons used for this finding back in 2009. Imagine a Ping Pong ball, a bowling ball, and a softball taking alternate paths down a gravely hillside. Furthermore, few things can delay gamma-ray photons like these, so they might travel for unimaginably long distances unimpeded. You wouldn't notice the scattering over short distances, but across 7 billion light-years (when supernova took place), the quantum foam might knock the light around enough to notice. And three photons from the same gamma-ray burst might not have crashed through the Fermi telescope in a dead heat. However, they did. So, graininess might be either below Planck scale or it is simply not there. Of course, there is always a possibility of a statistical fluke, or that space-time foam interacts with light differently than we imagined. With that in mind, I do not expect holometer to find anything at all.
Simulation Argument is somewhat different beast. Or religion if you want. I also fail to see why something like that would be reality, but it is also ambiguous to expect reality to match our own expectations - we are after all almost nothing is vast space of our Universe. Still, idea of running in simulation goes back to Greek times and has been picked up in modern times by Swedish philosopher called Nick Bostrom. He came with interesting idea: if computer power continues to grow, we will be able to simulate reality. With growth, number of such systems will be such that statistically it will be more likely that world is running in simulation than reality. With that in mind, how do you know that our own reality is not simulated? Today, we simulate certain processes and laws of physics at rather small scale of things so power required to simulate our Universe would be at much higher power of course. Based on our own experience with simulations, we would also expect to see some glitches within our own simulated reality. Once again, if we probe smallest parts of our Universe, we would expect to see some sort of grid or lattice structure and get an idea that we are running in simulation. However, before going anywhere probing smallest parts of Universe at high energy scales, what would be the reason to simulate Universe? If we selfishly assume it is us, why create such big Universe in the first place? If simulating Universe with different parameters for constants, then this would apply that emergence of life is fundamental quality of such simulation. However, energy required to do that is just beyond comprehensible reach and rather unlikely. With such power, why would anyone run any simulation instead of using it to probe its existing reality directly? Recently two blogers, Sabine Hossefelder and Lubos Motl have both spoke on this subject and I find hard to not to disagree with them. Therefore I won't add anything there on this subject. Simulation argument, even with quantum computers, is just geeky version of God existence. And most importantly, without any proof.
When it comes to mutiverse, and if I have to choose to what to believe in, I would subscribe rather to extra dimensions. While I won't claim those dimensions would contain any form of intelligence, emergence of extra dimensions is nothing new in physics and almost done deal if mathematics of string theory. It also does provide rather nice conceptual explanation for gravity. Most importantly, it does emerge from math which per se does not mean anything, but it is always nice indicator of what path to choose if in doubt. Science will, soon or later, be able to clear this out too. Meanwhile, I will focus on reality - which is that I will go to sleep now and will wake up next morning with 15cm of new snow in Berlin (unless weather forecast was wrong which hopefully it was).