Astrophysicists keep finding things that “shouldn’t exist”. I think I know why.

[This is a transcript with links to references.]

We’ve seen a lot of headlines in the past years saying there are things in the universe that supposedly shouldn’t exist.  You may have been wondering how many things can astrophysicists possibly find that supposedly shouldn’t exist until concluding that maybe something is wrong with their ideas of what should exist in the first place?

Yes, I’ve been wondering about this, too. And in this episode I want to explain why I think these headlines keep appearing and why I’m pretty sure they’ll continue to keep appearing.

These objects that supposedly shouldn’t exist aren’t all of the same type, so let’s first have a closer look at what we’re talking about.  We have black holes that are too heavy,  galaxies in the early universe that got too large too quickly,  galaxy clusters that are too large after a collision,  structures larger than galaxy clusters which should never have formed.  And then every once in a while there’s a galaxy that’s too dark or small or faint or whatever. But most of the things that shouldn’t exist seem to be issues of being too big. It’s like the universe has its own obesity problem.

The reason for why the headlines say these objects shouldn’t exist is, well, that it’s a catchy headline and yes, of course I’ve done it myself.  But the scientific reason is that astrophysicists had predictions for what they expected to find,  and those predictions didn’t pan out.  So if they have all these many predictions that turned out to be wrong, why aren’t they panicking? Why aren’t there any paradigms shifting, to use Kuhn’s expression?

 The first thing that might spring to your mind is that astrophysics is a peculiar research area because we can’t carry out experiments. We can only observe what has happened. And yes, that puts limits to what we can do. But as a scientific discipline, astrophysics isn’t unique in this regard.  If you’re digging up dinosaur bones it’s a similar story, except possibly that dinosaur bones tend to not go supernova which is a shame really. So yes, this is one of the reasons why astrophysics is much more difficult than say, particle physics where we can make dedicated experiments.

But there is another reason that makes astrophysics more difficult than particle physics. It’s that it deals with very big objects. Stars, black holes, galaxies, galaxy clusters, the entire universe.  And these objects are dramatically more complicated than the small, individual particles we deal with in particle physics.

 You see the protons in your body and the protons in my body are for all we currently know identical, except for their location. I could swap out my protons with yours and it wouldn’t make any difference. But galaxies are not elementary particles.

Yes, galaxies come in different types like spiral galaxies , and elliptical galaxies, and dwarf galaxies, and so on. But no two galaxies are really alike.  They were born at different times in different locations, they have different stars and a different gas content, they came about by different mergers and have undergone different collisions and live in a different neighbourhood. Each galaxy is unique.

In some sense I think, and I hope astrophysicists will forgive me for saying that, the problem with astrophysics is similar to the problem with sociology.  In sociology, study results depends on who asks what and how at which time and whether the study participants already had lunch and what the result of the football game the night before was and so on.  That is to say, if you wanted to understand sociology, you’d need to keep track of a lot of parameters which are currently just not captured in the literature.

You also have this in medicine and biology, when they use “animal models” as they now put it.  But animals aren’t models, they’re living creatures. Whether a mouse is doing well can depend on all kinds of things, how much sunlight they get, how big the cages are,  whether their human caregivers talk to them, whether they see their compatriots dying and god knows what else. If you wanted to make sense of the mouse model data you’d have to keep track of all sorts of things that currently aren’t being kept track of. And that’s why in sociology and biology it’s so difficult to draw conclusions from conflicting studies.

And that returns me to astrophysics.  Because in astrophysics it’s a similar story. In most of the analyses for the things that supposedly don’t exist the issue that it’s not clear what the observations say to begin with. There’s just too much information missing.

 A typical problem in astrophysics is for example that there are hundreds or so  of telescopes  that have scanned this or that part of the sky or this or that era. But every telescope is different.  How much you can see with it,  and how well you can see it depends on the telescope.

The data in and of itself  can’t be interpreted without knowing how it was collected. There is also the issue as we have discussed in an earlier episode  that sometimes the data analysis already contains assumptions about the theoretical model. If you take for example the issue of the galaxies that got big too fast,  you might ask, how do we really know how old they are?

Basically in astrophysics, if you want to compare the predictions with observations, you have a lot of ingredients.  On the one side you have the theory that you want to test. From that you create a model for the situation at hand, say, a galaxy. Then you use a computer simulation and make a prediction. On the other side, you have the observations themselves, the instrumental bias, the data analysis, and then you compare that to the prediction.

And the thing is now that throwing out the underlying theory is the last resort.  Scientists will first look for problems with all of the other ingredients, the observations, the instrumental bias, the data analysis, the model, the computer simulation.   

And this I think is why there is so much discussion in astrophysics that isn’t going anywhere.  Each time someone says this thing shouldn’t exist, someone else says, reasonably enough, actually we can’t tell because we don’t know this, or we haven’t observed that, or our computer simulation is missing that.

That’s a pretty bad situation because it prevents the field from making progress.  It’s very clear that something is wrong because you know, it’s not good if predictions constantly disagree with observations. But I really think astrophysicists need to consolidate their data and maybe get a bit more serious about making predictions.

But since I don’t actually think they’ll listen to what I say, I predict that we’ll see more headlines about things that supposedly shouldn’t exist.