What is Time?

[studiot]

26 minutes ago, geordief said:

Same here (as michel123456)  . "Interesting" was approbatory ,not trying to find any flaw.

Your phrase "the third fundamental dimension of Physics" was new to me. and "interesting" .It is not obvious to me why mass differences should not have the same relevance as spatio-temporal differences (because of my level of familiarity,certainly)

 

I realise that, I just don't know what more you guys wanted?

[michel123456]

51 minutes ago, studiot said:

 

What questions?

 

IIRC it was Ernst Mach who stated that an accurate description of the Universe should ideally involve only relative instances (quoting very loosely from my untrustworthy memory).

Edited March 22, 2018 by michel123456

[geordief]

11 minutes ago, studiot said:

I realise that, I just don't know what more you guys wanted?

Well in what sense is mass a dimension ? If it is ,as you say the "third fundamental dimension" then  it seems like I am missing a fundamental understanding .

 

The earlier part of your post where you  described intervals as being fundamental (we measure intervals in  ,eg time ,not time itself) was easily understandable even if it needed to be said....

 

It reset my appreciation of relativity using a form of words I had not found explicitly used before. 

[studiot]

1 hour ago, michel123456 said:

IIRC it was Ernst Mach who stated that an accurate description of the Universe should ideally involve only relative instances (quoting very loosely from my untrustworthy memory).

I didn't know this and I find it an overgeneralisation that is prone to my outsmarting by Nature proposition.

1 hour ago, geordief said:

Well in what sense is mass a dimension ? If it is ,as you say the "third fundamental dimension" then  it seems like I am missing a fundamental understanding .

 

The earlier part of your post where you  described intervals as being fundamental (we measure intervals in  ,eg time ,not time itself) was easily understandable even if it needed to be said....

 

It reset my appreciation of relativity using a form of words I had not found explicitly used before. 

 

Quote

Studiot

I am fond of saying that despite our best efforts to categorise and pigeonhole things, we are often outsmarted by the diversity of Nature.

 

We are moving somewhat off topic, but every time I try to open up my own thread for discussion of these topics the pack of baying hounds here drowns out serious discussion.

 

Any way I should have said the basic dimensions of Mechanics, not Physics or Science as there are more.

Here is an interesting tabulation of dimensions for properties, qualities or quantities in Mechanics, taken from an old Fluid Mechanics book because they are arranged in an interesting way.

Note they are based on Length, Time and Mass

 

Such a classification is incredibly useful in Science.

 

But it does not tell the whole story.

 

Some of these have (need) a start point and an end point for a measurement.

Length and time are are of this nature. This is because there is no absolute system of length and time.

Some need no start/end points.

Mass is one of these. There is either x amount of mass or there is no mass.

But note this has nothing to do with the units we measure in.
We use units so that we can compare one length/time/mass with another.

However this is where Nature starts to play tricks.
Some units have a foot in both camps.

So the volt is the unit for both (electric) potential and potential difference and both have (different) meanings.

Temperature is different again since, unlike mass, there is an absolute scale constructible.

 

Then again variables are classified as extensive (eg mass) or intensive. (eg temperature)

It is often said that extensive variables depend upon mass but that is not always true.

 

The point of all this is that length and time are intimately connected and many subsidiary variables can be formed using only these two.

It is difficult to find many variables with only mass and one other (see my table)

 

 

[swansont]

1 hour ago, geordief said:

Well in what sense is mass a dimension ? If it is ,as you say the "third fundamental dimension" then  it seems like I am missing a fundamental understanding .

 

The earlier part of your post where you  described intervals as being fundamental (we measure intervals in  ,eg time ,not time itself) was easily understandable even if it needed to be said....

 

It reset my appreciation of relativity using a form of words I had not found explicitly used before. 

Dimensional analysis sense. Length, time, mass, charge, etc.

[geordief]

3 minutes ago, swansont said:

Dimensional analysis sense. Length, time, mass, charge, etc.

Yes I have been looking at Studiot's table.

Can it be said that it is an aim to find a common  source for mass and charge (and perhaps other similar things)?

 

Length and Time seem to have such a common source in Relativity but  seem to be very different from Mass,Charge  etc....

[swansont]

35 minutes ago, geordief said:

Yes I have been looking at Studiot's table.

Can it be said that it is an aim to find a common  source for mass and charge (and perhaps other similar things)?

 

Length and Time seem to have such a common source in Relativity but  seem to be very different from Mass,Charge  etc....

Length and time are relative. Rest mass and charge are not. But none of them can be expressed as combinations of the others.

[gwb]

My thoughts on the subject is that time is a consequence of the relationship between objects. For instance, a day is a result of the relationship between the earth's surface, its axis and the sun. A year is an expression of the earth's orbit around the sun.

Similarly, an old analog clock, the seconds, minutes and hours are the result of the relationship between the various gears. And a quartz watch, time arises from the relationship between an electrical circuit passing through a crystal.

Time arises from the relationship between two or more objects. And it cannot be any two objects, because it needs to be a durable and predictable or very stable relationship.

[beecee]

On 3/21/2018 at 3:20 AM, 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.   

Important that anyone interested in cosmology need to accept that.

[swansont]

8 hours ago, gwb said:

My thoughts on the subject is that time is a consequence of the relationship between objects. For instance, a day is a result of the relationship between the earth's surface, its axis and the sun. A year is an expression of the earth's orbit around the sun.

Similarly, an old analog clock, the seconds, minutes and hours are the result of the relationship between the various gears. And a quartz watch, time arises from the relationship between an electrical circuit passing through a crystal.

Time arises from the relationship between two or more objects. And it cannot be any two objects, because it needs to be a durable and predictable or very stable relationship.

That's peripherally related to time measurement. But the choice of the length of a day or year, or a second, is one of units. Similarly, a meter is a unit of length, but it is not length itself.

A second is 9,192,631,770 oscillations of a Cs-133 ground state hyperfine transition. While there are physics reasons why that's a good choice for a standard, there is no physics that demands that it be the definition of the second. Put another way, we are free to choose another transition to define the second, or redefine fundamental constants in some other way, and someday that will happen.

[studiot]

On 22/03/2018 at 3:15 PM, swansont said:

Length and time are relative. Rest mass and charge are not. But none of them can be expressed as combinations of the others.

 

On 22/03/2018 at 2:37 PM, geordief said:

Yes I have been looking at Studiot's table.

Can it be said that it is an aim to find a common  source for mass and charge (and perhaps other similar things)?

 

Length and Time seem to have such a common source in Relativity but  seem to be very different from Mass,Charge  etc....

 

It should not be thought that mass, length and time is the only viable scheme (for mechanics)

Charge was at one time used as the electrical basis but has been replaced by current.

 

Here is a mechancial scheme based on force, length and time as opposed to mass, length and time.

This is interesting because mass is a scalar but force is a vector.

Length can be either a scalar or a vector and time is neither a vector nor a scalar.

[geordief]

 

59 minutes ago, studiot said:

 

 

 

 

This is interesting because mass is a scalar but force is a vector.

Length can be either a scalar or a vector and time is neither a vector nor a scalar.

Can you give an example where Length is a scalar and another where it is a vector?

[swansont]

1 minute ago, geordief said:

 

Can you give an example where Length is a scalar and another where it is a vector?

"1 meter" is a scalar. "1 meter in the x direction" is a vector.

[geordief]

15 minutes ago, swansont said:

"1 meter" is a scalar. "1 meter in the x direction" is a vector.

Can it be said that length as a scalar is an abstract property (right choice of word?) whereas as a vector it is used in a physical way?

 

I am thinking now about point particles  (without knowing very much about them )

[Sensei]

38 minutes ago, geordief said:

Can you give an example where Length is a scalar and another where it is a vector?

Suppose so, we have points:

x0 = 0, y0 = 0, z0 = 0

x1 = 10, y1 = 2, z1=5

Delta (aka "displacement vector") between them will be:

dx = x1-x0

dy = y1-y0

dz = z1-z0

dx,dy,dz is 3d vector

length = sqrt( dx^2 + dy^2 + dz^2 )

(or length = sqrt( dot_product( delta, delta ) ) )

length is scalar. Distance between one point and another one.

 

dx' = dx/length

dy' = dy/length

dz' = dz/length

dx',dy',dz' is 3d normalized vector (aka "normal", "unit vector"). Length of it is equal 1.

Multiplication of normal by length gives you original vector back.

 

This is often used in 3d graphics equation:

world_position = ray_origin + ray_direction * ray_length

world_position, ray_origin are 3d vectors

ray_direction is normalized 3d vector (it's length is equal 1)

ray_length is scalar (>=0.0 typically)

 

You can reverse entire equation:

ray_length = sqrt( dot_product( world_position - ray_origin,  world_position - ray_origin ) )

 

Edited March 28, 2018 by Sensei

[studiot]

34 minutes ago, geordief said:

 

Can you give an example where Length is a scalar and another where it is a vector?

 

The length of the side of an arbitrarily oriented cube is a scalar.

In the equation work = F.dl

Work is a scalar, being the dot product of two vectors force and length.

[geordief]

Getting out of my depth now. I will hopefully reflect on these replies  over the medium term.

[swansont]

22 minutes ago, geordief said:

Can it be said that length as a scalar is an abstract property (right choice of word?) whereas as a vector it is used in a physical way?

I don't know what "used in a physical way" actually means. And something like charge, or mass, which are scalars, are physical properties, so I don't think these distinctions have any meaning.

[geordief]

Just now, swansont said:

I don't know what "used in a physical way" actually means. And something like charge, or mass, which are scalars, are physical properties, so I don't think these distinctions have any meaning.

I think I used it in the sense that all physical processes seem to be capable of being represented in a mathematical way whereas the opposite  is not true.

[swansont]

7 minutes ago, geordief said:

I think I used it in the sense that all physical processes seem to be capable of being represented in a mathematical way whereas the opposite  is not true.

Does "An object moves 1 meter" represent a physical process?

(It can be in the context of e.g. work being done by friction, where the direction of motion does not matter)

[geordief]

3 minutes ago, swansont said:

Does "An object moves 1 meter" represent a physical process?

(It can be in the context of e.g. work being done by friction, where the direction of motion does not matter)

Does the direction of motion being immaterial mean that there is not a direction of motion?

 

Is that an "abstract" usage?

 

Like Studiot's cube which is "arbitrarily oriented" but has to be oriented in one way at a time  .

 

When waveforms are collapsed they collapse in one direction  (stop me me  my replies are inconsequential,argumentative,unfocused   or overly ignorant-or just not worth answering )

[swansont]

1 hour ago, geordief said:

 Does the direction of motion being immaterial mean that there is not a direction of motion?

In classical physics it will have a direction, but you might not know what it is. It has no bearing on the answer, and it represents a physical process.

1 hour ago, geordief said:

When waveforms are collapsed they collapse in one direction  (stop me me  my replies are inconsequential,argumentative,unfocused   or overly ignorant-or just not worth answering )

QM waveform collapse doesn't have a direction. Or are you thinking of something else?

[geordief]

Just now, swansont said:

 

QM waveform collapse doesn't have a direction. Or are you thinking of something else?

Well, I was thinking that when a particle was detected its property ,such as spin or "up or downness" would  be  shown.(and that would be a direction of sorts)

 

 

[swansont]

30 minutes ago, geordief said:

Well, I was thinking that when a particle was detected its property ,such as spin or "up or downness" would  be  shown.(and that would be a direction of sorts)

Wave function collapse can be energy states. Energy is not a vector.

[studiot]

4 hours ago, studiot said:

Here is a mechancial scheme based on force, length and time as opposed to mass, length and time.

 

3 hours ago, geordief said:

Getting out of my depth now. I will hopefully reflect on these replies  over the medium term.

 

Whilst reflecting consider that changing from a MLT system to an FLT system has implications for the OP.

Pressure, for instance is a function of time in the MLT system, but not in the FLT system.