Many people have toyed with the concept of time travel and the paradoxes it presents. Some explore the paradox posed by the question: 'What would happen if you went back in time and killed your grandfather as a child?' Others address this dilemma by hypothesising that the universe splits and splits again at every decision point so that somewhere there are worlds where JFK wasn't shot and others where the Allies lost the Second World War. This theory spawns apparently insoluble questions of its own. We like to play with the big picture.
Physicists tell us that while it may be possible to move forward through wrinkles in time, it may not be possible to move back. But even so, there are books, films and TV shows galore which play with the spirals and circles and paradoxes of subverting causality by going into the past or back to the future.
And then someone asks 'But if it was possible to travel in time, why isn't there any historical evidence?'
This is a good question. What time travellers could resist the temptation to walk the streets of Ancient Athens? What future historian would pass up the opportunity of a field-trip to the Renaissance?
'There are no anachronisms', this argument goes. 'And so obviously there never will be any travellers with time machines'.
Breadcrumb trails and hidden clues
This is an argument which cuts both ways. If you take a look at history and cause and effect you can find things which appear not to have happened in a sensible chronological order.
The people in this camp argue that if the pyramids were not built by aliens, they 'must' have been built by a future civiliation. They ask how could Leonardo have imagined the helicopter; and what exactly happened to the Marie Celeste? And how come the Greeks had clockwork over 2000 years before its 'natural' development in the 18th Century?
Some of them take it further. They point out that Time Travellers will cause anachronisms, and since there are so few anachronisms they go on to postulate Time Police too. A band of people dedicated to correcting errors and eddies in the space time continuum, and to returning history to it's 'pure' path if it has been tampered with by Time Travellers.
So these people argue that the Time Police ensured that the secret of clockwork was hidden for long enough for technology to catch up. After all, the last mechanism went down in a ship wrecked in the Mediterranean. And they say that this not only shows that there have been careless Time Travellers; it also shows that Temporal Secret Agents have been here on containment and damage limitation missons.
The more fanciful suggest that Atlantis was one giant anachronism, and it was drowned in an attempt to hide this 'fact'.
These are said to be the smoking guns of the ultimate universal conspiracy theory.
But when you come to prod these theories, they all fall apart.
The Egyptians were skilled masons with an almost infinite supply of slave labour; Leonardo's helicopter could not in fact fly, and wasn't a helicopter anyway; the Marie Celeste was an insurance scam that went wrong, and the ancients' thought of knowledge as a mystery to be guarded and so their technologies disappeared with their civilisations. And as for Atlantis; well, do you really need to explain something that never existed?
And so the arguments go away.
But there is one anachronism which doesn't yield so easily to rational explanation. It is simple, and almost always overlooked.
We can imagine physicists and historians arguing the toss backwards and forwards over unseen university dinners. The baton passes from archeologist to chemist. They discuss Egyptian masonry over gin and tonics, and the tensile properties of Rennaissance metallurgy while they drink their soup. And as they put french dressing or mayonnaise on their side salads, they discuss whether or not the classical clockwork mechanism was an anachronism, and they miss the point entirely.
The mystery of mayonnaise
Let's be realistic about this culinary goo. Who on earth would stand in a kitchen, looking at salad greens, eggs and oil and vinegar, and not simply hard boil the egg, and chop it over the salad, and serve the whole thing with french dressing?
Who - hungry and with ingredients to hand - would say: 'Egg yolk, oil, vinegar: I know! I can make a thick and greasy emulsion and won't that be delicious?'3
You see, most physicists and many historians don't know how to cook, so they miss the absolute improbability of mayonnaise.
To make mayonnaise you separate the eggs, and gently beat the vinegar or lemon juice into the egg yolks. You carefully add one drop of oil, and beat it in; (more than a drop, and the mixture curdles).
Then you add another drop, and beat that in.
And another drop. And beat.
And another drop. And beat.
And another drop. And beat.
If the eggs or the oil are too warm or too cold or if you add more than one drop of oil at a time you have lumps of egg yolk sitting in oil. Not pretty, certainly not delicious, and no amount of beating will make it emulsify.
The whole process, done with a fork or even an egg whisk, takes 20 minutes or so.
Eventually, after adding about half of the oil one drop at a time, you can speed the thing up; adding entire tea-spooonfuls at a time.
Et Voila! Delicious gunge.
Mayonnaise is not an evolutionary step on from french dressing.
It requires a paradigm shift of tremendous proportions to think of eggs and oil and vinegar and conceive a creamy-white dressing. Who is going to look at those ingredients and say 'I am going to try something out here - It'll be new! It'll be daring! It'll be delicious! I'll make culinary history, and dress the salad with that!'
Not very likely, is it? Making mayonnaise requires a recipe in order to be able to do it. Which is a circular paradox, as all time paradoxes are.
A slip in time...
So, here it is. The ultimate slip in time will almost certainly not be a weapon, or a mechanism, or a boys' toy at all.
It will probably be an overweight, overworked Time Cop working on damage limitation and control: ('Your next assignment is to go back to 1756, someone has got us into hot water in a kitchen way back then - How'd it happen? Who knows? Who cares? Just sort it out, Mac!').
He likes to grab instant food between shifts, as cops always have and always will. And he just won't be able to give up the habit of sending out for sandwiches.
We already know what he orders: it will be 'Pastrami on rye, with extra mayo'.