Archive for the 'black holes' Category

At Last - GLAST!

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Clifford
on June 11, 2008
in astronomy, black holes, cosmology, dark matter and science
. 0 Comments

GLAST launch in progressGood news everyone! GLAST has been launched successfully. GLAST stands for Gamma-ray Large Area Space Telescope, and it does exactly what it says on the packet. It is an instrument designed to look more closely at gamma rays from outer space. More here. It will help (alongside other instruments such as SWIFT) get better understanding of a wide range of gamma-ray emitting objects, that pertain to a wide range of issues, astrophysical to cosmological.

“Gamma ray bursters” are obvious super-powerful sources of gamma rays out there, largely due to macroscopic astrophysical objects (collapsed stars or stars in the process of doing so, or merging with each other - see earlier posts) doing violent things, or interacting violently with their surroundings. So are active galactic nuclei, powered by black holes. We’d like to better understand all of the processes that allow these objects to generate gamma rays.

Other sources could include particles and antiparticles annihilating each other and (by Continue reading ‘At Last - GLAST!’

Some Unusual Recipes

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Clifford
on April 18, 2008
in Los Angeles, black holes, science and string theory
. 1 Comment

Quark Gluon Plasma RecipesWell, I’ve been quiet here because I got rather swamped with lots of things over the last few days. The biggest thing was yesterday. I gave a colloquium at Caltech entitled “Cooking with Quarks and Gluons: Recipes from the String Theory Kitchen”*. The abstract is given below**. It is mostly based on what I wrote about last Summer.

With all the other things I had to do (including writing and giving two fun two hour lectures on cosmology in my undergraduate GR class) I still decided that it was time to totally rethink how I tell this exciting physics story, and how I present it. This meant designing and building many new slides. Each slide can take a long time to prepare, so this took two solid days of hiding away while designing and building them, only breaking for the other stuff.

Well, it was fun in the end, and today I am exhausted. I decided that you should not miss out entirely on the treats, so I made a little movie of the first parts of the talk to Continue reading ‘Some Unusual Recipes’

So What Are the Odds?

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Clifford
on April 15, 2008
in black holes, humour and science
. 9 Comments

John Howe’s Glorund vs Turin imageWell, I’ve said (and pointed to) enough on the matter, but I could not resist a quote from today’s essay by Dennis Overbye in the New York Times (do have a look at the rest of it):

Besides, the random nature of quantum physics means that there is always a minuscule, but nonzero, chance of anything occurring, including that the new collider could spit out man-eating dragons.

Excellent! Proper flying, armoured, fire-breathing, talking, treasure-hoarding, Continue reading ‘So What Are the Odds?’

All Creatures Great and Small

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Clifford
on April 4, 2008
in astronomy, black holes, galaxies and science
. 10 Comments

The previous post was a farewell to black holes in the class, not here on the blog. (And it was not quite a farewell there either, since the midterm yesterday was all about the properties of the Reissner-Nordström black hole, representing a black hole with an electric charge, and a nice computation involving cosmic censorship.)

There have been two rather notable discoveries in the black hole astrophysics world this week. The first is the discovery of what seems to be another case of an intermediate mass black hole (there was only one example known before). Not the supermassive ones that live at the centers of galaxies (tens to hundreds of millions of times the mass of our sun), and not stellar mass ones of a few times the mass of our Continue reading ‘All Creatures Great and Small’

A Farewell to Black Holes

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Clifford
on April 2, 2008
in Los Angeles, black holes, science and work
. 4 Comments

Yesterday here at USC was my last lecture in the class about black holes (see also here). We’ve got to move on to other topics (Cosmology, Einstein’s equations, etc) and so cannot do any more. It was a fun last lecture though. I pulled together a few scraps of things I did not finish in the previous lecture (such as the extraordinarily high percentage of binding energy per unit rest mass you can extract with rotating black hole orbits - just what you need to power things like quasars) and then finished with:

  1. A taste of Hawking radiation, the Bekenstein-Hawking entropy and the wonderful and beautiful subject of black hole thermodynamics that opens up when you combine gravity with quantum mechanics*, followed by…
  2. A quick discussion of the Penrose process for extracting energy from rotating black holes. (I’m sure that all (past, present or future) super-advanced civilizations must be using them as the ultimate emissions-free means of generating energy for heating their homes and so forth. No, really.)

*Of course, all undergraduates commonly hate it when you dare bring in stuff from other classes, so to Continue reading ‘A Farewell to Black Holes’

More Trouble for LHC?

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Clifford
on April 1, 2008
in black holes, politics, science and science and society
. 8 Comments

[Update:- NB: This was an April Fool joke. -cvj]

CMS detector - New York TimesSome breaking news for a change. I’ve only heard snippets of this and so I’ll update later with more as I get it. That silliness that was in the news about two physicists pursuing a lawsuit against the Large Hadron Collider has suddenly become serious. (Image right: the CMS detector at the LHC, taken by Valerio Mezzanotti - from a NYT article about the LHC last year.)

Recall that the issue was that there would be the possibility of the experiment creating mini black holes that could gobble up the earth and that the CERN scientists have not done enough to demonstrate that this was not a safety issue. Of course, and has already been said in several places (see e.g., Phil’s general level post about the physics and the case here), this is utterly ill-conceived and in any case certainly not the way to go about things, but it seems that the legal route can be quite damaging for science, in the right hands.

What seems to have happened is this. Since the suit was filed in Hawaii, it falls under US Federal jurisdiction, and has been taken up as an emergency issue before the Supreme Court. Somehow the litigants got a hearing on this with the help of powerful friends who have what can only be thought of as another example of the anti-science agenda we’ve a lot of in various branches of the government in recent years.

The upshot is that the Supreme Court has announced today that they are requiring all Continue reading ‘More Trouble for LHC?’

Law Vs Law

Published
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Clifford
on March 30, 2008
in black holes, science and science fiction
. 11 Comments

A silly lawsuit vs the search for physical law, that is. What’s the story?* An attempt to stop the Large Hadron Collider (LHC) in Geneva from operating over fears that the experiment will destroy the earth by creating a black hole that will swallow it up. Or some other bogeyman. Article by Dennis Overbye here, or here, and there’s a Fox News story by Paul Wagenseil here.

The lawsuit, filed March 21 in Federal District Court, in Honolulu, seeks a temporary restraining order prohibiting CERN from proceeding with the accelerator until it has produced a safety report and an environmental assessment. It names the federal Department of Energy, the Fermi National Accelerator Laboratory, the National Science Foundation and CERN as defendants.

Quite an entertaining read can also be found at the two plaintiffs’ website. The main Continue reading ‘Law Vs Law’

Bigger than the FCC

Published
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Clifford
on March 27, 2008
in Los Angeles, black holes, science and string theory
. 6 Comments

We’ve been studying rotating black holes in my class this week, which has been fun. We get to apply the techniques we’ve been honing in the context of the Schwarzschild solution (link to recent posts below) to a bit more complicated solution, the Kerr solution, which includes rotation. Some equations follow, although you needn’t be put off by them. Most of this will make sense without really understanding them much. Just so you can see the shape of the things we scribble, I’ll show you the equation that captures this curved spacetime geometry, with no real explanation (sorry):

kerr solution

Here \Delta\equiv r^2-2Mr+a^2 and \rho^2\equiv r^2+a^2\cos^2\theta\ . The parameter a is the ratio of the solution’s spin or angular momentum J to its total mass M, measured in appropriate units. It’s a very important solution to get to grips with, since it’s not just fantasy physics, but highly relevant for astrophysics since black holes that are “out there” are unlikely to be non-rotating, and in fact, one can expect them to be rotating at quite a clip in many cases. A good many black holes - including some of the Continue reading ‘Bigger than the FCC’

Tipping the Light Cone: Black Holes

Published
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Clifford
on March 10, 2008
in art, astronomy, black holes, cosmology and science
. 26 Comments

Black Holes by Tamsin Van Essen: http://www.vanessendesign.com/

Black Holes, by Tamsin Van Essen. Part of a series of lovely ceramics with a physics theme. For more, visit the websites here and here.

As you may recall from the post I did some time ago, the “Light Cone” is a rather important concept in physics, and keeping track of it in a given physical scenario is an extremely important tool and technique for understanding many physical situations. (I urge you to review that post before continuing reading this one.)

One way to understand a most important concept - the event horizon - is by keeping track of lightcones, and so let’s go ahead and explore that here. The outcome is that Continue reading ‘Tipping the Light Cone: Black Holes’

Beyond Einstein: Fixing Singularities in Spacetime

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Clifford
on March 3, 2008
in black holes, cosmology, mathematics, science, string theory and work
. 21 Comments

Not long ago David Morrison (UCSB) came to the mathematics department here at USC to give a colloquium.

David Morrison Colloquium at USC

This was a treat for me for many reasons. Here are three:

  1. It’s always good to see Dave. He’s one of the people I’ve known in the field was since my very first postdoc when I was learning to survive in the big bad world on my own after graduate school. I mostly could not understand a word he or anyone there else said in those days (IAS Princeton, right in the belly of the Continue reading ‘Beyond Einstein: Fixing Singularities in Spacetime’

Cosmic Ray Guns

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Clifford
on December 20, 2007
in black holes and science
. 0 Comments

black hole jet striking another galaxy

From the Chandra X-ray Observatory site (where you can find lovely larger versions of this image):

Continue reading ‘Cosmic Ray Guns’

The Universe Tomorrow

Published
by
Clifford
on December 3, 2007
in Los Angeles, astronomy, black holes, cosmology, science, science education, science in the media and television
. 6 Comments

Over on Correlations, I talked a bit about the History Channel’s science show “The Universe” (as I have here), and pointed out that the new season (season two) has already begun being broadcast. Here’s hoping that it’s a good series of programmes that will be enjoyable and informative. The show’s website is here.

Well, I’ve learned that the second episode, tomorrow’s (showing at 9:00pm), is one of those that i did some shooting for over the last two months at a number of places around LA. Rather than repeat, here’s what I said:

The next one, to air on Tuesday the 4th December, is called “Cosmic Holes” (yeah, I know), and the subject matter will be right on the edge of the known and the unknown, talking about black holes, white holes, and wormholes. While we know that the first are out there, the second two, while also solutions of Einstein’s General Relativity, are still theoretical constructs (and not without problems). The show explores some of the ideas and the prospects for the ideas surrounding Continue reading ‘The Universe Tomorrow’

Warped Ambitions?

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Clifford
on November 17, 2007
in black holes, science and science fiction
. 4 Comments

Just spotted this in the Guardian:

starship enterprizeNext Thursday, the British Interplanetary Society is bringing together physicists for a conference entitled Faster than Light: Breaking the Interstellar Distance Barrier. “The main purpose is to raise awareness of this obscure field of research within general relativity and quantum field theory and attract new and particularly young researchers to work on the technical problems,” said organiser Kelvin Long.

Wow! I had no idea there was such a meeting. Did anyone reading go?! What is the British Interplanetary Society? From their site I found this quote:
Continue reading ‘Warped Ambitions?’

Lookin’ For Some Hot Stuff

Published
by
Clifford
on September 1, 2007
in black holes, books, music, research, science and string theory
. 8 Comments

___________________________________________________________________________________
Hot, hot, hot, hot stuff
hot, hot, hot
hot, hot, hot, hot stuff
hot, hot, hot

- from “Hot Stuff”, by Donna Summer (1979). I refer to not only the physics but the c. 100 oF temperatures we’ve been having here every day recently.
___________________________________________________________________________________

On my way back from the conference, I spotted this book (below left) last Saturday in Foyles (the booksellers) in London1. Quark Gluon Plasma book It is a collection of reprints of a lot of the papers forming the foundations of the physics of the quark-gluon plasma (QGP) idea, going back the early to mid 1970s with such papers as Collins and Perry (Gosh, I had no idea Malcolm was one of the early workers on this idea. He’s much more thought of as associated with black holes, gravity, strings and so forth, ideas which - ironically - have recently turned out to be relevant to the discussions of the physics too. See my recent post, and there are also various popular articles to be found2).

Putting aside the usual ridiculous price that Springer Elsevier charges for books, I found myself in two minds about this book, in view of the surprises being uncovered about the properties of this remarkable state of matter at the RHIC experiment. Is this collection of early papers a useful working tool, or is it now just of historical interest, since many of the basic expectations about the properties of the plasma seem now to be incorrect?

rhic collision of gold ionsWell, after a bit of thought, I decided that the latter view would be way too hasty. First and foremost, on a general level, even if some of the computations in some papers were done in the “wrong” light (it’s a strongly coupled liquid that flows, not a weakly coupled gas of quarks and gluons), much of their content will still be useful in many ways - good and correct calculations last for all time, it is the sense of the words decorating them that may crumble over time. More specifically, one can worry about whether there were assumptions (and approximations based on those) that went into Continue reading ‘Lookin’ For Some Hot Stuff’

Exploring QCD in Cambridge

Published
by
Clifford
on August 22, 2007
in black holes, research, science and science in the media
. 17 Comments

exploring qcd sign

So the conference here at the Newton Institute in Cambridge is simply marvellous. I’m so glad I came, and so happy that I was invited to attend and make a contribution to it by giving a talk and having discussions. It’s a rather splendid combination of experimentalists, phenomenologists, and various hardcore theorists of various sorts, and there are ideas just flying around and bouncing off the walls. The title is “Exploring QCD: Deconfinement, Extreme Environments and Holography”, (it’s organized by Nick Evans, Simon Hands, and Mike Teper) and the focus is very much the fascinating nuclear physics of heavy ion collisions at the RHIC experiment at Brookhaven, and the experiments to come on heavy ion collisions at the LHC at CERN. The latter is an aspect of the physics to be done at the LHC that you don’t hear about much because it is sidestepped in favour of discussions about the Higgs, origin of mass, supersymmetry, theories of everything - such as strings, microscopic black holes, extra dimensions and all that other good stuff. (See earlier discussions here, here and here.)

Well, the great thing is that there’s been plenty of discussion of black holes, extra dimensions, strings, and so forth at the conference because of a great deal of promise of its relevance to nuclear physics. It’s been right alongside the discussion of experimental results, and other theoretical approaches such as work on computer simulations of aspects of QCD (”lattice QCD”) and studies involving other techniques. There’s very much a spirit of open-minded exchange among all the various parties Continue reading ‘Exploring QCD in Cambridge’

The Scary Universe?

Published
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Clifford
on August 21, 2007
in astronomy, black holes, fun, galaxies, science and television
. 3 Comments

Ok, there’s “The Elegant Universe”, and “The Ambidextrous Universe”…. even “Stephen Hawking’s Universe”… and so on for these titles. But how about “The Scary Universe” or “The Dangerous Universe”? (Personally, I wish we’d just stop with the whole “The fill-in-the-blank Universe” stuff, so I probably should have not written this first paragraph.)

Well, I myself don’t think of the Universe that way, but tonight (at 9:00pm) the History Channel will be presenting the next show in their series (called “The Universe”), which is about (they say) the Most Dangerous Place In The Universe”. It looks as though it will be a survey of various places where a lot of very energetic activity is taking place, powering some of the most powerful phenomena we’ve ever seen, such as quasars, magnetars, and so forth. So black holes will feature quite a bit, I imagine, and although I probably should not really be telling you about it before I’ve had a chance to see it (recall my remarks about the windy shooting conditions), I think (I’m not sure) that I’ll be making an appearance as one of the contributors. (I did not get caught off guard this time.)

The whole “dangerous” motif is a sort of deliberately sensational way of presenting Continue reading ‘The Scary Universe?’

News From The Front, VI: Simultaneity

Published
by
Clifford
on July 30, 2007
in black holes, personal, science, string theory and work
. 7 Comments

aspen from gondolaI stopped the previous post rather abruptly (I had to do another task and then run some errands) without getting to tell you a little twist at the end of the story. Here it is.

Having chipped away at the thoughts that Strominger’s talk stirred in my head for several days last week, scribbling equations to check that all I was thinking was on the right track (and chatting a couple of times with Nick Halmagyi down the hall), I decided that it was all fitting together so nicely that the framework and my extensions of it just had to be true. There was that feeling that it was too nice to be wrong, and it passed all the obvious checks I could think of. There were two independent consistency checks everything had to pass (using my way of formulating things) and they gave exactly the right results as required by the general setup, with no room for maneuver.

When that happens so nicely, usually at that point in thinking about a physics problem, a thought occurs to me. If I’m playing with a good idea and everything is working so well, then there’s at least 200 other people in the field who probably are also playing with it, and 199 of them have way more time than I do to think it through and write it up before I can. One should not really worry about these things in an ideal world, but I’d be lying to you if I said it did not come up as a concern from time to time. I’ve a history of having my thunder stolen out from under me several times in the field (and not always accidentally), so I’m a bit gun shy.

Anyway, I started writing a draft of the paper on Thursday the way I usually do: I write Continue reading ‘News From The Front, VI: Simultaneity’

News From The Front, V: Microscopic Weekend Diversions

Published
by
Clifford
on July 30, 2007
in black holes, personal, science, string theory and work
. 5 Comments

I’ve been spending the day so far as an administrator, and not a researcher, since I have to present the results of two committees’ deliberations at one of the big annual organizational meetings tomorrow here at the Aspen Center for Physics. So I’ve been gathering and arranging data in a presentable form. Enough. I will take a break and blog a tiny bit before turning to a truly riveting task - reviewing an introductory physics textbook for a publisher… (Sigh…it is not so easy to escape these things, even out of semester time.)

I had big plans to do a hike each day on the weekend, but physics intervened. I should explain a bit more. Earlier last week I eventually got around to following Nick’s suggestion from an earlier post to take a look at Andy Strominger’s Strings 2007 talk entitled “Search for the Holographic Dual of N Heterotic Strings”. It was the usual nice Strominger talk, where he motivates the physics very well, and presents interesting and clear D-branesthoughts on the problem in hand. I shall try to say a bit more about what it is about later on, but the general gist of it is that it is to do with understanding certain types of four dimensional black hole in string theory. As you may know, one of the extraordinarily successful results in string theory in the last decade (and slightly more) has been that we can understand one of the most central results of semi-classical quantum gravity -that they have an entropy and behave like thermodynamical objects (the work of Bekenstein and of Hawking from the early 70s)- in precise terms in the full theory of quantum gravity that string theory appears to present us with. This started with the work of Strominger and Vafa in 1996, that showed how to describe a large class of black holes as essentially made of extended objects called D-branes (about which I’ve spoken at length earlier1).

Just to fill in the gaps roughly: Hawking’s result that black holes can radiate as thermodynamical objects comes from taking Einstein’s theory of General Relativity and combining it with Quantum Mechanics in a partial way. He could not really do much better since there was no proper quantum theory of gravity at the time, but even in Continue reading ‘News From The Front, V: Microscopic Weekend Diversions’