This post begins on a personal note. My Mum passed away, suddenly, last week.
Mum got me writing, encouraged me to write – and was an avid reader of what I wrote. Including this blog, where her favourites were my science posts. Mum taught me to wonder about everything – about the way our curiosity fuels our lives, and about the magic of a universe that unfolds for us, so wonderfully, before our thoughts and imagination.
I never did do a post for her on one of the most amazing ideas of modern physics. I was going to.
This post is for my Mum.
There is something magic about dark matter.
There’s apparently a lot of it – far more, in fact, than everyday matter. Nobody’s seen it directly. It exists only as a gap in current theory. And yet it might explain the universe.
Dark Matter is needed because, according to the cosmological discoveries of the twentieth century, the universe isn’t expanding as fast as it should, meaning it has less total mass than needed to fit the observed size and rate of expansion.
Various ideas have been proposed to explain this. One is to suppose that Einstein’s theory of gravity – General Relativity – isn’t right. But it has been proven true every which way. Another is to suppose that there is a lot of missing mass.
Cosmologists reasoned that this mass had to be somewhere – and it wasn’t just a trivial figure, either. It was a lot of mass. Specifically, around 80 percent of the total mass of the universe is either Dark Matter or its equivalent, Dark Energy (mass and energy are the same thing as far as Einstein is concerned).
So – there’s ordinary matter, which we see, feel, touch and taste; and there is Dark Matter – which doesn’t interact with electromagnetic energy (light), so it’s invisible, but which does everything else understood by Special and General Relativity, along with all the work done on particle physics and energy interactions.
Dark Matter has never been seen directly, though last year an X-ray spike was spotted coming from the Andromeda galaxy, and another from the Perseus galaxy cluster. We’ve also seen indirect hints such as a ‘gravitational lensing’ ring around a distant galaxy, spotted by the Hubble telescope. And there is evidence that so-called ‘sterile’ neutrinos are produced by Dark Matter.
Personally I’m not convinced. The idea of Dark Matter – apparently non-existent here but nonetheless the majority component of the universe, so elusive it is even invisible out where it might exist, but still somehow real – plays on our imaginations; it dovetails with the world of faerie and with the human condition. It ties up loose mathematical ends. But to me, however it’s been intellectualised, there seems something somehow odd about matter that is the same in every respect as ordinary matter, except it doesn’t interact with electromagnetic force. Why?
It wouldn’t be the first time science has been led down a logically consistent blind alley. Remember the ‘aether’? This was a late seventeenth century invention, developed and popularised by Robert Boyle and Isaac Newton. The logic was impeccable. It wasn’t possible for light and heat to travel from the Sun to the Earth through space, because vacuum couldn’t of itself transmit the energy. So emerged the idea of ‘luminiferous aether’, an invisible, intangible material in space that allowed energy to be transmitted.
The concept was worked out in every detail. But then in 1887 Albert Michelson and Edward Morley ran a practical experiment to measure the motion of matter through the stationary aether. They failed. Why? Because, it turned out, the aether didn’t exist.
That set in motion a physics whirlwind which led Albert Einstein to come up with his Theory of Special Relativity, which remains one of the foundations of modern physics. The actual answer, it turned out, was that electromagnetic energy doesn’t need a transmission medium, because it transmits itself (wave/particle duality).
I could go on with other examples, including quantum physics. I have doubts about the current Copenhagen Interpretation, which has led to curious outcomes. Einstein – who helped invent it – thought it had problems and the real issue was that they’d missed something. I am inclined to agree.
And that’s the point. A lot of the way we see the universe today flows from the discoveries of the past 150 years. Our understanding isn’t complete. We postulate all sorts of things – everything from a universe made up of vibrating strings, through to ‘spooky action at a distance’, through to Dark Matter, to explain the gaps. All these ideas either jar in various ways with what we observe. Or if they do work smoothly (like string theory) we can’t find any evidence.
If proper proof can be found of Dark Matter – well, hey, that’s fine by me. In any event, I’m sure answers will be found to all our current paradoxes and questions. Although I add that on past precedent, those answers will likely be something very different from what we consider certain today. Including the ‘alternative theories’ which, like it or not, spring up as a response to current thinking and its gaps. Think about it.
Can we call it magic? From today’s perspective, perhaps. And maybe, when we do find the final secrets of the universe – if they ever yield to us, or if we can ever understand them – I suspect they will appear, in any case, as magic.
I’d certainly like to think so.
Copyright © Matthew Wright 2015