It may surprise you to know that the disparate, motley, collection of individuals that make up the professional astronomical community are as subject to the swings and roundabouts of fashion as anyone else, but nevertheless it’s true. Fashions can change the way we think about our research (can that pet project be pitched as vital for cosmology, or as contributing to ‘astrobiology’?), and infect the language that we use to talk about ideas.
There comes a time, however, when it is necessary to draw a line in the sand and defend it against all who dare to try to cross. In this spirit, I’m declaring war on all those – scientists, press officers and journalists – who use the word ‘dark’ to describe a new discovery.
First, we had ‘dark matter’. Astronomers discovered that pretty much wherever they looked, from galaxies to galaxy clusters, the stuff we can see can’t possibly be all there is. In order to hold objects together, we need stuff which has gravity – and thus can help keep galaxies in one piece – but doesn’t shine. In other words, we need matter which is dark, and we can chatter happily about ‘dark matter’ without raising my blood pressure.
Second, along came ‘dark energy’. Observations of distant supernovae revealed that the expansion of the Universe is accelerating, not slowing down under the influence of gravity as it should do. While the cause remains unknown, most researchers believe we are seeing the effects of a fifth fundamental force (to add to the traditional four : the strong and weak nuclear forces, electromagnetism and gravity). Such a force must be associated with energy, so I’ll concede the second word. But why, oh why, oh why (etc) do we have to call it ‘dark’ energy? Is gravity ‘dark’? What would it mean to have a light or dark weak nuclear force? It’s arrant nonsense, it’s confusing (as it encourages lumping in with dark matter, almost certainly a completely separate problem) and it makes my blood boil.
Nonetheless, probably because I didn’t have a blog at the time, ‘dark energy’ has become a standard term. This should strengthen our arms for the fight ahead, though, because looming into view is the monstrosity that is the ‘dark flow’. The result is interesting, although I haven’t had time to read the papers and am still somewhat sceptical. Taken at face value, a new analysis seems to suggest that hundreds of galaxy clusters are being carried along at roughly 2 million miles an hour, pulled by matter beyond our observable Universe.
As I said, interesting enough. But the press release and the papers, although mercifully not the titles of the papers, call this a ‘dark flow’. What does that even mean? How would a ‘light flow’ appear? Surely here we can all agree that using the word ‘dark’ doesn’t help us understand what’s going on – it’s just confusing.
Something must be done. I’m not sure what, so let’s just call it the dark campaign for now. Whatever it is, it starts here.
Aleks on September 29, 2008
I can live with a dark world, as long as all the dark things are really in the dark, metaphorically speaking, meaning that we don’t know how they are. But what happens when we shine light (again metaphorically) on dark matter and dark energy? Do we still call them dark? I would expect that we switch to more useful names, as soon as we find out what dark matter and dark energy actually are. Until then, I’m fine with any name, although question marks instead of words would probably be the honest solution. Just doesn’t give good headlines: New evidence for the existence of ??? in the Universe! Seriously, who wants to read that?
Alice on September 29, 2008
We could start comparing it to Harry Potter. “This force must be in league with Voldemort. He probably wants to turn that energy into a Horcrux”. “Oh dear, there are Dementors in that galaxy!” “Who’s the Defence Against the Dark Arts professor this year? Is that job still jinxed?” Press releases at least might at least try to avoid it in order to sound more serious.
No slur on Harry Potter intended; I love those books!
Aristarchus on September 29, 2008
I went outside last night and there was a lot of dark dark about.
Nick Cross on October 1, 2008
I don’t like the term dark energy, but nor do I like the other terms people use for it either: cosmological constant – not sure yet if it is a constant term yet or vacuum energy, which it might be, but the theoretical values and the observed values differ by so much that I don’t think it is useful to describe it as that at the present time.
Nereid on October 1, 2008
I am looking forward to your comments on the ‘dark flow’ paper, particularly on the extent to which you think Kashlinsky et al. have not only unambiguously detected the kinetic SZE but also extracted a clean signal from the relevant data using it …
Stephen on October 16, 2008
Dark Energy. Dark Matter. Not as bad names as “Brown Dwarf”, “Planetary Nebula”, “LGM 1″.
There aren’t any black dwarf stars yet. Should they be renamed “dark dwarf stars”?
I think i’ll go out and discover an asteroid. I’ll name it after Pamela. She has publicly stated she doesn’t want one using her last name. Where’s the fun in that? If i’m lucky, it’ll turn out to be a contact binary.
AndrewG on October 22, 2008
Dark matter I can kind of get. Maybe it is dark in the sense that it gives off no radiation. Dark energy though???? Shouldn’t it be anti-gravity, if it does what we think it does?
Colin Slater on October 15, 2009
There is no such thing as dark energy – it is all leverage. If you accept that at some point when a black hole forms and becomes a singularity the laws of space and time become meaningless then if you have a supermassive black hole one side of the universe and over the other side you have another then at some point in the collapse on each one the laws will break down. This means the conditions become identical and with space and time out of the picture the two points snap together. Therefore you can have any number of black holes but one and only one singularity.
From the above everything else falls in to place. Dark energy is replaced by leverage – the side of the supermassive black hole, immediately above the singularity point, closest to the next one will collapse (and be compressed) through the point fractionally earlier than the opposite side (which will be stretched). Thus the black holes will move away from each other taking their galaxies with them. The driving force being the matter falling in to the (one and only singularity). If you accept the single singularity then it must lie at the centre of the universe. As the supermassive black holes snap to the singularity then the matter pouring in has to pass through all that lies between although because space is no longer meaningful there is no distance at all. Therefore the singularity occupies a point at the centre of the universe at the same time as occupying all points between. Spread the mass of the singularity across the universe and you have a week force somewhat like gravity. There is more but I don’t know how much this post will take before it collapses into a black hole of its own!
Bjorn Saw on December 21, 2009
Dear Colin,
Sounds good! I do not have the academic background to understand exactly what you mean but it resonates with my own understanding. Singularity especially. Are you speaking about what propels the universe’s expansion, and/or of the force that will make dark energy obsolete?
I enjoy the theory of the singularity that is located in all and every point in space, and as such being the “place” in which a black hole collapses, and at the same time being that place of origin where from the Big Bang emerged 13.7 billion years ago. Together with the understanding of the ever continuous emergence of spacetime from that very source, as layers upon layers in breathtaking velocity. Light being the expression and the creation and the vehicle of spacetime, that propels the expansion of the universe.