I know this is a silly question, but I'm only asking this because I honestly can't seem to find a good definition of time that doesn't include another word that relies on the definition (or logical understanding rather) of time.  For example, in many dictionaries the definition of time is as follows:     Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them.   But the concept of 'past', 'present', and 'future' (mostly the first and last) rely heavily on time.   My best shot at a definition of time is this:     Time is the dimension on which the evolution of state of a system is allowed to occur.   Is this question senseless? Is the notion of time best left axiomatic? Do you know of a good/better definition of time? (The more concise the better)
62369
If you ask any person about time, she/he will give you some answer.  I suspect that it is extremely difficult, (if not impossible) to define time. Is there a definition of what it is in physics? Is it an "axiom" that has to be taken as it is, without explanations? I also noticed that the tag "time" has no pop-ups with comments/definition/explanations.
62037
Where such a term would reference the location/time of an object, almost like it was of a property of the object. That is to say, if a duck is red, blue, yellow etc, we describe it has having a certain colour. If it's a nanometre, or 10km big, then it's property of size.  Now I know that where/when an object exists an object isn't a property of an object, but it is something unique to that object, so I think it would be useful to have a shorthand for 'geographical location', and 'time of existence'.  There are terms describing both time and location, such an event, or rendezvous (which I think is used to describe the when and where of a meeting between two humans) but I wan't a term that just describes one of each.
35076
In a day, we have different names for different times of it. For example, morning, afternoon, night, evening, noon.  I need a hypernym for them all. What word should I use?
62158
I am not professional physicist; but I am curious about Stephen Hawking's "imaginary time". It would be better to elaborate exactly what it is. I am not confused because of the word "imaginary" but I find it confusing to imagine a two dimensional "plane time". If we express time in a plane instead of a one dimensional axis, then what does the movement of an observer along the imaginary axis signify physically?
88355
Does time stretch all the way back for infinity or was there a point when time appears to start in the universe?  I remember reading long ago somewhere that according to one theory time began shortly before the creation of the universe.  Does time have a starting point of note?
94997
Suppose we want to define a first-order language to do set theory (so we can formalize mathematics). One such construction can be found . What makes me uneasy about this definition is that words such as "set", "countable", "function", and "number" are used in somewhat non-trivial manners. For instance, behind the word "countable" rests an immense amount of mathematical knowledge: one needs the notion of a bijection, which requires functions and sets. One also needs the set of natural numbers (or something with equal cardinality), in order to say that countable sets have a bijection with the set of natural numbers.  Also, in set theory one uses the relation of belonging "$\in$". But relation seems to require the notion an ordered pair, which requires sets, whose properties are described using belonging...  I found the following in Kevin Klement's,  (pages 2-3).  "You have to use logic to study logic. There’s no getting away from it. However, I’m not going to bother stating all the logical rules that are valid in the metalanguage, since I’d need to do that in the metametalanguage, and that would just get me started on an infinite regress. The rule of thumb is: if it’s OK in the object language, it’s OK in the metalanguage too."  So it seems that, if one proves a fact about the object language, then one can also use it in the metalanguage. In the case of set theory, one may not start out knowing what sets really are, but after one proves some fact about them (e.g., that there are uncountable sets) then one implicitly "adds" this fact also to the metalanguage.  This seems like cheating: one is using the object language to conduct proofs regarding the metalanguage, when it should strictly be the other way round.  To give an example of avoiding circularity, consider the definition of the integers. We can define a binary relation $R\subseteq(\mathbf{N}\times\mathbf{N})\times(\mathbf{N}\times\mathbf{N})$, where for any $a,b,c,d\in\mathbf{N}$, $((a,b),(c,d))\in R$ iff $a+d=b+c$, and then defining $\mathbf{Z}:= \{[(a,b)]:a,b\in\mathbf{N}\}$, where $[a,b]=\{x\in \mathbf{N}\times\mathbf{N}: xR(a,b)\}$, as in  question or  on Wikipedia. In this definition if set theory and natural numbers are assumed, then there is no circularity because one did not depend on the notion of "subtraction" in defining the integers.  So my question is:     Question Is the definition of first-order logic circular?   If not, please explain why.   If the definitions are circular, is there an alternative definition which avoids the circularity?   Some thoughts:   Perhaps there is the distinction between what sets are (anything that obeys the axioms) and how sets are expressed (using a formal language). In other words, the notion of a set may not be circular, but to talk of sets using a formal language requires the notion of a set in a metalanguage. In foundational mathematics there also seems to be the idea of first defining something, and then coming back with better machinery to analyse that thing. For instance, one can define the natural numbers using the Peano axioms, then later come back to say that all structures satisfying the axioms are isomorphic. (I don't know any algebra, but that seems right.) Maybe sets, functions, etc., are too basic? Is it possible to avoid these terms when defining a formal language?
48162
Why can we use the following statement when we mean future events?     What time do you get there?   Or should we rather say:     What time will you get there?   Is there a difference?
98291
What would be a word for a moment in time defined with beginning and end?    This is for a database system where people have predefined time spans that are defined with a beginning and an end point in time (like 2014-04-11 22:15 UTC until 2014-05-22 18:22 UTC). I don't find a decent term for that. The best I could come up so far is "time frame".
69596
I have read many online articles. I've read questions and answers on this site. I still can't get my head wrapped around the difference between past simple and present perfect  I know the difference is between finished time (use past simple) and unfinished time (use present perfect). But as a non-native English speaker, this still makes no sense to me. I am not implying any kind of time period.     I have posted on SE   I posted on SE   I just want to convey that the action completed in the past. I don't want to provide any connotation whether the action just completed, or completed at certain period in past.  Maybe with "I", I know the time period, but what if I am talking about someone else.     He has posted on SE   He posted on SE   I don't know the time frame that "he" did the action. I don't know what "he" was planning (continuous action, or at specific time). I just know the action took place in the past. I don't know if it just finished. I don't know if there is a consequence to the action or not.  It seems to me that I am forced to imply a time frame. So my question is: if I don't want to imply any time frame, or at least to imply as little as possible, what should I use?
121533
The title may be a bit confusing. See the below example:     The movie (was/is) so good.   The simplest guideline on deciding which tense to use, past tense or present tense, to describe an object comes down to whether the description was only true that that time or is true even to the present point of time.  But now we talking about literary work(movies,books,etc) of which quality tend to stay the same over time, which tense should we use?
80010
Is the  defined as before or after ? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've been doing some reading while writing up my thesis and I'm finding conflicting definitions of the Big Bang.  Everyone agrees that in standard Big Bang cosmology, the Big Bang is defined as the singularity; the moment in time when the scale factor goes to zero. Okay, but when you include the theory of inflation, it gets a bit murky.  So here's what I mean by conflicting definitions. As an example, in The Primordial Density Perturbation by Lythe and Liddle, they define the Big Bang as the beginning of the era of attractive gravity after inflation. However, Modern Cosmology by Dodelson defines the Big Bang as coming before inflation; it effectively uses the old definition that the Big Bang is the moment when the scale factor approaches zero.  This contradiction is evident in multiple places. When doing a google search for it, one can find many persuasive explanations for both definitions. All definitions agree that we cannot any longer define it as the singularity where $a=0$. But every one makes sense in its own way and so, I become more and more confused about which is right the more of them I read.  The argument for the Big Bang coming after is that inflationary theory diverges from the standard Big Bang cosmology around $10^{-30}s$ before we'd expect to run into the singularity, when inflation ended, and that we have no evidence to anything coming before that, thus the big bang is now defined as the initial conditions for the hot, expanding universe that are set up by and at the end of inflation.  The argument for the Big Bang coming before seems to be that inflation is still a period where the scale factor grows and as such, the Big Bang can be defined as the closest value to zero (which is before inflation), or rather, the earliest time as the scale factor approaches zero. This essentially seems to be based on saying "well, we defined it as the moment when the scale factor was smallest before inflation was added. Why would we not continue to have that as the definition after inflation is added?"  The former argument has merit because it defines the start of the epoch where the universe is describable (practically) by the standard Big Bang cosmology. But the latter argument has merit because of its simplicity and that it uses the spirit of the original definition; the smallest scale factor and the moment when the expansion of the universe seems to begin.  Thus, my root question: Which definition is correct? Do we say the Big Bang came before or after inflation?  P.S. I realize that asking this here only serves to add one or more additional persuasive arguments to an already crowded debate. However, this is Physics.SE, so I figure whatever we decide here can be definitive. Even if we can't find a truly correct answer, this can set the record straight, or at least, firmly crooked.
107146
I hear the word "measurement" thrown around a lot in quantum mechanics, and I have yet to hear a scientific definition that makes sense. How do we define it?
68917
In French, if I want to quantify a very small amount of time (but not fixed: it can be 5 ms or 0.1 ms) I can use a pouième. Is there an equivalent in English?  I'm not looking for an expression but for a standalone word.  EDIT : In fact, I need to create a  which will measure time and be equal to a 1/600s. In French, pouième is a cute word which can means a . The issue is that I must write english code and that's why I would like to find a standalone equivalent.
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I know "I have no time." is correct.     I have no much time.   But as to "I have no much time." to mean "not enough time", the sentence seems to have self-contradiction in a sense.  Is the sentence correct?
46782
I am wondering what the difference between a definition and an axiom.  Isn't an axiom something what we define to be true?  For example, one of the axioms of Peano Arithmetic states that $\forall n:0\neq S(n)$, or in English, that zero isn't the successor of any natural number. Why can't we define 0 to be the natural number such that it isn't the successor of any natural number?  In general, why is an axiom not a definition?   Are there cases where we can formulate definitions as axioms or vice versa?
107307
What is a good definition on Space,  and the most specific topic ""? Because someone told me that spacetime is the foundation of the entire universe?  And also, Is it possible to create spacetime?
123143
How do you exactly define what is and isn't a ? I heard somewhere that it is "anything you can move through" but if that is right, why wasn't time and space considered a dimension before Einstein?