A Daft Question re string tension

[The Reverend 48]

When you leave a guitar for a few days why do the strings tighten I would expect them to slacken ie relax

[hooper]

The changes that I notice seem to be related to temperature which causes the metal in the strings to either expand or contract. So these days, while running A/C with cool drafts of air around the room it would seem logical for the strings to tighten.  To prove the opposite works too you could put a guitar inside a hot parked car for a few hours (which obviously you really don't want to do) but I guarantee that would cause the strings to go slack.   

[guitarron]

tension from the truss rod-it's normal

[Sprocket]

Humidity.(probably really rainy over there?)
Humidity isnt such a bad thing though, itll straighten out your neck and your guitar will be more resonant. I hydrate my guitars every couple of months for the above reasons, but Id really like to get a humidifier and hygrometer to do it more consistently.
If youre worried about it get a hygrometer and be certain its a safe level for your instruments.

Heres an article bout hydration...although the author has the opposite problem.
http://www.compareguitarlessons.com/Article-Guitar-Humidifier.html

[guitarron]

Humidity.(probably really rainy over there?)

yes that too

[The Reverend 48]

If its atmospheric why do they never slacken?
does anyone else always find the strings tighten
Or have I got rock elves that play while I'm asleep

[Sprocket]

If its atmospheric why do they never slacken?

Leave it in your hot car for an hour.(not usually recommended)
Im thinking you live in a really humid environment, not unlike mine...although mine tends to go to extremes one way or the other. But with heavy A/C usage, the room my guitars stay in tends to be very dry.   

Although it could be youre really heating up those strings, retuning, playing more...and then as they cool they go sharp. Thats why its best to play a little, then tune.
But I still blame humidity.[countless edits, Im done]

[Sprocket]

Hey Mike, have you sorted this out or come to any conclusions?

[The Reverend 48]

My monies on the rock elves!

[Tony W]

The changes that I notice seem to be related to temperature which causes the metal in the strings to either expand or contract. So these days, while running A/C with cool drafts of air around the room it would seem logical for the strings to tighten.  To prove the opposite works too you could put a guitar inside a hot parked car for a few hours (which obviously you really don't want to do) but I guarantee that would cause the strings to go slack.  

I've been pondering this for days. My dream acoustic is a Rainsong, (All Graphite) because I like to play in different environments, possibly one day underwater, who knows. I dream of taking a guitar on a several day kayak trip.

With the concept of the strings expanding and contracting.... then even these guitars would lose tuning, negating the concept of a a graphite guitar.

Then again, if I spent over 2k on a guitar, I probably wouldn't take it outside, so what would be the point?