## Sometimes there is Smoke without Fire

…Or at least, not always the fire you’re looking for. So, as suspected for several months now, the signal seen by BICEP2 experiment and dubbed “a smoking gun” type of direct evidence for cosmic inflation (for which we have lots of strongly suggestive indirect evidence, by the way) is likely an artefact of the effects of galactic dust. I spoke about this in a post a while back, so I won’t repeat myself here. What everyone has been waiting for has been the results of a joint analysis between the BICEP2 people and the ESA’s Planck mission. The Planck satellite, you may recall from reading here or elsewhere, is also designed to carefully study the polarisation of the cosmic microwave background (the earliest light to shine in the universe), and so can (through thorough analysis of the effects of dust that it has measured independently) help rule in or out whether there is a signal. Planck studies essentially the whole sky, not just the patch that BICEP2 was carefully looking at, and one of […] Click to continue reading this post

## Dark Energy Discussion

I was sent an interesting link a while ago* that I thought I would share with you. It is a really good discussion about Dark Energy – what do we think it is, why we think it exists, why some think it does not, and how to move forward with the discussion of what is, after all apparently *most* of our universe. It is a panel discussion that was hosted by the Institute for Arts and Ideas (which I *love* the idea of!). The discussion is described on the site as follows:

Dark energy is supposed to make up two-thirds of the universe. But troublingly CERN has yet to find any evidence. Have we got our story of the universe wrong – might dark energy be the aether of our time? Do we need a new account of the universe, or is it too soon for such radical solutions?

The Panel
The BBC’s Sue Nelson asks Templeton Prize winning cosmologist George Ellis, Cambridge physicist David Tong and mathematician Peter Cameron to seek the invisible.

Ok, the “troublingly CERN has yet to find any evidence” part puzzles me a bit, since nobody’s really expecting CERN to find any evidence of it, in any large scale experiments that I’m aware of (please correct me if I am wrong)… Is the writer of the abstract confusing Dark Energy and Dark Matter? Even then I think it is an odd phrase to lead with, especially if you don’t mention the huge amount of evidence from astronomy in the same footing… but I imagine the abstract was maybe not written by a physicist?

Nevertheless, I strongly recommend it as a thought-provoking discussion, and you can find it embedded below. Do also check out their many other interesting […] Click to continue reading this post

## News From the Front, XI: Holographic Heat Engines!

Yes, you heard me right. Holographic Heat Engines. I was thinking recently about black holes in universes with a cosmological constant and their thermodynamics. I had an idea, it led to another, then another, then some calculations, and then a couple of days of writing, calculating, and thinking… then a day to cool off and think about other things. Then I came back to it, decided it was still exciting as an idea and so tidied it all up as a paper, made some diagrams, tidied some more, and voila! A paper submitted to the arxiv.

I’m sort of pleased with all of it since it allowed me to combine a subject I think is really fun (although often so bleakly dull when presented at undergraduate level) – heat engines – with contemporary research ideas in quantum gravity and high energy physics. So I get to draw some of the cycles in the p-V plane (graph of pressure vs volume) representing the inner workings of engines of particular designs (just like you might have seen long ago in a physics class yourself) and compute their efficiency for doing mechanical work in exchange for some heat you supply. It is fundamental that you can’t do that with 100% efficiency otherwise you’d violate the second law of thermodynamics – that’s why all engines have to have some exhaust in the form of heat, giving an efficiency represented by a quantity $$\eta$$ that is less than one, where one is 100% efficient. The diagram on the left illustrates the key pieces all engines must have, no matter what working substance you’re using. The details of the design of the engine are what kind of cycle you taking it through and what the properties (“equation of state”) your working substance has. In the case of a car, for example, the working substance is cleverly mixed up with the source of heat – the air/gasoline mix forms a “working substance” that gets expanded and compressed in various ways (in the green bit of the diagram), but the fact that it also burns releasing heat means it is also the source of the heat that comes into the engine (the flow from the red bit) to be (in part) turned to work, and the remainder flowing out to the blue (exhaust). Very clever.

The cool thing here is that I’m using black holes as the working substance for […] Click to continue reading this post

## TED Youth Talk – Hidden Structures of the Universe

You might recall that last year I gave a talk at TED Youth, in their second year of short TED talks aimed at younger audiences. You’ll recall (see e.g. here and here) I made a special set of slides for it, composed from hundreds of my drawings to make it all in graphic novel style, and somehow trying to do (in 7 minutes!!) what the TED people wanted.

They wanted an explanation of string theory, but when I learned that I was the only person in the event talking about physics, I kind of insisted that (in a year when we’d discovered the Higgs boson especially!) I talk more broadly about the broader quest to understand what the world is made of, leaving a brief mention of string theory at the end as one of the possible next steps being worked on. Well, they’ve now edited it all together and made it into one of the lessons on the TED Ed site, and so you can look at it. Show it to friends, young and old, and remember that it is ok if you don’t get everything that is said… it is meant to invite you to find out more on your own. Also, as you see fit, use the pause button, scroll back, etc… to get the most out of the narrative.

I’m reasonably pleased with the outcome, except for one thing. WHY am I rocking […] Click to continue reading this post

## Known Unknowns Decreased a Bit

Well, the day is here. The Planck collaboration has announced a huge amount of results for the consumption of the scientific community and the media today. The Planck satellite looks with unprecedented precision at the very earliest radiation (“cosmic microwave background radiation”, CMB) from the universe when it was very young (a wee, cute 380,000 years old) and helps us deduce many things about what the universe was like then, and what it is like now. Here’s one of the representations of the universe using the new sky mapping Planck did (image courtesy ESA/Planck):

There’s a ton of data, and a raft of papers with analysis and conclusions. And there’s a very nice press release. I recommend looking at it. It is here, and the papers are here. The title of the press release is “Planck reveals an almost perfect Universe”, and some of the excitement is in the “almost” part. A number of anomalies that were hinted at by the previous explorer of the CMB, WMAP, seem to have been confirmed by Planck, and so there are some important things to be understood in order to figure out the origin of the anomalies (if they ultimately turn out to be real physics and not data artefacts). [Update: Andrew Jaffe has two nice posts I recommend. One on the science, and the other on the PR. Jester also has a nice post on the science from a particle physicist’s perspective.]

What is the title of my post referring to? Well, the refined measurements have allowed us to update some of the vital statistics of the universe. First, it is a bit older than previous measurements have indicated. The age is now measured as 13.82 billion years. (I’m already updating pages in the draft of my book…) Second, the proportion of ingredients […] Click to continue reading this post

## Heaven’s Parameters

Oh… I forgot to get around to letting you know the result of designing the universe required in a previous post. The result is that it is a radiation (“light”) filled universe with positive cosmological constant $$\Lambda$$(and so space wants to expand due to negative pressure – much like ours seems to be doing). The radiation density wants the thing to collapse. There’s a balance between the two, and it turns out that it is when the two densities (radiation, and vacuum energy) are equal. This is only possible when there is positive curvature for the universe (so, not like ours), as you can see from the Friedman equation if you were that way inclined. So the universe is a 3-sphere, and if you work it out, the radius of this 3-sphere turns out to be $$a=\left(\frac{3}{2\Lambda}\right)^{1/2}$$. The temperature of the radiation is then computed using the usual Stefan-Boltzmann relation.

The equality of densities turns out to result from the fact that the effective potential of the equation is at a maximum, and so this universe turns out to be unstable… It is a radiation-filled version of Einstein’s matter-filled static universe, which is also unstable. It is larger than Einstein’s by a factor of $$\sqrt{3/2}$$.

Einstein was said to have arrived at his static universe on the grounds of what he thought was observationally clear – the universe was unchanging (on large scales). […]
The equality of densities turns out to result from the fact that the effective potential of the equation is at a maximum, and so this universe turns out to be unstable… It is a radiation-filled version of Einstein’s matter-filled static universe, which is also unstable. It is larger than Einstein’s by a factor of $$\sqrt{3/2}$$.

Einstein was said to have arrived at his static universe on the grounds of what he thought was observationally clear – the universe was unchanging (on large scales). Hubble […] Click to continue reading this post

## Project Heaven

This is an extra homework that some students of the General Relativity class did to make up for one that did not count earlier in the semester. While writing it, I realized that this universe is in fact, Heaven! You know, we become beings of light, and live forever, etc…

I thought it would be fun to share its final form:

“You work in the design section of the company that manufactures universes. (This is […] Click to continue reading this post

## The 2011 Nobel Prize in Physics

Ok. So who was surprised by this one? My hand is not up… is yours? (That’s a screen shot from the Nobel Prize site to the left. More here. Cheeky of me, but it’s early in the morning and I’ve got to pack, shower, and cycle like mad to the subway to get to my train to Santa Barbara, so time is of the essence.)

I was pretty sure that this would be the prize sometime very soon, although I’ll not say that I knew it would be this year’s for sure. It is well deserved, since this was a genuinely major change in how everyone in the field thinks about the universe, and we’re still trying to get to grips with it today. The acceleration of the universe that they […] Click to continue reading this post

## Heretic…?

We had a really interesting discussion of the quantum physics of de Sitter spacetime yesterday here in Aspen, starting with a review of the behaviour of scalar fields in such a background, led by Don Marolf, and then, after lunch, an open-ended discussion led by Steve Shenker. This is all quite difficult, and is of course quite relevant, since a piece of de Sitter is relevant to discussions of inflation, which seems (from cosmological observations) to have been a dominant phase of the very early universe. As the most symmetric space with positive cosmological constant, de Sitter may also be relevant to the universe today, since dark energy (first recognized after 1998’s observations of the universe’s accelerating expansion) may well accounted for by a positive cosmological constant.

So we need to understand this type of spacetime really well… and it seems that we don’t. Now there’ve been a lot of people looking at all this and doing really excellent work, and they understand various issues really well – I am not one of them, as I’ve not worked on this in any detail as yet. Do look at the papers of Marolf, and of Shenker, and collaborators, and references therein, and catch up with what’s been going on in your own way. For what it is worth, the sense that I get is that we’re trying to solve very difficult issues of how to interpret various quantum features of the spacetime and getting a lot of puzzles by trying to make it look a lot like things we’ve done before.

Now, we may solve all these puzzles…. but my current take on this all is that we’re […] Click to continue reading this post

## Planck Matters

You can read a bit about the work of my colleague Elena Pierpaoli and her postdocs and students in this article in one of USC’s in-house publications. It focuses on the Planck observatory (image right from NASA/ESA), which we’ve discussed here before. (Recall the launch?) There’s a lot of exciting physics about the very young universe to be discovered as more data from the mission get gathered and analyzed.

Enjoy the article!

## The Big Day!

Tomorrow is the Big Day. For what? The launch of Planck and Herschel – Major new windows on our universe. Keep your fingers crossed for luck!

They’re on the launch pad right now. See here.

So, what are the missions and objectives of these fine spacecraft, I hear you ask.

Well, from the Planck site: […] Click to continue reading this post

## Distractions in the Dark

Well, you’ve probably guessed that I’ve been somewhat distracted for several days. In fact, my main focus for the past week has really been on computer issues, frustratingly. I’ll give you the blow by blow later, I hope, but the last couple of days have been the most frustrating of all, and so I’ve not been dealing with much else, including blogging. Part of that is actual logistics – some of the things I wanted to post are on the afflicted computer – and some just the sheer annoyance of not having solved the issues driving me to do something totally non-computer related like going for a hike or seeing a movie.

So tonight i think I have a new theory – well, hypothesis- of what’s wrong, after a good deal of the day spent on detective work. It is a conjecture that is supported only by […] Click to continue reading this post

## Tales From The Industry XX – Sporting Locations

Wow, doesn’t time fly when you’re having a busy semester! I meant to tell you about this early March shoot a while back, but got swamped and it fell off the desk. I recalled that I’ve been neglectful because I learned that the show in which some of this will be used will air on Tuesday night (9:00pm I think – “The Universe” on the History Channel). The episode discusses the end of the universe, as far as I know. The point is to discuss the various speculations that have been made about how the universe might end, and what current knowledge (such as the famous 1998 supernova observations showing that the universe’s expansion is accelerating) seems to suggest about which of those scenarios might be more likely. Of course, for the discussions to make sense, you need someone to talk about some of the basics, such as what it means for the universe (indeed, the whole of spacetime) to expand and collapse. Who you gonna call?
Ok. I’m one of many you can call. It was a new (to me) producer/writer, Savas Georgalis, who called this time, and we worked together on plans about how we might […] Click to continue reading this post

## Still Crazy After All These Years

I don’t mean that in a bad way. It is what it is. Quite varied and wonderful, our universe is, with unexpected features I don’t think many would have guessed at not long ago (like the fact that we only understand what about 4% of it is!! Crazy, in a […] Click to continue reading this post

## Two Rings

Now have a look at this object (and its enlargement on the right):

What is it? It’s a double Einstein ring! An Einstein ring is formed by gravitational lensing – the bending of light from one object by the gravity of another object – and is typically formed when a distant galaxy lines up with another, closer galaxy. The result is a rather nice ring shape.

To find a double Einstein ring is rare! In fact, this is the first one that’s been announced. Not only is it novel, it can also use used to do a good deal of science, such […] Click to continue reading this post