At Home in a Changing Universe
Our cover this issue isn’t really a bold proclamation that “dark matter is dead”, because of course it isn’t. It’s just that there is a possibility it might not adequately solve the problems we hoped it would solve – namely that galaxies appear to rotate “too fast” to both contain the number of stars they seem to contain, and not fling those stars outwards like a bunch of drunken uni students getting hurled o a merry-go-round.
Dark matter could help our understanding of the universe, but for an enduring problem. We’re yet to confirm the stu exists, and in any case, we only “need” dark matter if our other ideas about how far away galaxies are, how gravity works, and various other things, aren’t in some way flawed.
And they may be. That’s something you should always keep in mind about this big, big picture stu . The science of the extremely large is still, if not in its infancy, then at best adolescent.
It seems incredible, but humans did not realise there was more than one galaxy in the universe until Edwin Hubble (and others) confirmed their observations in the 1930s.
Why incredible? Because for all of human history (and prehistory), we’ve been able to see the galaxy we call Andromeda with the naked eye. But it was barely a century ago that we understood it isn’t a little smudgy nebula, but rather a vast galaxy, bigger than the Milky Way, 2.5 million light-years away and, as it happens, getting closer.
Why mention this? Because it highlights how much we have left to learn, not just about how the universe works, but what it even looks like.
From the very small to the very large, our understanding is constantly changing. This might seem nonsensical or ridiculous, but it’s one of the strengths of science.
We make observations that give rise to questions. We develop a theory, and test the theory with more observations. New observations challenge the theory, we adjust the theory until it can reliably predict the next set of observations.
Then scientists publish the theory, and other scientists immediately start trying to tear it apart. If the theory holds, it becomes slowly accepted as “true”. Right up until the point new observations contradict or challenge it. Then the process repeats. Is this the most e cient and e ective way to develop a deeply true understanding of what the universe really is and how it works? Probably not. But it has allowed us to unlock far more of our potential than any other system so far.
Right now, one of the most exciting things about fundamental physics is the way that our “standard model” is incredibly good as predicting say, what gauge steel we need to ensure a bridge doesn’t fall down. And it can predict how fast the bridge will fall, based on the gravitational field the bridge finds itself in. Yet the standard model cannot adequately explain what gravity actually IS. It can’t explain why ever other part of our “system” fits together neatly, but gravity is out on its own, weirdly di erent.
A proper theory of gravity that links it to the rest of fundamental physics, is the rocket fuel our science needs to launch us into the next orbit of understanding. Dark matter theory exists because our understanding of gravity doesn’t fit with our observations of how fast distant galaxies rotate.
Fix gravity, and we fix our understanding of the universe. What happens after that? Who knows. But I can’t wait to find out.