# The Naked Scientists Forum

### Author Topic: Is There Such a Thing as Space Density?  (Read 10002 times)

#### Ron Hughes

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##### Is There Such a Thing as Space Density?
« 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.

#### namaan

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##### Is There Such a Thing as Space Density?
« 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 ;)

#### Ron Hughes

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##### Is There Such a Thing as Space Density?
« 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 »

#### graham.d

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##### Is There Such a Thing as Space Density?
« 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.

#### Ron Hughes

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##### Is There Such a Thing as Space Density?
« 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?

#### yor_on

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##### Is There Such a Thing as Space Density?
« 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?

#### Farsight

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##### Is There Such a Thing as Space Density?
« 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.

#### 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.

#### 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 »

#### The Naked Scientists Forum

##### Is There Such a Thing as Space Density?
« Reply #33 on: 19/02/2010 22:23:22 »