Re: Good News for Big Bang theory


John (Liberty) Bell wrote:
george@xxxxxxxxxxxxxxxxx wrote:
rloldershaw@xxxxxxxxxxx wrote:
George Dishman wrote:
For recent specific predictions, note that the angular
power spectrum of the CMBR was predicted before WMAP
using GR both with a cosmological constant and without
but including quintessence instead as the nature of
dark energy. the subsequent results are a better fit to
the cosmological constant than quintessence so GR made
a prediction and passed the test.

This is mostly model-building, ...

Nope, the predictions were made before the results
were known, not fitted retrospectively. GR passed
the test, you have not yet even provided a prediction.

Hmm.

I think there may be some misreading of what was said
above. Let me first be clear about something, the big
bang is certainly a model-building excercise rathe than
a theory in that a model is constructed in terms of
initial parameters which is then rolled forward using
'real' theories such as GR, thermodynamics and the
"Standard Model" of particle physics to pick out just
a few.

On the other hand, I think it unfair to say that the match
of the WMAP data to a CC rather than quintessence is
"model fitting" since neither was fitted to the data
retrospectively. The two make different predictions for
the ratios of the acoustic peaks AIUI and those
predictions were made prior to the mission.

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.

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, 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'.

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, 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.

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.

(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.

George

.

Relevant Pages

  • Re: Good News for Big Bang theory
    ... using GR both with a cosmological constant and without ... the cosmological constant than quintessence so GR made ... the predictions were made before the results ... claimed as a great success of the predictive power of GR with a CC, ...
    (sci.astro)
  • Re: Good News for Big Bang theory
    ... using GR both with a cosmological constant and without ... the cosmological constant than quintessence so GR made ... the predictions were made before the results ... claimed as a great success of the predictive power of GR with a CC, ...
    (sci.astro)
  • Re: Good News for Big Bang theory
    ... using GR both with a cosmological constant and without ... the cosmological constant than quintessence so GR made ... the predictions were made before the results ... claimed as a great success of the predictive power of GR with a CC, ...
    (sci.astro)
  • Re: Good News for Big Bang theory
    ... quintessence were retrodictions after the fact of an astronomically ... be adjusted to fit observation. ... parameters hence little scope for 'tuning'. ... two predictions suggests the universe is "flat" in some ...
    (sci.astro)
  • Re: Good News for Big Bang theory
    ... quintessence were retrodictions after the fact of an astronomically ... observed failure to decelerate in accordance with the predictions of ... claimed as a great success of the predictive power of GR with a CC, ... predictions made involving prior assumptions about a CC. ...
    (sci.astro)