[juggernot]

The following is my philosophical opinion. I'm not a scientist, and have not looked into time in relation to the theory of relativity.

In my understanding, Time is the record of matter, and the past is its history. I believe we can all agree that matter exists. Matter also has a state, which is all that is true about that object. Object state could include position, mass, density, etc. The position and properties of matter can change. Of course the original position of all matter was the gravitational singularity of the big bang, and since then matter has changed position and properties constantly due to forces and energy. If we call any change in matter due to other forces an event, than time is merely a list of events. It is clear to us that multiple events can happen at the same moment. To be clear, when I say change I do not mean a complete change such as the collapse of the star or getting a hair cut. I mean when the state of the object changes AT ALL. I would define a moment as a point in time, referring to a particular state of the object(s). Therefore the present refers to the object(s) state we are percieving currently. Therefore a period of time would refer to multiple object states, and the changes between them. The future is simply our interpretation of likely events based on past events. As humans we have the wonderful ability to record and recall object states that we percieve. This is of course, our memory.
This definition of time is dependant on trust of our senses. I believe I could explain this better, but I'm tired and must go to bed.

In summary, I submit that if there were no events, if all matter were stationary there would be no time. Therefore time is dependant on energy acting on matter.

[Rade]

Originally Posted by modest

Would everyone agree that:

1. The past cannot be changed.
2. Anything that is spatially separated from us (at any point in time) we cannot currently (at that point in time) experience. In other words, the only things we currently (at one point or slice of time) experience are the things touching us.

On first glance, it would appear that #1 must be an axiom of logic, that is, that time has an arrow of movement always to the future, hence it not possible to change any event in the past.

But, on the other hand, the words appear to get in the way of the logic, since I can think of many examples where the "past" clearly has been "changed". A few examples will do to show the problem. In golf there is the mulligan, the past drive into the swamp is changed to the present drive into the fairway, and your stroke score remains 1in both past and present but the past position of the ball has been changed. In American football is the instant replay--where the past decision of the call on the field is changed based on new evidence from the camera.

So, is it possible to restate #1 in such a way that the common sense logic of the axiom is maintained yet the exceptions I raise removed ? For, as it is now stated, I do not see how I can agree that statement #1 is always true for all uses of the words 'past' and 'change'.

[Moontanman]

Does anybody really know what time it is? Does anybody really care? About time!

[modest]

Originally Posted by Rade

But, on the other hand, the words appear to get in the way of the logic, since I can think of many examples where the "past" clearly has been "changed". A few examples will do to show the problem. In golf there is the mulligan, the past drive into the swamp is changed to the present drive into the fairway, and your stroke score remains 1in both past and present but the past position of the ball has been changed. In American football is the instant replay--where the past decision of the call on the field is changed based on new evidence from the camera.

It seems like you're describing situations where the past affects the present, but it doesn't sound like the past is being changed. The errant ball is still in the swamp and the replay doesn't change the official's first call, it merely gives him a chance to make a second call.

The largest problem I see with an axiom of "the past can't be changed" is the problem of testing it. If the past actually were changed, would we know? It may be like star trek where everything suddenly changes including everybody's memories and nobody notices.

~modest

[RanchDressing]

Originally Posted by CraigD

In various forms, this question seems to come up a lot on scienceforums, stirring considerable debate.
Answers include:

• time is something defined by any clock
• time is something defined by only certain kinds of clocks
• time isn’t defined by clocks of any kind
• time is a dimension that cannot be translated into other dimensions
• time is a dimension that can be translated into other dimensions
• time in quantatized (eg: can only be measured in multiples of 5.391 × 10-44 sec)
• time has something to do with increases in disorder/information/entropy
• there is no such thing as time – it’s just a psychic construct to prevent everything from being perceived at once
• Zeno’s paradox
• time exists, but can’t be meaningfully discussed in any natural language

Perhaps this discussion would benefit from if it left its various parent threads, and continued here. What’s do you believe time is, or is not, and why?

Simply put,

Time is a means that sequence is measured.

[Michael Mooney]

Moontanman:

Does anybody really know what time it is? Does anybody really care? About time!

Moontanman,
Ypu asked me this in my "spacetime" thread
QUOTE]
(" Do you have a better idea of what time is?[/quote])
but never replied to my answer. Here it is again.
It belongs in this thread anyway as time-specific.

Two answers to consider simultaneously...
One:
It is the *concept/measure* of event duration, like
A: one rotation of earth (day and standardized divisions thereof... hours, minutes, seconds... nanoseconds)
B: one earth orbit around sun (measured three different ways giving three technically different *spans of time*)
C: the great cycle of the precession of the equinox
D: a complete "bang/crunch" cycle, if my favorite comology is true...
...You get the idea.
Two: Now, the present is always present, not sliced into units of time in the real world/cosmos. As I've said many times, future is not yet real and present and past is not still real and present, and there is no "time" between future and past. Therefore "time" is not a natural reality in the strict ontological sense of what is real.
So, "spans of time", as above are as real as we make them. There is no cosmic counter clicking at every complete earth rotation, year, etc. Yet we can "be on time" to work by common consensus on the convention, time. and we can plug in "time" as a component of velocity and calculate and execute a round trip to the moon.

It is also conventional to call "time" the fourth dimension added to the obvious spacial three which describe volume. Then we can avoid having two airplanes at the same coordinates in air-space at the same time. A very useful convention.
But it doesn't expand and contract as an actual entity of any kind... See Two above.

Michael

[Little Bang]

Time is a variable dependent on the proximity of matter. It is also variable as inertia, an object has it's time slow down during acceleration. So why is that link there. what is it about the acceleration of matter that slows time?