# JOST A MON

Aug 16, 2010

## Flip Turn Rotate

You know you're supposed to flip your mattress periodically, right? Sure you do. This is to enable an even amount of compression in the springs or the filling so that you don't end up in later years in an orthopaedic ward with a misaligned back. And so you do your back in today flipping the mattress around just to avoid doing your back in at a later date.

But I get ahead of myself.

Flipping or turning or rotating? Any of these actions, if carried out a sufficient number of times, results in the mattress ending up as it started. That is because the mattress, a cuboid, has only so many degrees of freedom. The set of operations you can carry out even forms a delightful mathematical object called a group; in particular, it is a non-commutative group, because combining the actions in different sequences sometimes result in different orientations of the mattress.

You can read all about it in the inestimable Brian Hayes's book Group Theory in the Bedroom, and Other Mathematical Diversions, and please get your minds out of the gutter right now.

But that's not what I want to talk about.

The wife legged it to India recently with instructions for me to procure a new mattress for our downstairs bed before she came back. Until a couple of days ago, I had the excuse that I was studying to avoid going into the store. Today, however, I ran out of procrastinatory reasons, and I went to John Lewis (who are never knowingly undersold) to check out the mattresses on offer.

For some reason, the place was seething with couples. All were intent on trying out the mattresses. Every mattress I looked at had hetero- and homo- duos canoodling or lolling about or lying back and concentrating on the ceiling. It got so bad that when I, locating a likely mattress, lay down on it myself - strictly because I was beginning to get a tad tired - I found myself next to an exasperated-looking woman.

Thinking she was exasperated at me, I leapt off the bed. She complained loudly that it was too soft.

I pottered around a bit more, studying the information tags. Some mattresses, I learned, needed to be turned. This got me thinking. What does 'turn' mean in this context? Flip? Rotate? Evidently there was an entire vocabulary here that I had to absorb. On another mattress, the flyer said that it didn't need turning. Low-maintenance, it announced. You only need to rotate periodically, it said.

Okay, so that was clear. You really don't want to flip the mattress about too much, especially if right next to the bed is your wife's centuries old ivory-inlaid side-table, and you forgot to move it aside.

Er, it was an accident, darling, honest!

What I'd really like, though, is a Tempur. Ah, a Tempur. Material with memory, moulds itself to your contours, hypoallergenic, low maintenance. Simply a delight. I plonked myself on one, and fell asleep promptly.

The problem (besides the mind-numbing expense of it) is that it really needs two people to try it out. Especially if the weight-differential between them is considerable. Furthermore, one needs to choose just the right springiness as well - too soft, and one's back is toast; too hard, and one's sleep is akin to that princess on a pea. And one person's hardness is another person's softness. It has to be a collective decision, therefore.

All in all, I figured I might as well wait for the wife's return. We'll both go and try out the mattresses, and the wife will decide which one we'll get.

PS: The side-table is fine.
PPS: No, really.