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starship-design: Quasar spectra


It seems I found what I was looking for. The abnormal redshifts are not
really there according to


If I understand correctly, the way in which redshifts are measured depends
on the intensities of different spectral lines.
So as long as you know what the intensities should be, you can determine the
redshift. But QSO's cause unexpected relative intensities and therefore
disturb the expected pattern (that is, if you don't look well enough, you
will be fooled)

One might expect that figuring out the redshift from spectral data is not
that difficult, after all, just apply the frequency shift formula and see if
the adjusted spectra match known emission frequencies.

This indeed would be the case, if the quality of the spectra was very good.
But in reality the spectra are poor (much overlapping peaks, etc), and a bit
of educated (=knowing the physics behind the peaks) guesswork is involved.
As long as things are normal the guesses will usually be right, but if
unexpected things (=increased spectrum lines by natural laser action) happen
in the spectra then mistakes will be made.


For the curvefitting the PLS (partial least squares) model is used.
Check out
to figure out what it is and what assumptions are made.