On the number of blog posts and PET/MRI scanners

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How many blog posts or status updates can you write?

The limited space in this slot means that there is a finite number of different status updates. After we reach this limit, we will only be able to repeat or copy. — Daniela Balslev

Facebook status messages can apparently only be 420 characters long. If you disregard capital letter, “foreign” characters and punctuations you get something like 27^420 different Facebook status messages. This was discovered after some discussion on Facebook between people in Daniela Balslev’s network. It is a bit difficult to compute with such a large number as it doesn’t fit in standard IEEE floating point representation that are ubiquitous in computing. However, the programming language Python is, with its “long int” representation, able to find the number:


>>> str(len('qwertyuiopasdfghjklzxcvbnm ')**420)[:5] '14886' >>> len(str(len('qwertyuiopasdfghjklzxcvbnm ')**420))-1 601


That is 1.4886 x 10^601. (This number does not reflect that consecutive spaces don’t really change the message)


So you are able to write an over 600-digit long number of Facebook statuses. — If they are suppose to be different. I guess it is not so interesting to repeat a message. It will take many many years before we repeat ourselves even if we type really fast – well over a 500-digit long number of years.


I recently ran into an announcement stating that they in Tübingen university hospital has got a combined MRI/PET scanner. Wow, I thought. This is really news. I had only heard of combined CT/PET scanners and wasn’t aware of that they could combine MRI and PET. I should give such a news a blogpost or at least a tweet.


As a read the announcement it occured to me that I already had done a blogpost on combined MRI/PET scanners some years ago. That was on the late ‘Machine Culture’ blog (practically the only memory the Internet has of that post is a reference on a page in the Internet Archive: “Simultaneous PET/MR brain scanner”). So it seems that I am beginning to repeat myself with around 3.5 years interval. That number is not in correspondence with the above calculate number.


I note the MRI/PET scanner they got in Tübingen is a “Ganzkörper” type. Maybe I should focus on “Ganzkörper” this time instead of repeating myself. Maybe I should also pop in and have my head examined: A Ganzkopf-MR-PET scan.

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