Time is an illusion, lunchtime doubly so. So what time do you make it right now? Probably
every single person watching will have a different answer, not just because you watched this
video at different times during the day, but also because we have to deal with time zones,
different clocks and varying degrees of accuracy, but mostly because you bought that suspicious
“Rilex” watch for $5 in Singapore. The idea of time existed long before clocks
so how do we define it, what is time and what are some of the amazing and strange ways it
can affect our lives? Early attitudes towards time were relatively
simple; we used the motions of the sun to give us an understanding of our place in the
day. Sun high; find food, kill food, eat food. Sun low, find woman, go to cave, shout at
woman till she make fire. There were also the shifting seasons which we weren’t able
to measure but you would learn to follow them and predict them from the way that nature
changed around them. The first instruments to make time measurements
were sundials. But these were highly localised and, from our perspective as clock users,
the times would be different each day since the amount of daylight increases and decreases
steadily throughout the year, by just over 2 minutes per day in fact. This means that
a specific point on the sundial would actually be reached slightly early or later the following
day. There were various other measures, like sand
timers and water clocks, or just counting how many teeth you had left. It wasn’t until
the early 19th century that we had reliable mechanical clocks. Still, they weren’t all
running at the same speed, but at this point, it didn’t really matter. People in each
town worked to one main clock, and the bells would ring out every hour on the hour and
that’s how the day would be organised. Then, when you went to a different town, you would
then work off that clock, which might run at a different speed. But the difference was
so small that you wouldn’t notice the change. Then, came along one significant technology
that made us realise that we had to synch up all of these different clocks. And that
thing was railways. Imagine trying to organise a train schedule where every stop on the line
thinks it’s a different time, partly because of their own town clock but also due to their
different positions on the globe. A city like Bristol, only a couple of hour’s car journey
West of London, would have a solar noon, that’s the point when the sun is at its highest in
the sky, about 10 minutes later than London thanks to the 2.5 degree difference in position.
So we needed a standard or it would be chaos. On December 1st 1847, time really began, with
the adoption of Greenwich Mean Time, which was often referred to as railway time. Until
1880, when it became all of Britain’s legal time, many clocks would show both local and
GMT on separate faces. The time zones in the US became vital since the differences over
such a large country were even greater. That’s also where the word “hello” comes from.
A telephone greeting needed to be adopted, rather than good morning or good afternoon,
since you could be talking to someone thousands of miles away and their morning might be your
afternoon. Alexander Graham Bell, inventor of the telephone, preferred the phrase “ahoy-hoy”.
Imagine how much more fun the world would have been if that had stuck.
Soon each county in Britain had standardised time and then the world began to coordinate
as communication and travel became ever faster. Most countries related their time to GMT by
1929 but it wasn’t until Nepal signed up in 1986 that we had a complete global system.
Okay, so that’s the basic history, now let’s talk about the theory. What exactly is time?
Or at least, how can we define it? Well time is really three things or concepts that share
a common name. First, it is a way to label and order events
in the universe. I buy a tub of ice cream, I eat all the ice cream, I feel sick and slightly
ashamed of myself. I need something that can show that buying comes before eating, and
then sickness and shame follow it. This is ordering, like a calendar.
Second, it’s a way to measure the distance between two events. The ordering tells me
which comes first but it doesn’t say how far apart they are. If I get a new job and
then a new car will they happen 2 weeks or 2 months apart?
And thirdly, and this one is a little more abstract, time is a medium we move through
that allows us to see that change has actually happened. The leaves turn from green to orange,
wrinkles grow under your eyes and that beer belly swells ever larger. This gives us the
concept of past and future. It’s interesting that the Ancient Greeks saw the future as
something that snuck up, unseen, behind their backs, while the past was laid in front of
them, for them to stare out into. Sneaky future, you never know what it’s up to.
This third concept is really important because it’s the only one that requires us to have
an arrow of time, a direction it moves in and never changes. The future cannot come
before the present; the smoke never returns from the air into the cigarette, the milk
never un-swirls out of our coffee and I don’t eject that ice cream into the tub, walk backwards
to the shop and exchange it for money, that would be weird and gross.
The reason many things seem strange when you play them backwards is because of Entropy.
Entropy is the second law of thermodynamics and of all the rules of physics, it’s probably
the one we are surest about. To put it simply, entropy is the measure of the order or disorder
of a system. The law states that the entropy of a closed system will either remain constant
or increase with time. This means that you always go from ordered to disordered. Think
about your bedroom. You tidy it and then it always slips slowly into a chaotic mess. And
say in that mess you find a chocolate bar; that is a nice, ordered, delicious collection
of energy. But then you stuff it in your face and that stored calorie energy turns into
kinetic energy for walking, heat, even sound for when you tread on something in the dark
and scream. I told you your room was messy. At least now you know it’s not your fault.
It’s just entropy. Think about a coffee with milk in it. The
milk will always stay mixed throughout the coffee, it will never separate so you have
an area in the cup of just milk and an area of just coffee. If it does, then your milk
was really out of date and has evolved into a sentient being.
But why is this? Well, it’s really just probability. The amount of ways you can organise
something into a useful or ordered way, is much much smaller than the ways you can organise
it into a chaotic, meaningless way. Let’s take writing as an example. If you
close your eyes and randomly bash letters on your keyboard for a minute, it’s unlikely
that you will make many words because there are so many combinations of letters but only
a few combinations make real words. Take the word “Piggy”, “P I G G Y” there are
no other words in English made from just those 5 letters; yiggp, giypg, pygig, no.
One more example. Put an ice cube in a bowl of water and it will melt and you’ll end
up with a bowl full of slightly more water. Now if you reversed time, you would expect
the ice cube to form out of the water; but how would this be possible? How would all
those water molecules decide which of them had to become the ice and which would stay
as water? It doesn’t make sense. Entropy is how we know that time is destined to move
in one direction. Alright so we know that time has a direction
but what about a speed? Is time moving at the same rate for everyone and everything?
No, it isn’t, it’s relative to the speed you are moving and by gravity. The faster
you are moving, the slower you experience time compared to someone who is not moving.
This is part of Einstein’s Theory of Relativity. You can see relativity in action every day.
For example, if you’re on a moving train and you throw a ball up in the air then catch
it, you only witness the ball moving at the speed you threw it. Whereas someone stood
on the platform as the train shoots past them at high speed, watching you throw the ball
in the air through the window, will see the ball move much faster. Because they will see
it move at the speed you threw the ball plus the speed of the moving train.
Now, the problem comes when we swap the ball for a beam of light. Most of the time the
speed of light is fixed, although it can be slowed down nothing can travel faster than
it. So take the same example but swap the ball for a beam of light, the train is moving
and you throw the beam of light up in the air. So in this instance the onlooker would
see the light beam travel at the speed of light plus the speed of the train. But that’s
not possible because you can’t exceed the speed of light. So something must have happened
to the time to make up for the lost speed, therefore in this example, you and the onlooker
would be experiencing time passing at a different rate.
This is called time dilation and it’s a great excuse for being late, since you can
claim your watch was just going slower because you walk so fast. But in reality, this difference
is negligible. The astronauts racing around the earth at almost 8km/s in the ISS have
aged about 0.005 seconds less than us back on Earth in the past 6 months. Gravity also
affects the flow of time in the same fashion. The stronger the gravity the slower time passes.
So if you were stood on a planet with several hundred times the mass of Earth for just one
hour, a whole year will have passed back here on Earth.
Relativity will never truly have an impact on our lives, until we can build ships that
can move at close to light speed. Then, you could go off on a trip to some star and come
back to find all of your relatives long dead and buried and a bill of £14 billion because
you forgot to cancel your phone contract.
That’s the physics side of things but what about personal relativity. Why is it that
your current situation affects how fast that you feel time is passing you by. One hour
in a chemistry class definitely doesn’t feel the same as one hour out in a bar, unless
you really love chemistry or you’re rubbish at drinking.
When you’re a kid, summer seems to stretch on forever but as you grow into adulthood,
summer is gone in a blink and you can’t remember what year it is and you realise that
you missed your mum’s birthday again. And what about those rare moments of extreme danger
or intensity? If you’ve ever been in a serious accident, you’ll remember that feeling of
time slowing almost to a halt and it seems like you’re processing everything at a far
quicker rate than ever before. A neuroscientist called David Eagleman became
fascinated with this idea and with how the brain measures time. Your brain is incredibly
accurate when it comes to time. Take sound for example. When you hear a loud bang, you
turn your head towards the source of the sound, but how do you know where it’s coming from?
Well, that sound travels from the source and hits each of your ears at a slightly different
time, thanks to the width of your head, which is how far apart your ears are. This time
difference is as little as 9 microseconds, that’s 9 millionths of a second, but your
subconscious brain is still able to recognise and use this information to calculate where
the sound is coming from. You also track the rhythms of the day and night, without needing
to see the sun. Your brain can measure seconds, minutes and hours passing by with incredible
accuracy. Ever woken up exactly 1 minute before your alarm goes off? That’s no coincidence,
your brain is like a little Swiss watchmaker’s house, stuffed full of various time keeping
devices, and possibly some cheese. Eagleman tried to test the effect of high
intensity situations. The problem was, you can’t just go around pushing people in front
of cars or dropping their pets out of windows to see how they react. So he found something
called a suspended catch air device, that basically involves dropping people through
a hole, while they face upwards so they can’t see the safety net behind them. He gave each
volunteer a screen on their wrist, which would flash a random number slightly faster than
the eye can normally see. If they did experience time slower, then hopefully they’d be able
to see the number. Sadly, it didn’t work but they did note that when asked how long
they thought the fall had taken, volunteers overestimated by an average of 36% so something
was happening to their perception of time, but this phenomenon still largely remains
a mystery. And finally, we can’t talk about time without
mentioning time travel. Travelling to the future is clearly possible, thanks to special
relativity, all you need to do is keep travelling close to the speed of light and life on earth
will race by much quicker than your personal experience of time. Traveling close to light
speed is no easy task though, it would require absolutely enormous amounts of energy. And
imagine how disappointed you’d be if you got out your ship and still no one had invented
x-ray glasses or a reverse microwave to make your beer cold in an instant. Without those,
the future is totally pointless. Travelling to the past is a little trickier
and we’d almost certainly need some sort of wormhole to achieve it. But it’s at least
theoretically possible, having a wormhole to the past would not defy the laws of physics,
even if it does lead to the potential for paradoxes, such as the bootstrap paradox.
This could be where a young man travels back in time, meets a girl and gets her pregnant.
He leaves, because he didn’t get into the time travel game to get tied down. But the
woman gives birth to a boy, who ends up being the time traveller. He is, without knowing
it, his own dad. It would make parents evening at school very confusing.
So time is many things, it can be a measurement, a concept and even a way of travel. We still
don’t fully understand the complexities of time and maybe we never will. But in the
end it doesn’t matter what it is, or how long it is, it’s what you do with
it that counts.