10 Jan 2007 0:58:02 UTC

Topic 192286

(moderation:

This falls along the lines of the Einstein@Home project, but I'm curious what tests or studies have been done to determine the effects of electricity or electromagnetic fields in space? Please post any links to your replies if possible.

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## Study of electricity/electromagnetic effects in space

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Hi Admin,

Perhaps you can refine your question. Without electromagnetic fields we wouldn't be able to see anything. Actually, there wouldn't be any chemistry either without them, hence no biology....

Do electromagnetic fields interfere with gravitational wave radiation? As I understand it, the EM fields don't affect the gravity waves in the least, but EM fields nevertheless play a crucial role in the detection of the warped space-time that results from a gravity wave as it passes by. See the Detector Watch threads in this forum for more information.

Maybe a way to best sum up the effects of EM fields can be learned by observing what our galaxy looks like in each of the many different wavelengths. Here's a link to Multiwavelength Milky Way Images

[aside](from looking at the concentrations of matter in the atomic and molecular hydrogen images)

So the size of our galaxy is attributed to the merger of many smaller galaxies. After observing how the concentration of dark matter is stripped from the visible matter during a merger, it makes sense that a halo of dark matter will form around the product of the merger. It would be possible for a clump of stripped dark matter to have an ellipticity during the merger, relative to the new center of mass, such that the clump will pass through the parts (e.g., one of the spiral arms) of the newly formed visible galaxy, say after a couple billion years after the merger. As the clump of dark matter (gravitationally bound to itself and returning from being flung during the merger) passes through the arm of visible matter, it will alter the relative motions of everything in the region through which it passes. True or false?

[/aside]

## Magnetar Contributions to the

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Magnetar Contributions to the Gravitational Wave Background

http://cgwp.gravity.psu.edu/gravlens/GravLens2005_4.pdf

## RE: Magnetar Contributions

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Thanks for that Tomas. That's an effect I hadn't considered. (Perfect name for the newsletter!:))

## The whole article can be

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The whole article can be found here http://arxiv.org/PS_cache/astro-ph/pdf/0509/0509880.pdf

## RE: The whole article can

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That's some interesting work. I would have guessed that at the higher energies of neutron star formation, the asymmetries between the forces would be â€œmendedâ€? (i.e., the reverse of electroweak symmetry breaking), and hence produce a more symmetric object in terms of shape, but it's not as simple as that. :) I'm looking forward to learning about the various types of supernovae, as time permits.

What's meant by 'the energy needed to close the universe'?

## RE: What's meant by 'the

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I see I asked a tuffy of a question there :)

The phrase was used in the article on magnetars, referring to a ratio in the equations, and of course I've seen it in other papers. Always marveled: what physics could be more impressive than the physics that has terms for everything known and unknown, in the entire cosmos, for all time?

But energy needed to close the universe? Looks like knowledge of fluid dynamics and relativity is required to fully understand the answer. If I have it right, a closed universe corresponds to the geometry of the surface of a sphere. I recall posting the WMAP results on measurements showing the geometry of the universe to be pretty much flat. The other possibility investigated was on a hyperbolic geometry. (Why no parabolic geometry? It wouldn't then yield a solution to the field equations?)

So when it comes to open/closed, it makes sense that the surface of a sphere is closed back on itself, whereas the other geometries can be considered as being open, or extending infinitely far in space. And the specific part of the answer to my question on energy closing the universe has to do with the energy density, because that's one of the factors that will curve the geometry of the universe, according to the metric of a solution for the field equations that uses a fluid dynamic model of a perfect fluid. In addition to the density, another important factor pertaining to curvature is the pressure. But in getting to the Friedman equation, the pressure is allowed to go to zero, hence showing how curvature is related to density.

But I think you can do the same thing to arrive at an equation that keeps the pressure term, by letting the density term go to zero. Either way, there will be a critical amount (of density or pressure) that will be sufficient to curve the universe enough to 'close' it. And there doesn't appear to be enough density or pressure, from the latest WMAP results, so the universe appears to have a flat, and 'open' geometry.

If I have this part right, my understanding of it all is still vague at best, and my mind is fairly boggled right about now. :)

## RE: But energy needed to

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Isnâ€™t a paraboloid right on the boundaryâ€” e = 1 â€”between ellipsoid & hyperboloid? (Assuming we can extrapolate to the number of dimensions concerned.) So it might be something like a perfectly circular orbit: too metastable to exist anywhere but in theory.

## RE: RE: But energy needed

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Yes, but the parabolic geometry looks like it's missing a 'squared term' along one axis (considering just the 2 dimensions needed for describing the curve), while it's present in the elliptical and hyperbolic geometries (where these terms are summed for elliptical, or take their difference for hyperbolic). I was guessing that the field equations would necessarily yield all 'squared terms' along each axis, or else loose some symmetry somehow.

If the geometry of the universe was curved, wouldn't that imply a preferred direction? Can there be a preferred direction?

## RE: Yes, but the parabolic

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I donâ€™t think the form of the Cartesian equations tells us anything essential. Consider that all the conic sections can be described by polar equations of the form r = l / (1 + eÂ·cos(theta)). Here the anomalousness or asymmetry of the parabola is much less apparentâ€”indeed the circle would seem a more obvious choice in the â€œone of these things is not like the othersâ€? game.

## RE: RE: Yes, but the

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Hmm, good point. It's interesting how methods can have different appearances (as with terms and their equations), and yet be mathematically equivalent. (I wonder if String Theory's 'embarrassment of riches' is similar?)

I think part of my trouble is trying to compare the discriminant (B^2 â€“ 4AC) and/or the eccentricity (e), with the density parameter (Omega). Specifically, the possible geometry of the universe doesn't go from spherical > parabolic > hyperbolic, but instead goes from spherical > flat > hyperbolic (with values less than one, equal to one, or greater than one, respectively). I think I need to learn a lot more of the maths. :)