Is There Such a Thing as Space Density?

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Offline namaan

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Is There Such a Thing as Space Density?
« on: 19/01/2010 00:25:47 »
Hey all,

This is something that recently caught my attention. I'm no expert at all so I'm hoping someone can point me in the right direction. I was reading about the velocity of waves for my physics class and what determines it (i.e. how the velocity isn't determined by either the wavelength or frequency, provided there's no shift of medium). Anyway, it piqued my curiosity when I started reading about EM waves. I know space is supposed to be "medium-less", but doesn't it bend and compress via relativity (i.e. being next to a massive object) just like air does (well...for a different reason)? Can space be treated as a medium?

If space is thought of as a medium, does it have a density like other mediums? A mass?
Take it with a grain or two of salt...

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Offline yor_on

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« Reply #1 on: 19/01/2010 01:47:29 »
The paths of all things containing a momentum bend to gravity. And gravity seems to be a property of mass existing as some sort of field, possibly also as 'particles' like the Higgs boson or 'gravitons'. And we have space that contains 'distances' without, to us macroscopically, containing anything 'matter like'.

But it's not a medium in the ordinary sense. It's an absence of 'matter'. If you look at a photon it won't exist until interacting with matter. And if we assume that space is 'empty' then we have no way of proving that it exist there between 'source and sink'.

Space is more or less the ultimate definition of 'distance' to me. But matter travels in space, so maybe?

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Offline Geezer

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« Reply #2 on: 19/01/2010 05:00:17 »
Namaan: An excellent question. I think what you are saying is,

"How can waves propagate through something that is supposed not to exist?"

I've been trying to find the answer to that question for a very long time. I've decided (based on little to no evidence) that space actually is "something", but we just don't know how to describe it. But, don't believe me. That's just my unsubstantiated opinion.
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Offline Vern

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« Reply #3 on: 19/01/2010 05:30:00 »
We know that the empty space has two properties. Maxwell held these to be electric permittivity and magnetic permeability. Maxwell developed equations based upon these two properties that work pretty well to predict electromagnetic phenomena. The most exacting of this phenomena is relativity. All of relativity phenomena that we can observe behaves exactly as if the most elemental constituent of all physical reality is the electromagnetic field.

This is not new. We have known it since Maxwell. That was more than two hundred years ago. Why do we still try to ignore this most elemental historical fact? 
« Last Edit: 19/01/2010 05:31:46 by Vern »

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Offline Geezer

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« Reply #4 on: 19/01/2010 05:43:01 »
Vern: Personally, I don't (ignore it, that is). I believe these are fundamental properties of "Space". It's my impression that, somewhere along the line and for whatever reasons, we became rather seduced by particles.
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Offline namaan

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« Reply #5 on: 19/01/2010 06:11:49 »
Why do we still try to ignore this most elemental historical fact? 

I'm assuming you aren't asking me that. I'm only hear to learn; on that note, thanks for the link, I'll take a good look at it when I get time.

We know that the empty space has two properties. Maxwell held these to be electric permittivity and magnetic permeability.

I can't help but wonder, for space to be permeable to something implies it has structure; a framework of sorts. If gravity is, as theorized (and as far as I understand it), the end product of the effects of 'gravitons', for example, then this suggests to me that particles such as 'gravitons' or Higgs bosons are the components of that framework.

I'm not familiar with the details, but to put it more generally, there appears to be a framework out there in space that allows for the permeation of EM waves, and something comprises it (whether it's plain matter or perhaps photon-like quasi-matter). If that's the case, what's to prevent this 'empty' medium from behaving like other mediums through which waves traverse?
Take it with a grain or two of salt...

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Offline Geezer

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« Reply #6 on: 19/01/2010 06:33:43 »
Namaan:

There is strong evidence to suggest that atomic and sub-atomic particles do exist. However, as far as I am aware, nobody has ever captured a photon. Photons are only detected when they interact with matter. Photons can behave like particles, but they can also behave like waves. All forms of EM radiation, including visible light, are attributed to photons.

I think we still have a lot to learn!
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Offline namaan

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« Reply #7 on: 19/01/2010 12:43:20 »
Namaan:

There is strong evidence to suggest that atomic and sub-atomic particles do exist. However, as far as I am aware, nobody has ever captured a photon. Photons are only detected when they interact with matter. Photons can behave like particles, but they can also behave like waves. All forms of EM radiation, including visible light, are attributed to photons.

I think we still have a lot to learn!

As I said, I'm not so sure about the specifics myself. My only point was that regardless of whether the mainstream particle view is taken or the one you are suggesting or even a more exotic one where EM waves travel through a higher dimensional structure so it only appears that they are traveling through a vacuum, I am still left wondering that there appears to be some framework out there in space that is composed of something that allows for the permeability of EM waves. If this is the case, than why shouldn't space be treated like a medium?
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Offline acsinuk

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« Reply #8 on: 19/01/2010 15:36:05 »
If you look up fabric of electromagnetic space you will get an alternative electric view of the universe
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Offline namaan

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« Reply #9 on: 19/01/2010 15:42:28 »
If you look up fabric of electromagnetic space you will get an alternative electric view of the universe
CliveS

I'm not sure I understand. Are you implying that such an electric universe precludes the treatment of space as a medium? Could you elaborate please?
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Offline Ron Hughes

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« Reply #10 on: 19/01/2010 18:13:03 »
We have been unable to detect any substance to space. I have considered the possibility that EM waves interact in someway with EM waves and we have not been able to detect this interaction. If that were true, since all of space is filled with EM waves to varying energy densities, it could be said that EM waves are the medium of space. I have thought of a test that might shed light on this possibility. Shine a beam of light through two polarizing lenses oriented in the same direction and then place a magnet at the midpoint between the two lens. If there is any interaction this could possibly show it. If someone could perform such a test it would be interesting.
« Last Edit: 20/01/2010 04:39:47 by Ron Hughes »
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Offline namaan

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« Reply #11 on: 19/01/2010 23:13:45 »
I'd say that everything is on a spectrum (ie, no real absolutes), and it seems that there's approximately 1 atom per cm³ of outer space.

I understand what you're saying, but the matter that so happens to be out there at the fringes of space isn't what I'm referring to. I'm talking about space, the dark empty stuff, itself being some form of exotic structure or otherwise. This is implied from how space next to a mass is able to bend, compress, expand (via relativity) just like air does (via Newtonian physics). Is there a clear difference that would preclude us from treating space as a medium for EM waves as we would air for sound waves?
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Offline Geezer

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« Reply #12 on: 20/01/2010 02:25:09 »
I'm talking about space, the dark empty stuff, itself being some form of exotic structure or otherwise. This is implied from how space next to a mass is able to bend, compress, expand (via relativity) just like air does (via Newtonian physics). Is there a clear difference that would preclude us from treating space as a medium for EM waves as we would air for sound waves?

Well, you could take a rather extreme view (which, as it happens, I do [:D]) that there really is no such thing as matter. There is only space and energy, and matter is merely a manifestation of energy "encapsulated" by space. Just don't ask me to prove it or explain how this could possibly come about! Anyway, if that were the case, it does not seem too strange to me that we cannot examine space, because we are trying to examine space with space itself.
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Offline Pmb

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« Reply #13 on: 20/01/2010 04:46:19 »
Hey all,

This is something that recently caught my attention. I'm no expert at all so I'm hoping someone can point me in the right direction. I was reading about the velocity of waves for my physics class and what determines it (i.e. how the velocity isn't determined by either the wavelength or frequency, provided there's no shift of medium). Anyway, it piqued my curiosity when I started reading about EM waves. I know space is supposed to be "medium-less", but doesn't it bend and compress via relativity (i.e. being next to a massive object) just like air does (well...for a different reason)? Can space be treated as a medium?

If space is thought of as a medium, does it have a density like other mediums? A mass?
If the space is totally void of all matter then it's still possible for a wave to pass through it. Such a wave is called a gravitational wave and its spacetime itself which is doing the waving. If there is an electromagnetic wave mocving through the space then the space is not void of matter since an EM field is considered to be matter. I.e. it can have both energy, momentum as well as stress/tension.

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Offline Geezer

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« Reply #14 on: 20/01/2010 05:11:14 »

Okay.  I'm interested in the idea that space is the norm and that matter is the exception that displaces space thereby causing gravitational forces.  Has anyone heard of this?

I'm not sure it's all that different from String Theory, although I confess I gave up trying to understand string theory when it got into more dimenstions than I could handle.
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Offline namaan

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« Reply #15 on: 20/01/2010 17:04:47 »
I have to say, I'm rather surprised at the responses this thread has produced. I was expecting some sort of cold hard physics explanation to nip this idea at the bud from at least someone. Or maybe someone did and I missed it?

Just to make sure that this thread appropriately receives the full attention of the mainstream school of thought, I'll lay out a controversial claim: if one thing is clear from the responses, it seems that there is no good solid reason to rule out space from behaving as a medium. And a related point being, as mentioned in the title, that space may have a density, and thus a 'mass' and 'volume'.

Btw, I'm well aware that I'm speaking without approaching the mathematics behind it. I don't have the time for that right now, so in the mean time I at least want to get some good background knowledge on the subject.

Do add nuance to my understanding where appropriate!
« Last Edit: 20/01/2010 17:11:46 by namaan »
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Offline Geezer

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« Reply #16 on: 20/01/2010 18:16:43 »
Okay.  I'm interested in the idea that space is the norm and that matter is the exception that displaces space thereby causing gravitational forces.  Has anyone heard of this?
I'm not sure it's all that different from String Theory, although I confess I gave up trying to understand string theory when it got into more dimensions than I could handle.

I'm with you on String Theory.  I got as far as 10 dimensions and vibrating strings, and I said to myself, "Okay, that more than I needed to know.  Next wacko theory, and a bit fewer dimensions, please, I'm trying to hold onto my sanity."

What if, instead of being "nothing", space is "something" ... but a "something" that's incompatible with matter, so matter displaces it, and this displacement causes gravity.  It's not the matter that causes gravity, but the displacement of space.  We can't measure the "something-ness" of space because you can't measure it with equipment -- maybe because matter and space are incompatible.

I think that's well worth considering. In my case, I think there is just too much going on that suggests space is "something". We know "matter" and "energy" are derivatives of each other, so why can't "space" be the medium that supports the transformation. From there it's not too hard to say "Well heck, why can't it all be space?" This, without a trace of math! People will be after me, I'm sure.
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Offline JP

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« Reply #17 on: 20/01/2010 23:36:29 »
Just to make sure that this thread appropriately receives the full attention of the mainstream school of thought, I'll lay out a controversial claim: if one thing is clear from the responses, it seems that there is no good solid reason to rule out space from behaving as a medium. And a related point being, as mentioned in the title, that space may have a density, and thus a 'mass' and 'volume'.
I'm not quite sure what you mean by "density."  Space certainly isn't like air, for example, which carries sound waves and behaves differently depending on its density.  Air is a medium since the air itself is wiggling about to transmit the waves.

The current understanding is that space is filled with fields, and these fields can carry energy/matter in the form of waves/particles.  Space itself isn't a medium since the space isn't waving.  It might distort a little due to concentrations of matter and energy, but it isn't wiggling like the waves passing through it.  However, even "empty" space still has these fields in it, and due to quantum mechanics, the fields can never have zero energy (even at the lowest possible energy, they have slightly non-zero energy).  In a sense, therefore, empty space does have an energy associated with it. 

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Offline namaan

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« Reply #18 on: 21/01/2010 03:07:05 »
I'm not quite sure what you mean by "density."  Space certainly isn't like air, for example, which carries sound waves and behaves differently depending on its density.  Air is a medium since the air itself is wiggling about to transmit the waves.

The current understanding is that space is filled with fields, and these fields can carry energy/matter in the form of waves/particles.  Space itself isn't a medium since the space isn't waving.  It might distort a little due to concentrations of matter and energy, but it isn't wiggling like the waves passing through it.  However, even "empty" space still has these fields in it, and due to quantum mechanics, the fields can never have zero energy (even at the lowest possible energy, they have slightly non-zero energy).  In a sense, therefore, empty space does have an energy associated with it. 

I have to ask, is there a mathematical or otherwise good reason for space not being able to 'wave'/oscillate (as a medium should in order to accommodate wave propagation)? I mean we certainly can't directly measure or observe in any way the curvature of space (as far as I understand). Isn't it just a mathematical necessity? Math also tells us some weird things about dimensions. It might be correct. But it might not be.

For example, if you take a really inflexible rope (I'm big on analogies) that you might otherwise think is unable to serve as a medium for wave propagation since it presumably can't oscillate, such a rope may still be able to propagate macroscopic waves or waves of a higher scale (as in the whole length of the rope oscillating at it's fundamental frequency).

Here's a hopefully interesting hypothetical: let's assume for a second that somewhere in the universe there is such a thing as an oscillating black hole; a black hole that for whatever reason is oscillating between very strong and weaker gravitational forces on space. These oscillations will then be passed on to space itself which will oscillate on a massive wavelength. This is purely a hypothetical, and it is possible that the very assumption of an oscillating black hole breaks the premise of the hypothetical. If not, then we must consider: if space can oscillate with wavelengths in orders of magnitude, then what would prevent it from oscillating in EM wavelengths?

More poignantly, how do we really know that space isn't oscillating to accommodate EM wave propagation? I'm not implying anything, only sincerely asking.
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Offline JP

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« Reply #19 on: 21/01/2010 03:31:40 »
The reason we know space doesn't oscillate in EM wave propagation is that we should be able to detect it doing so.  If a medium oscillates in wave propagation, then if you move in that medium along with the wave, the wave slows down.  Electromagnetic propagation in space doesn't have this property.  There are also plenty of modern theories that contain this assumption (special and General relativity, relativistic quantum mechanics, and even classical electromagnetism), all of which are supported by experimental evidence. 

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Offline namaan

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« Reply #20 on: 21/01/2010 04:16:09 »
I understand your point about the constancy of EM speed, but I'm not seeing it's connection with whether or not space oscillates. In other words, if a wave propagating in a particular medium maintains a constant speed, why does that imply that this medium can't oscillate? I think I kind of have an idea, but I'm having difficulty formulating a clear picture.
« Last Edit: 21/01/2010 05:09:13 by namaan »
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Offline JP

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« Reply #21 on: 21/01/2010 15:36:46 »
If space itself is waving, it must be waving with a certain speed.  If you run alongside that wave, you could in theory catch up with it.  This isn't the case with light traveling in space, since it always seems to move with the same speed no matter what you're doing.

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Offline acsinuk

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« Reply #22 on: 21/01/2010 16:10:52 »
Electromagnetic energy is massless but it cannot travel through an unmagnetized space.  Its like trying to generate electricity in a alternator with a wooden core. It will not work! Space needs to be magnetized to support EM energy transfer.
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Offline Ron Hughes

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« Reply #23 on: 21/01/2010 16:35:52 »
Since we don't have a clue as to what space is made of,other than the fact that is full of EM, how do we know it is magnetized?
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Offline JP

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« Reply #24 on: 21/01/2010 16:46:03 »
Since we don't have a clue as to what space is made of,other than the fact that is full of EM, how do we know it is magnetized?

It isn't.  An EM wave consists of an electric and a magnetic field, but space itself doesn't get magnetized.  Magnetization is something that happens to matter, not space.

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Offline Ron Hughes

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« Reply #25 on: 25/01/2010 23:03:30 »
An EM wave exhibits momentum. The shorter the wavelength the greater the momentum(energy). With that said, why couldn't we say that the density of space is the amount of energy in a given volume of space? For instance, the density of space at the center of a black hole would be enormous. The density of space within a hundred meters of an exploding hundred megaton hydrogen bomb would be much greater than a million meters from it.
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Offline namaan

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« Reply #26 on: 26/01/2010 02:24:02 »
With that said, why couldn't we say that the density of space is the amount of energy in a given volume of space?

In this case I think the question becomes more of a semantic one: what is space to you? Or even, what is density to you? If you define space as nothing, then it has no density (presumably). If you define it as a ubiquitous EM field, then density may be approached as you have in terms of amount of energy per volume. But if you consider that space itself is 'something', specifically something that serves a purpose (perhaps serves the task of defining a coordinate axis of sorts), then it might not need to contain something to have density.

Well, this is all vague stuff, taken with several grains of salt ;)
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Offline Ron Hughes

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« Reply #27 on: 26/01/2010 17:34:18 »
http://www.thenakedscientists.com/forum/index.php?topic=28159.msg295422#msg295422

The above link shows supporting evidence of space being an oscillating electric field.
« Last Edit: 26/01/2010 17:39:04 by Ron Hughes »
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Offline graham.d

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« Reply #28 on: 26/01/2010 17:47:26 »
Would you not define gravitational waves as waves of time-space distortions propagating at lightspeed? In GR terms that is the only medium available. How this ties up with a Higgs field I'm not sure.

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Offline Ron Hughes

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« Reply #29 on: 26/01/2010 18:33:25 »
I am not convinced that gravitational waves ( http://www.thenakedscientists.com/forum/index.php?topic=24337.msg271862#msg271862) exist. Likewise, the Higgs will never be found.

On space density, an interesting thought occurred to me. What was the density of space when matter formed right after the BB?
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« Reply #30 on: 26/01/2010 23:57:49 »
Okay, first of all. Gravitational waves might exist.

"While gravitational waves have not been directly detected so far, there is strong indirect evidence. The smoking gun is a system of orbiting neutron stars with the catchy name PSR1913+16. Einstein's theory predicts that gravitational waves carry away energy. For a system of orbiting stars, such a decrease in total energy leads to an ever faster and closer orbit. Over decades, radio astronomers have monitored the time that it takes the stars of PSR1913+16 to complete each successive orbit, and lo and behold: this orbital period decreases over time exactly as predicted by general relativity. This is strong evidence that the speed-up is indeed due to the radiation of gravitational waves, and the reason Russell Hulse and Joseph Taylor were awarded the Nobel prize for physics for the year 1993."

And there namaan comes your idea of a black hole oscillating in too. It can't but if you have two rotating around each other they might.

I would recommend this site as a very good one for those interested in gravitational waves, black holes and general relativity. I find it quite easy to read. Gravitational waves

When we discuss space I agree with JP and Pmb in that EM needs 'matter' of some kind to propagate in. You really need to prove it otherwise :) And that I expect to be quite hard, and worth a Nobel prize if you succeed.

As for Geezer, he's just being plain weird :)
Like me ::))

We're both wondering a lot over what space and matter 'really is' but that doesn't stop us from admitting to what we can prove. And that is that we need a medium for something to be seen as 'propagating'

Neither light nor EM (electromagnetism) can be proven to exist in a absolute or, as it is called too, 'free vacuum.' As for DDaves question about matter being the exception? That's a good one. If we (Baryonic matter) only constitute around five percent of the known universe? We sure seem to be underrepresented :)

But we must look to what our experiments show us, and in them there can be no interaction in free space, of any kind. If free space exists that is :)

All interactions we build our ideas from is with matter inside Planck time. Let us assume that 'free space' exist. Let us also assume that it contains JP:s energy description as well as 'virtual photons'. Hell, let us assume that 'free space' is nothing but a compact virtual mass of energy, just waiting for us to 'tap it'. How do you suggest we do it??

By interacting with something, right?
Like 'matter' perhaps?
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Offline Farsight

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« Reply #31 on: 27/01/2010 13:04:57 »
namaan: in mechanics a shear wave travels at a velocity determined by the stiffness and density of the medium. There’s an equation for it that goes like this: v = √(G/ρ). The G is the shear modulus of elasticity, The ρ is the density. A shear wave travels faster if the material gets stiffer, and slower if the density increases. In the velocity equation is remarkably similar: c = √(1/ε0μ0). Vern mentioned permittivity and permeability, and they're related by impedance Z0 = √(μ0/ε0). Impedance is resistance to alternating current, and if you take a look at a light wave and a plot of alternating current, they aren't that far apart. So, does the impedance of space change? Ordinarily we'd say no, but take a look at the Shapiro time delay, or more generally, gravitational time dilation. What's happening to a photon in region where clocks run at a slower rate? What's happening if those clocks are light clocks? The bottom line is that the light goes slower. You can't measure it locally of course, because how are you going to measure the slower rate? With a light clock?

As to what the electromagnetic wave actually is, take a look at Maxwell's Space and Time. Two pages from the end he talks about the electron's magnetic field and gives a wrench analogy. Now take a look at Maxwell’s On Physical Lines of Force where he talks about a screw mechanism: http://en.wikipedia.org/w/index.php?title=File:On_Physical_Lines_of_Force.pdf&page=53. Nobody seems to have read the original material, and they don't see the significance: think about the right hand rule, then find a drill bit and push it up into your right fist. It has a twist, so it turns. I don't know if you know anything about Weyl gauge change, but there's a geometry to this, and you end up thinking of the electromagnetic wave as something very similar to a gravitational wave. The best way I can describe it is as a wave of "spacewarp". The most significant property of space is distance, and it seems that distances can change.

If you know anything about pair production you'll perhaps understand what I mean when I say space isn't made of anything. Instead, everything is made of space. So whilst it has a density of sorts, it's an energy density at best, rather than the sort of density we're familiar with from material objects.

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Offline Ron Hughes

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Is There Such a Thing as Space Density?
« Reply #32 on: 27/01/2010 16:09:54 »
No thoughts on the density of space post BB? That would seem to be a very important time in the history of the Universe.
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Offline yor_on

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Is There Such a Thing as Space Density?
« Reply #33 on: 19/02/2010 22:23:22 »
You asked for it Ron :)

Space as 'something' is a 'nothing' according to the tome of me.

Space is what we move through, all of us. If there was a density to it, like a 'fog' of some sort then we would have noticed it a long time ago. The idea of an aether was just a try for finding a 'density' existing in 'space'. When we come to 'energy' it's another 'matter' :) We don't have any definition for what 'energy' is as an 'entity'. We have very good descriptions for how it can express itself though, and through what types of interaction it might do so.

When we discuss 'space' having an 'energy' we're not defining it with a new entity hiding in it, we plain don't know, as I see it, what energy in itself need to be existent. What we do seem to know is that it is everywhere, but only expressed in its interactions. So everything, from light to matter to space seems to be possible 'carriers' of that. What we also can notice is that we have two (or more) definitions of time. One macroscopically (times arrow) defining our place in SpaceTime and how it will appear macroscopically. Another at the quantum mechanic level where 'times arrow' seems to become more undefined in direction, allowing for 'virtual particles' and a lot of other strange things. And time will change SpaceTime as related to the one observing. Speed, velocity, distances is all expressed in time and depending on energy spent you can see a new SpaceTime as you accelerate. And lastly we have invariant mass aka matter that seems to have much of an equivalent 'force' as energy spent aka acceleration have.

It's easy to see the equivalence between free falling -- accelerating -- down a gravity well due to SpaceTimes geodesics ('deformations') and accelerating. But if we accept that density as a definition isn't applicable to Space we still have to understand the difference. Geezers idea of space being some kind of predecessor to matter isn't impossible, just as the idea of EM fields being matter have an validity too. The problem is that even then, looking at only 'empty space' we can't really say that we are looking at the 'original'. To me the concept of 'energy' then would seem 'closer' or as I see it 'time' itself, not its arrow, but time.
« Last Edit: 19/02/2010 22:27:09 by yor_on »
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