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Asked by edrienepadua to Christina, Colin, Jess, Samaneh, Steve on 14 Jun 2013. This question was also asked by teniola.
Question: What is time?
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Steven Gardner answered on 14 Jun 2013:
Wow that’s a deep question!
Time is a dimension that we use to describe things that happen. To describe an event that has happened, it’s no good just giving the place, you also need the when. We can use three dimensions to describe the place of anything (we usually call these x, y and z), time is just an extra one of these.
The funny thing about time is you can only go one way. Sounds like an obvious thing to say but you can go forwards and backwards and up and down and left and right, so why not forwards and backwards in time? Well if you could it would break a law called causality. The law of causality says that a ’cause’ must always happen before an ‘effect’ (For example, the doorbell doesn’t ring until you press it!). If you could go back in time, you could easily break that law. If cause and effect get mixed up it would be impossible to predict anything, so it’s a good thing they don’t!
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Jess Bean answered on 14 Jun 2013:
Time is a weird and funny thing! Sometimes it feels like it goes by in a flash, sometimes it can drag on for ever! In modern times it is defined by atomic decay, but in the past was done with the sun.
Time is a dimension that we can use to split up the day, measure how long something takes to happen, work out how old someone is and also use as a way of describing if something happened in the past, present or future. Time also has an annoying knack of making people, trains and buses late.
These seem really normal concepts to us, as we use them every day, but imagine if you had no way of conveying time? The Amondawa tribe in the Amazon have no word for “year”, “month” or indeed “time”!
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Christina Pagel answered on 14 Jun 2013:
Jess and Steven’s answers are really good! I don’t think I can add anything useful to their answers…
I guess I’d only say that one of the reasons time is so important in science is that a lot of science is about trying to understand how things change… and to do this you need to have a good theoretical, universally agreed, way of measuring time and changes over time. Newton & Leibniz started the modern theory off by inventing calculus in the 17th century – now fundamental to almost every part of science!
Einstein and his theory of relativity made sure that very few people understand time in the sense that he proved that moving really fast means you age really slowly (compared to everyone else)!
Comments
geobullet commented on :
Time is wibbly wobbly timey wimey stuff, any doctor who fan knows this!!!!!
desorgherm commented on :
I read somewhere that time isn’t as constant and can be affected by the mass of nearby matter but how? that makes no sense to me, how can mass affect how slowly stuff happens? and would you age slower on another planet with different gravity? Why?
Steve commented on :
Yes you would!
Einstein, in his theory of special relativity, showed that when you increase in speed you travel more slowly in time.
Ten years later Einstein realised that acceleration and gravity could be considered the same thing. He called this the principle of equivalence and called it his ‘most beautiful thought’. I’ll explain with an example.
Imagine you’re standing on the bottom of a spaceship with no windows and it’s completely sound proof, and when you jump off the floor you come back down. The question is, can you tell if your spaceship is accelerating upwards or if it is just sitting on the earth? The answer is you can’t, if the spaceship was accelerating upwards you would fall to the floor in the same way you would if it was on the ground. Since you can’t tell which of these situations you are in, you have to treat them as if they are the same thing. Since acceleration causes time to go slower, then gravity must do as well!
And it does! The satellites that make up the global positioning system have extremely accurate atomic clocks inside them, these clocks have to be very slightly adjusted because they are higher and so feel slightly less gravity than those on the ground. When they first ran the GPS system, the engineers apparently refused to believe it was important, and the system kept losing track of things. When they used Einstein’s correction it worked perfectly.
It’s important to realise though that this doesn’t mean you notice time running any slower. If you moved to a high gravity planet, a second is still the same as it was to you, you just see everyone else’s clocks running fast, and they see yours running slow.