Tuesday, August 26, 2014

A Supervoid cannot explain the Cold Spot

from Blank On The Map

In my last post, I mentioned the claim that the Cold Spot in the cosmic microwave background is caused by a very large void — a "supervoid" — lying between us and the last scattering surface, distorting our vision of the CMB, and I promised to say a bit more about it soon. Well, my colleagues (Mikko, Shaun and Syksy) and I have just written a paper about this idea which came out on the arXiv last week, and in this post I'll try to describe the main ideas in it.

First, a little bit of background.

Wednesday, July 16, 2014

Short news items

from Blank On The Map

Over the past two months I have been on a two-week seminar tour of the UK, taken a short holiday, attended a conference in Estonia and spent a week visiting collaborators in Spain. Posting on the blog has unfortunately suffered as a result: my apologies. Here are some items of interest that have appeared in the meantime:
  • The BICEP and Planck teams are to share their data - here's the BBC report of this news. 

Friday, June 27, 2014

The Trenches of Discovery - obsolete components in the human machine

In the Trenches this week - are we slowly losing our genetic integrity to genetic drift? Find out more in the Trenches here.

Monday, May 5, 2014

The Trenches of Discovery - replacing damaged components

In the Trenches this week - how we are beginning to look under the bonnet of the human machine and fix things at the genetic level.

Read more in the Trenches: here.

Tuesday, March 25, 2014

BICEP2: reasons to be sceptical, part 2

This is the second part of three posts in which I wanted to lay out the various possible causes of concern regarding the BICEP2 result, and provide my own opinion on how seriously we should take these worries. I arranged these reasons to be sceptical into three categories, based on the questions
  • how certain can we be that BICEP2 observed a real B-mode signal?
  • how certain can we be that this B-mode signal is cosmological in origin, i.e. that it is due to gravitational waves rather than something less exciting?
  • how certain can we be that these gravitational waves were caused by inflation?
The first post dealt with the first of the three questions, this one addresses the second, and a post yet to be written will deal with the third.

Read more>>

BICEP2: reasons to be sceptical, part 1

As the dust begins to settle following the amazing announcement of the discovery of gravitational waves by the BICEP2 experiment, physicists around the world are taking stock and scrutinizing the results.

What I wanted to do today is to possibly contribute to that by gathering together all the main points of concern and reasons to be sceptical of the BICEP result. This is partly for my own purposes, since writing things down helps to clarify my thoughts. I will divide these concerns into three main categories, addressing the following questions:
  • how certain can we be that BICEP2 observed a real B-mode signal?
  • how certain can we be that this B-mode signal is cosmological in origin, i.e. that it is due to gravitational waves rather than something less exciting?
  • how certain can we be that these gravitational waves were caused by inflation?

Monday, March 24, 2014

The Trenches of Discovery - finely tuned sensors

In the Trenches this week, find out how your sense of smell works and why it may be millions of times more powerful than we previously thought!

Read more here.

Saturday, March 15, 2014

B-modes, rumours, and inflation

The big news in cosmology circles at the minute is the rumour that the "major discovery" due to be announced at a press conference on Monday the 17th is in fact a claimed detection of the B-mode signal in the CMB by the the BICEP2 experiment.


Tuesday, February 4, 2014

Blank On The Map: Does the multiverse explain the cosmological constant?

At the end of the last post on falsifiability, I mentioned the possibility that the multiverse hypothesis might provide an explanation for the famous cosmological constant problem. Today I'm going to try to elaborate a little on that argument and why I find it unconvincing.

It is sometimes said that Steven Weinberg showed that anthropic reasoning and the multiverse hypothesis correctly predict the value of the cosmological constant. This is however no longer true. This is partly because Steven Weinberg's argument, though brilliant, relied upon a few assumptions about the theory in which the multiverse was to be realised, and theory has subsequently developed not to support these assumptions but to negate them. And it is partly because, even given these assumptions, the original argument gives the wrong value when applied to cosmological observations from 2014 rather than 1987. Both theory and observation have moved away from the anthropic multiverse.

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Monday, February 3, 2014

The Trenches of Discovery: picoscale engineering in the human machine

In the Trenches this week, learn how movements of trillionths of a metre are required to control a process that allows you to breathe properly, and how biological engineering on the subatomic scale keeps us alive.

Read more here.

Monday, January 27, 2014

Blank On The Map: Is falsifiability a scientific idea due for retirement?

Sean Carroll argues that it is.

He characterises the belief that "theories should be falsifiable" as a "fortune-cookie-sized motto"; it's a position adopted only by "armchair theorizers" and "amateur philosophers", and people who have no idea how science really works. He thinks we need to move beyond the idea that scientific theories need to be falsifiable; this appears to be because he wants to argue that string theory and the idea of the multiverse are not falsifiable ideas, but are still scientific.

This position is not just wrong, it's ludicrous. 

What's more, I think deep down Sean – who is normally a clear, precise thinker – realises that it is ludicrous. Midway through his essay, therefore, he flaps around trying to square the circle and get out of the corner he has painted himself into: a scientific theory must, apparently, still be "judged on its ability to account for the data", and it's still true that "nature is the ultimate guide". But somehow it isn't necessary for a theory to be falsifiable to be scientific.

Now, I'm not a philosopher by training. Therefore what follows could certainly be dismissed as "amateur philosophising". I'm almost certain that what I say has been said before, and said better, by other people in other places. Nevertheless, as a practising scientist with an argumentative tendency, I'm going to have to rise to the challenge of defending the idea of falsifiability as the essence of science. Let's start by dismantling the alternatives.

Read more>>

Tuesday, December 10, 2013

The Trenches of Discovery: Microscopic art

In the Trenches this week, science inspires art as part of a growing trend. Read more here.

Monday, October 28, 2013

The Trenches of Discovery: non-standard components in the human machine

The human machine is not all it appears to be - our most central components are not, in fact, human but the result of invasion by bacteria. Find out more in the trenches: here.

Thursday, July 11, 2013

Quasars, homogeneity and Einstein

from Blank On The Map

People following the reporting of physics in the popular press might remember having come across a paper earlier this year that claimed to have detected the "largest structure in the Universe" in the distribution of quasars, that "challenged the Cosmological Principle". This was work done by Roger Clowes of the University of Central Lancashire and collaborators, and their paper was published in the Monthly Notices of the Royal Astronomical Society back in March (though it was available online from late last year).

The reason I suspect people might have come across it is that it was accompanied by a pretty extraordinary amount of publicity, starting from this press release on the Royal Astronomical Society website. This was then taken up by Reuters, and featured on various popular science websites and news outlets, including The AtlanticNational GeographicSpace.comThe Daily GalaxyPhys.orgGizmodo, and many more. The structure they claimed to have found even has its own Wikipedia entry.

The reason this paper got so much publicity is because of the claim that this structure violates the assumption of homogeneity. Is this true? Does the existence of such a large structure mean that the Universe is not homogeneous, the cosmological principle is wrong, and the foundation on which all of modern cosmology is based is shaky?


Monday, July 1, 2013

The Trenches of Discovery: the business of ignorance

A look in the Trenches this week at how unscrupulous people can exploit lack of scientific understanding in vulnerable people to the tune of millions of dollars.

Read more here.

Thursday, June 13, 2013

Cosmological perturbations post-Planck - wrap up (TToD)

I'm very sorry. As I wrote last week, we just hosted a conference here in Helsinki. I wanted to cover it as the conference happened and I just didn't have the combination of time and mental energy to do so. I won't be covering it in any detail retrospectively either because I need to get on with research. Nevertheless, this blog is slightly more than a hobby for me, it is also slightly ideological, so I will try to work out how to do it all better next time and try again then (this will be the annual theoretical cosmology conference "COSMO" in early September).

Here's a summary of some of the more interesting aspects that I'll quickly write up, starting with some closure concerning the topic I was halfway through in my last post...

David Lyth, the curvaton and the power asymmetry

Read the rest at The Trenches of Discovery-->

Tuesday, June 4, 2013


from Blank On The Map

This week I am attending this workshop in Helsinki. The focus of the workshop is on re-evaluating theoretical issues in cosmology in light of the new data from the Planck satellite. 

Wednesday, May 29, 2013

Inspiring Science: The viruses that made us

Viruses make their living by breaking into cells and using the machinery and energy in the cell to reproduce. Once inside, some viruses immediately hijack the cell and make copies of themselves which burst out into the world to infect new cells. Other viruses take a staid approach, though. Instead of taking over the cell, they quietly slip a copy of their genes into its DNA. When the cell divides, it copies the newly acquired viral genes along with the rest of its genome. It’s a better deal for the virus, since all of the cell’s descendants will be carrying viral genes which can eventually come out of hiding to commandeer the cell and replicate. A really lucky virus is one that finds itself inside an egg cell. Getting into the DNA of a single cell means getting copied into all of its daughter cells, but getting into the DNA of an egg cell means getting copied into every cell in the organism that grows from the egg…and from there into all of the organism’s offspring. Lucky viruses that succeed in pulling off that trick can still break out and cause trouble, but they can also become integrated into their host’s genome; instead of struggling to reproduce, they can then just kick back and enjoy the ride while we lumber along, making copies of them whenever we make new cells or have children.

Join the discussion at Inspiring Science...

Tuesday, May 28, 2013

An inconsistent CMB?

from Blank On The Map

When the Planck science team announced their results in March, they also put out a great flood of papers. You can find the list here; there are 29 of them, plus an explanatory statement.

Except if you look carefully, only 28 of the papers have actually been released. Paper XI, 'Consistency of the data', is still listed as "in preparation". Now, what this paper was supposed to cover was the question of how consistent Planck results were with previous CMB experiments, such as WMAP. We already knew that there were some inconsistencies, both in the derived cosmological parameters such as  the dark energy density and the Hubble parameter, and in the overall normalization of the power seen on large scales. We might expect this missing paper to tell us the reason for the inconsistencies, and perhaps to indicate which experiment got it wrong (if any). The problem is that at present there is no indication when we can expect this paper to arrive – when asked, members of the Planck team only say "soon". I presume that the reason for the delay is that they are having some unforeseen difficulty in the analysis.

However, if you were paying attention last week, you might have noticed a new submission to the arXiv that provided an interesting little insight into what might be going on.

Read more>>