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## what is time exactly

I was about to suggest to a mentor to lock the thread, but you, being the expert, have taken better care of it. A bit rough on Aristotle, who, by the standards of his day and two millennia after, is considered to be one of the greatest minds in recorded history.
 Recognitions: Gold Member Science Advisor Staff Emeritus I think in summary then Rade, Aristotle would consider time as the interval between events. Its interesting his use of the term indivisible moments. Does this imply Aristotle thought there was a minimum 'duration' (i.e. interval between events) in which one could not have any smaller duration. In essence a quantum theory of time.
 Time is not the changing of events but the change between events to one another. An event itself cannot change, an event is definite. Now if an event is definite it has certain characteristics about it that cannot change either. An event cannot be past, present, and future at the same time. Event A starts out as a future event, it then becomes present, and goes on to past. This is how we know time, from future to past. So A "has been" future, "is" present, and "will be" past. "Has been" only being distinguished from "is" by being existent in the past, and "will be" is only distinguished by being existent in the future. So if the future is the presents past, and the past is the presents future, how much sense does time being real make?
 Recognitions: Gold Member I say that time is what clocks measure, and that is all it is. In other words time is measured by events. There is no room in physics or philosophy for anything else. There is no time thing which 'flows' and oh you can measure it with clocks. Classically all proper clocks would be thought of as agreeing regardless of time, space and movement, in relativity that is changed in an understood way, but different true clocks travelling together have to agree.

 Quote by epenguin ...different true clocks travelling together have to agree.
Well, they agree because they're calibrated to agree.
 Recognitions: Gold Member The best ones we call standard have to agree with each other surely? To within a certain amount then we say our best clocks have measure time that accurately. With those we callibrate other less satisfactory ones. It is not that any clock is as good as any other. Once the rotation of the earth was our clock, so it would then have made no sense to say the earth was slowing, for that we must have a clock we know is better, it is not arbitrary.
 Here is what gets me; Time slows down due to relativity, so if we take the famous thought experiment of a man on a train travelling near the speed of light and a man on the waiting bay for the train to pass. The man on the bay (lets call him B) saw that the man on the train (lets call him man A)'s time slowed down, i.e. B saw A's time slow down, but also, A saw B's time slow down. First of all, 1) Whose right, they both cant be right? 2) Is there some field surrounding the train where time is allowed to slow down or what? 3) WTF times infinity

 Quote by epenguin I say that time is what clocks measure, and that is all it is. In other words time is measured by events. There is no room in physics or philosophy for anything else.
Very good. Now you have to define the word "clock".

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 Quote by epenguin I say that time is what clocks measure, and that is all it is.
 Quote by lightarrow Very good. Now you have to define the word "clock".
He has already defined it in his above post...

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 Quote by kurt.physics So if we take the famous thought experiment of a man on a train travelling near the speed of light and a man on the waiting bay for the train to pass. The man on the bay (lets call him B) saw that the man on the train (lets call him man A)'s time slowed down, i.e. B saw A's time slow down, but also, A saw B's time slow down. 1) Whose right, they both cant be right?
They are both right.
 2) Is there some field surrounding the train where time is allowed to slow down or what?
There is no field. That each of the two men see the other man's clock running slower than his own is purely a function of the non-zero relative velocity between the two men.

 Quote by Shooting star He has already defined it in his above post...

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 Quote by epenguin I say that time is what clocks measure, and that is all it is.
 Quote by lightarrow Very good. Now you have to define the word "clock".
 Quote by Shooting star He has already defined it in his above post...
In effect, he has already defined clock as that which measures time.

This is a circular definition. However, irrespective of how many links you introduce in the chain, ultimately it will be just a big circle. Isn't that why we are still discussing this, on record, approximately over two and a half millennia?
 Hi, Im kinda new here. Me and some other dude had a discussion about if Time did really exist. Instead of making a new thread about time, I though crashing/hijacking this thread instead. Edit by Evo: Let's keep this thread to the discussion going on here.
 Recognitions: Homework Help A tremendous effort, but could you please reduce the length of your essay the next time? Something happens to me after a minute... (Seriously, it's too big, with all those links.)
 Hehe, I didn't realized that I was making an long "essay", so I apologize I made the short resumè of the discussion we had, so you could skip those links. but then again, It wouldn't have made sence if I leaved out those links. (Links are there so you wouldn't have to search for relevant post among the troll posts)

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 Quote by Shooting star In effect, he has already defined clock as that which measures time. This is a circular definition. However, irrespective of how many links you introduce in the chain, ultimately it will be just a big circle. Isn't that why we are still discussing this, on record, approximately over two and a half millennia?
I don't think it is, at least it is trying not to be. I think we can accept without further analysis that there are observed regularities in nature, and of events, and then of events 'happening together', resisting the temptation to say 'at the same time.' We can count. We can say 'every 365 days' - idea of duration not needed but only of events like a shadow passing a mark - 'the stars go back to the same position'. We do not need the events to be repetitive, in fact the best clock for thinking about it is the Tait clock, which is successive relative positions of some stars which are in free (not being accelearated by attractions) motion. Work it out, that is not circular. What we need is:
more than one such clock and to find that they agree;
a reason to believe that they are simple and understood. For the Tait clock the reason would be that each star is very far from the influence of other bodies.

These things are observable. Time is not a thing, but just what you invent to relate these observations; you could just relate them to each other. You invent 'seconds' as a convenience. It is like you might live buying and selling real things, to do this you can have dollars $or other currency units in a bank which you never see. Currency units do not need to be real. You are so used to talking about them you may think of them as real. You might prefer the most stable currency, the one with most constant relation with the most important simple desirables. In fact ideally you would make such a desirable your unit of currency. Then in physics you observe things which are not as regular as your clock, and you then say they are complex and need theories to be invented to explain why and exactly how they are not regular. Equations in tems of t which you think of as real like you think of$ as real, but you are just relating phenomena to your clocks which you think are simple.

 Quote by Kurdt I think in summary then Rade, Aristotle would consider time as the interval between events.
No, this is not my understanding. Time is an interval between "moments" for Aristotle. An "event" is not a moment, an event is what occurs within the interval called time--a coming to be or a doing away with.
 Quote by Kurdt Its interesting his use of the term indivisible moments. Does this imply Aristotle thought there was a minimum 'duration' (i.e. interval between events) in which one could not have any smaller duration. In essence a quantum theory of time.
The term" indivisible moment" is my term, Aristotle defined time as being intermediate between moments, then defined moments as being indivisible, so he should have no problem with the term "indivisible moment" since the opposite for him would be a logical contradiction.

Your second question is interesting--here is what I found.

In quantum theory, there is no time smaller than Planck Time, so what would Aristotle say about this ? I think we find the answer in Physica, Book III, Chapter 6. Recall that for Aristotle time is not a magnitude, but "time is a kind of number" (Book IV, Chapter 11), it is "what is counted" between moments, and in Chapter 12 he states "since time is number". So, it it safe to claim that Aristotle holds that time is number, a kind of number related to what is counted about motion between moments.

Now, in Book III, Chapter 6 Aristotle discusses the infinite. And here he claims this...."it is natural too to suppose that in "number" (quote added) there is a limit in the direction of the minimum". Thus, since time is number for Aristotle, I suggest that he would hold that time also has a limit in the direction of the minimum, and that this concept of the limit of time in the direction of the minimum is what we today call Planck Time. Furthermore, Aristotle makes this claim..."hence number must stop at the indivisible". So, here we see that Aristotle would claim also that "time" must stop at the indivisible, and recall that the indivisibles between time are the moments. Thus I conclude that Aristotle would agree that there exists a smallest time duration between any two moments--what we call today Planck Time--it would appear that Aristotle is the great..great grandfather of quantum theory as relates to time as a number of what is counted in relation to motion.