It's just a chip off the old block universe
Your look at the development of a strange idea from the 1980s, that time may be a quantum illusion, took me back to Karl Popper’s essays on the ancient Greek Pre-Socratic philosophers, in particular Parmenides and his block universe, in which he said past, present and future co-exist (8 June, p 10).
To me, Parmenides’s idea was a thought experiment where he stepped out of the world, looked back and, as with the contemporary version, was also “a truly external observer” and “would see a completely static, unchanging universe”, though he couldn’t have known it thus in our modern terms.
I think the strange and wondrous idea you reported on, and the experiments to test it, would have pleased such great thinkers.
Simulated cosmos could explain rather a lot
Bernd-Juergen Fischer rightly points out that a simulation of the universe would only need to take account of the inner world of the subjective “I” and whomever and whatever they interact with (Letters, 1 June).
Taking that concept further, most of the universe would need only be stored as a vague set of probabilities, which would only have to be set in stone as subjective reality when the “I” observes something. Wait a minute, that sounds familiar!
More benefits from using wood in your home
Graham Lawton writes that wooden buildings don’t give off heat like brick buildings after soaking in warmth all day (8 June, p 24).
But I have seen an effect. In winter, I put the heating on after the house has dropped to around 12 掳 C (54 掳 F). The room temperature stagnates at 16 掳 C (61 掳 F) for about 2 hours. After several winters, I have worked out that the furniture is soaking up the heat: the oak table and sofa warm up by up to 6 掳 C (11 掳 F) in those hours. They feel warm to the touch. Once this has happened, the room rises to my set 18 掳 C (64 掳 F). The next morning, those items feel cold, but the room is still at 16 掳 C 鈥� they give off heat at night. Saves me a fortune!
Direct air capture is a dead duck for climate change
Your recent analysis of the potential wider use of direct air capture to remove carbon dioxide from the air is right to be circumspect about its prospects. This would be the most expensive, inefficient and convoluted way to avoid climate change (25 May, p 12).
How time dilation could affect the quantum realm
When it comes to the idea of retrocausality in the quantum realm, how does time dilation affect entanglement? If you sent one of a particle pair much faster than the other and then measured one of them, would this affect the other particle immediately, whose time goes at a relatively different pace? If so, it would seem to be another way of affecting the past (1 June, p 32).
Extra potassium in the diet isn't for everyone
I started using low-sodium “heart” salt about four months ago, having read about its effect on reducing blood pressure. I am in my 70s and I have regular blood tests. After a test five weeks ago, my doctor was concerned about high potassium levels in my blood, so I told him what I had been doing (8 June, p 32).
I take amlodipine/valsartan to control my blood pressure, which apparently helps the body store potassium. If you are also consuming potassium chloride in salt, this can lift potassium to dangerous levels. I stopped using the “heart” salt immediately and my potassium levels have returned to normal.
Thinking without words is indeed possible
David Werdegar says language is necessary for thought. Long ago in this magazine, a reader posed the question: “Do you think in language?” The consensus was: “No, I think in thoughts.” Never mind hominids, chimps have thoughts such as those we would word as “If I crush these leaves into a sponge, I will be able to use it to collect water from that hollow.” That is language-free thought (Letters, 15 June).
It's hard to say what has consciousness
Your review of Christof Koch’s new book on consciousness says he believes that AI has little or no causal power 鈥� only the imitation of it. I would say it is incumbent upon somebody claiming that what appears to be causal power is actually only an imitation of it to have to prove or cite some distinctive rule as to what is an “imitation” and what is “real” (8 June, p 28).
What makes our causal power “real” and something that appears to be the same kind of power an “imitation”? This seems like a way to avoid defining consciousness. Does it mean a person who is “locked-in” has no consciousness? After all, they have no causal power. Consciousness clearly can’t depend on “causal power”.
And a vote in favour of Dyson spheres
Jim McHardy suggests that advanced civilisations won’t need Dyson-style, whole-star, solar energy-collection structures because they will have minimised their energy consumption (Letters, 8 June).
But as far as we know, creating or accelerating matter requires a non-negotiable amount of energy (given by E=mc2 and E=陆mv2, where m is mass, c is the speed of light and v is velocity), as does exchanging detectable non-random information.
If aliens want to create exotic materials, send themselves or their machines between stars or just communicate with the neighbours over interstellar distances, they will need all the energy they can harvest.