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Asked by Ayrton to Ed, Kerrianne, Nina, Oli, yoyehudi on 7 Nov 2017.
Question: What is time?
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Kerrianne Harrington answered on 7 Nov 2017:
This is actually a good question! Time in physics is kind of less philosophical, and we take it to literally be “what a clock reads”. We use it to define so many of our quantities, and it is one of the seven fundamental physical quantities.
However, the fun starts when we ask the question “Whose clock?” One of Einstein’s wild ideas was that the speed of light is the speed limit of the universe, and this has implications for time. The faster the traveler, the slower their clock runs. So depending on your frame of reference, how time behaves changes between observers.
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Ed Bracey answered on 7 Nov 2017:
Hard question! I really don’t think we know what it is.
There’s what humans call time, using things like the rotation of the earth to decide how long hours and days are.
Our brains also have a rhythm – some brain cells fire in regular waves of activity, which might contribute to our sense of time. Some of these cells detect light and so change our brain and body clocks depending on the light we get at different times of day.
I guess you could also think of time as the movement of all subatomic particles in space. Let’s see, it’s 18.51 now. If I could put all the subatomic particles in the universe back where they were at 18.50, would everything have moved back in time?
Kerrianne is the physicist, maybe she knows!
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