B What is time? How can we see it?

[yashwanthippili]

What is time and how can we describe time?

 

[Abullais Ghazi]

Time is a measure of duration and is also referred to as the fourth dimension. No, we cannot see it.

"All things change and yet we all remain the same." Time is the one constant. It is the one thing that exists in all places. We can use time to measure our lives and the Earth's life. We can measure time by the position of the stars and the planets.

 

[Nugatory]

We cannot see time, but we can measure it. There are lots of things (for example, weight and temperature) like that.

 

[russ_watters]

We cannot see it, but we can measure it. There are lots of things (for example, weight and temperature) like that.

Except insofar as we can see, with our eyes, how "long" something is in both the space dimensions and time dimension...you just have to wait a while to observe something's duration.

 

[Drakkith]

how can we describe time

Time is that which a clock measures.

 

[axmls]

Time is that which a clock measures.

This. We describe the quantities we speak of with the measurements we use to determine them. All distance is is what we can measure with a meter stick.

 

[lightarrow]

Time is that which a clock measures.

How do you define "clock"?

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lightarrow

 

[Drakkith]

How do you define "clock"?

https://en.wikipedia.org/wiki/Clock

 

[anorlunda]

I am fond of the following definition from Wikipedia and a two-stage definition of time

Time is a measure in which events can be ordered from the past through the present into the future.​

I like to think of that as the basic definition of time. It allows reasoning such as "before and after" and "causality" without reference to the quantity of time.

Next, the "advanced" definition of time adds the quantity of time, i.e. what a clock measures as Drakkith said. Hence the full Wiki definition.

Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them.​

I also like to think of a basic clock as a machine which generates an ordered list of tick events. Clocks can be fast (small interval between clicks) or slow, or even non-uniform but nevertheless useful in logical reasoning. For example, if event A happens before tick 99 and event B happens after tick 99, then A must be before B in time.

An advanced clock has equal intervals of time between ticks.

 

[Gaz]

Time is a measurement of the rate of change of everything in the universe.
Eg atomic clocks are the measurement of motion of electrons.
We measure motion then give it a time frame based on its speed in relation to other motions.

 

[ZapperZ]

how can we describe time

https://www.physicsforums.com/threads/what-is-time.806638/
https://www.physicsforums.com/threads/what-is-time.451115/
https://www.physicsforums.com/threads/what-is-time.617345/
https://www.physicsforums.com/threads/what-is-time.643834/
https://www.physicsforums.com/threads/what-is-time.300088/

And many, MANY more...

Zz.

 

[lightarrow]

https://en.wikipedia.org/wiki/Clock

That doesn't seem a good link to answer my question, because it says:

"A clock is an instrument to indicate, keep, and co-ordinate time."

We can't answer to the question "what is time?" with the answer "it's what a clock measures" if a clock is what written up...
We need a better definition of "clock", a one which of course doesn't use the concept of time.

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lightarrow

 

[Isaac0427]

Just remember, in the technical world of physics things that you thought were basic, are very complicated. Honestly, I think what you and many others have asked about time doesn't fall in our knowlage right now. In fact, there are multiple theories I have seen describing time (or spacetime) that are still disputed. For example, I have had an interesting convorsation on here about the Big Bang and what t (time)=0 meant. What I got from that was nobody knows what happened at t=0, and I don't think you can fully describe what something is if you can't fully describe what happened when it wasn't there.

 

[Isaac0427]

That doesn't seem a good link to answer my question, because it says:

"A clock is an instrument to indicate, keep, and co-ordinate time."

We can't answer to the question "what is time?" with the answer "it's what a clock measures" if a clock is what written up...
We need a better definition of "clock", a one which of course doesn't use the concept of time.

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lightarrow

I agree, but clocks need time to work, and time doesn't need a clock to exist. In other words, clocks are dependent on time, and time is independent of clocks. Therefore, the definition of a clock should stay the same, and it is time that we need to have a better definition for.

 

[russ_watters]

That doesn't seem a good link to answer my question, because it says:

"A clock is an instrument to indicate, keep, and co-ordinate time."

We can't answer to the question "what is time?" with the answer "it's what a clock measures" if a clock is what written up...
We need a better definition of "clock", a one which of course doesn't use the concept of time.

Why not? Try the similar question: what is length?

 

[Drakkith]

Just remember, in the technical world of physics things that you thought were basic, are very complicated. Honestly, I think what you and many others have asked about time doesn't fall in our knowlage right now. In fact, there are multiple theories I have seen describing time (or spacetime) that are still disputed.

I don't know of any accepted theories other than GR that describe time. My opinion is that we know a great deal about what time is, just as we know a great deal about what distance is.

For example, I have had an interesting convorsation on here about the Big Bang and what t (time)=0 meant. What I got from that was nobody knows what happened at t=0, and I don't think you can fully describe what something is if you can't fully describe what happened when it wasn't there.

My understanding is that we choose t=0 to be at the big bang because it makes the math easier, not because time literally started at the big bang (which isn't what the big bang theory says). But I could be wrong.

 

[Isaac0427]

I don't know of any accepted theories other than GR that describe time. My opinion is that we know a great deal about what time is, just as we know a great deal about what distance is.

Look at my other post called the beginning of time. I share how two very well-respected physicists (Stephen Hawking and Brian Greene) have written contradictory things about time.

My understanding is that we choose t=0 to be at the big bang because it makes the math easier, not because time literally started at the big bang (which isn't what the big bang theory says). But I could be wrong.

Really? I thought t=0 gives is weird infinites in our math. Also, t=0 means that time actually started.

 

[Drakkith]

Look at my other post called the beginning of time. I share how two very well-respected physicists (Stephen Hawking and Brian Greene) have written contradictory things about time.

Their opinions have nothing to do with the nature of time, but with the question of did time (and anything else) exist prior to the big bang. They certainly don't count as theories. See Nugatory's post (post #2) in your thread.

The ONLY accepted theory that deals with what time is and how it works is General Relativity unless you count the fact that we usually just use the plain old Newtonian idea of time in our everyday lives since it's MUCH easier than GR. The Newtonian concept of time being absolute and the same for all observers is, of course, known to be inaccurate/incomplete, which is where GR comes in.

Really? I thought t=0 gives is weird infinites in our math. Also, t=0 means that time actually started.

I don't think you plug a 0 in for time anywhere. I think it's that if you continue to look backwards in time, you reach a point where the density reaches infinity based on current models. As far as I understand it this point in time is labeled t = 0 for convenience. I could very well label it t = -13.7 billion. Most equations that have time as a variable only care about the elapsed time between two events, not the 'absolute' time.

That's my understanding of it at least. Someone correct me if I'm wrong.

 

[Isaac0427]

The ONLY accepted theory that deals with what time is and how it works is General Relativity unless you count the fact that we usually just use the plain old Newtonian idea of time in our everyday lives since it's MUCH easier than GR. The Newtonian concept of time being absolute and the same for all observers is, of course, known to be inaccurate/incomplete, which is where GR comes in.

I don't believe that GR gives us a full understanding of time. It can't answer every question about time, and if it could, there would be no controversy on how time behaved at the Big Bang.

 

[lightarrow]

Why not? Try the similar question: what is length?

To define "clock" we need something which allow us to distinguish it from other Instruments, or we could use a ruler to measure durations.

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lightarrow

 

[ZapperZ]

I don't believe that GR gives us a full understanding of time. It can't answer every question about time, and if it could, there would be no controversy on how time behaved at the Big Bang.

What exactly are these "controversy" at the Big Bang?

Please note that there are many things that are not clearly determined and known at the Big Bang, not just time. One can easily argued that the different scenarios given have more to do with what we don't quite know well, rather than an issue with a parameter such as time and space.

Besides, do you think you are THAT well-equipped to actually say such a thing, considering that in another thread, you clearly indicated that you haven't fully understood even the classical idea of time (as in Lagrangian mechanics, etc.)?

As a side note, we are once again going off on our own here, considering that the OP appeared to have done a post-and-run. And considering the numerous threads on this topic already, are we really discussing anything new here?

Zz.

 

[Isaac0427]

What exactly are these "controversy" at the Big Bang?

Please note that there are many things that are not clearly determined and known at the Big Bang, not just time. One can easily argued that the different scenarios given have more to do with what we don't quite know well, rather than an issue with a parameter such as time and space.

Besides, do you think you are THAT well-equipped to actually say such a thing, considering that in another thread, you clearly indicated that you haven't fully understood even the classical idea of time (as in Lagrangian mechanics, etc.)?

As a side note, we are once again going off on our own here, considering that the OP appeared to have done a post-and-run. And considering the numerous threads on this topic already, are we really discussing anything new here?

Zz.

I am, in no way, saying I understand all our knowlage of time. All I know is that our knowlage is incomplete. I mean, we don't even know if time had a beginning or not.

 

[ZapperZ]

I am, in no way, saying I understand all our knowlage of time. All I know is that our knowlage is incomplete. I mean, we don't even know if time had a beginning or not.

But that's a meaningless statement because ALL of our knowledge is incomplete and will NEVER be complete! That doesn't negate the fact that we do know quite a bit about what "time" is, so much so we actually can define it and know its properties. Just because we don't know if time has a beginning or not (whatever THAT means) does not mean we don't know what it is. We don't know why exactly the cuprate superconductors become superconducting, but that doesn't mean we know nothing about it, or that there are questions that they ARE superconductors!

You need to reexamine your logic.

Zz.

 

[Isaac0427]

But that's a meaningless statement because ALL of our knowledge is incomplete and will NEVER be complete! That doesn't negate the fact that we do know quite a bit about what "time" is, so much so we actually can define it and know its properties. Just because we don't know if time has a beginning or not (whatever THAT means) does not mean we don't know what it is. We don't know why exactly the cuprate superconductors become superconducting, but that doesn't mean we know nothing about it, or that there are questions that they ARE superconductors!

You need to reexamine your logic.

Zz.

I am not saying we know nothing, I am justd saying that there is a lot about time we don't know.

 

[ZapperZ]

I am not saying we know nothing, I am justd saying that there is a lot about time we don't know.

Repeat that with practically everything else in physics. So what's the point?

You've gone BEYOND that when you make a claim that you don't believe GR tell you everything about time, as IF you actually have understood GR, or have you? If not, from what basis do you make that claim?

Thanks to you, this thread is in danger, like most of the previous thread on this topic, of being shut down.

Zz.

 

[Isaac0427]

Thanks to you, this thread is in danger, like most of the previous thread on this topic, of being shut down.

I was having a discussion on this thread with a mentor before you came in. If I were doing something wrong he would have told me. I have read all the guidelines on PF, and I was not breaking them.

 

[ZapperZ]

I was having a discussion on this thread with a mentor before you came in. If I were doing something wrong he would have told me. I have read all the guidelines on PF, and I was not breaking them.

You didn't answer my questions.

Zz.

 

[William White]

How do you define "clock"?

seriously?

http://lmgtfy.com/?q=Oxford+English+Dictionary+Clock

 

[William White]

We need a better definition of "clock", a one which of course doesn't use the concept of time.

That's utterly absurd

Its like saying you need a better definition of a yard stick that doesn't use the concept of distance.

Putting clock in quote marks does not change its meaning. ("yard stick" is still a yard stick).
Maybe you could try your statement with your boss when you turn up for work 20 minutes late.

 

[lightarrow]

That's utterly absurd

Its like saying you need a better definition of a yard stick that doesn't use the concept of distance.

Putting clock in quote marks does not change its meaning. ("yard stick" is still a yard stick).

Maybe you could try your statement with your boss when you turn up for work 20 minutes late.

I imagine that with silly posts like this, they will have easy room to terminate the thread.
If this is not your purpose, stop a little and think a bit longer about what I've written.

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lightarrow

 

[russ_watters]

To define "clock" we need something which allow us to distinguish it from other Instruments, or we could use a ruler to measure durations.

Please elaborate. I see no difference between the statements:
"Clocks measure time"
and
"Rulers measure distance"

Both are recursive definitions that apply only to their chosen dimension. IE, since by definition a ruler measures distance it is obviously incorrect to say that a ruler measures durations.

We need a better definition of "clock", a one which of course doesn't use the concept of time.

I agree with WW: a definition that does not make reference to/use of the concept it is defining is useless. The whole point of a definition is to explain the concept it is defining.

 

[William White]

lightarrow no, I shall not stop to ponder pseudo philosophical twaddle. Lifes too short - there are bigger problems.

Clocks measure time.

if you have an issue with that, you are the one in need to stop and think a bit

 

[William White]

use a ruler to measure durations?

so, the train leaves at 12 : 00 clock train from Euston to go to Glasgow; I want to know how long it takes; let me find that ruler...

 

[lightarrow]

Please elaborate. I see no difference between the statements:
"Clocks measure time"
and
"Rulers measure distance"

Both are recursive definitions that apply them only to their chosen dimension. IE, since by definition a ruler measures distance it is obviously incorrect to say that a ruler measures durations.

What you haven't grasped is that I'm not talking of logic or of syntax here. I'm talking of physics.
Someone asked what is time and someone else answered that "time is what a clock measures". Very good. Just to avoid ambiguity, this is the same answer I would give (and that I've really given, many times, in the past).
But then I need a clock. Would I choose a device at chance and I would stick the label "clock" to it? Of course not. We are advantaged, nowadays, because we already have clocks. But, if we wouldn't have any, which devices or other would we construct and why, which we could call a "clock"? It's not an easy answer at all.
It has to do with the physical fact that exists phenomena, perceptibly associated to "duration" and "repetition", of which we can verify the synchrony. The physical concept of "clock" starts from here.

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lightarrow

 

[Dale]

Thanks to you, this thread is in danger, like most of the previous thread on this topic, of being shut down.

Yup.

Thread closed.

Everyone, please try to avoid the philosophical navel gazing.

PS clocks can be defined by instructions to build them. Similarly with rulers, and scales.