Time and space

[beecee]

15 hours ago, Eise said:

Time and space are not fundamental at all. They are abstractions. 

 

11 hours ago, studiot said:

 

First of all neither time nor space are things so their fundamentality is moot.

I'm not sure if those statements are correct. Why don't we ask ourselves is a magnetic field real?...or just an abstraction? I see it as analogous to asking is space and/or time real. Does something have to be physical to be real? My answer to the last one is no. Space and time, [as we know them] both evolved from the BB. Then if we progress to the following statement.... 

"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

Now we have another example of something that is not physical yet is real and certainly compulsory when describing the universe we inhabit in line with GR and the known laws of physics. Fundamental or emergent?? good question!

The following short interview videos I believe tell it like it is at this time.

and.....

 

Just some food for thought.  

Earlier I made the comparison between magnetic fields and spacetime: While we are unable to see a magnetic field directly, we are able to observe its properties such as the attraction and/or repulsion between ferrous objects. Simarilly with spacetime, we see gravity emerge when mass warps/curves it, or when that same warpage/curvature causes gravitational lensing and light following geodesic paths which we also observe.

Edited July 17, 2018 by beecee

[Eise]

13 hours ago, swansont said:

Instead of regular. I'm not sure what you mean by that. 

Ah, I understand. Formally you are completely right, but I really meant 'regular'. It is easier to measure time using a periodic process where every period has the same duration, and so we can safely assume that 'time' goes linear with that process. It basically 'reduces' timekeeping to counting (you have such an easy job... ). In my example processes, the falling stone and the water leaking from the can, the processes are not linear with time, which makes them not very practical for timekeeping.

8 hours ago, beecee said:

Why don't we ask ourselves is a magnetic field real?

OK, this depends on what you call 'real'. My definition is as follows: something is physically real if it has causal effects, or can be causally effected by physical processes. According to this definition a magnetic field is definitely real: it causes moving electrical particles to change their paths, attract iron, repels most other substances, etc etc.

How would time and space in themselves play a role in causal processes? I think it is even exactly the other way round. Think about how Hume, as an empiricist philosopher, treated causality: not as a law of nature, but as a tendency of us humans. According to Hume, we tend to describe causality to events that:

• happen at the same place 
• happen at the same time
• and similar events are observed repeatedly (or can repeatedly created)

I do not completely agree with Hume, but he has a point. I would take his points methodologically: not just as a tendency we have to associate events, but a the way we recognise the causal relationship between events. But as you see, time and space are the necessary background for causality, but they cause nothing in themselves. So they do not exist physically, according to my definition of physically real. 

I am happy to see another definition of what is physically real, so that time and space become just as real as processes, objects, fields, etc etc.

8 hours ago, beecee said:

Now we have another example of something that is not physical yet is real and certainly compulsory when describing the universe we inhabit in line with GR and the known laws of physics. Fundamental or emergent?? good question!

That is not the question as I see it. The question does not arise when you do not take space and time as physically real. Then they are neither fundamental, nor emergent. They are more or less substitutes for an imagination: that in every physical system there is, we have a scale for distances and durations, and that we can normalise these scales in such a way that we can compare processes in these different systems. In this comparison, we e.g. discover that in systems that are moving fast in relation to each other, we need a scaling factor (the 'gamma' of special relativity) to correctly compare how long distances and durations are of processes in the respective systems.

13 hours ago, Markus Hanke said:

Quantities can change with respect to other quantities, without the need for time.

That is an interesting point. (When a philosopher says something like that (or e.g. 'that is a good question'), it means 'I have no idea'. Yet.) Let me think about it. Or better in this context: 'Give me some time.'

Answer is not guaranteed... 

[pavelcherepan]

9 hours ago, beecee said:

I'm not sure if those statements are correct. Why don't we ask ourselves is a magnetic field real?

Feynman famously said the following about electron:

Quote

The electron is a theory we use; it is so useful in understanding the way nature works that we can almost call it real.

So by following his line of thought - electromagnetic field is a theory, so long as it conforms to what we expect of it, we can consider magnetic field to be almost real. But in the real world that we can experience what's real are charged particles moving along predictable routes and other effects.

Otherwise, magnetic field is just a matrix describing strength of magnetic force in any given point in space. Can't bring myself to think of it as being 'real'.

10 hours ago, MigL said:

A single particle can decay immediately today, yet repeat the same experiment tomorrow and it can take ten years for a like particle to decay.
And since it can be different every time, a single particle's behaviour is not time dependent.

Are they 'like' particles or different if they have different lifetimes? On a statistical level we can group them together and have a half-life defined that on a statistical level particles conform to, but if you look at them in separation, they are different, because they have different lifetimes. 

 

Edited July 18, 2018 by pavelcherepan

[studiot]

Good Feynman quote, Pavel. +1

[swansont]

4 hours ago, Eise said:

Ah, I understand. Formally you are completely right, but I really meant 'regular'. It is easier to measure time using a periodic process where every period has the same duration, and so we can safely assume that 'time' goes linear with that process. It basically 'reduces' timekeeping to counting (you have such an easy job... ). In my example processes, the falling stone and the water leaking from the can, the processes are not linear with time, which makes them not very practical for timekeeping.

Periodic is helpful, but people use non-periodic processes, too. Candles burning at a regular rate. Radioactive decay. Some clocks exhibit drift, meaning their frequency changes in a nonlinear fashion, but if it's predictable it can be factored out and the clock can be very useful. (Hydrogen masers being a prime example of this)

[geordief]

Does that Feynman quote really only apply to quantum systems?

We wouldn't talk the same way about  a cat in a box** would we ? The cat would be real and the box would be real .

Not that it would be necessarily helpful to point that out but it would be pretty indefensible and bewildering to say that things we interact with on an everyday basis were somehow "not real" or "almost real" would it?

 

** not that cat

Edited July 18, 2018 by geordief

[swansont]

2 hours ago, geordief said:

Does that Feynman quote really only apply to quantum systems?

Think about classical systems. Are electric fields real?

[geordief]

4 minutes ago, swansont said:

Think about classical systems. Are electric fields real?

Yes.  I know when they were first discovered they seemed magical (seemed like action  at a distance) but does that not apply to any new discovery?

Do colour blind people doubt that colours are real?

[swansont]

1 hour ago, geordief said:

Yes.  I know when they were first discovered they seemed magical (seemed like action  at a distance) but does that not apply to any new discovery?

Do colour blind people doubt that colours are real?

We now get to the point that we always seem to get to when this comes up: which sense of "real" are you applying? Because it gets very muddled if one jumps back and forth between them.

1) Real, as in not an illusion?

or

2) Real, as in it physically exists, i.e. is not a model or abstraction.

They Feynman quote is using #2, and in that sense electric fields aren't. Even though nature behaves in a way that they seem to actually exist.

I'm not sure color fits into this, since it's not really physics; it's a perception and at best, a property of something (and not necessarily an inherent quality), so that may not be a proper analogy. And I have no desire to follow anyone down that particular rabbit hole.

 

[geordief]

28 minutes ago, swansont said:

We now get to the point that we always seem to get to when this comes up: which sense of "real" are you applying? Because it gets very muddled if one jumps back and forth between them.

1) Real, as in not an illusion?

or

2) Real, as in it physically exists, i.e. is not a model or abstraction.

They Feynman quote is using #2, and in that sense electric fields aren't. Even though nature behaves in a way that they seem to actually exist.

I'm not sure color fits into this, since it's not really physics; it's a perception and at best, a property of something (and not necessarily an inherent quality), so that may not be a proper analogy. And I have no desire to follow anyone down that particular rabbit hole.

 

Sure . Well I answered yes ,that electric fields exist physically and are not a model.

 

Are you saying that they are just a model?

 

To expand  I would say (not wishing to presume as my education  is nothing to write home about) that "electric field" could equally refer to the abstract model as to the "real thing" that I am claiming it is.

 

Language is inadequate to draw the distinction  (well it has not seemed necessary to use language to draw the distinction ,maybe except in a roundabout way)

 

But ,yes it seems to me that we can **feel an electric field and so would assume it was a real thing just like any other (but would not feel the same way about the abstract model that attempts to  describe it on its own terms)

 

**eg we can feel electrostatic fields when they make our hair stand up

[swansont]

3 hours ago, geordief said:

Sure . Well I answered yes ,that electric fields exist physically and are not a model.

Are you saying that they are just a model?

And my answer is no they don't, and it is a model. But nature behaves as if they were real.

The real thing is the interaction.

3 hours ago, geordief said:

To expand  I would say (not wishing to presume as my education  is nothing to write home about) that "electric field" could equally refer to the abstract model as to the "real thing" that I am claiming it is.

Bingo.

3 hours ago, geordief said:

 But ,yes it seems to me that we can **feel an electric field and so would assume it was a real thing just like any other (but would not feel the same way about the abstract model that attempts to  describe it on its own terms)

 

**eg we can feel electrostatic fields when they make our hair stand up

So you know an interaction is taking place, but that doesn't actually tell you that the field is real. How would you test it to see if it physically exists?

 

 

[geordief]

52 minutes ago, swansont said:

And my answer is no they don't, and it is a model. But nature behaves as if they were real.

You mean we cannot distinguish between thee two? You must agree that nature is indifferent to our models .I am sure we would all agree that.

So you know an interaction is taking place, but that doesn't actually tell you that the field is real. How would you test it to see if it physically exists?

 

 

You know something (different) exists. It is just a matter of putting a name to it.

 

Yes there could be any amount of phenomena causing the effect (interaction) but we only give a name for those we can distinguish between (in this case I am guessing there is but one kind of electric field  but I could well be mistaken)

We could apply a similar argument to "is a donkey real?"  We know something there is real ,but is it a donkey? Maybe its an ass.. or a facsimile   or Trump on one of his better days.

I wonder if the onus is not rather on  anyone who doubts whether any particular thing is real (as opposed to "exactly so")  rather than on the  common sense main on Maine St who knows something is real but doesn't claim to be able to say what exactly it is (even it it seems blindingly obvious)

[swansont]

Quote

You mean we cannot distinguish between thee two? You must agree that nature is indifferent to our models .I am sure we would all agree that

Yes. 

 

1 hour ago, geordief said:

You know something (different) exists. It is just a matter of putting a name to it.

Not sure what you mean by "different" here.

1 hour ago, geordief said:

Yes there could be any amount of phenomena causing the effect (interaction) but we only give a name for those we can distinguish between (in this case I am guessing there is but one kind of electric field  but I could well be mistaken)

What we can do is describe how things behave. Two charged particles repel orvattract in a predictable way.

1 hour ago, geordief said:

We could apply a similar argument to "is a donkey real?"  We know something there is real ,but is it a donkey? Maybe its an ass.. or a facsimile   or Trump on one of his better days.

I wonder if the onus is not rather on  anyone who doubts whether any particular thing is real (as opposed to "exactly so")  rather than on the  common sense main on Maine St who knows something is real but doesn't claim to be able to say what exactly it is (even it it seems blindingly obvious)

Much of the physics that falls under this are things we can't see with our naked eyes. But "is a donkey real" really isn't discussing physics.

[geordief]

59 minutes ago, swansont said:

 

 

Not sure what you mean by "different" here.

I think I meant "underlying" or "responsible" ,something behind the facade. (is that turtle territory?)

Quote

What we can do is describe how things behave. Two charged particles repel orvattract in a predictable way.

Actually, are there different kind of charged particles? Are there particles that carry the weak/strong  force  which repel or attract similarly to electric charges? 

Quote

Much of the physics that falls under this are things we can't see with our naked eyes. But "is a donkey real" really isn't discussing physics.

No ,but physics (physical models) are,to my mind  a subset of natural phenomena and so  the "is a donkey real" question  could perhaps  be seen as category of thing/name** question  that bore a relation to  the model vs the modeled question  (well it is a question I have asked myself) which does seem to crop up   from time to time  on these forums. (it seems   easy to mistake the model for the modeled  and this gets pointed out occasionally ,esp when it comes to spacetime)

**can the  "name" be considered as  a model of the  "thing" in a kind of way?

Edited July 18, 2018 by geordief

[MigL]

Look at it this way Geordi...

!50 yrs ago the model said an electron was like a raisin embedded in sweet bread.
!00 yrs ago the model said it was a little billiard ball orbiting the nucleus.
75 yrs ago it was a probability distribution localized at or in the vicinity of the nucleus.
As of 50 yrs ago it is an excitation of the electron field that permeates all space.

All these models made testable predictions; some more so than others.

What is an electron really ?

Is it not the best model we have available ?
( and at the same time, it isn't )

Edited July 18, 2018 by MigL

[geordief]

53 minutes ago, MigL said:

Look at it this way Geordi...

!50 yrs ago the model said an electron was like a raisin embedded in sweet bread.
!00 yrs ago the model said it was a little billiard ball orbiting the nucleus.
75 yrs ago it was a probability distribution localized at or in the vicinity of the nucleus.
As of 50 yrs ago it is an excitation of the electron field that permeates all space.

All these models made testable predictions; some more so than others.

What is an electron really ?

Is it not the best model we have available ?
( and at the same time, it isn't )

Still,I have heard people say that the universe does not need our observation for its processes to continue their merry way (in response to some who claim that  things only happen when we observe them)

I agree**  with that former  view and wonder whether  we can extrapolate (maybe it's just an analogy rather than an extrapolation)  and say that "the modeled" exists in spite of our error prone attempts to model it (albeit,apparently more and more closely) 

 

As an aside I am interested that you say that the electron field permeates all space as I had been wondering if it was the case.

Is one of the theories that this field is quantized? Would that place a limit on its "range"?

 

**why I  do  agree apart from innate bias ,I can't say. 

Edited July 19, 2018 by geordief

[Eise]

6 hours ago, MigL said:

150 yrs ago the model said an electron was like a raisin embedded in sweet bread.
100 yrs ago the model said it was a little billiard ball orbiting the nucleus.
75 yrs ago it was a probability distribution localized at or in the vicinity of the nucleus.
As of 50 yrs ago it is an excitation of the electron field that permeates all space.

What is an electron really ?

There is a difference between two questions:

1. Do electrons really exist?
2. What are electrons really?

The first question, using my definition of 'physically real', we can say that electrons exist: they play a role in causal processes. So this question was solved when the electron was discovered. To know what electrons really are, one must know exactly how it behaves in all possible causal relationships. Now on purely methodological grounds one must say that one can never surely know that we know we have covered all possible causal relationships of electrons. But your list shows how in time we understood more and more causal relationships of the electron.

16 hours ago, swansont said:

They Feynman quote is using #2, and in that sense electric fields aren't. Even though nature behaves in a way that they seem to actually exist.

As there is no way to make observations of what lies behind our observations (in the end that is already a self-contradiction), we could very well say they do exist. There is no way to solve the question if electric fields just seem to be real or are real. So from a practical point of view, I would say they exist. 

12 hours ago, swansont said:

The real thing is the interaction.

Exactly. 'Interaction' is more or less another word for 'causal relationship'. And it is my opinion, as sketched above, that if we know all the possible interactions of 'something' we know everything about the object in question; with the amendment that there is no way to know if we really know all possible interactions, which explains why science still can progress, and even change its models of reality. 

Now, nothing of this applies to space and time: space and time do not interact with physically real objects. E.g. the Lorenz transformations do not describe physical processes. They describe more or less how the perspective on physical processes changes dependent on how observers move relative to each other. There is no causal mechanism that slows time down. 

[geordief]

1 hour ago, Eise said:

There is a difference between two questions:

1. Do electrons really exist?
2. What are electrons really?

The first question, using my definition of 'physically real', we can say that electrons exist: they play a role in causal processes. So this question was solved when the electron was discovered. To know what electrons really are, one must know exactly how it behaves in all possible causal relationships. Now on purely methodological grounds one must say that one can never surely know that we know we have covered all possible causal relationships of electrons. But your list shows how in time we understood more and more causal relationships of the electron.

As there is no way to make observations of what lies behind our observations (in the end that is already a self-contradiction), we could very well say they do exist. There is no way to solve the question if electric fields just seem to be real or are real. So from a practical point of view, I would say they exist. 

Exactly. 'Interaction' is more or less another word for 'causal relationship'. And it is my opinion, as sketched above, that if we know all the possible interactions of 'something' we know everything about the object in question; with the amendment that there is no way to know if we really know all possible interactions, which explains why science still can progress, and even change its models of reality. 

Now, nothing of this applies to space and time: space and time do not interact with physically real objects. E.g. the Lorenz transformations do not describe physical processes. They describe more or less how the perspective on physical processes changes dependent on how observers move relative to each other. There is no causal mechanism that slows time down. 

Nothing to add. It seems like  we might  have a similar approach. Perhaps you can point out  any bad errors or   misstatements (it is all the fashion these days ) in my own past 3 or 4 answers in this thread.

 

Do you like my "model of the modeled" idea.? What about my idea that models are  a subset of natural processes and not set apart from them?

Not entirely sure about your last point,which (I italicised) .....although I would like it to be correct.

 

 

Edited July 19, 2018 by geordief

[swansont]

11 hours ago, geordief said:

 Actually, are there different kind of charged particles? Are there particles that carry the weak/strong  force  which repel or attract similarly to electric charges? 

Coulomb's law works. The weak and strong force have their own interaction characteristics. So far as we have been able to tell, charge is charge, and independent of other properties.

11 hours ago, geordief said:

No ,but physics (physical models) are,to my mind  a subset of natural phenomena and so  the "is a donkey real" question  could perhaps  be seen as category of thing/name** question  that bore a relation to  the model vs the modeled question  (well it is a question I have asked myself) which does seem to crop up   from time to time  on these forums. (it seems   easy to mistake the model for the modeled  and this gets pointed out occasionally ,esp when it comes to spacetime)

**can the  "name" be considered as  a model of the  "thing" in a kind of way?

And physics is a subset of science. Just because you are talking about science doesn't mean you are talking about physics. And "is a donkey real" is arguably philosophy, rather than science.

2 hours ago, Eise said:

 As there is no way to make observations of what lies behind our observations (in the end that is already a self-contradiction), we could very well say they do exist. There is no way to solve the question if electric fields just seem to be real or are real. So from a practical point of view, I would say they exist. 

We've had discussions where people insist that particles don't exist and what we're seeing is field excitations. Because that's the model that they are using. Using a model that employs a particular phenomenon may lend itself to assuming that the model represents something real. When you look at electromagnetic interactions in QM, it's photon exchange. 

 

[MigL]

But space-time does causally interact, Eise.
The model was conceived solely by analyzing the causal interactions ( granted, as a thought experiment )

The curvature ( if real ) of space-time, or more accurately the distribution of energy-momentum causes test masses to follow specific trajectories.

I say 'if real', because the model GR, ascribes a curvature to the co-ordinate system.
Whether that means space-time actually curves or not ( or is real ), is anybody's guess.

[geordief]

13 minutes ago, MigL said:

But space-time does causally interact, Eise.
The model was conceived solely by analyzing the causal interactions ( granted, as a thought experiment )

The curvature ( if real ) of space-time, or more accurately the distribution of energy-momentum causes test masses to follow specific trajectories.

I say 'if real', because the model GR, ascribes a curvature to the co-ordinate system.
Whether that means space-time actually curves or not ( or is real ), is anybody's guess.

But something is real that has led us to model it as a curvature (of  coordinates) ,isn't it ?We don't know what it is and anyway the question of what was behind that would repeat itself,wouldn't it?

 

Does the definition of "real" as a modeling process   that repeats itself (like turtles) allow us to actually better define what we mean when we say "real"? (a bit like the calculus of the limits)

[Eise]

10 minutes ago, MigL said:

The model was conceived solely by analyzing the causal interactions ( granted, as a thought experiment )

Interesting point. The only thing I can think about, that obviously gravitation just as speed also changes the perspective. In the end, when you are falling in a gravitation field, nothing in your (small) falling laboratory can distinguish between falling in gravitation field or being in constant motion. 

26 minutes ago, MigL said:

The curvature ( if real ) of space-time, or more accurately the distribution of energy-momentum causes test masses to follow specific trajectories.

But a test mass follows just a strait line (its geodesic).

When you think about Newtonian gravity, you are right: then gravitation is a force that causes changes. But not in GR.

36 minutes ago, MigL said:

Whether that means space-time actually curves or not ( or is real ), is anybody's guess.

That is also an interesting point. I was astonished lately that it is possible to formulate GR in flat space, see Is spacetime really curved? Kip Thorne also mentions it in his book on black holes.

But what would your view be? It seems to me there is an essential difference between physical objects, existing in spacetime, and spacetime itself. I cannot ask you to change the time, or space itself. However we can change events in space an time, e.g. we can change an appointment to another time and place.

[beecee]

8 hours ago, Eise said:

 

9 hours ago, MigL said:

The curvature ( if real ) of space-time, or more accurately the distribution of energy-momentum causes test masses to follow specific trajectories.

I say 'if real', because the model GR, ascribes a curvature to the co-ordinate system.
Whether that means space-time actually curves or not ( or is real ), is anybody's guess.

 

That is also an interesting point. I was astonished lately that it is possible to formulate GR in flat space, see Is spacetime really curved? Kip Thorne also mentions it in his book on black holes.

But what would your view be? It seems to me there is an essential difference between physical objects, existing in spacetime, and spacetime itself. I cannot ask you to change the time, or space itself. However we can change events in space an time, e.g. we can change an appointment to another time and place.

Throwing in my $2 worth, if a model is successful and widely used, I believe it can logically be referred to as real.  Newton told us that gravity is the attraction between masses, but that he did not have any clue why. Einstein came along and informed us that the background metric against which we locate events and call spacetime is curved and warped in the presence of mass, and this curvature is why masses attract and which we call gravity.

GR is Einstein's theory of gravity and curved spacetime: SR is simply a special subset case of GR, is it not? and one in which spacetime being flat, gravity does not play a part.

That's the way I see it, obviously I'm not in real deep to the philosophical question of what is really really "reality" and again, see the successful model as being real.

A noted astronomer once told me that any future QGT will encompass the BB and GR, not invalidate them.

[geordief]

 

 

11 hours ago, MigL said:

 

I say 'if real', because the model GR, ascribes a curvature to the co-ordinate system.
Whether that means space-time actually curves or not ( or is real ), is anybody's guess.

Apparently it is now. But when we look back on the astonishing discoveries  that have been made in all sorts of areas of science and physics it does not seem to me unlikely that  at some (perhaps quite near) point that that particular mystery will be resolved (to be replaced by another head scratcher)

 

The way forward ,it seems to me is simply  by making and assimilating further observations  .They are the two headed sword that clears the path ahead  but makes an almighty new  mess as it does so.(if  metaphors can be thus  mangled ) 

Edited July 20, 2018 by geordief

[pavelcherepan]

21 hours ago, Eise said:

There is no way to solve the question if electric fields just seem to be real or are real

As MigL has correctly pointed, there is another way of looking at it. Is it likely that our understanding of space-time or electric fields will change significantly in time?

Since electromagnetism or GR are both theories, we are meant to update and change those if conflicting evidence shows up. Therefore, our understanding of what those phenomena are can, and most likely will change over time. New theories based on new observations can show it in completely different light. At the same time observable effects of space and time or electric fields, or electrons, will still stay the same. Therefore, I would consider those as 'real', but any theory or model can only be 'real' at one particular point in time.