What is time ?

[Time Traveler]

On 2/5/2021 at 10:14 PM, joigus said:

And what is speed? And what is change? Isn't time already implied there?

Changes(Transformations) ,Speed of changes and Causality are fundamental properties of the Universe....I think every intelligent being perceives them because intelligent beings are 'designed' to survive. They do not perceive time as they perceive change, the speed of change, the causality -cause precedes effect-(that gives the arrow of time ....past....present....future), which are fundamental properties of the universe.Time is a human concept very useful.It is important/exists only for everything that exists and who have changes and a certain speed of change .

On 2/5/2021 at 11:39 PM, beecee said:

It is as far as Einstein's theories are concerned, and as yet we have no reason at all to doubt them.

We observe simply at a rate/time it takes photons to reach our eyes.

Changes or passages of time simply depend on one's frame of reference. These are indisputable facts, as evidenced many times.

Instead of your continuing statements of certainty, do you have any evidence? or perhaps a new hypothesis?

The frame of reference....Imagine you are a common observer at a demonstration of a great illusionist /magician....You have your reference's frame...Other common observers , from TV for exemple or near the magician  has their reference frame.Do you think a human observer who is 'programed to survive'  and not to be a deep Universe observer ( we humans perceive reality true in our way , a codification of reality ....remember colors are only a human representation of a part of electomagnetic radiation)....he can't understand if he not are prepared to understand what the grand magician do. He understand what the magician wants That's how we are now ...we great humans observers

On 2/5/2021 at 11:10 PM, studiot said:

 

Do you think lack of change is unimportant?

 

No....I observe only that:Transformations ,Speed of transformations ,Causality are fundamental properties of the Universe and Time is a concept very useful for survive and not only

On 2/6/2021 at 4:01 AM, Col Not Colin said:

  I think several people have already mentioned what time is assumed to be for most models in Science.  Time is another co-ordinate we need (in addition to the usual spatial co-ordinates) to specify where events happen in spacetime.

I understood .... If I will ask you to go at an adress  .... point A (x, y, z) where you will find a treasure is better to ask you to go at point A (x, y, z, t) because the treasure will be there at time t in the future not now......Conclusion:Space-time a useful concept

[Time Traveler]

On 2/5/2021 at 11:49 PM, MigL said:

The OP's opinion is easily falsified.
His question gets asked time and time again, but the answer never changes.
So it would seem, time is independent of change.

( sorry if I'm being snarky, had to put my cat to 'sleep' today )

Changes/Transformers are always in a period of time ...not instantaneous..... sometimes maybe cvasi instantaneous

Edited July 12, 2022 by Time Traveler

[MigL]

How do you assess whether a change is instantaneous or happens over a period of time, without a separate, independant notion of 'time' ?

[Time Traveler]

On 2/5/2021 at 6:06 PM, swansont said:

Is there a testable hypothesis here? A model, or evidence?

I will try to build a model: ( I am sorry because I have no time to spend too much ....very occupied at work....very tired about work...life is hard for many of us....)

Imagine 100 000 years ago Alice and Bob (Forces +Laws of physics+Causality+Designer+Builder) will build a City from something like LEGO BRICKS (from different shapes and colors) , in a week working with different Speeds .

Changes: from 0 buildings to 100 buildings:C1.....C100 and will use 100 Bricks for 1 Building(1 Change/Transformation)

They will use let say 3 Speeds : S0....no changes,S1=Slow and S2=Hi Speed

Assumption: Alice and Bob don't know what time is  because endowed for survival not for research and they know only about Transformations/Changes,Slowness or Speed of changes and Causality ....causes precede  effects and events take place  in a certain  sense .They have knowledge about periodic changes like day and night and have a primitive hourglass who they observed their periodic changes when they used it. Also we assume they know how to count.

They start to build  the City: First day will use a lot of bricks to make 5 Changes =5Buildings....5000 bricks using all 3 Speeds:S1,S0,S2.They observe when use S0 ...no changes,when use S2 the most changes.They already know using the hourglass let say in a day their hourglass will be emty 24 times.Using an emptyng for  the hourglass .... 1 hour.... and S2 they observed ......

I am sorry but I am very tired and I will continue if someone will be interested

29 minutes ago, MigL said:

How do you assess whether a change is instantaneous or happens over a period of time, without a separate, independant notion of 'time' ?

Building a clock like hourglass who measure changes/slowness of changes.....I told time is very important for us but is not a fundamental property of the Universe . You understand Time=Change/Speed.Please Choose only 2 fundamental property from 3. Speed and time ,speed and changes or changes and time

[MigL]

Maybe it's a language issue, but, of the three so called 'undamental' choices you present, only one is actually fundamental.

Speed is a change in distance per period of TIME.
Change is the diference in something over a period of TIME.

TIME is the only fundamental variable, of the choices you presented.

Maybe try again when you are less tired ....

[Greg A.]

On 2/6/2021 at 2:52 AM, Time Traveler said:

 

My point of view about time

The human observer invented the concept of time and clock because it was difficult for him to measure change and speed of change (rapidity of change or slowness of change) which along with: space, matter, energy, forces, fields, .... are fundamental constituents and properties of the universe.
Time is nothing but the relationship between change and the speed of change. Time only makes sense for what is changing at a certain speed, so it is a function of these two.
Time is relative depending on the nature of the change: life time, half-life for radioactive substances, reaction time, astronomical time ....

Quote

There is time, the measure that relates to motion and distance, and there is Time where events are arranged in a chronological order, the past, present, and the future.

Is Time real is the question. And it doesn't look good for the romantics. That is if we see ourselves as being on 2 dimensional plane of motion, then there is no future only an ongoing present, the past is a concept, and we can go back to the Time of our birth only to the extent that change allows. Our hometown and the hospital where we were born, relatively static objects, these as close to the instance of our birth as we will get. We could visit the dinosaurs too, but once again, their fossils, and dust spread around us is the only option there is to doing that.

But then I don't know anything much about physics and it could be that all motion is contained in Time and can be reversed and revisited even?

 

 

 

 

 

[Intoscience]

On 7/13/2022 at 1:04 PM, Greg A. said:

we can go back to the Time of our birth only to the extent that change allows

There is no evidence that it is possible to travel back in time. However it is possible to travel forward in time relative to another frame of reference.

[Greg A.]

5 hours ago, Intoscience said:

There is no evidence that it is possible to travel back in time. However it is possible to travel forward in time relative to another frame of reference.

Neither are possible if Time does not exist. Both may be possible if it does exist. Traveling forward in time requires a chronology that we have been a part of ourselves. How would the time traveler be aware that he has traveled into the future if he hadn't lived though that same or similar sequence of events.  Suppose the brother returned from his journey at relativistic speeds to find that his identical twin was now actually younger than he was. He would need to believe he had traveled back in time. But that's when his brother had simply undergone de-aging therapy. 

[Time Traveler]

On 7/12/2022 at 8:42 PM, MigL said:

How do you assess whether a change is instantaneous or happens over a period of time, without a separate, independant notion of 'time' ?

In my opinion Changes and Speed of Changes are fundamental.Humans were endowed by nature for survive not for scientific subtle observations . If we analize definition of units of time , second,day,year,..... we observe that are a fraction or a unit of a periodic change divided at speed of that change.Speed of change is 1 for a day who is a slowness change for example.Changes and speed or slowness were easy observed by ancient humans but many changes are at high speeds very hard or impossible to detect by humans. Invention of clocks was a very important technological step because could be calculated those high speeds

From Wikipedia: "

The

 second (symbol: s, also abbreviated: sec^[1]) is the base unit of time in the International System of Units (SI), historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each (24 × 60 × 60 = 86400).

The current and formal definition in the International System of Units (SI) is a much more accurate timekeeper:

The second [...] is defined by taking the fixed numerical value of the caesium frequency, Δν_Cs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s^–1.^[2]

This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with caesium clocks.^[3] Because the speed of the Earth's rotation varies and is slowing ever so slightly, a leap second is added at irregular intervals to civil time^{[nb 1]} to keep clocks in sync with Earth's rotation"

My conclusion : Time=Change/Speed of change

 

[MigL]

I thought someone had already mentioned this ...
( must have been in another thread )

36 minutes ago, Time Traveler said:

My conclusion : Time=Change/Speed of change

Even assuming 'change' is fundamental, by definition, Speed of Change = Change / Time, which, upon substitution gives 

Time = Change / ( Change / Time )

and cancelling out 'Change' gives the deeply meaningful ( HaHa! ) result

Time = Time

Would you care to try again with something that makes sense ?

[Fly135]

Time is a count of the "vibrations of the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom".  Not saying I know exactly what all those words mean, but that's what time is.

[hoola]

time seems a measure of change within a particular system with a default periodicy essentially the same everywhere, but modified by large gravitational forces. I see the fundamental increment of time a function of the appearance/annialation frequency of the virtual particles. If the orbits of the particles within the system  are elongated by gravity, that slows time, as in black hole dynamics.  Relative velocities slow time, but by a seemingly different mechanism.

[MigL]

On 8/26/2022 at 1:30 PM, Fly135 said:

Time is a count of the "vibrations of the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom".

Except for the fact that 'frequency' is measured in 'cycles per unit time'.
You are then using something, frequency, which is defined using time, to define time itself.
Kind of circular reasoning.

Incidentally Swansont designs/builds the equipment that measures the 'hyperfine transition frequency of caesium-133'; his area of expertise is atomic clocks.

[Fly135]

On 8/28/2022 at 12:18 AM, MigL said:

Except for the fact that 'frequency' is measured in 'cycles per unit time'.
You are then using something, frequency, which is defined using time, to define time itself.
Kind of circular reasoning.

Incidentally Swansont designs/builds the equipment that measures the 'hyperfine transition frequency of caesium-133'; his area of expertise is atomic clocks.

A count is not the same as a frequency.  If you doubt that, check your units.  You define a unit of time as a count from a specific source, which has an accepted constant of unit time/count.  Perform a count and you can convert it to time.  Put your caesium-133 in a gravitational field and the transition frequency is slower than outside the field.

[MigL]

Atomic clocks are a frequency standard.

"The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency."

From     Caesium standard - Wikipedia

 

It seems

On 8/26/2022 at 1:30 PM, Fly135 said:

Not saying I know exactly what all those words mean, but that's what time is.

you don't know what frequency is either.

[swansont]

14 hours ago, MigL said:

Atomic clocks are a frequency standard.

They aren't, actually, when one gets down to the brass tacks. It's a subtlety that few people care about, but I am one of them.

Frequency standards measure a frequency, and can be used as a clock, of sorts, but they are more like a stopwatch, measuring a time interval. Many of them get turned off (often for months at a time), and when they are off you aren't keeping track of the time, so they can't be considered clocks by themselves.

Most people just call them clocks, though, because the distinction isn't important to them. The same people (generally) refer to THE atomic clock, as if there is only one, rather than many clocks that make up a master clock that keeps track of the time in the larger countries. (There are undoubtedly some countries that have just one atomic clock contributing to the BIPM)

The clocks that I have helped build do not measure a frequency (and most do not use cesium). You can calibrate them with a cesium frequency standard so you know the length of a second. But they run continuously, so you can keep track of the time.

 

19 hours ago, Fly135 said:

A count is not the same as a frequency.  If you doubt that, check your units.  You define a unit of time as a count from a specific source, which has an accepted constant of unit time/count.  Perform a count and you can convert it to time.  Put your caesium-133 in a gravitational field and the transition frequency is slower than outside the field.

That's why the second is defined at the geoid, and in the absence of any other perturbing effects. You make corrections for the elevation of the clock.