If you consider a vacuum to be the absence of air pressure, then it is still a vacuum - there are no air or other molecules/atoms/hadrons inside the vacuum. But if you imagine a clear glass bottle with all of the air sucked out of it, the fact that you can hold it up in the air and see through it tells you that light particles (photons) are moving into the bottle (through the glass), entering and exiting, before hitting your eye. Photons are the force carrying particles for the electromagnetic force.

I was so excited for the prospect of having the Olympics in Chicago. One of the venues was literally just going to be across the street from my condo. But if you look at the bid details on Rio's site (http://www.rio2016.org.br/en/) and Chicago's site (http://www.chicago2016.org/). Rio's was more complete - and more honest about what they need to do.

Most notably to me, Chicago failed to address transit improvements. Transit plans have been critical in recent past Olympic bids. Venues are far apart. There needs to be a fast and efficient way to get from venue to venue. Rio promised a new high speed train linking all of the venues. You could go from beach volleyball to basketball in 30 minutes or less on a modern, efficient train.

In Chicago, there's no proposal for improving the decrepit state of Chicago's train systems. In fact, they actually had the nerve to claim that the atrocious Amtrak service is actually an asset (http://www.chicago2016.org/our-city/transportation/rail.aspx).

Chicago transit is horrible. Some of the train lines are over 100 years old. It's not good enough for the Olympics.

As it is, traffic grinds to a standstill on surface roads and train platforms crowd to dangerous levels when smaller events like the 4th of July or the Taste of Chicago food festival occur. The Olympics would dwarf anything that Chicago has ever seen. It would be a traffic (and security) nightmare. And they largely ignored it and ignored suggestions from people like myself who tried to make that and other suggestions.