[paul cotter (OP)]

What are the properties of space? I can only think of two, C(itself a composite of permeability and permittivity) and G. In thermodynamics two independent properties can define a system(in equilibrium), is there any correlations here. Right, this is wooly thinking, no doubt about it. However I have often been asked an utterly stupid question and in the process of untangling what the other person actually wanted to know I have learned a new perspective on the matter in question. Any ideas?

[Halc]

What are the properties of space? I can only think of two, C(itself a composite of permeability and permittivity) and G.

Both G and c (lower case) seem meaningless in the absence of something other than space, but even space itself is undefined in the absence of something to occupy it.

A property of our space is that it is 3 dimensional, something not necessarily true even in another universe with similar c and G. G seems to be a property of gravity. c is a constant that has meaning to the geometry of spacetime, but not to the geometry of space.
The two are not entirely independent properties since they share some common units, but one could always select those units so that the constants are both 1.

I'd say both are a set of constants (tunings) to our physics, along with a fairly short list of other constants, but these define how our physics works as compared to the behavior of the same physics with different constants. That makes them properties of our universe, but since there would still be space regardless of different tunings, I'm not sure if they're properties of space itself.

In thermodynamics two independent properties can define a system(in equilibrium), is there any correlations here

Equilibrium in what way?

[paul cotter (OP)]

In thermodynamic equilibrium, uniform temperature, pressure, volume so that these independent state variables can be defined.

[Halc]

I know, but in what way would 'space' be in equilibrium such that these constants can be defined? And why just these two constants and not others. It would seem to require more than space to do this. Time for instance.

[paul cotter (OP)]

Halc, I did say that this is wooly thinking. It might sound strange but the asking of ill defined questions often leads to unexpected insights, for me at least(maybe i'm just weird!).

[Eternal Student]

Hi.

...but even space itself is undefined in the absence of something to occupy it...

    Space is just a set of points in a co-ordinate system.   

The Schwarzschild solution of the EFE is a vaccum solution.   It has infinite space and nothing material in it.
The Milne Model, which you (@ Halc ) are fond of pulling out as an example to generally foul things up when required,  that's another vaccum solution with infinite space.
Minkowski Space is another example (which isn't different from Milne, it just has a different co-ordinate system).

A property of our space is that it is 3 dimensional...

   Yes, there aren't any string theorists on this forum.

I'd say both are a set of constants (tunings) to our physics, along with a fairly short list of other constants, but these define how our physics works as compared to the behavior of the same physics with different constants.

   Yes.... and exactly this sort of thing is done.   Physicists do consider how the universe might be different if we adjust the value of certain key constants of the universe.
   Our universe seems to be finely tuned for the development of life, for example.    Before getting too complicated and trying different values for some constants,  we can even consider what happens if there are less than 3 dimensions,  say only 2 spatial dimensions.   Then  organisms can't evolve which have a digestive system with an entrance (a mouth) and a separate exit (let's call it an exit),  since that will inevitably cut the organisms into two separate bits - two organisms.   This alone is thought to seriously limit the complexity of life that can evolve.
      It's also possible to adjust the constants in such a way that some physics effectively disappears.   For example, if we put the constant c → ∞  then we can still have special relativity but it's just that it doesn't matter anymore.   Length contractions and time dilations become 0   etc.   It is as if the effects of special relativity have gone and we have Gallilean relativity.    We do also get some unusual and possibly undesirable consequences,  for example every point in spacetime is causally connected to every other point in spacetime - but there's no reason to assume that just because some thing can move at an arbitrary speed it will,  there may still be a practical limit for the speed of anything and hence a practical limit on causality.
     Anyway, just as we can make some physics become less important  (e.g. SR disappears as c→∞),  we can imagine that there are already some laws and some constants that are so small (or so large) that some physics has effectively been hidden from us.  Change those constants and we experience some new physics that we were unaware of.

What are the properties of space? I can only think of two, C(itself a composite of permeability and permittivity) and G. In thermodynamics two independent properties can define a system(in equilibrium), is there any correlations here.

    Well, on a vaguely similar line of reasoning....   Energy is or was thought to be one of the most important things in Physics.   There are several ideas about the universe being in an equilibrium of different sorts of energy.   You ( @paul cotter ) started a recent thread about this and had replies like this one from me:
https://www.thenakedscientists.com/forum/index.php?topic=84890.msg679741#msg679741
     Where Stephen Hawkings put up some ideas and discussion.

...this is wooly thinking, no doubt about it.  However I have often been asked an utterly stupid question and in the process of untangling what the other person actually wanted to know I have learned a new perspective on the matter in question. 

    Sounds fine to me and there's every reason why something like this should be discussed.
If it gets too woolly or speculative,  then it might be better off in the "Just Chat" secton or the "New Theories" section, or somewhere like that.    I'm not a moderator and I don't mind, it's just that it's difficult to apply one rule for person X and another for person Y.   So don't be too surprised or disappointed in some way if this thread does get re-located eventually.   Personally, I like an open-ended "what-if" and  "what may come of this"  discussion about science and I think it's exactly what a forum can and should offer - but this isn't my forum and there are some rules and policies.   Otherwise the main sections are filled with junk etc.

Best Wishes.

[Halc]

Space is just a set of points in a co-ordinate system

Indeed. It reduces space to an abstraction of sorts, since coordinate systems are abstract/arbitrary.

The Milne Model, which you (@ Halc ) are fond of pulling out as an example to generally foul things up when required,  that's another vaccum solution with infinite space.

Guilty as charged. It pretty much fouls things up, but is also the only way to crudely describe distances to galaxies relative to Earth's frame.

Our universe seems to be finely tuned for the development of life, for example.

For complex structures, even like atoms for instance. Most tunings don't allow something as complex as a hydrogen atom to form.

If it gets too woolly or speculative,  then it might be better off in the "Just Chat" secton or the "New Theories" section, or somewhere like that.    I'm not a moderator and I don't mind, it's just that it's difficult to apply one rule for person X and another for person Y.   So don't be too surprised or disappointed in some way if this thread does get re-located eventually.

Questions and learning are very encouraged. What gets moved to the lighter-side section are  topics where the OP explicitly denies accepted science, as opposed to just asking questions.

[paul cotter (OP)]

Makes no difference what this is filed under. You can call it nonsense or fiction, I just enjoy the discourse and what I may learn from it . Thanks again for indulging me.

[alancalverd]

Space is what separates bodies of stuff. Not sure about "properties" beyond μ and ε, but we can certainly describe the static (fields) and dynamic (particles and waves) contents of regions of space. So if you want to be philosophical you could describe the ability to contain such phenomena  as a property of space, but I suspect this is a sterile  intellectual cul-de-sac.

Is G a property of space? I think not.  g is an observable property of stuff, and you could argue that G is merely a constant of proportionality that relates the observable g to m and r, because if you interpose a third body of any length between your two experimental masses it doesn't alter the original gravitational attraction by filling space, but adds to it by virtue of its own mass.

[geordief]

What is it that makes stuff separate from itself? (rarified?)

Why is it not happy just being together with itself,with no distance between its constituent parts?

Are all the separate bits of stuff  forever connected or forever  separate? (both?neither?)

Is that a very poor philosophical question as well as a poor scientific question?

Do we just start with what we observe and not try to second guess  what is out there and in here?

[Eternal Student]

Hi.

Space is what separates bodies of stuff.

   Yes.... and also time does that.   Two bodies can be in the same space but at different times.    As I'm sure you know, there's sometimes no difference between space and time separation except which frame of reference you use.

we can certainly describe the static (fields) and dynamic (particles and waves) contents of regions of space. So if you want to be philosophical you could describe the ability to contain such phenomena  as a property of space, but I suspect this is a sterile  intellectual cul-de-sac.

    Well, I was tempted to go down those lines.   There are various fields defined on space and assumed to exist throughout all of space.  That does seem important and essential that space can support this.
     Another important thing about space is that it has some inherent structure.   I would be tempted to say mathematical structure but let's get things in the right order:  Our concepts and development of mathematical structures were obviously influenced by the way space seems to be.   If space had been different, you can be pretty sure we would have developed different ideas of geometry and such like.   So the only important thing is that space does seem to have some inherent structure and properties - something that we will ultimately call geometry, the properties of a vector space, topology  etc.
     I'm biased toward favouring General relativity, so you can tell where I'm going with this....  the metric seems to be an inherent property of space.

@geordief ,  sorry your post appeared after I had started writing and it's too late to reply to all of that today.

Do we just start with what we observe and not try to second guess  what is out there and in here?

    That isn't the human way.  We are very inquisitive.   You've just asked plenty of questions for example.

Best Wishes.

[alancalverd]

Current consensus is that the big bang produced a lot of stuff dispersed in space, and gravitation gradually makes it coalesce into lumps, so the observed separation is temporary. Except that some stuff seems to be receding at an ever-increasing rate, presumably into more space.

[paul cotter (OP)]

I would argue that G is a property as it tells us the degree of warping a given mass will produce. Just as mu will tell us the H field produced by a current and epsilon tells us the E field produced by a charge. (hope I used the correct case, I already got told off for use of C instead of c!)

[Halc]

I would argue that G is a property as it tells us the degree of warping a given mass will produce.

I can buy this. Gravity, expressed as geometry (like it is in GR) makes G a property of spacetime at least, if not space.

Just as mu will tell us the H field produced by a current and epsilon tells us the E field produced by a charge.

Well, some tips then. These symbols are right there just above your edit window. No need for special keyboard or tex just to express μ and ε respectively.
Physics has so many things with so many units, and 26 letters in upper and lower case each just isn't enough to express even the common things, let alone all the new concepts. But greek has only so many symbols as well. Perhaps we can borrow some from Tolkien's elves or maybe the Klingons.

[Eternal Student]

Hi again.

What are the properties of space?

    I don't know.   You ( @paul cotter ) probably need to start by examining what you consider to be space.   Some of the previous posts have done a bit of that - but what do you think or want to consider as space?
    One thing that hasn't been discussed is whether space is continuous or discrete.   Is there a smallest unit of length?   (or a smallest unit of time?)    If there is then a lot of our ideas about the geometry or inherent properties space aren't quite right.  For example, Special relativity and its predictions of length contraction are in trouble.

I can only think of two, c (itself a composite of permeability and permittivity) and G

   You seem more interested in the fundamental physical constants rather than anything else about space.    There's a bit of discussion about what the fundamental constants are or should be in Wikipedia:   https://en.wikipedia.org/wiki/Physical_constant#Number_of_fundamental_constants .        G  and c  which you suggested do get into that list.   There are some complications, for example the way the speed of light, c, and "the metre" has been defined in the SI units has been modified a few times and now it's not possible to adjust c,  instead you would be adjusting the metre or challenging the time interval of an Atomic clock based on Caesium.  So some would say that to adjust c, you need to go at it indirectly by doing something like adjusting the fine structure constant.   
   Basically, identifying the fundamental physical constants is a contentious issue and if we discover more physics, there's likely to be more fundamental physical constants required.

Best Wishes.

[paul cotter (OP)]

That is quite a lot to respond to. I am not in a position to respond right now, I have an injured cat to deal with plus the usual myriad of minor problems associated with daily living-i'll get back to you on this subject.

[alancalverd]

I would argue that G is a property as it tells us the degree of warping a given mass will produce

But doesn't that make it a property of mass rather than spacetime?

[paul cotter (OP)]

HI, eternal student, I said I would respond to your arguments. I have composed several replies only to delete them as I was not happy with them. The bottom line is that I am using an engineering mindset to understand the universe as best I can, however inadequate that may be. Engineers tend to be hard-nosed and no nonsense types(not  at all suggesting any nonsense in any of the replies). How we define units will, as you said, affect the basic nature of our constants but to an engineer a bar of platinum/iridium in some standards lab in france is good enough for the metre for all intents and purposes. How much can we know for certain?, very little I think: many years ago I saw a scientist argue that "there is no objective reality outside of the self". I can't remember his arguments but I was impressed at the time(alancalverd will have a contract out on me for contaminating a science forum with the dreaded philosophy)

[Eternal Student]

Hi.

    I fully understand your comments, @paul cotter  .    Replies are always optional.   The forum is meant to be for interest and when it starts to feel like an obligation or burden then it's time to re-examine what you're doing and why you think you should.
      The comment you made about the metre is a perfectly good one.   However the idea of defining a metre by as how far light travels in 1 / 300 000 000   th  of a second* isn't completely silly or arbitrary and it does open the door to looking at things in different ways.   That means a few more minutes of hopefully interesting discussion, if nothing else.
*LATE EDITING:  Yes, it's actually 1/ 299 792 458  - it's just that the exact numbers aren't important and get in the way of the general idea.

      For example, how would you realistically measure big distances?    Presumably with a radar or laser measuring device,  you'd just time how long it takes to get a signal back.    How would you know if the distance between two objects has increased after 100 years, or if the speed of light has actually decreased as time evolved?    More significantly, would there be any difference to how physics behaves?  These ideas are always worth a moments thought and well worth revisiting every now and again.   Usually you can discern a difference between distance increasing and light slowing down but it get's murky again if you consider that maybe your measurement of  time is also changing.  Maybe there are some important dynamic fields in the universe and the frequency of radiation emitted by Caesium-133 atoms is changing as a result of that, so that the atomic clocks used to define the second are not actually keeping the correct time.
     For simplicity, we can consider trying to view the universe from some other place or point of view.   One easy option is to adopt the language used by those who suggest our Universe might be a giant simulation (much as if it's running on someone's laptop).   If their laptop starts to run more slowly (perhaps because the processor is overheating and it gets throttled-back) then they notice that our ideas of time have changed, it takes longer to get their action hero across a room.   However, the simulations don't notice any difference, everything in the simulation moves slower in the correct proportion.    Similar things happen if distances suddenly doubled (in all directions) but everything can move twice as fast as before.   The computer simulation action hero can still fire an arrow across the room in the same time.   
    Overall then, you have to decide that something(s) is (are) "locked down" or held constant.   Typically you'd start with time and assume the simulations have some awareness of a flow of time and it doesn't matter if it changes relative to the gamer's time outside the laptop, it's constant and fixed for the simulations.  Then build up from there systematically, considering if it's possible for something else (like the speed of light inside the simulation) to change or if it would be indistinguishable from some other combinations of things changing.

Best Wishes.

[alancalverd]

Maybe there are some important dynamic fields in the universe and the frequency of radiation emitted by Caesium-133 atoms is changing as a result of that, so that the atomic clocks used to define the second are not actually keeping the correct time.

If said fields are homogeneous, then we'll never know because everything is coming and going at the same time. Except that the light received from an object umpteen light years away will have a different frequency from what we have calculated, and whatever determines the field vectors must have some supraluminal means of directing them.

And if the fields are not homogeneous, then we can blame GPS navigation errors  on something we can't sense or predict, i.e. local wobbles in the Eternalstudent field. But so far, no evidence - I get the blame every time for not updating the database.