Here's our version of a concept map for the EDU 2.0 site. Once we've made a few improvements we're going to add it to our 'tour' page because we think it provides a good visual overview of the main site features.
I just found this awesome article about EDU 2.0 (Spanish version, Auto-translated English version) and it includes the following "concept map" of the site features. We've decided to create some similar maps that we will use on the site to help our users understand how it all works.
I ran across this blog entry today by Kirby Chittenden, an educator for Grand Haven Area Public Schools. He mentioned that his school had received some new laptops, which they were using to access - EDU 2.0!
Their school site is at http://lakehills.edu20.org and if you look carefully, you can even see the EDU 2.0 site on the laptops in one of the blog photos.
We switched over to Amazon EC2 at the beginning of the week and so far things have gone very smoothly. The Extra Large Instances are performing well and we are benefiting from the extra RAM.
The only glitch was related to sending email. Our system used sendmail to send out email, and on our previous host this was no problem. Reverse DNS was set up correctly so that when mail servers received our emails they could look up our originating server from the IP address and confirm the email was not spam.
However, Amazon EC2 does not support reverse DNS lookups on its servers, so shortly after our system sent out its first batch of emails, we received a notice from Amazon saying that some servers had reported us as sending spam and that we had to contact Amazon within 24 hours or have our servers terminated.
The solution has been to move our SMTP server to an off-Amazon server that also hosts our SVN repository and other miscellaneous items. So now our Amazon servers send email via our off-site server and things seem to be working fine.
We have a few remaining tasks left for next week - setting up automatic incremental backups using ESB snapshots and some automated monitoring processes.
As of 8pm today, EDU 2.0 is officially running on Amazon EC2! So far, the transition seems to have gone smoothly, but it's not uncommon for a few glitches to show up in the first week of any major change.
The Rails processes are all running on "Extra Large" instances (15GB and 8 compute units). Each EDU 2.0 Rails process uses about 300MB, so we could theoretically have 50 processes running per server, but right now we've capped it to 12 processes. We use NGinx as the web server, Passenger to coordinate the processes, and Capistrano for deployment.
The database server is running MySQL on a "Large" instance (8GB and 4 compute units). The database storage is on an Elastic Storage Block and we're going to use snapshots for backup. The server also hosts a Memcached server (we only use it a little bit right now) and a Sphinx process for text searches.
We use NewRelic (Silver) to monitor the Rails application and Amazon Cloudwatch to monitor the servers. All user files are stored in Amazon S3 (around 160,000 of them so far).
Based on some initial observations, my guess is that we'll move the Rails processes from "Extra Large" (15GB, 8 compute units) instances to "High CPU Extra Large" instances (7GB, 20 compute units) because the Rails processes seem to need proportionately more CPU than RAM. We'll pay for the instances on an hourly basis until we figure out the best mix, then we'll move to reserved instances to save money on a yearly basis.
I'll post a follow-up to this blog entry based on how things go.
Nine months ago, I posted about my first Lucid dream, which is where you "wake up" in a dream, realize that you're dreaming, and can often control the dream. In addition, Lucid dreams are often incredibly realistic, and your vision in the dream is as crisp as real life.
Two nights ago, I had my second Lucid dream and it was even more remarkable that my first. First of all, it lasted a long time (at least from my perspective) and was 100% realistic. Second - and this is the best part - I was able to fly.
When I woke up in my dream, I was at the base of a Swiss mountain and I could see the lights of a town twinkling in the distance. I sensed I could fly so I lifted off the ground and started flying up the mountain and then down the valley between the mountains towards the town.
I was flying quite fast and went high above the mountains at one point so I could see the entire mountain range and the towns below me. Then I gradually descended and landed in one of the towns where the next part of the adventure took place.
It's hard to describe how incredible it felt to fly in a Lucid dream, since everything seems perfectly real. It's not some kind of blurry memory that you experience, it literally feels like you are flying and you experience everything with the same kind of detail that you experience everyday life.
When I finally woke up, I just went "wow". It was a lot like the video below, except better because it was at night and the lighting was spectacular.
I've just read part II of David Chalmers' book "The Conscious Mind" and thought I'd jot down my rebuttals to all 5 of his arguments as to why consciousness cannot be explained as an emergent property of a physical system.
First of all, let me state for the record that my own belief is that consciousness is an emergent property of physical systems, and that this occurs on many levels. For example, I believe that NASA, the US, and the Earth are all conscious. So I don't think that consciousness is something that's unique to animals. I am also working on a theory to explain consciousness and seem to be making good progress.
The only reason I wrote the last paragraph is to underscore that one working hypothesis for consciousness is that it's an emergent property of particular kinds of system and that this hypothesis has not been disproven as far as I know (except perhaps by Chalmers, but it's based on circular reasoning and thus not a proof). For the rest of this post, I will call this un-disproven hypotheses "H".
In Part II of his book, Chalmers lays out 5 reasons why he thinks consciousness cannot be an emergent property of physical systems. For each reason I will state the title, a synopsis of his reasoning, and then my rebuttal.
Argument 1. The logical possibility of zombies
In this section Chalmers states that it is possible to have an exact physical replica of himself (presumably down to the subatomic level) that, unlike himself, experiences nothing. He calls this his "zombie twin". However, if H is correct, then such a thing would be impossible, since any system with the same physical structure would experience the same. In other words, if H is true and Chalmers is conscious, then his identical twin would also be conscious. Chalmers then states the the burden of proof that a zombie is impossible lies on those who believe it's impossible. However, that's not true, since the possibility that H is true does not imply that it's true; just that it's a possibility. Chalmers though is trying to prove that H is false, which means that the burden is on him!
Argument 2. The inverted spectrum
In this section Chalmers says that if two physically identical systems can experience different things given the same stimulus (for example, having a different experience when stimulated by the wavelength of red light), then this shows that there are properties of consciousness that are not determined purely by the physical aspects of a system. However, if H is true, then two identical systems would always experience the same spectrum. Chalmers provides no proof that an inverted spectrum is possible with two physically identical systems, but uses examples from famous reductionists who have "conceded" that such a thing is possible if, say, the animals have different underlying neurophysiological properties or if one was based on silicon instead of carbon. However, in both cases the physical systems are different, so they prove nothing.
Argument 3. From epistemic asymmetry
In this section Chalmers states that because the existence of consciousness is so surprising and non-obvious, there must be something special about it. This is a weak argument at best. A simple counter-argument is that the problem is tough and so it's taking us a long time to figure it out; the answer might be self-evident to higher intelligences.
Argument 4. The knowledge argument
In this section Chalmers says that a human (called Mary) who had never been exposed to light of a particular wavelength (red) should be able to experience it by knowing everything there is to know about light and the brain. However, if H is true, our experience of red light is probably due to (or perhaps simply is) a particular pattern of neural activity. The only way for Mary to experience red would be for her to activate that particular pattern in her brain. But the part of Mary's brain that knows about her brain and the physical aspects of the color red don't have the ability to directly stimulate the part of her brain that is activated when her eyes detect red light. So there's nothing mystical going on here, it's simply that some parts of her brain can't directly stimulate other parts of her brain.
Argument 5. From the absence of analysis
In this section Chalmers says that his opponents need to be able to show an alternative explanation of consciousness if they want to successfully defend against arguments 1..4. Well, I just rebutted 1..4 without any need to prove H; I just needed to assume that H was potentially true. Argument 5 suffers from the same weakness as argument 3; just because no-one's proved H so far doesn't mean that it's false, it could just mean that it's a tough problem.
I started by assuming that H, the hypothesis that "consciousness is an emergent property of some kinds of physical system", could potentially be true. This is a hypothesis that many people, including myself, believe is true and are trying to prove. I then showed that none of Chalmers' 5 arguments proves that H is false. Therefore Chalmers' argument that he has disproven that consciousness could be an emergent property of a physical system is invalid.