For Daniel, our top family physicist, and for Aaliya, who gave me Carlo Rovelli's wonderful book, Seven Brief Lessons on Physics, who both delightfully debated these daft and difficult theories with me.

Is it not true that many great scientific discoveries have been the outcome of accident or luck, of scientists observing what actually happens, developing a theory to explain why it happens, and then devoting their lives to carrying out endlessly complicated experiments to prove their theory correct, or - if the theory is someone else’s - incorrect? I think this is so, and centuries of experience support the method.
 
Thus we now better understand some everyday occurrences and circumstances, things taken for granted until properly observed and thought about by the logically precise mind of the natural scientist: that apples fall on your head if you sit under an apple tree long enough in autumn; that cows don’t get smallpox; that chairs push upwards when you sit on them (and therefore Newton could be said to have headed the apple); that this solid earth is in fact composed of billions of atoms and not solid at all; and the even more staringly obvious discovery that these tiny tiny atoms are made of even more minute minute particles. Each of these physical phenomena is obvious, once you think about it. 
 
On this sound scientific basis, therefore, I have a theory of time to propound. I don’t know if I am breaking new ground with what follows, but like Newton, I am simply extrapolating an explanation from clear factual events. I shall start by describing the initially inexplicable circumstances, before presenting my theory of time and offering some supporting evidence.  

Every morning, now that Jane and I don’t have to reluctantly rise and dully shine, I make us a cup of tea to enjoy in bed while we consider what must be done in the day that stretches ahead of us. (This used to happen only on a weekend, but every day is the weekend now.) At home, in the minor foothills of the moderate English Chilterns, these cups of tea are too hot to drink when first brought to the bedside. Idle chat ensues until I can commence drinking mine. Jane does not enjoy her tea at the apparently extreme temperature that I do, so she waits until I have drained my mug before rousing and turning her attention to her own tea, which she drinks with clear satisfaction. This order of events is crucial to the discovery upon which this learned paper is founded.  
 
Now, we are currently having a short pre-holiday in the French Alps prior to our main gap year holiday here for the first half of 2017. As is customary, I rise reasonably betimes to make the tea and bring the two brimming mugs back to bed. Once there, as at home, I soon commence to drink my tea; it seems to me to be less hot than usual. As I approach the last two or three sips, I thoughtfully suggest that Jane abjure her usual habit of waiting for my finishing drinking as the signal for her to start, because her tea will be decidedly coolish by the time she gets half way down the mug, unless she starts before I finish. She does so and finds no discomfort of undue heat in tea, indeed, it is cooler than she had anticipated; her observation of the facts of the case agrees with my own. The tea is not as hot here as it is at home. What is the explanation?  
 
There is an existing theory, which I think I recall from Physics lessons (Grade 5 O Level, 1969 – no travesty about this grade). This is something to do with air pressure and the belief that water boils at a lower temperature at altitude, if I remember rightly. However, everyone knows that water boils at 100 degrees C. It is one of the facts of life, incontrovertible, like the sun rising and setting, and the UK’s weather always moving from left to right on BBC maps; like like repelling and unlike attracting (magnets), and like attracting and unlike repelling (people); and walking so you face the oncoming traffic on roads with no pavement. These are the rules. And water boils at 100 degrees C is one of them. But if the morning tea is not as hot half way up an alp in Planvillard as it is half way up Stanley Hill in Amersham, and if the tea has been made with water poured from a kettle that gives every indication of having done what it was put on to do and boiled the water, then it seems to me that the problem here is not one of air pressure, but of time. The water reaches boiling point too quickly, the kettle isn’t on long enough, and so the tea is not as hot and cools too quickly and Jane has to stir herself to stir her tea sooner than she has to at lower levels.  
 
Therefore, my theory is that time moves faster at altitude. This has such credible and elegant economy of expression that it almost convinces just by itself. But once the theory is embedded in the scientific consciousness, as with all these cracking science theories, things you took for granted begin to make more sense. And this is a far more straightforward explanation than that air pressure stops your kettle working properly.

Think about mountains and some of the ramifications of this revelation become clearer. Who has ever come back from a ski-ing holiday saying it was too long, or even that it was long enough? No-one I have come across; more usually, they say the days seemed to go by too quickly and it was all over too soon. It is clear now that this is a precise description of what has actually happened! Time passes faster at altitude. 
 
Again, what is it that anyone venturing onto a mountain in any season is warned about? The suddenly changing weather. It was gloriously sunny when you set out, with not a cloud in the sky, but now two hours later, you are being drenched by a thunder storm. By the time you return to base, the pleasant breeze has well-nigh dried you and your clothes to the point of giving you a chill. Once you appreciate that time moves faster at altitude, you can easily surmise the reason for your unsatisfying walk: it is because, during the walk, you have experienced more than one day’s weather. 
 
Climbers on Everest, those who do not make it to the summit but have to turn back down, often explain that the expedition ran out of time. They might dress this up as adverse weather conditions (see above), or running out of supplies, or lack of oxygen, or being unable to make a decent cup of tea, or having to get back to school by the beginning of term, but all these reasons are simply to explain the overriding fact that they did not have enough time to get to the top. I could add a hypothesis to my theory of time, which would be that it is likely that time accelerates the higher you go. Further research is needed. Perhaps getting up to make the tea at a range of heights. I’d need to think about the practicalities of this. 
 
Sceptics will be quick to point out that once the altitude increases so that we have to consider time in space, my theory does not apply at all. Sceptics will cite the unproven (but wonderfully bonkers if true) proposition that twins separated as children, and one sent into space on a years long mission, will be different ages when the space twin returns. But conversely to my theory of time, the space twin will have aged more slowly than the earthling twin. The main question about this hypothetical experiment though is, if this is true, would they still share the same birthday?  
 
Anyway, I am quite content to amend my theory to allow it to be reversed once you leave the planet. There is an unimpeachable authority to support this amendment: “This is space; it doesn’t co-operate.” (Matt Damon in The Martian.) Great line, great film, maybe a tad on the long side. 

13th December 2016
 

If you enjoy reading High Time, there is more in a similar vein, though a lot less scientific, HERE