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john hunter
2006-Feb-21, 11:49 AM
The frequency to which LISA (the gravitaitonal wave detector) will be most sensitive is the millihertz range:

http://lisa.esa.int/science-e/www/object/index.cfm?fobjectid=31380

and solar oscillations occur at the same frequency:

http://bison.ph.bham.ac.uk (see solar oscillations section)

So won't LISAs intended signal be swamped by solar oscillations???

John Hunter.

Gsquare
2006-Feb-21, 02:39 PM
The frequency to which LISA (the gravitaitonal wave detector) will be most sensitive is the millihertz range:

http://lisa.esa.int/science-e/www/object/index.cfm?fobjectid=31380

and solar oscillations occur at the same frequency:

http://bison.ph.bham.ac.uk (see solar oscillations section)

So won't LISAs intended signal be swamped by solar oscillations???

John Hunter.

Not if it doesn't work any better than LIGO! he, he

Nereid
2006-Feb-21, 05:22 PM
The frequency to which LISA (the gravitaitonal wave detector) will be most sensitive is the millihertz range:

http://lisa.esa.int/science-e/www/object/index.cfm?fobjectid=31380

and solar oscillations occur at the same frequency:

http://bison.ph.bham.ac.uk (see solar oscillations section)

So won't LISAs intended signal be swamped by solar oscillations???

John Hunter.You've lost me John, just because the two have an overlapping frequency range, how does it follow that LISA data would be "swamped" by solar oscillations?

More particularly, what is the predicted signal detected by LISA induced by solar oscillations? What would be the physical process pathways that would induce such a signal?

Peter Wilson
2006-Feb-21, 05:56 PM
So won't LISAs intended signal be swamped by solar oscillations???

Well, you would assume its designers have taken that into consideration. As the article points out, the trio of satellites will be able to locate a source to some degree of accuracy. Like any space-based telescope, it must be pointed away from the sun. The rub, as they point out, is the signal-to-noise ratio. Since they mention solar wind and numerous other sources of interference, you can only assume they have considered solar oscillations as well. Granted, some assumptions have been wrong before...

Gsquare
2006-Feb-21, 06:06 PM
So won't LISAs intended signal be swamped by solar oscillations???

John Hunter.

I'd be more concerned about minute changes in the orbital path due to unanticipated variations in radiation pressure and/or solar wind.

G^2

john hunter
2006-Feb-23, 11:16 AM
Dear Nereid, Gsquare and Peter,


Granted, some assumptions have been wrong before...

This may be the case with LISA.

The designers have assumed that the gravitational mass of the sun is independent of its density. According to the conjecture in www.gravity.uk.com the change in radius of the sun might alter its gravitational mass, and hence the orbital position of the three satellites.

Using G(effective) = c^2/(c^2/G + m/r) , or similarly G(eff) = G(1-Gm/rc^2),
G may vary by about a factor 10^-15 (Gm/rc^2 is about 10^-6 and the radius of the sun might vary by a factor of about 10^-9)

This would cause a change in arm lengths of factor 10^-15, which might be of the order of micrometers for LISA (arm lengths will be 5X10^9m) - larger than the anticipated effect from gravitational waves.

True, the conjecture has not been shown convincingly to be either true or false - but with such an expensive and complicated project, shouldn't they consider every possibility and design the experiment accordingly?

All the best,

John Hunter.

Nereid
2006-Feb-23, 12:51 PM
Dear Nereid, Gsquare and Peter,



This may be the case with LISA.

The designers have assumed that the gravitational mass of the sun is independent of its density. According to the conjecture in www.gravity.uk.com the change in radius of the sun might alter its gravitational mass, and hence the orbital position of the three satellites.

Using G(effective) = c^2/(c^2/G + m/r) , or similarly G(eff) = G(1-Gm/rc^2),
G may vary by about a factor 10^-15 (Gm/rc^2 is about 10^-6 and the radius of the sun might vary by a factor of about 10^-9)

This would cause a change in arm lengths of factor 10^-15, which might be of the order of micrometers for LISA (arm lengths will be 5X10^9m) - larger than the anticipated effect from gravitational waves.

True, the conjecture has not been shown convincingly to be either true or false - but with such an expensive and complicated project, shouldn't they consider every possibility and design the experiment accordingly?

All the best,

John Hunter.I'm not sure I follow what you're saying John Hunter, that the Sun oscillates, with a radial component as large as 1 ppb, with characteristic frequencies in the mHz range?

Fortis
2006-Feb-23, 01:15 PM
The designers have assumed that the gravitational mass of the sun is independent of its density. According to the conjecture in www.gravity.uk.com the change in radius of the sun might alter its gravitational mass, and hence the orbital position of the three satellites.
If it is true that this hypothetical dependence could affect the results from LISA, wouldn't this also be worthwhile science? If what you are suggesting, actually occurs, then that would probably have as great an impact on our understanding of the universe (and gravity in particular) as the original intent of LISA.

So where's the problem? ;)

john hunter
2006-Feb-24, 10:28 AM
Dear Gsquare,

The LISA masses are shielded against such pressures by a case which measures its distance to the test masses and fires tiny rockets to adjust.

Dear Nereid,

There are oscillations of the suns surface as large as 50km, global oscillations occur of the order of 10m. There are different modes, but even a mode which turns sphere-ellipsiod, will change the average m/r ratio.

Dear Fortis,

Yes, if LISA detects a larger effect it would be interesting for physics/astronomy, but if the effect is too large, maybe it would spoil the experiment, if it hasn't been planned for - incidentally, there might be other unknown effects (nothing to do with the G conjecture), which might produce large motions - so shouldn't LISA be able to detect and measure larger motions too.

All the best,

John Hunter.