Going down a black (rabbit) hole (1)
In his article “What’s inside a black hole?”, Stuart Clark is troubled at the thought of conceding that “the universe is not entirely ruled by physics”(4 October, p 28).
As a physicist, I am content to think that the universe is always ruled by physics, and in fact that is a tautologous statement. But I am happy 鈥� in fact quite excited 鈥� by the thought that we don’t yet know some of that physics. How desperately sad it would be if the only thing left to do was to apply our existing theories to yet more systems.
The universe doesn’t need our theories or our permission to do what it does. I sometimes wonder whether some of my colleagues haven’t themselves gone down a black rabbit hole in their failure to accept that.
Going down a black (rabbit) hole (2)
Stuart Clark doesn’t mention Carlo Rovelli’s idea that singularities can exist only in the future. In his book White Holes, he says that because time slows down in a strong gravitational field, a point of infinite density with infinitely strong gravity would take an infinite amount of time to form.
So, from our point of view outside the black hole, what we are seeing is a potential singularity, but the collapse to a single point will take forever, and perhaps the physics won’t break down within the lifetime of the universe. This makes a lot of sense to me 鈥� what am I missing?
Going down a black (rabbit) hole (3)
Are gravastars, electroweak stars, boson stars and fuzzballs really needed to do away with singularities?
From our perspective, standing beyond the black hole, gravitational time dilation means that anything that falls into it slows down as it approaches the event horizon and takes an infinite amount of time to actually reach it. So, from the exterior point of view, the material falling into a black hole never crosses the event horizon.
Meanwhile, black holes are believed to emit Hawking radiation and “evaporate” over a very long, but nonetheless finite, time. If matter takes infinite time to enter, but finite time to leave a black hole, then the singularity never forms.
Going down a black (rabbit) hole (4)
I always understood that time grinds to a halt at a black hole’s event horizon. If so, it is surely nonsensical to ask what is inside a black hole, and by implication, whether at this moment it contains a singularity.
So if I were to fly my spaceship across the event horizon of a black hole, I’d see the entire future of the universe play out in my wing mirrors before (if ever) hitting a singularity!
Why AI is right only some of the time (1)
I was interested to read your article about the inaccuracies of AI search tools, headlined: “AI doesn’t have all the answers”. This could be contested 鈥� by the comedian Eric Morecambe, for example, who would probably argue: “No, it’s giving the right answers. But not necessarily to the corresponding questions(27 September, p 17).”
Why AI is right only some of the time (2)
My experience with large language models (LLMs) is that questions about technical systems, such as Windows 11, produce fairly good answers because the information comes from professionally produced documentation. Everything else is a mixed bag. The reason why is evident and not easily fixable. If LLMs are trained on unfiltered data from the web, then they must necessarily be unreliable due to the well-known dictum, rubbish in produces rubbish out.
What value should we place on a human life?
Your article on covid-19 vaccines’ economic benefits lays out the stark disparity between the value that governments and businesses put on human lives (the lower estimated benefit of $5 trillion), and the value that individuals do ($38 trillion). No wonder so many of us feel that “society” doesn’t value or care about us: these figures highlight just how much it doesn’t(20 September, p 8).
On the carbon-capture-and-storage debate
Paul Broady suggests plans to capture carbon from the air are a distraction, and we should focus on deep cuts in emissions. He is half right. We do urgently need to make deep and permanent emissions cuts and to keep cutting until we get as close to zero as we can. But this won’t be enough(Letters, 11 October).
We are already 1.5掳C (2.7掳F) above pre-industrial temperatures. The latest science shows that we need to get this down to 1掳C (1.8掳F), and the only way to do this is to remove carbon dioxide from the air. The limitations of current carbon-capture systems aren’t reasons to ignore this option. In fact, we should see these limitations as reasons to invest more in carbon capture R&D.
Fermentation is not just a matter of taste
As a lover of “mouldy” cheeses, I very much enjoyed Graham Lawton’s article on fermented foods, though I would have to dispute that all blue cheeses taste the same 鈥� perhaps we can lure him out to Australia to sample some of our offerings(4 October, p 32).
But you list fish sauce 鈥� nam pla in Thai 鈥� as a fermented food. It may be, but no microorganisms are involved: it is just a product of autolysis, natural enzymes in the salted fish breaking down complex proteins. It’s just like your Marmite or our Vegemite. So there isn’t really any potential for refinement.
Serious science or just navel gazing?
Your article “Uncovering the ins and outs of belly buttons” must be wrong about the historical lack of study into the umbilicus: haven’t millions of people been accused of contemplating their navel(11 October, p 16)?
For the record
The artefacts associated with newly discovered rock art in Saudi Arabia indicate links with Pre-Pottery Neolithic people in the Levant (11 October, p 16).