Dear Dark Matter: A Potential Breakup Song
Complicated like it's 2008.
“You took too long…
This is the potential breakup song…
This is the potential makeup song
Please, just admit you're wrong
Which will it be?” – Aly & AJ“You’re impossible to find.” – Secondhand Serenade.
First, like any good drama, I have to give you some background.
Dark Matter – it’s the most mysterious stuff in the universe. We can’t feel it, see it, smell, taste, or hear it. And yet, if our calculations are to be believed, it makes up 85% of the material in the universe. Not just invisible. Impossible to detect by any physical sense: no X-ray, radio wave, or even giant space cup can scoop it. Whatever it is, it passes through our cameras, our bodies, even our planet utterly undetectable.
So how then, do we know that it’s there? Well, we see the heavy effects of its gravity. Dark matter gravitationally pulls on the visible objects of the universe. Just as the gravitational pull of the sun keeps earth bending around its planetary orbit, the gravitational pull of dark matter keeps stars bending on their galactic ones. It pulls on hydrogen atoms between galaxies, heating them up, and it pulls on the galaxies themselves. We even see it move entire galaxy clusters. Its fingerprints are everywhere. And yet, we know not what it is.
Nor do we have good leads on what it can be. Sure we have hypotheses. There have been some very good ideas, ranging from tiny black holes to abundant rogue planets to exotic matter that might, in just the right situation, cause some extra nuclear decay. Some have suggested dark matter is “hot” - made of relativistic particles like neutrinos. And others, the predominant paradigm for now, that it’s “cold” - made of slower moving but weirder particles like “wimps” or “axions.” But each experiment we’ve designed to test these hypotheses has come up empty. Every time we look, we find, well, nothing to see.
It’s gotten frustrating. Thus, it has grown more popular over the last several years to again argue that dark matter doesn’t exist. A great misunderstanding. It isn’t extra matter in the universe pulling on the stars, it’s that we don’t actually understand gravity. Modify gravity, the thinking goes, and the problems go away.
Which of course, is a nice thought, except it also turns out to be problematic. How do you change gravity without everything we know falling down, or at least apart? How do you explain those sticky instances like the bullet cluster or those weird “ultra-diffuse” galaxies? It’s a tricky problem. Dark gravity, they should call it. Gravity that we can’t see, that we can’t capture in our equations, no matter what we try.
But it’s a seductive idea, and many an astronomer in 2024 is moving in with the cool dark gravity crowd. That’s the way of things when our evidence is superficial at best. Which way you go might tend toward the trends. Like some high school hallway drama - who’s in, and who’s out? I mean dark matter is popular, but so last year. It might come back later, but the cool kids are over it.
So today, I thought I’d share a rough draft of a silly idea I had. An over-the-top letter from the broken heart of a dark matter astronomer:
Dear Dark Matter,
You don’t make any sense! You know I’ve been looking for you and thinking about you for all these long years. Won’t you let me see you, know you, just a little better. Even just one glance, one short peak would be enough. Or not enough. I want to know your ways, what moves you, what stresses you, what keeps you so dark, what would make you shine. Why won’t you show me? I’ve given my life to you - pursuing you - isn’t that enough? I’m your biggest fan!
You puzzle me, Dark Matter. I see the effect you have. The way you pull on the soaring stars and make them orbit faster, faster, faster than they should. Like my beating heart. It’s amazing: you keep them from flying apart; you hold us together. I wouldn’t exist without you. No one would. Dark Matter, we need you.
I see the way you shape galaxy clusters, those giant galactic cities, pulling galaxies into otherwise impossible orbits, and pulling that intergalactic hydrogen into your warm embrace. I see you heating it, stirring it into a 10 million degree frenzy impossibly hot but for your irresistible pull.
Oh Dark Matter. You bend everything to your wishes: not just stars, galaxies, us, but even light bends at your touch. Like a great cosmic lens you magnify and focus the light of the most distant galaxies into magnificent arcs and rings, an artistic masterpiece smiling down on us from on high. You make Mr. Einstein proud, Dark Matter.
But who are you? What are you? You’re elusive. So shifty. I’ll say it again, you puzzle me, Dark Matter. You know I’ve tried to catch you, of course. I thought I had you figured out. I thought you might just be the faint stuff we were missing with our telescopes. Small rocky bodies, rogue planets, miniature black holes, dwarf stars – the outcasts we too easily dismissed. But I looked and looked and didn’t find you. I was wrong, Dark Matter. Then I thought you must be something else, something entirely new. Which you probably are. That seems the most likely thing. But everything I can imagine doesn’t seem to work. I built mines for you in the center of the planet where only you could penetrate, filled them with Xenon which I thought only you could touch. But no, nothing, all these long years. Not even a sign.
I’m starting to wonder, Dark Matter, are you really there? Could it be that all this time what I thought was you was really just an act - a screen - gravity teasing me? Gravity acting different on large scales. Dancing differently in an arena I couldn’t grasp or understand? Could it be that you really weren’t there? Really just gravity: disguised and misunderstood?
Dark gravity. It’s nice I guess. We’ve been hanging out a little bit. Perhaps I’ll give it a whirl. Because I can only take so much! Dark Matter: it’s like Katy Perry says:
you're hot then you're cold You're yes then you're no You're in then you're out You're up then you're down
But … oh Dark Matter … why do you hide?!