Cosmology Meets Astronomy in Philadelphia

By Mark Trodden | March 16, 2009 7:03 pm

After spending a splendid Spring break back in Syracuse, hanging out with friends between working on a paper, a review article and two grant proposals, on Friday I drove back to Philadelphia, where in the evening I was giving a talk to the Delaware Valley Amateur Astronomers (DVAA). The talk was a slightly more technical version of the public lecture – Modern Cosmology and the Building Blocks of the Universe – that I have given in many different places over the last few years, and at this point I’m quite comfortable with it.

However, I am more nervous giving talks to amateur astronomers than to any other group. This is because, for a cosmologist, I know remarkably little about astronomy. It isn’t that I’m a complete ignoramus, but just that my knowledge is relatively rudimentary, and amounts to less than the content of an undergraduate astronomy degree, although I do know some extra things about a few advanced topics. My training is in mathematics and physics, and I’ve basically picked up the astronomy I know through necessity either because of research topics or teaching.

Nevertheless I bravely soldiered on, and the DVAA crowd proved to be quite delightful. My talk begins with a brief tour of the major pillars of the big bang theory – the Hubble expansion law, the microwave background radiation, and the abundances of the light elements – then proceeds with a summary of open questions. This is then followed by a discussion of the challenges these pose for fundamental physics, and some of the possible solutions and how they may be tested in upcoming experiments. In particular, I focus on candidates for dark matter, and their possible origin in beyond the standard model physics at the TeV scale, on models of baryogenesis, and on the logical possibilities for the origin of cosmic acceleration – the cosmological constant, dynamical dark energy and modified gravity.

Obviously this is a cursory treatment, since a detailed discussion isn’t really what people expect from a public lecture. And there are huge numbers of topics I’d love to touch on but just don’t have time for, like inflation, and topological defects, and extra dimensions, and … You get the picture.

But when you’re speaking to an audience like this one, people tend to already have questions about all kinds of things that you didn’t explicitly mention in the talk. And not just any questions, but subtle and technical ones. So afterwards I spent a while discussing the status of tests of the inflationary paradigm, the anthropic principle and its implementation through eternal inflation in the string theory landscape, the problem of measure in the multiverse, and other related topics. Not your usual collection of post-public lecture questions, and a lot of fun!

CATEGORIZED UNDER: Science and Society
  • PeterS

    Would you be able to make available a text of your talk? This would be useful to many.

  • dg

    at the end of astro talks sometimes i have a page-long list of things i need to look up on wikipedia.

  • Phillip Helbig

    My strategy: When non-scientists asked me what I did for a living, I replied
    that I was an astrophysicist. I couldn’t say “cosmologist”, since most people
    don’t know what that is. I couldn’t say “astronomer” because I didn’t want them
    to tell me what sign they are or ask me what mine is (yes, many people do
    confuse astrology with astronomy). Among astronomers, I always said I was
    a cosmologist, since otherwise people would expect me to know about spectroscopy.
    Among cosmologist, if I was among theorists, I said I worked more directly with
    observational data (note: I didn’t say I was an observer); if I was among observers,
    I said I worked on more theoretical stuff. (Both were true: I worked mainly at the
    interface between observations and theory, often also involving gravitational
    lensing and/or statistics.)

    When I wanted money from the bank, I said I was a physicist.

  • Phillip Helbig
  • Tod R. Lauer

    It is worth remembering that roughly half of professional astronomers started out as amateurs before going off to college. The clubs that you speak to may well have members that will be future colleagues. I was one myself, indeed our club was just across the river from Philadelphia. To raise money, we held star parties for Edmunds Scientific. And regardless of whatever work I do as an observational astronomer, I still enjoy taking my telescope out from time to time, finding my own way around the sky…

  • Cormac O Raifeartaigh

    ! I’m giving a similar talk to the local Astronomy Ireland group here next week!
    I have been attending a nightclass in astronomy this semester just for fun – when the lecturer found out that I teach a course in cosmology, he asked me to give one session on the Big Bang model.

    I must say I’m glad – although I have enjoyed the course no end, the astronomer’s view of cosmology is very different from ours. I found the one session on cosmology a bit peculiar. Instead of concentrating on the three planks of evidence for BB (and then possibly on problems like the horizon, flatness and singularity problems), the lecture focussed almost entirely on all the stuff we don’t know – dark energy, dark matter etc. There was almost no refernce to GR and it made all of cosmology sound v speculative indeed. Hope to balance this a little next week…regards Cormac

  • Stephen Serjeant

    The Oxford department for continuing education has a similar vibe.

    dg: wikipedia is very useful but caveat emptor – especially when it’s free! I once edited an article, but found I spent much longer batting away the loons, and eventually gave up.

    I wonder how long it will be before large-scale structure / precision cosmology is colloquially considered to be another ‘plank’? Perhaps now the model is becoming over-determined, eventually we won’t speak of planks at all. I’ve read that it was, in part, the diverse yet converging constraints on Avogadro’s number that led to the widespread adoption of the atomic theory of matter, and we don’t usually speak of ‘planks’ of evidence that atoms exist, at least not nowadays.

  • Phillip Helbig

    I think the comparison with Avogadro’s number is valid. There wasn’t one experiment
    which made it clear that atoms are real, but rather the convergence of several lines
    of investigation. Pais describes this in his “Subtle is the Lord…” biography of Einstein.
    (I prefer Einstein’s own translation of the German phrase: God may be slick, but he
    ain’t mean.)

    How I miss the Quarterly Journal of the RAS! It was an interesting mixture of reports
    from observatories (where, in the pre-internet age, one could read that John Barrow
    had a dozen single-author papers in refereed journals in one year (in which he also
    wrote a popular book)) and “philosophical reviews” of cosmological topics by the likes of
    Barrow, Harrison, Rees, G.F.R. Ellis, Longair etc. In one, Longair points out that when he
    started out, his advisor, Peter Scheuer, said that there were only two-and-one-half
    facts in cosmology. At the time of writing, it was up to nine facts. Today, there are

  • http://None Greg Smith

    Is there a copy of the full remarks of the DVAA lecture? I saw a couple paragraphs included on a Discover website, but couldn’t find a link for the entire speech.



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About Mark Trodden

Mark Trodden holds the Fay R. and Eugene L. Langberg Endowed Chair in Physics and is co-director of the Center for Particle Cosmology at the University of Pennsylvania. He is a theoretical physicist working on particle physics and gravity— in particular on the roles they play in the evolution and structure of the universe. When asked for a short phrase to describe his research area, he says he is a particle cosmologist.


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