What I am referring to as antigravity is an Easter egg in Python 3.
By default, Python 2 is installed on most systems. If you want to install Python 3, then in Fedora I use:
# yum install python3
On the Raspberry Pi, or in Debian-based distributions in general like Ubuntu or Mint, I use:
$ sudo apt-get install python3
After the install finishes, in a GUI environment open up a terminal and start the Python 3 interpreter:
Python 3.2.3 (default, Jun 8 2012, 05:40:06)
[GCC 4.6.3 20120306 (Red Hat 4.6.3-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
It will pop up your browser to view this web page:
If you don't have a GUI started, then no web browser will pop up, and nothing happens. It looks like this: