How does the scientific community define time?

[MACHO-WIMP]

I was just wondering how time is defined by the scientific community; because whenever I try and think about it I have a very tough time defining it. Please post comments and discuss below.

 

[Uglybb]

It has always been hard to define

http://en.wikipedia.org/wiki/Absolute_time_and_space

Will give you the background from Newton to later Einstein with neat animation on the side :-)

At science we define time via atomic clock (http://en.wikipedia.org/wiki/Atomic_time)

TAI as a time scale is a weighted average of the time kept by over 200 atomic clocks in about 70 national laboratories worldwide. The clocks are compared using satellites.[2] Due to the averaging it is far more stable than any clock would be alone (see signal averaging for a discussion). The majority of the clocks are caesium clocks; the definition of the SI second is written in terms of caesium

 

[MACHO-WIMP]

Yes but wouldn't the atomic clock still be influenced by Relativity?

 

[Uglybb]

Yes and it does hence why they SI organization standard.

Most units require definition (http://www.bipm.org/en/si/)

The kilogram for example has been causing some problem because the SI standards have changed weight :-)

http://www.physorg.com/news/2011-01-weighty-mission-scientists-redefine-kilo.html

If you follow relativity there is no real zero frame so you can't really define time to it. In that any time is as valid as any other time in relativity our somewhat arbitrary time is as valid as any other.

Most units require a standard that scientists simply agree on.

 

[Uglybb]

I should also say at its heart our unit of time the second is based on the orbit of the Earth you know the 365 days broken into 24 hours broken into 60 min broken into 60 seconds

So if for example we met an alien race they would never agree on what a second is there homeworld would probably not have an orbital period of 365 days we would need a conversion :-)

 

[Blibbler]

Space is where information is encoded by the arrangement of matter.

Time is where information is encoded by the rearrangement of matter.

It makes no sense to talk about moving in space without also moving in time although one can talk about moving in time without moving in space.

The rate at which an object moves in time is related to how fast it moves in space relative to a frame of reference.

The closer the rate at which an object moves relative to a frame of reference gets to the speed of light the closer the rate at which it moves in time time gets to zero.

 

[cosmik debris]

The practical definition is: time is what a clock measures.

 

[James A. Putnam]

A clock measures duration. Duration is cyclic activity used as a standard for mechanically measuring the passage of time. Time itself is an indefinable property, unavailable for emprical testing. Empirical testing is always about patterns in changes of velocity. Time cannot be shown to undergo changes of velocity.

James

 

[Drakkith]

A clock measures duration. Duration is cyclic activity used as a standard for mechanically measuring the passage of time. Time itself is an indefinable property, unavailable for emprical testing. Empirical testing is always about patterns in changes of velocity. Time cannot be shown to undergo changes of velocity.

James

I'll agree that time is always the same for an observer, no matter what frame they are in, but there is a difference in time between two observers in diferent frames if they have velocity relative to each other or are in different gravitational fields, correct?

 

[James A. Putnam]

I'll agree that time is always the same for an observer, no matter what frame they are in, but there is a difference in time between two observers in diferent frames if they have velocity relative to each other or are in different gravitational fields, correct?

Duration as measured by mechanical means is different in different frames with relative velocities. The t in physics equations never referred to time directly. It has always referred to duration.

 

[Drakkith]

Duration as measured by mechanical means is different in different frames with relative velocities. The t in physics equations never referred to time directly. It has always referred to duration.

That doesn't make any sense to me. Time is part of our measuring system used to compare durations of events. If it is different in one frame from another frame, how is time unmeasurable and such like you said? Are you saying that time is "something" just like you were saying force and energy were "things" in the other thread?

 

[James A. Putnam]

That doesn't make any sense to me. Time is part of our measuring system used to compare durations of events. If it is different in one frame from another frame, how is time unmeasurable and such like you said? Are you saying that time is "something" just like you were saying force and energy were "things" in the other thread?

I am saying that duration and time are not the same. Duration takes place during time. Duration is measured by cyclic activity that certainly can and will change with changing conditions. Time is measurable within the accuracy limits of mechanical cyclic activity. However, that activity cannot be shown to control time. The t in physics equations has never represented time. It has always been an expression of duration. Duration is cyclic activity used as a standard for mechanically measuring the passage of time. Even that standard is not really a standard. A true standard, at least the best that we could ever hope to achieve, would be a universally constant measure of time. Duration as presently implemented does not represent a universally constant measure of time. Rather, it measures cyclic activity involving changes of velocity of objects.

 

[pallidin]

I have perhaps an overly-simplistic view of "time":

Without "change" there is no time.

Cheers...

 

[Drakkith]

To avoid an argument, all I'll say is that I disagree with you James.

 

[pallidin]

Oh, come on Drak, whereas PF is never about argument, it's always about responsible discussion.
Let it loose! Tell it like you think it is! You have good thoughts... let it rock.

 

[James A. Putnam]

I have perhaps an overly-simplistic view of "time":

Without "change" there is no time.

Cheers...

Hi Pallidin,

Perhaps, but I would have said that without change the existence of time cannot be proven.
Actually, if change never occurred, the question regarding the existence of time would not be relevant. However, the fact remains that everything we learn about the operation of the universe as it really exists is through changes of velocity. So duration, making use of particularly reliable patterns in changes of velocity, shows that we can make measurements during time and, I think, therefore, that time does exist. Since I cannot point to measurements of time that are not duration, I cannot prove this. It just seems to me that it may still be possible to discover a universally constant measurement of time. That in itself still does not capture time; however, it would free us from the constraints imposed upon theoretical analysis by the use of duration in its current variable form.

 

[Drakkith]

Oh, come on Drak, whereas PF is never about argument, it's always about responsible discussion.
Let it loose! Tell it like you think it is! You have good thoughts... let it rock.

I'm all talked out for today!

 

[pallidin]

However, the fact remains that everything we learn about the operation of the universe as it really exists is through changes of velocity.

James, "velocity" is only one aspect of "change"

To my knowledge, though without citation, velocity is not the dominant or even prominent determinant of universal change(resulting in "time")
Could be wrong...

 

[pallidin]

I'm all talked out for today!

Been there!

 

[Drakkith]

Been there!

Hey pallidin, did you realize you just hit 2,222 posts recently? That's what it's showing for me at least!

James, "velocity" is only one aspect of "change"

To my knowledge, though without citation, velocity is not the dominant or even prominent determinant of universal change(resulting in "time")
Could be wrong...

I believe you are correct.

 

[pallidin]

Oh... didn't notice, but thanks.
I hated that 666 bridge.

 

[James A. Putnam]

James, "velocity" is only one aspect of "change"

To my knowledge, though without citation, velocity is not the dominant or even prominent determinant of universal change(resulting in "time")
Could be wrong...

Good point. Now to clarify my remark. I rely upon the phrase patterns in changes of velocity because everything we learn arrives to us in a storm of photons. We have the incredible ability to find meaning from the wildly mixed innumerable numbers of photons constantly crashing into us. Finding meaning in that storm is a different subject. However, each one of those photons tells us only about a past change of velocity of a particle of matter located somewhere else.

 

[Uglybb]

OMG .. running away

This is going down the whole "if no one observes the moon is it really there argument from quantum physics"

Only its

"If no one is observing time does it exist"


Exit stage right ... that away ------->

 

[pallidin]

You can run but you cannot hide...

The moon exist regardless of human observation.

Time exists as long as there is change.

 

[MACHO-WIMP]

You can run but you cannot hide...

The moon exist regardless of human observation.

Time exists as long as there is change.

But why does change have to be involved in defining time?

 

[Uglybb]

LMAO this is the whole Quantum physics argument.

The moment it showed the act of observation changes things it leads directly into this problem.

Delayed choice Quantum erasure (http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser) is real and proven so this whole argument has no solution and hence why time is such a sticky problem is spacetime already completely defined and is there such thing as free will ... it goes on and on down the rabbit hole.

 

[pallidin]

But why does change have to be involved in defining time?

Without change, "time" has no meaning at all.

 

[pallidin]

LMAO this is the whole Quantum physics argument.

The moment it showed the act of observation changes things it leads directly into this problem.

Delayed choice Quantum erasure (http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser) is real and proven so this whole argument has no solution and hence why time is such a sticky problem is spacetime already completely defined and is there such thing as free will ... it goes on and on down the rabbit hole.

I'm well aware of the delayed choice experiment.
However, non-invasive observation can NOT influence the outcome of an event.

 

[Uglybb]

I am not a believer it all gets a bit esoteric.

However for the record not being a zealot I believe the logic goes like this when dumbed right down (zealots please feel free to chime in)

Atoms have been proven to be able to be entagled in 2007 at 1m(http://physicsworld.com/cws/article/news/31068) and later at much larger distances

In 2008 multi groups reported macroscopic object entanglement .. houston we have a problem.
(http://focus.aps.org/story/v22/st16 )
(http://www.physorg.com/news/2010-12-science-breakthrough-year-quantum-machine.html)

Follow the pauli exclusion principle (http://en.wikipedia.org/wiki/Pauli_exclusion_principle) read down thru matter stability and astrophysics section.

And your problem becomes physicists usually end up in one of two places

Copenhagen interpretation (http://en.wikipedia.org/wiki/Copenhagen_interpretation)
Many worlds interpretation (http://en.wikipedia.org/wiki/Many-worlds_interpretation)

In both interpretation time is well not really clear to say the least. And as was put to Einstein does the moon actually exist if it is not observed. To quote Hawking and Mlodinow

"No matter how thorough our observation of the present, the (unobserved) past, like the future, is indefinite and exists only as a spectrum of possibilities."

I adhere the bottom sentence of the Copenhagen interpretation

Many physicists have subscribed to the instrumentalist interpretation of quantum mechanics, a position often equated with eschewing all interpretation. It is summarized by the sentence "Shut up and calculate!". While this slogan is sometimes attributed to Paul Dirac[20] or Richard Feynman, it is in fact due to the lesser known David Mermin.[21]

So shutup and calculate ----> exiting stage right

 

[Dali]

The practical definition is: time is what a clock measures.

I agree. To my knowledge this is the only definition that the scientific community agrees on. Just as space is defined as "what we measure with meter-rods". This is how Einstein defined time and space, and it is precisely this "time" and "space" that relativity says anything about.

For example when we say that time slows down in a moving spaceship (as seen from a stationary observer), what relativity really says is that all clocks onboard the ship will slow down relative to stationary clocks. Same thing about a curved space-time; what is curved is "what we would measure with meter-rods and clocks". Nothing more, nothing less.

Of course there might be a debate on what a clock is. But a good thing is that relativity does not depend on that definition, as it says something about time as measured with any clock. And it is useful to remember that all clocks are made of matter. And such clocks are all we can say anything about. As soon as we talk about "time without matter" or "time without change", we are talking about some philosophical concept that we can not be sure is the same thing as relativity makes predictions about.

This might seem lika a dumb definition of time and space at first, but it is still remarkable that such a simple operational definition is what underlies the whole complexity of special and general relativity.