Kuhn sure knew what he was talking about. The dark energy controversy, the major elements of it that I’ve discussed in the previous two posts, are perfectly Kuhnian.

Recall that Kuhn says that controversies can arise when observations turn up anomalies in the theory; that is, when “nature has somehow violated the paradigm-induced expectations”.

When anomalies occur, Kuhn believes that there are two ways for them to be “made sense of” within a paradigm: the anomaly can be rejected or excused, otherwise the paradigm must be revised or reconsidered; the latter leads to moments of crisis within a paradigm.

Here, we’ve got anomalies arising from major discrepancies between observation and theory or expectation: the expansion acceleration anomaly, the enormous difference in calculated and observed values of the cosmological constant, and the coincidence problem. Attempts were made to reject the expansion acceleration anomaly through thorough flaw checking in the supernovae results and making many additional independent measurements, but the anomaly remained.

There are then three ways to resolve the crisis: putting it in the ‘too hard’ basket, dealing with it and retaining the paradigm, or adopting a new paradigm.

A new paradigm—Lambda-CDM—emerged from the expansion acceleration result, which resolved one crisis but introduced the crisis concerning the cosmological constant.

These two anomalies (the enormous difference in calculated and observed values of the cosmological constant and the coincidence problem) are interesting; some scientists appear to have, for whatever reason, found themselves able to reject or excuse them in order to maintain the Lambda-CDM model. But in general, I think that they’ve been put in the ‘too hard’ basket; it’s simply not yet possible to determine if one of the other proposed models is consistent with observation.

Win for Kuhn!

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But it was not the end of the controversy.

There are three major problems with the cosmological constant that have caused the dark energy controversy to continue. The cosmological constant is controversial because:

  1. It’s often been used in the past as a fudge factor, only to be gotten rid of after more information has been gathered
  2. When calculated theoretically using quantum mechanics, scientists get a value for it that’s 10^122 times LARGER than observed! OUCH!
  3. The density of dark energy as a cosmological constant is currently in the same order of magnitude as dark matter; this is an extraordinary coincidence; it means that we are in a special period of time at which we’re actually able to detect the accelerating effects of dark energy, which is frowned upon because we are scientists of Copernicus, who said we’re not special in space or time (this is now known as the cosmological principle).

Scientists have really gone the extra mile in the search for alternative explanations…

…even to the point of risking comparison with the Queen in Alice Through the looking-glass who practiced believing “as many as six impossible things before breakfast”.

(quote from article in the New York Times on May 5, 1998, by John Noble Wilford: Cosmologists Ponder ‘Missing Energy’ of the Universe)

Broadly, there are three other possible explanations for acceleration: it could be that dark energy evolves in time; that we don’t understand gravity correctly and don’t actually need dark energy to explain acceleration; or that we must do away with the cosmological principle (which is probably the least popular option). There are many theoretical models out there based on each of these.

However, because observations fit the Lambda-CDM model so well, cosmologists stick with the cosmological constant. It’s the easiest model to ‘take aim at’ at the present time, although some appear to firmly believe it’s more than that; that the three strikes brought against the cosmological constant can be ignored based on the observations, even though scientists have not yet determined how to distinguish the cosmological constant from some other possible models in observations.


In 1998, two separate teams, using different type Ia supernova data, went out to show that the universal expansion was slowing down due to gravity, but instead found just the opposite, that the universal expansion was accelerating. This was very controversial and very unexpected; in fact, it was so different to the accepted theory that scientists simply assumed they could quickly downplay the results.

Scientists were committed to ensuring that the supernovae results did indeed point towards an accelerating universe: potential flaws in the observations were analysed and over the next few years independent measures were taken that all supported the conclusion. The fact that it was two separate sets of data that original showed the acceleration result probably helped to win scientists over so quickly; within a few years, most scientists were convinced that the universe’s expansion was accelerating, perhaps due to some kind of dark energy. Ethan Siegel from Starts With A Bang says:

It suddenly occurred to me that if you wanted to eliminate this one thing, dark energy, it would take a minimum of six separate observations to be overturned. And that was it; it was suddenly unreasonable to me that I would reject dark energy.

While there was really no dispute over the acceleration result after checks and additional confirmations, scientists had really very little idea about what the dark energy actually could be. Despite this, scientists were quick to point out that the cosmological constant fitted the acceleration result; it’s exactly what you’d expect to see if a cosmological constant made up about 70% of the critical density. So, dark energy was introduced into the standard model in this way, which is known as the Lambda-cold dark matter model. This could have been the end of the controversy…


I find that I understand concepts much better when I use flow charts; I’ve had one for my controversy in the works for most of the semester, gradually evolving into this (hopefully) final flow chart:

You can see, in blue, the three levels of controversy I noted in my previous post and, in white, the causes and effects of these controversies (SN=supernovae, CDM=cold dark matter).

In the next few posts, I’ll explain each of the controversies and the controversy framework each fits into, and I’ll comment on the current status of dark energy.


Before I discuss the controversies surrounding dark energy and its introduction into the big bang paradigm, I figure I should make some kind of mention of what it is.

In my research I’ve come across, many times, the assertion that dark energy is the most famous and most embarrassing problem in physics. Maybe the most embarrassing, but the most famous? Really? I haven’t come across any non-astrophysicists who know what dark energy is; indeed, when I ever mention dark energy most people either have no idea what I’m talking about (the same goes for the fact that the universe expansion is accelerating, it’s big news to them!) or think I’m talking about dark matter (although, they mustn’t know much about dark matter either if that’s the case).

So… what exactly is it?

“We don’t know” seems like a good answer.

We call the force causing the universe’s expansion to accelerate “dark energy”. This information, that the expansion accelerates, has been confirmed by several independent cosmological probes, including measurements of supernovae , the cosmic microwave background, and galaxy clustering. So the acceleration itself generally is not in dispute, but the dark energy story gets muddy from here. The definition I use of dark energy is:

A property of empty space with negative pressure that counteracts gravity and causes the universe’s expansion to accelerate

Dark energy could be in the form of a cosmological constant, which is what many observations point towards, or it could be evolving in time as some type of quintessence model. Or it could be that general relativity is incorrect and dark energy doesn’t exist at all.

Besides the fact that there is a high level of uncertainty associated with dark energy, it seems to me that controversies arise in the dark energy story in three different ways:

  1. The initial supernovae measurements in 1998 that indicated that the universe’s expansion was accelerating
  2. Introducing dark energy as a cosmological constant (the Lambda-CDM model has come from this)
  3. It’s ugly

In the following posts I’ll cover each of these in more detail… I’m sure that those who are still reading will all be quivering in anticipation!


I was just about to open a book and continue my dark energy controversy research when I made a last, quick check of Twitter… and found these articles: Study predicts end of the universe from ABC and Countdown to oblivion from New Scientist.

Both of these articles regard a study from ARXIV (have a look here), where physics papers are uploaded before publication. This article has not been accepted for publication anywhere, so assumedly, has not been peer reviewed. I have issues with newspapers and popular science magazines picking up on wacky papers such as this and running stories on them as if they’re a true representation of current scientific thought (even though they state the paper is from arxiv, how many ABC news readers know what this is?)… it’s like they’re digging for a cosmic controversy. And here I may mean both the scientists and the journalists.

But, as usual, it’s the public comments that interest me the most. Here’s a selection of particularly painful comments from the ABC article (which are not only painful scientifically…):

The arrogant’s of man kind. We are babes in the woods and know very little about our universe. Yet we still get self important people make guesses about our future and past, then claim it as fact.
Yes that’s right I said guesses, ok they maybe educated guesses but still just that.
I’m still to be convinced the we know enough to even make claims about the “Big Bang”
Once upon a time nothing existed exepect alot of gas then one day the gas exploded and the universe came in to existance. Sounds like a line from a Sci Fi show.
Just crazy!

This article is complete nonsense. This ‘study’ which predicts the end of the universe in 3.7 billion years has no scientific grounding whatsoever. The data clearly indicates that the universe will end in 4.6 billion years (give or take a few million). Any estimation to the contratry is obviously incorrect.

were they paid to come up with these sort of rubbish? trying to win the Ignoble prize? any kid could pick a random number. as long as it’s over 1 million years, who really cares. they could have used 3.68937456 billion years to sound a bit more ‘scientific’

You would think that people would have more to do than try and establish the end of the universe in billions of years. This reminds me the bull sessions we used to have in college about the meaning of life. It’s fruitless and pointless and will net nothing in the grand scheme of things.

Obviously naughty man is responsible for this somehow and therefore governments of the world must make us suffer and introduce a new tax to fix this new ‘problem’ – I mean after all paying governments (and banks, fund managers, accountants, solicitors and all associated rent seekers) piles of cash is going to change the climate of the planet and the unstoppable process of natural climate change isn’t it?………anyone who believes that is either totally deluded and/or knee deep in gouging money for themselves from the scam.

All of these comments demonstrate points that we have covered in science communication… scientific illiteracy, distrust of science, and misunderstanding of scientific process. I don’t think news or popular science articles that dig for controversial material help to improve the public’s understanding of any of these points, but even in articles covering ‘acceptable’ cosmology, you can get comments similar to these. I’ve seen several articles about dark energy (that is, dark energy in cosmological constant form) that have many disgruntled comments from the public, with issues ranging from the aesthetics of a ‘dark’ universe to scientists making ideas up.

But, sometimes, you do come across a shining comment; a comment that you hope that other readers are paying attention to:

On a more serious note, studies of this type do increase our collective knowledge and understanding of our universe and its relationship(s) with other universes (within a multiverse context). The increase in our knowledge, even though the underlying assumption may be flawed due to its arbitraryness, has its own intrinsic value and should not be dismissed lightly.

So until our individual bubbles burst, I’m all for keeping our knowledge (and the universe) expanding.


I’ve spent a lot of time on this blog writing about scientific controversy theory, how it relates to modern Big Bang cosmology in general, and small aspects of the overall cosmic controversy, without going into too much detail about the specific controversy.

Cosmology is a huge subject, and as it’s based on observation, it has the tendency to be controversial (see this post). But with so many observations, so many ideas for and against the Big Bang theory in all its incarnations, it’s too much to cover as one enormous controversy!  As such, I will be focussing on one topic within it; dark energy.

What is dark energy?

It’s a negative energy, a negative pressure, making up 73% of our Universe (by last count) and causing the universe to accelerate. (As opposed to dark matter, which is matter that isn’t baryonic matter like us; dark matter makes up 23% of the Universe and baryonic matter and neutrinos make up the tiny rest.)

Why is it a controversy?

For a few reasons, all of which I will be writing about… on the surface, it’s uncomfortable to have such a large proportion of the Universe ‘dark’. The cosmological constant, which cosmologists use to describe dark energy (which is one aspect of this controversy), was introduced by Einstein as a ‘fudge factor’ in general relativity. However, even Einstein was not a fan of the cosmological constant (Kragh, H. (1996) Cosmology and Controversy. Princeton University Press, Princeton.):

 Since I introduced this term, I had always a bad conscience. . .. I am unable to believe that such an ugly thing should be realised in nature.