What is time?

Question

What exactly is time? We use it in physics equations and equations outside of physics, but what exactly is time? Did it ever have a finite begining? Will it have a finite end? or was it an infinite begining? and will it have an Infinite end?.... What is time?

Answer 1

To have time at all already presumes a number of things, such as that it even can be used a parameter. We cannot take for granted that "any" system we can think of necessarily has "time in it". But the notion of time is so ingrained in people's psyches, it's enormously difficult for anyone to even conceive of systems and worlds without time, but they do exist. What people often say is, "It just is! We cannot have anything without time in it! Time is the very first thing we have to have before there can be anything! Time is what keeps everything from happening all at once!"

I could go ahead and give one definition of time as that which it's the parameter for any Green's function that exists for the differential operator for the system of differential equations describing any system, because to too many people, this is just "babble". So, I'll try to give a simpler example where time is used as a parameter:

Let's imagine that I have a dense, tangled mess of a vast number of threads. how do I order this tangled mess? That is to say, is there any kind of practical "coordinate system" by which I can locate things in this mess, without referring to a coordinate system OUTSIDE of this tangled mess? Sure, we can use the length of the threads as a dimension, but we then have a vast number of "dimensions", all tangled together still. It's hard to imagine any simple parameter that will help us locate things. But let's suppose those threads get interwoven into a regular fabric. Then suddenly we DO have a means of devising a coordinate system, using the length of the threads which are orthgonal to each other. Now, imagine this world as being like the ordered spacetime fabric, where we do have this practical parameter which we call "time", but it's practical only because we have the SPECIAL case of the "ordered spacetime fabric". In topology, this is called a "metric space", and it's indeed a special case, not a general one.

This is how we could have had a "beginning of time". It's actually the formation of such an ordered spacetime fabric, not that there wasn't ever anything before it. It's the beginning of PRACTICAL time, where we just have ONE time variable as a parameter.

As for Blue Sky's very long excerpt from some website on it, the trouble with philosophers' arguments about time is that they offer no useful proposals that can actually be used in physics. We are now at the point in time where we dealing with things like black holes, planck dimensions, and cosmology, where we HAVE to have a much firmer mathematical understanding of what time is, and why we have it. Philosophers are rarely mathematicians but they do love to talk.

Answer 2

I won't claim to know if time has an end or proceeds infinitely (that's a question for people who know cosmology better than I do) but time, as we know it, had a finite beginning approximately 13.7B years ago. The universe burst forth from a singularity at that point. The reason that point marks the beginning of time is that the laws of physics, including time as an accurate measure, break down inside a singularity. There is no way for us to determine the state of the universe in said singularity or how long it existed in that form. It also makes it impossible for us to determine if the Big Bang occurred after some Big Crunch.

Answer 3

There are two distinct views on the meaning of time. One view is that time is part of the fundamental structure of the universe, a dimension in which events occur in sequence, and time itself is something that can be measured. This is the realist's view, to which Sir Isaac Newton subscribed.[1]

A contrasting view is that time is part of the fundamental intellectual structure (together with space and number) within which we sequence events, quantify the duration of events and the intervals between them, and compare the motions of objects. In this view, time does not refer to any kind of entity that "flows", that objects "move through", or that is a "container" for events. This view is in the tradition of Gottfried Leibniz[2] and Immanuel Kant,[3][4] in which time, rather than being an objective thing to be measured, is part of the mental measuring system. The question, perhaps overly simplified and allowing for no middle ground, is thus: is time a "real thing" that is "all around us", or is it nothing more than a way of speaking about and measuring events?

Many fields avoid the problem of defining time itself by using operational definitions that specify the units of measurement that quantify time. Regularly recurring events and objects with apparent periodic motion have long served as standards for units of time. Examples are the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and, currently, oscillations of Cesium atoms.

Time has long been a major subject of science, philosophy and art. The measurement of time has occupied scientists and technologists, and was a prime motivation in astronomy. Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human lifespans.

Answer 4

Some may think time is a human invention but I submit that is not true, the measurement of time is a human thing but time truly exist even if it were not measured.
The nature and existance of time can be seen simply by observing the change in state of any object. As it moves from one moment to the next and changes position or form, for example.

Answer 5

Time is passing non-stop, and we follow it with clocks and calendars. Yet we cannot study it with a microscope or experiment with it. And it still keeps passing. We just cannot say what exactly happens when time passes.

Time is represented through change, such as the circular motion of the moon around the earth. The passing of time is indeed closely connected to the concept of space.

Answer 6

Time, as used in physics, needs no beginning or end, so the question is irrelevant in physics.

Hawking is getting it right since he has changed his mind about the reversability of time's "arrow."

The only rational definition of time is the measure of change of entropy, and is only measured by entities that can remember from one moment to the next. It is our time-limited consciousness that creates the sense that anything "happens" over time, whether it is the "flow" of time or the changes in entropy. If we had no memory, we would not be aware of time.

Answer 7

Mankind's understanding of time has evolved over the millennia. Euclidean geometry is a model of space wherein time is irrelevant. Newton considered time as a way to measure motion through space. Relativity recognizes time as being as fundamental a constituent of the universe as space, and furthermore recognizes the 2 as being inseparable, as space-time. We now recognize that it is meaningless, or at least very artificial, to consider space outside of its context with time. What is time? Time is 1 of the 2 fundamental constituents of the universe, the other being space.

Answer 8

The forth dimension

Answer 9

Give me a minute and I'll come up with an answer.

Answer 10

Time is what keeps everything from happening all at once.