Thoughts on Time

What is time?

Time is not like other ‘things’.You cannot see it, weigh it, measure it. ‘Ah, you might say, we can measure it, we have very accurate clocks – some such as atomic clocks are very, very accurate. The record at the moment is held by a clock that loses or gains less than one second in 5 billion years. It ‘ticks 430’ trillion times a second.

OK, so that’s accurate but what does it mean by a second? It defines a second by the operation of the clock so there is a bit of tautology going on here.

Let’s think about time as it is experienced by humans. We have a pretty handy clock that is sunrise and sunset. If you measure the time between sunsets, it tends to be the same every day. OK, so the time between two sunsets, we call a day. For some reason we chop it up into 24 divisions, then 60 divisions then 60 again – why? Look at the front of your left hand. Use your thumb as a pointer. Each finger has three sections between the joints so, using all the sections of each finger, you can count to 12. So, logically there can be 12 hours in a day. 1 day = 1 night so there must be 12 hours in each night. so 24 hours between one sunset and the next. So now we have the duodecimal system – ( Base 12 ).

Now this almost works ok but, away from the equator the lengths of daylight vary according to the seasons. This means, if you want to keep 10 hours of daylight with an hour of twilight each end of the day then an hour has to be variable depending on the season, which it was for many centuries.  Then, Hipparchus gave us the “Equinoctial” hours where each hour is a fixed length of time. Most people, until the 14th century when mechanical clocks came along, were happy to continue with the variable hour. It didn’t really matter because there weren’t any trains to catch.

The Greeks found this not very useful or accurate for their astronomical observations so they divided each, Equinoctial, hour into 60 equal parts, presumably because the Babylonians used a sexagesimal ( Base 60 ) system. If you needed a smaller unit of time, just divide your measurement by 60 again – this gives you seconds.

It wasn’t until many years later that it was necessary to have a smaller unit if time than a second. By this time the sexagesimal system wasn’t used – people had started to use the decimal system where everything was to base ten. If you divided a second by 10 three times you end up with the millisecond. If smaller units were necessary then it was simple to divide by three tens again and that gave you the nanosecond – and so on.

So we can now measure time very accurately. Problem solved.

Along came Albert Einstein with his theory of general relativity that predicted that time changed with gravity. We knew by then from Newton that gravity decreased as it moved away from a spacetime disturbance by a mass such as the Earth according to an inverse square law formula. This mean that gravity decreased as you climb a mountain and time speeds up so that means that you age more slowly.

So what happens when you go near to a very massive object such as a black hole? It will have a huge effect on spacetime to its very large gravity will cause a huge slowing down of time. Your personal time will pass very slowly so when you then move away from the black hole you may find that the universe has moved on by many millions of years while you will feel you will have aged at a normal rate.

If we now go back in time to visit Isaac Newton and borrow an apple from him to repeat his, probably fictional, experiment of dropping an apple. He holds up the apple and then drops it. What has changed between the time he let it go and the time that it hit the ground? Nothing has changed except time – everything else is still the same except that the apply is now in a different place. So the apple has experienced a change while nothing else has. This is another way of saying that everything experiences its own time.

Can we prove this? Yes! Take two  of the identical super accurate clocks that we talked about earlier. Install one at a fixed place on the surface of the Earth and install the other one in an airliner. Fly around the world as high as possible. Then place them side by side and compare the time. There will be a difference. This is caused by the lower gravity experienced by the ‘flying clock’. If gravity affects time then it but a short leap of logic to say that gravity creates time. If gravity creates time and mass creates gravity by distorting spacetime then if there is no mass then there is no time.

Therefore time is everything. With no time, Newton’s apple would not fall – nothing would happen.

Did you have enough time to read this?

© Richard Kefford                                                                                 Eorðdraca

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