1. The smallest mass of a fissionable material that will sustain a nuclear chain reaction at a constant level.
2. The amount of matter needed to generate sufficient gravitational force to halt the current expansion of the universe.
3. An amount or level needed for a specific result or new action to occur: "The sudden national uproar over drugs and drug abuse has reached politically critical mass in Washington" (Tom Morganthau).
According to Wikipedia, there are around 300 Critical Mass cycling movements around the world. However, from the Ciclismo Urbano website I counted 37 in Spain alone. The idea is to challenge the status quo by encouraging thousands of people to get on their bikes and reclaim the streets from cars. The first Critical Mass movement was held, perhaps unsurprisingly, in San Francisco in 1992. After my successful foray into the centre of Madrid by bike, I thought I would check out when the next "Masa Crítica Madrid" was being held.
Now, I am of the opinion that if you want to provoke change, you need two things: (1) a message that your target audience will understand and hopefully accept and (2) a way of transmitting that message. It's clear that thousands of cyclists parading through the streets is certainly an effective way of catching people's attention (especially if they are naked) but it is the first point that is more critical, if you'll excuse the pun.
So I was pretty dismayed to read the comments following the last Bici Crítica, that leaves from Cibeles at 8 pm on the last Thursday of every month. Apparently there was an altercation with a car driver that resulted in his rear window being smashed. According to a witness, the driver had been driving recklessly, putting in danger some of the cyclists. His summing up comment was
"Lamentablemente, parece que muchas veces nos preocupan más unos cristales rotos que la violencia contra las personas."
"Unfortunately, it seems that we are more worried about a few broken windows than violence against people."
While his sentiment is perfectly understandable, the action completely undermines the whole Critical Mass idea - in particular, point (1) above - and therefore the whole point of being "in danger" in the first place. The conclusion that people less impassioned by vehicles of the two wheeled variety are bound to come to is that this is precisely the reason why bikes should not be allowed to be ridden on the road in the first place.
If this weren't enough, then, for some inexplicable reason (at least, no one who has posted a comment has been able to explain it) they decided to ride on the A2, which is a motorway. It may be true that you have to go to great lengths to avoid going on motorways - as I did to get into town last night - but the solution is not to allow bikes to ride on motorways but rather to provide convenient alternatives.