Re: Good News for Big Bang theory

"JB" == John (Liberty) Bell <john.bell@xxxxxxxxxxxxxxxxxx> writes:

JB> 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.

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

Because *when he introduced it*, it was to uphold a preconceived
notion.

At the turn of last century, the Universe was assumed to be largely
static. A large-scale expansion was simply not taken to be plausible.
Once the recession of galaxies became clear, i.e., once the data
became available, a non-zero value of the cosmological constant didn't
seem to agree with the data. That was largely the picture for the
next 70 years: The available data did not seem to require a non-zero
value for the cosmological constant. Only with the advent of modern
surveys of Type Ia supernovae surveys did data become available that
suggested that the value of the cosmological constant is non-zero.

I really don't see why this topic keeps coming up. If you look at the
actual equations, they are silent as to the value of the cosmological
constant:
G_{ab} = 8\pi T_{ab} + \Lambda
Einstein thought he needed a non-zero value for \Lambda, based on his
preconceptions. Absent any preconceptions, there's no way to tell the
proper value of \Lambda, short of using data. Turns out that
Einstein was probably right about the value of \Lambda, but for the
wrong reasons. So Einstein was a genius, but not infallible; what's
the big deal?


[I should point out that this problem of a static Universe was
recognized by Newton, one doesn't need GR. If you take a bunch of
massive objects (i.e., stars) at rest with respect to each other,
their mutual gravitation will cause them to collapse together. The
only way this could be prevented is if the stars had some expansion
that overwhelmed (at least temporarily) their gravitational
attraction. Newton invoked God's power to hold the Universe static.]

--
Lt. Lazio, HTML police | e-mail: jlazio@xxxxxxxxxxx
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
.

Relevant Pages

  • Re: Bill Bryson and the big bang
    ... >>GR allows for dark energy, ... >>theorists have realized that the cosmological constant is just one ... > original value fit for such a purpose, established by EInstein, is ... >>need for dark matter and dark energy. ...
    (sci.astro)
  • Re: general relativity website
    ... In order to make this possible Einstein ... that the OBSERVATIONAL evidence favoured a static universe. ... not just of the cosmological constant but of a specific value for it, ...
    (sci.physics.research)
  • Re: Albert Einstein as a Philosopher of Science
    ... >> Albert Einstein as a Philosopher of Science ... >> Einstein's philosophical habit of mind, ... Instead he inserted a cosmological constant because he ... > wanted the universe to be static. ...
    (sci.physics)
  • Re: Secrets of Dark Matter
    ... but the reasoning that led to Einstein adding the Cosmological ... Cosmological Constant, he didn't know that the universe was expanding. ...
    (uk.sci.astronomy)