Re: Good News for Big Bang theory


George Dishman wrote:
John (Liberty) Bell wrote:

Both the reintroduction of the cosmological constant and
quintessence were retrodictions after the fact of an astronomically
observed failure to decelerate in accordance with the predictions of
GR, if I understand correctly.

Well the CC was in the theory from long before the
acceleration was discovered. It was _assumed_ that
the value of the CC would be zero which in hindsight
was a mistake, science says that values should be
measured, not assumed, and nature has given us a
timely reminder.

Hmm. Why then did Einstein describe his original introduction of a CC
as "the biggest blunder of my lifetime"?. This hardly makes it sound
like an essential mathematical parameter of his theory, which needed to
be adjusted to fit observation.

If they are both 'fudges' in this
respect, you have a 50-50 chance of your preferred fudge giving a
better result than the other, just by pure chance.

Not true,

Check what I wrote. It is true.

the form of the CC was defined long before
and the form of quintessence is well defined from a
conceptual point of view as well which mean both
make numerical prdictions that have few free
parameters hence little scope for 'tuning'.

I did not say there was scope for tuning, just as there is no scope for
tuning the 'curvature' of a straight edge. It is, after all, a
constant. Nevertheless, you can choose any value of that constant you
like, to give the best retrofit to subsequently available data, which
is exactly what has happened, since its resurrection. What could be of
potential concern is that since that resurrection, it is becoming so
tightly constrained, that it will be virtually useless as a future
fudge factor, unless the next step is to delete that potentially
inconvenient word "constant".

This can hardly be
claimed as a great success of the predictive power of GR with a CC,
given the associated disasters that preceded this, in relation to
predictions made involving prior assumptions about a CC.

Indeed, but I didn't make any such claim,

Then we have no argument.

I only
pointed out that classing the fit of the WMAP data
as "model building" is inappropriate since the form
of the CC was set down decades ago.

Nearly a century ago, actually. Only the magnitude and sign have
changed (so far).

Although I readily accept that we would not have got very far without
GR, this particular example of predictive power sounds a bit like
extolling the superior predictive power of a straight edge when
employed to extrapolate a graphical set of known points, over, say, a
French curve, or vice versa.

Again I would say you are arguing against a claim
that I never made.

Again, then we still have no argument. ; )

(Incidentally, [and slightly tongue in cheek in this respect], you may
have already noticed that the age of the universe you get via the
latest GR models with a CC, are remarkably similar to what you would
get from straight line extrapolation of Hubble's constant, using a
ruler.)

Oh yes, and that has certain implications for the overall
density and the existince of dark matter.

Would you like to elucidate?

Similarly, do you (or Rob) know anything of resultant predictions
(within the model) for the required rate or rates of acceleration of
universal expansion. - And information on modern data that fits this
(or doesn't).

Regards

JB

.

Relevant Pages

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  • Re: Good News for Big Bang theory
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    (sci.astro)
  • Re: Good News for Big Bang theory
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    (sci.astro)
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