By Richard Webb
Albert Einstein’s general theory of relativity “didn’t have to be”
Hello, and welcome to November’s Lost in Space-Time, the monthly physics newsletter that unpicks the fabric of the universe and attempts to stitch it back together in a slightly different way. To receive this free, monthly newsletter in your inbox, sign up here.
Einstein’s forgotten twisted universe
There’s a kind of inevitability about the fact that, if you write a regular newsletter about fundamental physics, you’ll regularly find yourself banging on about Albert Einstein. As much as it comes with the job, I also make no apology for it: he is a towering figure in the history of not just fundamental physics, but science generally.
A point that historians of science sometimes make about his most monumental achievement, the general theory of relativity, is that, pretty much uniquely, it was a theory that didn’t have to be. When you look at the origins of something like Charles Darwin’s theory of evolution by natural selection, for example – not to diminish his magisterial accomplishment in any way – you’ll find that other people had been scratching around similar ideas surrounding the origin and change of species for some time as a response to the burgeoning fossil record, among other discoveries.
Even Einstein’s special relativity, the precursor to general relativity that first introduced the idea of warping space and time, responded to a clear need (first distinctly identified with the advent of James Clerk Maxwell’s laws of electromagnetism in the 1860s) to explain why the speed of light appeared to be an absolute constant.
When Einstein presented general relativity to the world in 1915, there was nothing like that. We had a perfectly good working theory of gravity, the one developed by Isaac Newton more than two centuries earlier. True, there was a tiny problem in that it couldn’t explain some small wobbles in the orbit of Mercury, but they weren’t of the size that demanded we tear up our whole understanding of space, time, matter and the relationship between them. But pretty much everything we know (and don’t know) about the wider universe today stems from general relativity: the expanding big bang universe and the standard model of cosmology, dark matter and energy, black holes, gravitational waves, you name it.
So why am I banging on about this? Principally because, boy, do we need a new idea in cosmology now – and in a weird twist of history, it might just be Einstein who supplies it. I’m talking about an intriguing feature by astrophysicist Paul M. Sutter in the magazine last month . It deals with perhaps general relativity’s greatest (perceived, at least) weakness – the way it doesn’t mesh with other bits of physics, which are all explained by quantum theory these days. The mismatch exercised Einstein a great deal, and he spent much of his later years engaged in a fruitless quest to unify all of physics.
Perhaps his most promising attempt came with a twist – literally – on general relativity that Einstein played about with early on. By developing a mathematical language not just for how space-time bends (which is the basis of how gravity is created within relativity) but for how it twists, he hoped to create a theory that also explained the electromagnetic force. He succeeded in the first bit, creating a description of how massive, charged objects might twist space-time into mini-cyclones around them. But it didn’t create a convincing description of electromagnetism, and Einstein quietly dropped the theory.
Well, the really exciting bit, as Sutter describes, is that this “teleparallel gravity” seems to be back in a big way. Many cosmologists now think it could be a silver bullet to explain away some of the most mysterious features of today’s universe, such as the nature of dark matter and dark energy and the troublesome period of faster-than-light inflation right at the moment of the big bang that is invoked to explain features of today’s universe, such as its extraordinary smoothness. Not only that, but there could be a way to test the theory soon. I’d recommend reading the feature to get all the details, but in the meantime, it’s about as exciting a development as you’ll get in cosmology these days.
Is the universe fine-tuned?
Let’s take just a quick dip into the physics arXiv preprint server, where the latest research is put up. One paper that caught my eye recently has the inviting title “Life, the universe and the hidden meaning of everything” . It’s by Zhi-Wei Wang at the College of Physics in China and Samuel L. Braunstein at the University of York in the UK, and it deals with a question that’s been bugging a lot of physicists and cosmologists ever since we started making detailed measurements of the universe and developing cogent theories to explain what we see: why does everything in the universe (the strengths of the various forces, the masses of fundamental particles, etc.) seem so perfectly tuned to allow the existence of observers like us to ask the question?
This has tended to take cosmologists and physicists down one of two avenues. The first says things are how they are because that’s how they’re made. For some, that sails very close to an argument via intelligent design, aka the existence of god. The other avenue tends to be some form of multiverse argument: our universe is as it is because we are here to observe it (we could hardly be here to observe it if it weren’t), but it is one of a random subset of many possible universes that happen to be conducive to intelligent life arising.
This paper examines more closely a hypothesis from British physicist Dennis Sciama (doctoral supervisor to the stars: among his students in the 1960s and 1970s were Stephen Hawking, quantum computing pioneer David Deutsch and the UK’s astronomer royal, Martin Rees ) that if ours were a random universe, there would be a statistical pattern in its fundamental parameters that would give us evidence of that. In this paper, the researchers argue that the logic is actually reversed. In their words: “Were our universe random, it could give the false impression of being intelligently designed, with the fundamental constants appearing to be fine-tuned to a strong probability for life to emerge and be maintained.”
Full disclosure – I’m writing something on this very subject for New Scientist’s 65th-anniversary issue, due out on 20 November. Read more there!
Closing the quantum loopholes
While I’m banging on about Einstein, I stumbled across one of my favourite features I’ve worked on while at the magazine the other day, and thought it was worth sharing. Called “Reality check: Closing the quantum loopholes”, it’s from 2011, a full 10 years ago, but the idea it deals with stretches back way before that – and is still a very live one.
The basic question is: is quantum theory a true description of reality, or are its various weirdnesses – not least the “entanglement” of quantum objects over vast distances – indications of goings-on in an underlying layer of reality not described by quantum theory (or indeed any other theory to date)? I talked about entanglement quite a bit in last month’s newsletter, so I won’t go into its workings here.
The alternative idea of “hidden variables” explaining the workings of the quantum world goes back to a famous paper published by Einstein and two collaborators, Nathan Rosen and Boris Podolsky, back in 1935. It led Einstein into a long-drawn-out debate about the nature of quantum theory with another of its pioneers, Niels Bohr, that continued decorously right until Einstein’s death in 1955. It wasn’t until the 1980s that we began to have the theoretical and experimental capabilities to actually pit the two pictures against one another.
The observatories atop the volcano Teide on Tenerife were one scene of a bold test of quantum reality.
Phil Crean A/ Alamy
I love the story not just for this rich history, but also for the way that, after each iteration of the experiments – every time showing that quantum theory, and entanglement, are the “right” explanation for what is going on, whatever they might mean – the physicists found another loophole in the experiments that might allow Einstein’s hidden variable idea back into the frame again.
That led them to some pretty impressive feats of experimental derring-do to close the loopholes again – the feature opens with a group of modern physicists shooting single photons between observatories on Tenerife and La Palma in the Canary Islands. In an update to the story that we published in 2018 (with the rather explicit title “Einstein was wrong: Why ‘normal’ physics can’t explain reality” ), they even reproduced the result with photons coming at us from galaxies billions of light years away – proving that, if not the whole universe, then a goodly proportion of it follows quantum rules. You can’t win ‘em all, Einstein.
One reason I’ve been thinking particularly frequently about Einstein and his work lately is that I’ve been putting together the latest New Scientist Essential Guide called “Einstein’s Universe”. It’s a survey of his theories of relativity and all those things that came out of it: the big bang universe and the standard model of cosmology, dark matter and energy, gravitational waves, black holes and, of course, the search for that elusive unifying theory of physics. I’ve just putting the finishing touches to the Essential Guide with my left hand as I type this, and I think it’s a fair expectation that you’ll find me banging on about that (and Einstein) a lot more next month.
Also in New Scientist
1. Talking of fine-tuned universes, if you haven’t done so already, you can still catch up with Brian Clegg’s New Scientist Event talk, “The Patterns That Explain the Universe”, from last month, available on demand.
2. If you’re fan of big ideas (I hope that’s why you’re here) and like casting your net a little wider than just physics, then a ticket to our Big Thinkers series of live events gives you access to 10 talks from top researchers from across the board, including Harvard astronomer Avi Loeb on the search for extraterrestrial life and Michelle Simmons and John Martinis on quantum computing.
3. It happened just after my last newsletter, but it would be remiss not to mention the awarding of this year’s Nobel prize to three researchers who played a leading role in advancing our understanding of chaotic systems – notably the climate. You can find out more about what they did here.
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