During COVID, New Scientist started doing a lot of online events, including courses and ‘talks’ by experts in various fields. I watched one of these talks last week by Claudia De Rahm titled What We Don’t Know About Gravity, which I thought was very good. It was informative and thought-provoking and therefore deserves special mention. Claudia is a young woman, Professor of Physics at Imperial College London, with a distinct Italian accent. She gestures a lot while she’s talking and exudes passion. Sometimes her face appeared childlike, especially at the end when she conveyed her appreciation to the presenter, Martin Davies. She’s won a number of awards and she’s done research in particle physics, gravity and cosmology.
One of the first things she told us is that Einstein’s GR (general theory of relativity) comes with its own ‘proof’ of its limitations. She didn’t use the word proof, but she demonstrated what she meant. If one tries to apply QM to Einstein’s mathematical theory you get probabilities of over 100%. I never knew this, but I found it a remarkable revelation. From what I could gather, it happens near the Planck scale where the curvature of spacetime becomes so large the physics breaks down. She pointed out that this doesn’t occur near the event horizon of a black hole, so for everything we can observe, GR is perfectly valid. But I was astounded to learn that GR predicts its own failure at certain scales of the Universe.
She also questioned whether GR breaks down at the other extreme of scale, given that there is disagreement on how fast the Universe is expanding to a significant degree (in her own words, ‘the chance of it being a fluke is 1 part in 14,000’). Of course, she also explained how 95% of the Universe is ‘missing’, meaning it can’t be accounted for. Personally, I think we’re ripe for another scientific revolution comparable to the one that occurred 100 years ago, which in turn was comparable to the one created by Copernicus, Galileo, Kepler and Newton.
This highlights a point I’ve raised before: the significance of scale in determining which ‘natural laws’ dominate, though they all seem to obey a Lagrangian (based on my limited knowledge of physics). Roger Penrose argues that scale is dependent on mass. If the Universe was all radiation then scale becomes irrelevant. This is essential for his CCC (Conformal Cyclic Cosmology) model of the Universe to work. Penrose also argues that there is no time without mass, because time is always zero for a photon. This creates a paradox, because the photon has an energy dependent on its frequency, which has no meaning without time. I’ve no doubt Penrose can resolve that, but I don’t know how. Perhaps gravity resolves that conundrum. But, as the Universe exists in its current epoch within our range of observations, scale plays a significant, even critical role in determining which mathematical formulations we use to model it.
Claudia tip-toed around the argument about whether gravity is a force or not, but gave me the impression she believes it isn’t. She did point out that a gravitational wave effectively creates a force and there are tidal forces, but this is not what people mean when they argue that there is a ‘force of gravity’ in the Newtonian sense. In answer to a question at the end, she pointed out that “gravity is related to the very structure of spacetime; you can never switch it off”.
On the subject of GR’s inherent limitations around a singularity inside a black hole, she seemed optimistic that new physics would overcome this eventually. Along with the questions around dark energy and dark matter, that comprise 70% and 25% of the Universe respectively, I think that only a revolution in physics and cosmology will rescue it. Towards the end of the talk, she put up a slide showing all the current theories in the running, without discussing any of them or mentioning any personal favourites she might have. She literally covered the screen with balloons of speculative ideas, demonstrating the burgeoning interest in this field.
And this segues into something else she said in answer to a question, where someone asked if all the current theories should be ‘thrown in the rubbish bin’ and replaced with something completely different. She pointed out that the current theories work extremely well, and whatever you replace them with has to, at the very least, account for what we already ‘know’, and you can’t just ‘throw them in the rubbish bin’. This touches on the subject of my last post where people sometimes argue that we really don’t ‘know’ anything and we only have 'beliefs'. In science, all theories have limitations. Truth is cumulative in science; just because we don’t know everything, it doesn’t mean that what we do know is wrong and should be thrown out. Personally, I don’t think there will ever be a TOE (theory of everything) simply because there’s never been one in the past, and people have always ‘believed’ that we know almost everything, which history has proved, repeatedly, is untrue.
And this brings me to the subject of pet theories or pet prejudices. If Claudia has her own pet theories she didn’t elaborate, yet I’m sure she has. People much smarter than me have their pet prejudices, some of which differ dramatically, so they can’t all be right, and that also applies to me. But, having said that, I like to think my prejudices are well informed and I acknowledge those who share them, and sometimes those who don’t.
I will quickly talk about one that is relevant and that is time. I contend that consciousness exists in a constant present, while everything we observe has already happened, which is why we ‘feel’ like we’re travelling through time. According to relativity theory, we are travelling through time just by standing still. But when we move, we start travelling through space and, as a consequence, we travel through time more slowly – that is, time slows down. In fact, if we could travel through space at the speed of light, we would stop travelling through time altogether. But here’s the thing: that’s only true in our specific frame of reference. There could be another frame of reference, like the horizon of the observable universe where space itself travels at the speed of light. I discussed this in another post.
This infers that everything travels through time and not just consciousness. However, while our consciousness remains in a constant present, our thoughts don’t. Our thoughts become memories as soon as we think them, otherwise we wouldn’t even know we think. Consciousness exists on the edge of time and so does the universe itself. I’ve no reason to believe that the edge of time we all experience isn’t concordant with the edge of time for the whole Cosmos. This is considered naive thinking, but it’s one of my pet prejudices.
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