The problems of big bang theory. What are they?

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- Some quasars calculated to be behind galaxies by their red shifts when in fact you can see the quasars are in front of them.

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You can't tell just by looking if a quasar is in front of a galaxy. Galaxies aren't solid masses, so it's quite possible to see through them.I think this may be a reference to the quasar seen "in" galaxy NGC 7319. This quasar's spectrum shows absorbtion lines consistent with the quasar's light passing through NGC 7319, meaning it can't be in front. It could be in, but there's no clear reason to think so. The simplest answer is that it is behind NGC 7319.Edited by Zhimbo, : added clarifying phrase "the quasar's light"

The section on Features, issues and problems in the Big Bang wikipedia entry seems to be a pretty fair overview.One important note is that the general outline of the Big Bang is accepted by virtually everyone.As a side note, it's always baffled me why many religious people have a problem with the Big Bang. It was once looked it a little oddly by scientists as being a little too similar to a Biblical moment of creation! Alas, the YEC crowed is so wedded to their ridiculously short time scale they must resist.

Herschel?

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"But the point was that the use of gravitational lensing showed that there was a quasar present behind the galaxy, that wasn't visible looking through the galaxy, contrary to the post to which I responded"

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Lensing of the kind you refer to only occurs with precise alignment and distant, massive galaxies or galaxy clusters, (and even more distant quasars), and are one proof of the vast distance of quasars. These are by far the exception, due to the large masses and precise alignment necessary for noticeable effects.Nearby and/or less massive galaxies, and poor alignment between us/the galaxy/the quasar, will have at best much less obvious effects that are not apparent in the vast majority of cases.Consider:

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"In fact,M101’s disk is so thin that the Hubble telescope easily sees many more distant galaxies lying behind it.Seeing these background galaxies shows that a galaxy’s disk is really mostly empty space."

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(from this pdf.)Why aren't these galaxies being "lensed" by the closer M101? Because detectable lensing is by far the exception, not the rule. Edited by Zhimbo, : No reason given.

The quasar is not shining through "the core" of the galaxy. Photos typically over-expose bright portions of the disk; the "core" is far smaller than is apparent in typical photographs.Go to this photo of Stephen's Quintet, and look at NGC 7319 in the upper left corner. This photo is less over-exposed than many. Notice the small, circular area in the center of the galaxy? That's the maximum extent of the truly dense "core" of the galaxy (and is likely over-estimating). The opaque portion of a typical spiral galaxy is really quite small in relation to the total disk. In this photo, I think the quasar is barely visible directly beneath the core, if you know where to look, but it's hard to tell. At any rate, comparing to other photographs, it's easy to tell it is well clear of the densest part of the core.Nor is the galaxy either far away nor massive enough to produce gravitational lensing, so we should not expect to see lensing here.There's no problem.Added by edit: Looking around for this, I've noticed several other quasars sighted "on" galaxy images, and it seems in every case the quasars show absorption lines in their spectra consistent with their light passing through the galaxy in question (e.g. NGC891, NGC4203). They're never in front of the galaxy. Again, based on this information alone, one could still say they are in galaxies, but we have plenty of other reasons to say they are more distant. Edited by Zhimbo, : No reason given.Edited by Zhimbo, : No reason given.