What is Time?

[Astrophysicist Shubham]

Time being the most experienced thing in this universe but can we really describe what time is? Are we in a state of describing time? 

Ask this question to yourself and then say that can we scientifically define what time is?

The motive of this discussion must be to scientifically define that what time is?

And ill tell my own theory to describe what time is?

[swansont]

In physics, time is what we measure with a clock. It is the phase of an oscillation.

Most discussions on "what time is" falls under metaphysics (philosophy), not physics.

[ydoaPs]

30 minutes ago, swansont said:

In physics, time is what we measure with a clock. It is the phase of an oscillation.

Most discussions on "what time is" falls under metaphysics (philosophy), not physics.

I thought clocks measure other clocks.

[Butch]

I would say that time is a frame of reference... We measure it with a "clock" a clock being a reference standard, that could be anything which has a constant period.

5 minutes ago, ydoaPs said:

I thought clocks measure other clocks.

Indeed they do, they also measure things that are not periodic.

https://physics.nist.gov/cuu/Units/meter.html

Edited March 15, 2018 by Butch

[beecee]

Simply put, time is what stops everything from happening together: Likewise, space is what keeps everything apart. 

[swansont]

3 hours ago, ydoaPs said:

I thought clocks measure other clocks.

All comparisons are with other clocks. 

3 hours ago, Butch said:

I would say that time is a frame of reference... We measure it with a "clock" a clock being a reference standard, that could be anything which has a constant period.

No. "Frame of reference" has a meaning, and that's not it.

[Shauno]

I think the definition that "time is what clocks measure" is a good one. Beyond that it become tricky.

Change happens with or without our ability to measure it - that is just the Universe we live in.

How do we know that clocks measures time homogeneously (i.e. not in fits and starts)? We can come up with some clever constructions which based on symmetry considerations should behave that way.

[michel123456]

Time is an element of the continuum called spacetime. Trying to cut the continuum in parts lead to errors. IOW there is no Time by itself, and there is no Space by itself.

[beecee]

On 3/19/2018 at 7:16 PM, michel123456 said:

Time is an element of the continuum called spacetime. Trying to cut the continuum in parts lead to errors. IOW there is no Time by itself, and there is no Space by itself.

Bingo!

"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."

Hermann Minkowski 

[michel123456]

This mesmerizing quote is close to 110 years old.

Which means that when you look at space (look around you), you are looking at time also.

[Strange]

Ethan Siegel: "We Still Don’t Understand Why Time Only Flows Forward: The past is gone, the future not yet here, only the present is now. But why does it always flow the way it does for us?"

https://medium.com/starts-with-a-bang/we-still-dont-understand-why-time-only-flows-forward-1187a8367d74

[geordief]

2 hours ago, beecee said:

Bingo!

"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."

Hermann Minkowski 

Shows, I feel that Herman Minkowski was still  coming to terms with the new reality.

 

So am I still. The maths and the model are fine (though we still don't know how things play out in extreme situations) but an intuitional grasp  may still elude us ,although those completely familiar with the model  may feel differently.

 

If there are those 100% comfortable with the space time relationship then they should perhaps also be able to present this in an easily digestible form to the layman (without him or her needing to wade through the physics and maths necessarily).

 

But I think those at the forefront of this physics disagree for now and for example as to whether spacetime is  a single static block or not. (I may have garbled that)

[StringJunky]

51 minutes ago, geordief said:

If there are those 100% comfortable with the space time relationship then they should perhaps also be able to present this in an easily digestible form to the layman (without him or her needing to wade through the physics and maths necessarily).

Some things require effort on the part of those that want to understand. Those that do understand didn't haven't it handed to them on a plate.

"It should be made as simple as possible but no simpler" - Einstein

Edited March 20, 2018 by StringJunky

[Strange]

53 minutes ago, geordief said:

If there are those 100% comfortable with the space time relationship then they should perhaps also be able to present this in an easily digestible form to the layman (without him or her needing to wade through the physics and maths necessarily).

I think there are some very simple conceptual models (for SR, at least). For example you can think of movement as "swapping" part of your movement through time for movement through space.

When you are stationary, you do not move through space and your time ticks at "1 second per second". 

When you are moving (relative to some other observer) then they will see you moving through space and, as a result, moving slightly more slowly through time.

This works because the Lorentz transform is actually a rotation between the time and space directions (dimensions).

57 minutes ago, geordief said:

But I think those at the forefront of this physics disagree for now and for example as to whether spacetime is  a single static block or not.

This is more of a philosophical issue: what does it "mean" when we represent time and space in this way. You can view it as all events in time and space being fixed in a block and, instead of time flowing for us, there is just a line that represents our existence in space-time.

 

[geordief]

12 minutes ago, StringJunky said:

Some things require effort on the part of those that want to understand. Those that do understand didn't haven't it handed to them on a plate.

"It should be made as simple as possible but no simpler" - Einstein

Yes ,we cannot wish away inherent difficulties  and our natural inclination to hold onto simple truths when they seem adequate for most purposes.

7 minutes ago, Strange said:

I think there are some very simple conceptual models (for SR, at least). For example you can think of movement as "swapping" part of your movement through time for movement through space.

When you are stationary, you do not move through space and your time ticks at "1 second per second". 

When you are moving (relative to some other observer) then they will see you moving through space and, as a result, moving slightly more slowly through time.

This works because the Lorentz transform is actually a rotation between the time and space directions (dimensions).

I have been starting to relook at the conceptual basis of complex numbers and that pesky i . Perhaps that might eventually help me to get a better feel for those rotations.

Edited March 20, 2018 by geordief

[swansont]

3 hours ago, geordief said:

 If there are those 100% comfortable with the space time relationship then they should perhaps also be able to present this in an easily digestible form to the layman (without him or her needing to wade through the physics and maths necessarily).

Easily digestible? I disagree. Nature has no obligation to be understandable to anyone.

To paraphrase Feynman, "I can't explain that in terms of anything else that's familiar to you"

So one's lack of understanding can't simply be pushed off onto the person doing the explaining. One has an obligation to learn the underlying science. Your wanting an explanation of an advanced physics phenomenon should not require that several year's worth of physics (and it literally takes years of learning to gain the comprehension) be explained to you.   

[geordief]

1 minute ago, swansont said:

Easily digestible? I disagree. Nature has no obligation to be understandable to anyone.

To paraphrase Feynman, "I can't explain that in terms of anything else that's familiar to you"

So one's lack of understanding can't simply be pushed off onto the person doing the explaining. One has an obligation to learn the underlying science. Your wanting an explanation of an advanced physics phenomenon should not require that several year's worth of physics (and it literally takes years of learning to gain the comprehension) be explained to you.   

Well maybe one can aim for helping the audience be comfortable with their lack of understanding (if they have no aim  or ability to remedy it)

 

But I also take the  point that an  audience can have unrealistic expectations .

[michel123456]

18 hours ago, geordief said:

Well maybe one can aim for helping the audience be comfortable with their lack of understanding (if they have no aim  or ability to remedy it)

 

But I also take the  point that an  audience can have unrealistic expectations .

About unrealistic expectations & the statements from Swansont

You can easily spot the lack of understanding even from the most educated: when they explain something and smile, it means they don't know. The more they get educated, the least they smile. When you get a Nobel prize he may simply admits "I don't know" without a shame.

Unfortunately smiles are not easily detectable over the Net.

 

[geordief]

Back to "Time" ,we have a model (s?)   and it seems to be internally consistent (Well I take that on trust as I must).

But the essence of the scientific method seems like the active welcoming of findings that contradict  current assumptions and understanding.

It does seem a stretch to imagine that our  understanding of Time could be revisited  but it would be a scientific wet dream if it came about.

 

I am not up to speed on Hawking's apparent final publication where he seems to be  be proposing that Time has a (presumably mathematical) imaginary property in  the first/final  analysis.

[koti]

What swansont said about having to have knowledge to understand complex problems is ofcourse right. What geordief said about the ability to explain difficult problems in easly digestable ways is also right. These two things seem unrelated. I’ve never heard any phycisist talk 100% comfortably about time because we simply do not have the means to explain what it is other than math. We can try all kinds of flexing of spoken of written language but it just never sticks. The wonderful quote by Minkowski above, Im sure can be difficult to understand to someone who has no idea about spacetime and GR. The other friday I was asked by a pharmacist at a social meeting over a drink about what I think about time...I imediately started to explain to him what spacetime is, what implications GR has to everyday life, what gravity is, GPS examples of time dilation, etc. I have many years of experience as a teacher teaching adults (not physics) and it was very difficult for me to get through this guys head that gravity is in fact spacetime curvature. He couldn’t grasp it, went over his head multiple directions not to understand it despite really wanting to. Hes a college graduate and he is a rationally thinking man, he couldnt get it.

Edited March 21, 2018 by koti

[michel123456]

Ha, spacetime curvature goes over my head too. Simply because gravity is an everyday phenomenon & spacetime curvature is not.

Anyway I have the feeling that the union of Space & Time announced 100 years ago is still not a part of our understanding.

For example, as an Architect I am measuring objects in space, while physicists should have told me that all objects are in Spacetime. But today's physicists actually tell me that I am correct and can continue to measure objects in space only. Although we all know (or should know) that it is incorrect, we are all continuing to discern space from time.

 

[koti]

6 minutes ago, michel123456 said:

Ha, spacetime curvature goes over my head too. Simply because gravity is an everyday phenomenon & spacetime curvature is not.

They’re both the same thing.

[Strange]

19 minutes ago, michel123456 said:

Ha, spacetime curvature goes over my head too. Simply because gravity is an everyday phenomenon & spacetime curvature is not.

Anyway I have the feeling that the union of Space & Time announced 100 years ago is still not a part of our understanding.

For example, as an Architect I am measuring objects in space, while physicists should have told me that all objects are in Spacetime. But today's physicists actually tell me that I am correct and can continue to measure objects in space only. Although we all know (or should know) that it is incorrect, we are all continuing to discern space from time.

 

That’s OK because we use the most appropriate model for the job. Calculating the path of a thrown rock can be done by treating gravity as a force. Small buildings can be designed assuming the Earth  is flat. 

On the other hand, some buildings need to consider the Earth’s curvature and some space missions have to take the curvature of space-time into account. 

[swansont]

2 hours ago, michel123456 said:

You can easily spot the lack of understanding even from the most educated: when they explain something and smile, it means they don't know. The more they get educated, the least they smile. When you get a Nobel prize he may simply admits "I don't know" without a shame.

The Nobel prize-winners I've met smile plenty, and admitting that you don't know doesn't require such lofty accomplishments.

1 hour ago, koti said:

What swansont said about having to have knowledge to understand complex problems is ofcourse right. What geordief said about the ability to explain difficult problems in easly digestable ways is also right. These two things seem unrelated.

Really?

1 hour ago, koti said:

I’ve never heard any phycisist talk 100% comfortably about time because we simply do not have the means to explain what it is other than math.

Also that science isn't in the business of explaining the nature of things. That's metaphysics.

1 hour ago, koti said:

I have many years of experience as a teacher teaching adults (not physics) and it was very difficult for me to get through this guys head that gravity is in fact spacetime curvature. He couldn’t grasp it, went over his head multiple directions not to understand it despite really wanting to. Hes a college graduate and he is a rationally thinking man, he couldnt get it.

Was that because you couldn't explain it properly?

[geordief]

5 minutes ago, Strange said:

That’s OK because we use the most appropriate model for the job. Calculating the path of a thrown rock can be done by treating gravity as a force. Small buildings can be designed assuming the Earth  is flat. 

On the other hand, some buildings need to consider the Earth’s curvature and some space missions have to take the curvature of space-time into account. 

What buildings would they be? Buildings housing telescopes or scientific experiments?