What is time?

[modest]

Originally Posted by Little Bang

If the universe were composed only of radiation of one frequency then time would be the distance between two peaks or two troughs.

If the universe were composed only of radiation then there would be no way to measure its wavelength.

~modest

[TheBigDog]

Originally Posted by modest

If the universe were composed only of radiation then there would be no way to measure its wavelength.

~modest

For beings that can only sense radiation this is the reality of the universe.

[Johndude969]

In my opinion time is a dimension of space. What we refer to when we say time is in fact a set of co-ordinates of the dimension. It is also my belief that the dimensions of time and space are fused. For this reason a set of co-ordinates are not just a place but a time as well. In that sense travel through space also translates as travel through time. The existance of time as a planar dimension that runns parallell to our own and is at the same time fused exists for the main purpose that events that have already happened cannot be changed as this could cause a tear in the fabric of Time-Space. As such the only reason for time to exist is to prevent cataclysmic (sorry if my spelling is poor) tears in reality forming. That is what time is in my opinion.

[Michael Mooney]

I guess my edited version of 'what is time?' belongs in this thread rather than in the "Is Time an Abstract Idea?" thread, as it's author is quite a bit more "abstract" about his/her philosophy of time than I.
Sorry 'bout the redundancy, but this version is an improvement over my last version above in this thread:
Quoting myself as per my usual violation of protocol:

Time is the *concept/measure* of event duration.
This can be any "event" from a designated period of cesium's radioactive decay (as calibrated in atomic clocks) to Earth's "great precession" cycle of around 26,000 years.
Most familiar "timed events" of course are Earth's period of orbit and rotation, and fractions thereof, down to seconds and very small fractions of a second.

However, none of these periods of "time" are ontologically real as entities or a malleable medium of any kind. They are, as you said, merely concepts or measurements of designated events, beginning and ending with the observer's 'clicks of the stopwatch.'

So, in truth, *now,* the present *is* always present, not sliced into units of time in the real world/cosmos.
The future is not yet real and present and the past is not still real and present, and there is no "time" between future and past. Time is the convention of event duration from one designated now to another.

So, "spans of time", as above are as real as we make them. There is no cosmic counter clicking at every complete earth rotation, orbit, 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 or speak in terms of "light minutes or years" as measures of distance.

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, i.e., not "real" in that sense, or in the sense that each location has its own "time environment." "It" is always, perpetually *NOW everywhere.* (Same "it" as in "It is raining..." no agent "it" making rain happen.)

Last time for the above, I promise.
Michael

[Boerseun]

The Earth is orbiting the sun. The sun is orbiting the galactic centre at a breakneck pace - something like once every 250 million years. Given the size of the galaxy, the sun is hammering along at a fair clip.

So are we orbiting the sun?

No.

We are orbiting the spot where the sun was, eight minutes ago.

Yet, that is currently "empty space" in the "universal now" that you propose.

There is no universal "now".

[freeztar]

Originally Posted by TheBigDog

For beings that can only sense radiation this is the reality of the universe.

I might be wrong, but I think Modest was implying that a universe consisting of only radiation would have no beings. Or, the beings in such a universe would *have* to be composed of only radiation.

In any case, they would (or not) have the same quandary with time. Assuming SR holds in a radiation-only universe.

[ldsoftwaresteve]

I like Theory5's response about time being a perception of linear events.
That puts 'time' into the context of a mental creation which is what I think it is.
We automatically assume that all of our perceptions indicate that something exists and I think that is a weak assumption.
We have memory. That allows us to perceive events and perform internal comparisons of those events. I see there a strong possibility for making a subtle mistake with profound consequences on our worldviews: we project time into existence because we perceive it internally. That is the argument for Time being simply an abstraction without any existential properties.
I am not attacking the efficacy of using the concept. I am simply saying that we cannot presume qualities or attributes of time as if it were something that actually exists.

[freeztar]

Originally Posted by ldsoftwaresteve

I like Theory5's response about time being a perception of linear events.
That puts 'time' into the context of a mental creation which is what I think it is.
We automatically assume that all of our perceptions indicate that something exists and I think that is a weak assumption.
We have memory. That allows us to perceive events and perform internal comparisons of those events. I see there a strong possibility for making a subtle mistake with profound consequences on our worldviews: we project time into existence because we perceive it internally. That is the argument for Time being simply an abstraction without any existential properties.
I am not attacking the efficacy of using the concept. I am simply saying that we cannot presume qualities or attributes of time as if it were something that actually exists.

If time doesn't exist, then it would follow logically that it could not be measured. Yet, this is not the case. We can measure time, regardless of our perceptions (Relativity helped seal (or open)the case for this).

I understand the quandry. We can't use our measurement of time as an essential quality of time. With that, I agree. I can measure the diameter of a basketball, but that tells me nothing about the game of basketball.

We are limited, conceptually. We have clocks and I can tell you that it's 9 AM, but I can't tell you why. I can measure the diameter of the ball at any given point, but I can't tell you a thing about basketball. Does that mean the game is not real?

[Little Bang]

Time is relative to the observers frame of reference which we all know. A clock in another moving frame of reference slows with respect to our observer. This goes back to post #580. If we had a one kg block setting on a frictionless surface and apply a force of 1kg.m/sec^2 it will accelerate at 1m/sec^2. The only way to increase this acceleration is to increase the applied force OR slow the observer's clock. Isn't this exactly what happens in a gravity well ?

[TheBigDog]

Originally Posted by freeztar

I might be wrong, but I think Modest was implying that a universe consisting of only radiation would have no beings. Or, the beings in such a universe would *have* to be composed of only radiation.

In any case, they would (or not) have the same quandary with time. Assuming SR holds in a radiation-only universe.

Yeah, I was just thinking about how we even realize what the universe is composed of. Imagine you were a thermometer. All you know is the current temperature. You have no memory. To you the whole universe is just the current temperature. You have no ability to understand cause and effect or make abstract connections because all you can perceive is the current temperature. No wind, no rain, no snow, no vacuum of space, no shade, just the current temperature. That is what inspired the response.

To a thermometer the universe is just heat and has no time.

Bill