Archive for Jim Peebles

How the Nonbaryonic Dark Matter Theory Grew [CEA]

Posted in The Universe and Stuff with tags , , on January 24, 2017 by telescoper

Another arXiver post, this time from the great Jim Peebles. Always a skeptic about dark matter, especially cold dark matter, it is the hallmark of a great scientist that he weighs up the evidence as objectively as possible.

This is a long review, but well worth reading for its important insights and historical perspective. I agree that the case for non-baryonic dark matter is compelling, but it is also far from proved and it’s still possible that an alternative, equally or more compelling, theory will be found.

arXiver

http://arxiv.org/abs/1701.05837

The evidence is that the mass of the universe is dominated by an exotic nonbaryonic form of matter largely draped around the galaxies. It approximates an initially low pressure gas of particles that interact only with gravity, but we know little more than that. Searches for detection thus must follow many difficult paths to a great discovery, what the universe is made of. The nonbaryonic picture grew out of a convergence of evidence and ideas in the early 1980s. Developments two decades later considerably improved the evidence, and advances since then have made the case for nonbaryonic dark matter compelling.

Read this paper on arXiv…

P. Peebles
Mon, 23 Jan 17
37/55

Comments: An essay to accompany articles on dark matter detection in Nature Astronomy

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No more ripples?

Posted in Biographical, The Universe and Stuff with tags , , , on July 27, 2013 by telescoper

Well, that’s the Ripples in the Cosmos meeting in Durham over and done with, and I’m back in Newcastle for a few days before moving on to Edinburgh next week. I’m not sure I’ll be able to blog much over the next few days because my internet connectivity will be a bit limited.

Anyway, the meeting was very exciting, as you can tell from the picture showing me (with the beard) and Brian Schmidt (with the Nobel Prize):

IMG_20130725_144131

Yesterday it was my job to round off the meeting with some concluding remarks leading into a panel discussion. I have to admit that although the programme for the conference was clearly designed in order to generate provoke discussion, I was a little disappointed that so few people said anything controversial. I’ve long held that there are too many cosmologists willing to believe too much, and this was further evidence that the scepticism that is a necessary part of a healthy science has been replaced by widespread conformity, especially among the young;
when I was a lad the students and postdocs were a lot more vocal at meetings than they are now. Perhaps this is characteristic of a change in culture of cosmology? To get a job nowadays it’s virtually essential to climb onto one of the big bandwagon projects, and to keep your place you have to toe the party line, refrain from rocking the boat, not speak out of turn, and avoid making ripples (That’s enough metaphors. Ed).

Anyway, I think there are still a great many things in modern cosmology we don’t understand at all, and I think a few more of the older generation should show the way by questioning things in public. In fact only got asked to do the concluding remarks because Jim Peebles was unable to come to the meeting. Jim’s an immensely distinguished physicist who has probably done more than any other living person to develop the standard cosmology, but he’s also never been afraid to play devil’s advocate. We need more like him, willing to articulate the doubts that too many of us feel the need to suppress.

It’s amazing how much progress we have made in cosmology over the last few decades, but we shouldn’t use that as an excuse to get complacent. Cosmology is about the biggest questions in science. That alone makes it an exciting subject to work in. It’s an adventure. And the last thing you want on an adventure is for the journey to be too comfortable.