The Cosmological Evidence – 25 Years Ago

Today Facebook reminded me that the picture below is now 25 years old. I have posted it before and it has done the rounds at a number of cosmology conferences (usually to the accompaniment of lots of laughter), but I thought I’d circulate again as a bit of nostalgia and also to embarrass all concerned with this image. The picture was taken at a graduate school in cosmology in Leiden (in The Netherlands) in July 1995. In my memory that was a sweltering hot summer, which is my excuse for the informality of my attire.

Anyway, various shady characters masquerading as “experts” were asked by the audience of graduate students at a summer school to give their favoured values for the cosmological parameters. from from top to bottom these are:

  • the Hubble constant H0;
  • density parameter Ω0 (not split into dark matter and `ordinary’  matter as is now customary);
  • cosmological constant Λ0,
  • curvature parameter k
  • and age of the Universe t0.


From left to right we have Alain Blanchard (AB), Bernard Jones (BJ, standing), John Peacock (JP), me (yes, with a beard and a pony tail – the shame of it), Vincent Icke (VI), Rien van de Weygaert (RW) and Peter Katgert (PK, standing). You can see on the hi-tech digital display screen blackboard that the only one to get anywhere close to correctly predicting the parameters of what would become the standard cosmological model was, in fact, Rien van de Weygaert. Actually he was the only one of us to include a non-zero cosmological constant. My own favourite model at the time was a low-density model with negative spatial curvature.

Nobody is suggesting that panel discussions are the right way to settle scientific questions, of course, but it is interesting to see the diversity of opinions that were around in 1995.

P.S. Note that not all the combinations of parameters presented there are consistent with a Friedman model, but nobody said they had to be!


8 Responses to “The Cosmological Evidence – 25 Years Ago”

  1. V interesting snapshot of history. I think people like Jim Peebles, Sean Carroll , Michael Turner and Lawrence Krauss had been arguing for a non-zero cc throughout the 1990s, isn’t that right?

    • telescoper Says:

      It was clear from about 1990 (I think) that Omega was in the range 0.2 to 0.4. Those who really liked models with flat spatial sections then favoured Lambda. The direct evidence for k=0 (CMB) and Lambda (SN1a) did not really come until 2000ish.

      • telescoper Says:

        The main arguments for a high density Universe were (i) galaxy vs CMB dipoles and (ii) galaxy peculiar velocity studies. These persisted until well after 1990.

      • telescoper Says:

        The evidence went away because the analyses were flawed. POTENT systematically overestimated Omega even in simulations, and the cosmological dipoles got a high mass density because they were assumed to converge long before they actually did.

      • telescoper Says:

        One of the problems with both of these methods is that it’s not a good idea to use something that depends only weakly on Omega as a means for estimating Omega. The dependence in both cases (assuming linear perturbations and no galaxy bias) is ~Omega^0.6

  2. I guess Van Waygaert represented this group, he was pretty much spot on !

  3. Regarding the so-called ‘flatness problem”, I think it’s fair to say that some theorists did find Dicke’s observation intriguing and somewhat puzzling, at least at the time. Some didn’t, but that doesn’t mean it wasn’t an issue for some

    • If you mean papers like Coles and Ellis 1994, they certainly find holes in probability arguments and inflationary arguments, but don’t seem to give a mechanism for omega much less than one that overcomes Dicke’s runaway argument … it may be a matter of comprehension for us non-theorists

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