After thinking and discussing with available peers i found that time cant be define without using the word time or something synonymous to the word time. I like to hear something from scientific forum on this matter.

Hello Dhruba, you are tapping a delicate and profound question.

From the physical point of view, the notion of an absolute time -- meaning, objective and external to subjective experience -- dates back to the invention of mechanical clocks in late XIV century. The notion was formalized by Newton in the preface of his Philisophiae Naturalis Principia Mathematica in the name of practicality -- although he himself admitted that such thing was difficult if possible at all to grasp for the common sense, it was useful (actually fundamental) for his calculations, and the success of his theory made the notion of absolute time a second nature for people. The echo of this formalization supported by the astonishing and unifying power of Newtonian mechanics still informs our daily life, although Einsteinian relativity should have proclaimed a different view where space and time do not exist separately but rather only in combination -- the space-time is what makes up our physical reality, with cheers to the notion of absolute simultaneity.

More recently, the attempt to combine quantum field theory with general relativity to understand gravity in a quantum framework has lead to new logical though buffling conclusions: space derives from the gravitational field, which needs to be quantized. Thus, space has to be quantized, or better it is altogether to talk about gravitational field than space. And thus, also time needs to follow this fate. That time does not actually exist is claimed by the founders of loop quantum gravity, namely Lee Smolin and Carlo Rovelli, both recently vulgarizing their views in fascinating books.

It is surprising to know if time doesn't exist at all then what we confusing this thing with something that only exist in mathematics. I believe time is most profoundly established by mathematics than real life.

I don't believe "time" is a physical observable or a natural phenomenon like frequency of light or gravity etc. It's something that helps us frame our thoughts like electric field lines. In that case that mental image helps us understand electric fields and so is "time" used in a similar way. It's a way conceptualizing an idea. That said, I really don't know how that impacts our thinking, whether it ultimately hurts or helps us to understand the physical world.

Try using any known equation without time maybe you can come up with a different way of evolving a system.

Can we see time as just a way of measuring the relative position of every particle in the universe in relation to the other particles?

That would make it impossible to go back in time, unless you can re-arrange all particles positions and states

I found this interesting article that relates time and something that ANC Garcia mentioned which almost sounds like entropy. Here is an article that relates those two ideas.

http://io9.com/5667872/does-entropy-increase-with-time-or-does-it-make-time

Of course one can define the word time without time. Scientifically, there are several ways to measure what we call time, but the measurement of time and the definition of what we measure are two separate things. Of course, the measurements and the definitions inform each other as a part of the scientific process, but they still shouldn't be confused.

If you are looking for a scientific definition of time, it would have to include some reference point. Time is often defined in terms of movement and change and some constancy in this change becomes the unit of measurement. What Einstein found was that since light moves at a constant speed in a vacuum, we can choose to measure time as a distance. This does not imply that time itself is defined in terms of a light-year or light-second, but that we can choose distance as the measurement when we talk about time since there is constancy in a light-year or light second. To find the definition of a light-second, we still have to look at constancy the rates of change in terms of movement. Today, we use atomic clocks to define our idea of a second. Based on the number of movements of a particular atom, we can define a second very precisely as the number of these oscillations. It used to be that a second was defined by the length of the interval between water drips in an ancient clock. While it is easier to measure water drips, it isn't as accurate, but the essence of the definition in terms of constancy in change of movement remains the same as the atomic clock. No need to define it in terms of time at all.

So the light second then is defined in terms of the measurement of atomic oscillations, where it is the length of the distance traveled by light in a vacuum (constant) for that many atomic oscillations. What we have observed is that the rate of the oscillations change (relative a third clock between two other clocks) based on the amount of gravity near the respective clock, thus, time changes and space bends respectively. But, if we wished, we could define time quite differently... It would be just as valid to make distance in space the constant based on the light-second (where the second is defined in terms of the meter and not atomic motion) and the number of the atomic oscillations would variate based on the clock's motion and the influence of gravity. But that wouldn't be so convenient or necessary for current scientific discourse. But still, time would not be a function of time, but perhaps the number of atoms aligned at the diameter of a silicon sphere or something like that.

Edit: I would like to add that if a definition is tautological, that doesn't imply that such a thing doesn't exist necessarily, only that it isn't necessarily useful (except as a postulate). The good news is that time can be defined and it is quite useful. Your semantic proposition that if something may only be tautologically defined, then it does not exist should probably be revised. For example, the definition of "to be" and "exists" are relatively tautological to each other (if something "is" it exists, if something "exists", it is.) and every definition depends on these words or some variation of them. Formally, we accept existence as a property of a being axiomatically, or as some postulate, an a priori truth. So your question regarding the relationship between tautology and existence reduces to the question of solipsism.

Time is not a SI unit- a word to express the life of an incident , a person and so on

you can choose some other word other than Time

Time is change. Without change there is certainly no time measurement that can take place. The variable ''time'' in the equations is used as a parameter in term of which the changes in the other variables is expressed. But wether or not it is possible to parametrize change with a parameter called ''time'' or not, change is what is fundamental. Not all changes can be parametrized and so there is not a spatial dimension where all changes can be accounted for by moving along this dimension. Because all that exist exist now. Yesterday do not exist any more and tomorrow does not yet exist. When yesterday existed it was in the now and tomorrow when it will exist, it will exist in the now. There is no possible moving outside of the now like the fiction of thinking that we can move in time as we can move in space. We are permanently stuck in the now.

(@Larry: sure, by vulgarization I meant the trasposition of recent research into laymen terms, and both Smolin and Rovelli are pretty good at that while keeping science correct).

Let's also note that, according to Rovelli, in loop quantum gravity equations do not contain time nor space as variables - they in fact relay on the relations among events and/or objects only. That something like this be not only possible but meaningful should indeed induce reflection.

@Louis: your (St. Augustin-inspired?) thoughts may be true for all practical purposes as our everyday experience alienates relativistic velocities - in fact, Einstein maintained an alleged view of standing, Parmenidean space-time sheets which we cross in our experience along the direction we associate to (the arrow of) time, but did not forbid any trespassing so to say.

As Kantian as this may sound, we call "time" the dimension along which we expose and analyze change. The origin of such dimension may then be directly related to the origin of change itself.

Time experience would be less puzzling if it did not include a perceived direction.

Massimo,

Change cannot be fully conceptualized as a dimension or as a one variable parametrization. Nobody can denied that this time parametrization strategy has provided us a lot of insights. The spatialization of time is probably the greatest physical discovery of all time; But I suspect that overcoming this time dimension metaphysics is our biggest challenge. To move from an Parmenidean to an Heraclitean metaphysics is our biggest challenge. In the Parmenidean picture all that exist is fixed and changes are explain as a moving along in one dimension of of this fixed block world. In the Heraclitean picture all that exist is change and it is this change that stabilize some aspect of what is being created but nothing is fixed only stabilized in being preserved. Contrary to you, I beleive that the naive human observer notion of time which is also reflected in pre-modern time metaphysics is closer to reality than the notion of time dimension, spatialized/geometrized change. The naive everyday experience of being in the now cannot be understood from a spatialized time. But imagine reality as a form and imagine change as change in this form, there is only a now in that picture of reality. Rovelli and many others are gradually moving physics away from spatialized time.

Dear Massimo,

I thought Lee Smolin in his new book had clung on to time (Reborn) as the teddy bear he saved from the burning house when he could only save one thing. He seems to part company with Barbour in this. Maybe he has had an epiphany.

I suggest that time is a word with lots of meanings and we should separate them. Newton made it clear that he had two times - ordinary man's time and the time of his physics - quite different things. Unfortunately he was not too illuminating on the difference. Locke wanted time realism in terms of a primary property but Leibniz made it clear that apparent time is as different from dynamic time as raspberry pink is from a mixture of 700 and 450 nanometers (or whatever).

Apparent time is a really weird brain contraption that allows now to include a sense of last Thursday. Animals have now and past and future but not last Thursday. So our apparent time includes a quirk of a new brain circuit.

But then is dynamic time a conflation of two different things? Maybe one meaning of dynamic time is the temporal component of the spacetime metric. Time is close to change but you do not get change without some spatial difference too. Maybe a quite different thing we call time is (directional) sequence, which is really the same as cause. Maybe there is no puzzle about time being an asymmetrical metric and space not because the metrics are symmetric but sequence is not the metric. As I see it within a quantum system we do not need to posit any directionality. It is only when the sequence takes us to the next quantum system that we need a direction. Maybe I'm wrong but I do wonder.

Louis, get me right: my point of view started observing that the modern notion of time came from mechanization, externalization of a flow embedded in a machine (the clock). No apology intended. My reference to Rovelli and Smolin has the same orientation as yours - new approaches to a non-spatial time conception. That Rovelli has a passion for Anaximander (whom he calls the first scientist) is no coincidence! This said, it is still true as a matter of fact that your picture excludes relativistic effects, which again is practically fine for everyday life (not being a relativistic particle).

Massimo,

I agree that I need to work out my conception in terms that would make it compatible with relativity.

Dear Louis and Massimo,

I am interested that you both think there is a problem for the reality of Louis's now - if I read this right. If Louis is suggesting a universe-wide presentism then this violates relativity for sure. However, if now is a local herenow, as in a Whiteheadian occasion, is this a problem? What if there is no static block universe in Parmenides's sense but every direct dynamic interaction, which is more or less a 'quantum system' in Bohr's terms I guess, is a relation between a quantised dynamic unit and a domain of universe under the constraint of speed of light etc and that this relation is a dynamic 'microblock' in the sense of there being no meaning to 'before' and 'after' within it? So every dynamic event is relativistic and its single spacetime metric has no asymmetry but all dynamic events connect in sequence, which gives the asymmetry to spacetime usage, rather than time. My only concern is that if any point in spacetime is a feature of many different microblocks then incongruities arise. But if all that is needed is metric congruity I am not sure that this is a problem?

I wasn't thinking that spacetime would have a perspective - I am not sure what that would be. I was thinking that each occasion would have a perspective but a quantum occasion could be light years across. For me there would be no quanta of spacetime, just quanta of usage of the spacetime metric. I think quantised dynamic units have to yield values to measurement somehow and I would not have thought that a Planck 4voxel could do that. I am puzzled b the nature of the puzzle here because I do not have the mathematical skills to see exactly how it arises in the theories.

Jonathan,

If there is only a NOW for me but for every entity in the cosmos, it is not necessary to assume that influences among quantity are instantaneous although quantum theory allows instantaneous change accross space for entangled entities. The idea of a dimension of time, a time variable came into being when the deterministic framework of science came into being. But since the middle of the 19th century, the world is not considered to be totally deterministic and the notion of a given state of the universe as determining all other ones was the what created that block universe idea. In the block universe there is no single time that can be identified with the NOW. The laws are the same for all time, only the configurations change along the time dimension. Since everything is known ahead of time, nothing really happen that is not predicated from the state and the dynamic. Although any scientific theory has a formal deterministic structure, modern quantum physics is predicating only probabilities. Creation in the now is implicit in quantum physics and even a full knowledge of the state of a system is not possible in principle. It is creation/emergence in the NOW that prevent the existence of formal time dimension. Our formal past is the stabilzed structure of the NOW and we do science by studying fossils in all phenomenal domains.

Another question: "Is the flow of time an illusion?" discusses the same questions.

The nature of time has been the subject of discussion by philosophers for 2000 years or more. In the last two decades their views have crystallised. If time flows - (1) How do we know? and (2) How do we measure its speed? In other words - what frame of reference can we use to measure time?

The philosophers' conclusion is that they would have to invent another time dimension for the purpose but this would then need a third time dimension to measure the flow of the second ..... and so on ad infinitum. This would be absurd and so they conclude that the flow of time is an illusion.

Relativity, Einstein and Godel (A World Without Time - Palle Yourgrau - Penguin Books, 2005)

According to the theories of relativity two observers can never agree on the simultaneity of two events that both witness and neither has a "preferred" position that makes one of them correct. This implies that all events already exist and that what we perceive as the flow of time is an illusion.

Godel showed that rotating universes were consistent with relativity and proved that in them it was possible to travel back in time. He immediately realised that this implied that the past must still exist and that what he called "intuitive time" is therefore an illusion. In 1949 he published a formal proof that time (in our intuitive sense) cannot exist in any universe. This uncomfortable discovery was ignored for nearly half a century but was revived by Julian Barbour in "The End of Time" and is now widely discussed and accepted by many physicists.

Our whole lives exist always but we only perceive a succession of "now"s defined by our memories and our expectations at that moment. This gives us the (false) impression that time passes and carries us with it.

Warren,

These mathematical conclusion come about demonstration done into a mathematical language which can only be expressed with fixed marks on a sheet and which can only express what is contain in records. Since there is no existing now in any of these records and that a record can never express a now then this conclusion is necessary by the very nature. Lets assume as an provisional hypothesis that the present moment is all that exist then how can you express that with fixed mark on a sheet of papers. Impossible I agree.

The fact that any of us asks, "how long have I/ you been here?" implies the existence of time. It is a duration from a point to another point, and time can therefore be measured naturally or mechanically.... Just a thought, guys.

Larry ,

It is important to distinguish the past in the NOW from the past as it was existing in past NOW. All that exist in the NOW had be constructed in past NOW. But what is recorded today in the NOW although it had to be stabilized over long time process, most of this is gone forever and will forever remain unknown. Only the fossilized remains, the cold ashes of the past, exist NOW. Take a fossilized remain of the fifth Beethoven symphony that is recorded into the groove of a vinyl record. This fossil when inserted into a sound system and played allow us to experience this music. This musical experience in the NOW is essentially different from the fixed groove pattern of the record although I need the fossil to re-enact this experience.