Archive for Expanding Universe

One Hundred Years of the Cosmological Constant: from ‘Superfluous Stunt’ to Dark Energy

Posted in History, The Universe and Stuff with tags , , , on November 21, 2017 by telescoper

Some months ago I did a little post on the occasion of the 100th anniversary of the introduction of the cosmological constant which included a link to the original paper on this subject by Albert Einstein. A nice thread of well-informed comments followed that post and one of the contributors to that thread, Cormac O’Raifeartaigh, is lead author of a paper that has just appeared on the arXiv. It’s quite a lengthy paper (62 pages) that gives an account of the cosmological constant in the context of modern observational cosmology. You can get a PDF of the paper here. It’s well worth reading!

The abstract reads:

We present a centennial review of the history of the term known as the cosmological constant. First introduced to the general theory of relativity by Einstein in 1917 in order to describe a universe that was assumed to be static, the term fell from favour in the wake of the discovery of cosmic the expanding universe, only to make a dramatic return in recent times. We consider historical and philosophical aspects of the cosmological constant over four main epochs: (i) the use of the term in static cosmologies (both Newtonian and relativistic; (ii) the marginalization of the term following the discovery of cosmic expansion; (iii) the use of the term to address specific cosmic puzzles such as the timespan of expansion, the formation of galaxies and the redshifts of the quasars; (iv) the re-emergence of the term in today’s Lamda-CDM cosmology. We find that the cosmological constant was never truly banished from theoretical models of the universe, but was sidelined by astronomers for reasons of convenience. We also find that the return of the term to the forefront of modern cosmology did not occur as an abrupt paradigm shift due to one particular set of observations, but as the result of a number of empirical advances such as the measurement of present cosmic expansion using the Hubble Space Telescope, the measurement of past expansion using type SN 1a supernovae as standard candles, and the measurement of perturbations in the cosmic microwave background by balloon and satellite. We give a brief overview of contemporary interpretations of the physics underlying the cosmic constant and conclude with a synopsis of the famous cosmological constant problem.

Origins of the Expanding Universe Conference – My Contribution

Posted in History, The Universe and Stuff with tags , , , , , on September 19, 2012 by telescoper

For those of you interested in such things, here are the slides I used in my talk at the Origins of the Expanding Universe conference. I spoke about the events on and after 29th May 1919, when measurements were made during a total eclipse of the Sun that have gone down in history as vindicating Einstein’s (then) new general theory of relativity. I’ve written quite a lot about this in past years, including a little book and a slightly more technical paper. This was a relevant topic for the conference because it wasn’t until general theory of relativity was established as a viable theory of gravity that an explanation could be developed of Slipher’s measurements of galaxy redshifts in terms of an expanding Universe.

“The Universe is Expanding…”

Posted in Biographical, Film, The Universe and Stuff with tags , , on September 16, 2012 by telescoper

Well, that’s the meeting over with. Now I’m off for a bit of sightseeing before going back to Phoenix for the evening flight back to London. I might be able to post some pictures when I get back, but for the mean time I’ll sign off with this clip which Michael Way used to end the last talk of the meeting!

The Origins of the Expanding Universe

Posted in Books, Talks and Reviews, The Universe and Stuff with tags , , , , on July 30, 2012 by telescoper

Not having much time to write anything particularly original, I thought I’d use this blog to advertise a forthcoming centenary celebration which I hope to attend and speak at, if my recovery goes to plan.  The text below is taken from the conference website for a meeting due to take place at the Lowell Observatory in Flagstaff, Arizona from September 13-15. I’m sure they won’t mind me borrowing it, as it helps promote the event.  Registration is open until 10th August…

On September 17, 1912, Vesto Slipher obtained the first radial velocity of a “spiral nebula” – the Andromeda Galaxy. Using the 24-inch telescope at Lowell Observatory, he followed up with more Doppler shifts, and wrote a series of papers establishing that large velocities, usually in recession, are a general property of the spiral nebulae. Those early redshifts were recognized as remarkable by Slipher, and were critical to the discovery of what came eventually to be called the expanding Universe. Surprisingly, Slipher’s role in the story remains almost unknown to much of the astronomical community.

The nature, and especially the distance, of spiral nebulae was fiercely argued – most famously in the 1920 Shapley-Curtis debate. Hubble’s 1923 discovery of Cepheids in Andromeda, along with Henrietta Leavitt’s period-luminosity relation for Cepheids, led to a distance scale for the nebulae, enabling Lemaitre (1927) to derive a linear relation between velocity and distance (including a “Hubble constant” and, by 1931, a Primeval Atom theory).

Meanwhile, a new concept of space and time was formulated by Einstein, providing a new language in which to understand the large-scale Universe. By 1932, all the major actors had arrived on stage, and Universal expansion – the most general property of the Universe yet found – acquired a solid basis in observation and in the (relativistic) concept of space. “Space expands”… or does it? How did Lemaitre and Hubble interpret this concept? How do we interpret it? It continues to evolve today, with cosmic inflation and dark energy presenting new challenges still not fully assimilated.

This conference is in honor of Vesto Melvin Slipher and is timed to coincide with the 100th anniversary of the first measured Doppler shift in a Galaxy (then known as a Spiral-Nebula) on September 17, 1912:Slipher 1913 Lowell Obs 2, 56

We are bringing together astronomers and historians of science to explore the beginnings and trajectories of the subject, at the place where it began.