Question: What is Time?????
Stephen Curry answered on 18 Jun 2010:
Five past eleven.
Oh, ‘time’, not ‘the time’? It is one of the dimensions that separates events.
Tom Hartley answered on 20 Jun 2010:
This is a great question, and I think it is one of the two or three toughest in all science. The short answer is that I don’t know. Physics has made some great in-roads into understanding space and time, and Steven Hawking’s book A Brief History of Time is probably one of the best places to read about them, though I imagine there are also some more readable books on the topic.
For what it’s worth (this is REALLY outside my field) I think there are some big problems with the way we tend to think about time which are bound up with the way we (human beings) experience time and causality (the way one thing makes another thing happen) and talk about these things. It’s hard (nearly impossible) to think about it any other way. Some very clever people have made some progress with this (Einstein springs to mind), but it is still incredibly difficult and I am not at all sure if we’ve reached the end of the road with it.
For a rough analogy, think of colour. Although some people (even scientist) get mixed up about this, colours are really something inside our heads – two things that look the same colour to us can be entirely different in terms of the physics (mixture of wavelengths) that produce the sensation, or they can be physically identical and produce the same sensation (I am looking forward to giving several cool examples of this so if you are interested, use the ASK button).
Of course if time is inside the head (or if physical and psychological time are as different as the physical and psychological “colour”) then memory is central to the psychological mechanism, so it may not be so far out of my area as it seems at the moment. Why do we remember the past, and not the future? How does seeing something change the future and not the past? Or are these just the way our brains force us to understand something rather different?
Without wanting to blow your mind (it blows mine), if time literally went backwards for a moment (including everything, photons moving backwards, chemical reactions reversed, entropy etc.) then we would also lose our memories. So we would feel and act as if nothing had happened. So maybe that is happening all the time? How would we ever know?
Pete Edwards answered on 21 Jun 2010:
Time is denoted by a symbol, usually t, in our mathematical equations. We happily use the idea of time everyday when we work with these equations. But as to what time actually IS – I have no idea!
Marieke Navin answered on 22 Jun 2010:
This is a very good question, and one that people still struggle to answer. One way of describing the passage of time is to look at how the level of complexity (known as entropy) of a system (such as the Universe) evolves. The universe tends towards increased complexity, so entropy is sometimes referred to as ‘time’s arrow’.
Steve Roser answered on 23 Jun 2010:
cor this is a tough one, which stumped Einstein. Here’s my go. Time behaves a bit like a dimension, but not completely the same as teh ones we’re used to – in particular time seems to have a direction (unlike space where you can go back). So in particular entropy increases with time (if you know what entropy is) and that shows us that time has only one direction. You can never unstir a cup of tea.