Re: How to best keep the carbonation in a bottle of coke

Your son is correct. Carbonation is kept in soda by pressurizing the container.
Carbon dioxide is not very soluble in water, so if soda sits open at 
atmospheric pressure (even if it's kept cold) it loses CO2 and goes flat. 
Keeping a tight seal will slow this process, as the CO2 above the soda will 
quickly reach equilibrium again at a somewhat lower level of dissolved CO2.

Decreasing the air pressure over the soda will only hasten the "flatting"
process.

                                                Dan Berger
                                                MadSci Administrator