### Einstein and Father Christmas

It's that time of year when scientists get dragged into silly press releases, usually by a PR company wanting to push a product, though this one seems to be a bit different. I first heard about this from Chris Evans (n.b. I do not listen to him by choice), who announced that Einstein had finally solved the problem of how Father Christmas/Santa Claus gets round all the world's children and down chimneys. My immediate muttering was that this was pretty impressive, given Einstein's been dead over 60 years and I was going to leave it at that. But then read one of the articles based on the press release (I assume).

It tells us that according to Dr Katy Sheen, a physicist in the geography department of Exeter University, it would all work if Father Christmas travelled at 6 million miles per hour. This would get him around the world in time, and, as a bonus, (enter Einstein) 'drawing on Einstein's special theory of relativity' Dr Sheen worked out that he would shrink in the direction of travel, and 'at Santa's speed the shrinkage in so extreme he will appear invisible.'

Leaving aside whether or not 'appear invisible' is oxymoronic, there are two issues here. First let's assume Dr Sheen is right, and the relativistic contraction is significant. This would also mean that time dilation would be significant. So by the time he got round everyone, there might be issues with him having moved well into the Earth's future.

However, in practice that isn't a problem, because the shrinkage argument falls apart. If it's literally true, it doesn't help because, as the newspaper article pointed out (but Chris Evans didn't) the shrinkage is only in the direction of travel - he'd be as wide as ever sideways. But just how big would the effect be at 6 million miles an hour? It certainly sounds very fast. It's around 9.66 million kilometres per hour, which is 2.69 million metres per second. Fast or what? But the speed of light is around 299.8 million metres per second. So Father Christmas is only travelling at 0.008c.

The formula for the contraction is not complex. It's the original length x square root (1-v2/c2).

So that makes Santa's new front-to-back size 99.99% of what it was before. Not very helpful. Given the relative closeness of 269 to 299, I do wonder if the intention was for him to be 100 times faster - but every newspaper story I can find uses the low number (I couldn't find the original press release).

Am I breaking a butterfly on the wheel? Probably. But there would have been nothing wrong with giving a more realistic velocity. I've got mixed feelings at the best of times about these wacky science stories - it's all too easy to make it sound as if public funded scientists are wasting their time on trivia. But if you're going to do it, at least do it in a way that makes sense.

Update - Katy Sheen has kindly pointed out that the i misquoted her - the disappearance was due to Doppler shift, not Lorentz contraction - though the speed was quoted correctly, and so the contract effect would certainly not help with chimneys.

1. I see your wacky science story and raise you mine. https://www.theguardian.com/science/2000/dec/14/uk.technology

### Why I hate opera

If I'm honest, the title of this post is an exaggeration to make a point. I don't really hate opera. There are a couple of operas - notably Monteverdi's Incoranazione di Poppea and Purcell's Dido & Aeneas - that I quite like. But what I do find truly sickening is the reverence with which opera is treated, as if it were some particularly great art form. Nowhere was this more obvious than in ITV's recent gut-wrenchingly awful series Pop Star to Opera Star , where the likes of Alan Tichmarsh treated the real opera singers as if they were fragile pieces on Antiques Roadshow, and the music as if it were a gift of the gods. In my opinion - and I know not everyone agrees - opera is: Mediocre music Melodramatic plots Amateurishly hammy acting A forced and unpleasant singing style Ridiculously over-supported by public funds I won't even bother to go into any detail on the plots and the acting - this is just self-evident. But the other aspects need some ex

### Is 5x3 the same as 3x5?

The Internet has gone mildly bonkers over a child in America who was marked down in a test because when asked to work out 5x3 by repeated addition he/she used 5+5+5 instead of 3+3+3+3+3. Those who support the teacher say that 5x3 means 'five lots of 3' where the complainants say that 'times' is commutative (reversible) so the distinction is meaningless as 5x3 and 3x5 are indistinguishable. It's certainly true that not all mathematical operations are commutative. I think we are all comfortable that 5-3 is not the same as 3-5.  However. This not true of multiplication (of numbers). And so if there is to be any distinction, it has to be in the use of English to interpret the 'x' sign. Unfortunately, even here there is no logical way of coming up with a definitive answer. I suspect most primary school teachers would expands 'times' as 'lots of' as mentioned above. So we get 5 x 3 as '5 lots of 3'. Unfortunately that only wor

### Which idiot came up with percentage-based gradient signs

Rant warning: the contents of this post could sound like something produced by UKIP. I wish to make it clear that I do not in any way support or endorse that political party. In fact it gives me the creeps. Once upon a time, the signs for a steep hill on British roads displayed the gradient in a simple, easy-to-understand form. If the hill went up, say, one yard for every three yards forward it said '1 in 3'. Then some bureaucrat came along and decided that it would be a good idea to state the slope as a percentage. So now the sign for (say) a 1 in 10 slope says 10% (I think). That 'I think' is because the percentage-based slope is so unnatural. There are two ways we conventionally measure slopes. Either on X/Y coordiates (as in 1 in 4) or using degrees - say at a 15° angle. We don't measure them in percentages. It's easy to visualize a 1 in 3 slope, or a 30 degree angle. Much less obvious what a 33.333 recurring percent slope is. And what's a 100% slope