Editor's pick: Out with obscure dark energy
As a humble, long retired physics teacher, I am delighted to read of qualified opposition to the notion of dark energy (18 June, p 28). Dark matter is indigestible enough, but it at least has the merit of a potentially discoverable particle to explain its existence. Dark energy, depending as it does on the overall uniformity of the universe, seems like a step too far in light of discoveries of enormous over-dense chunks of galaxies interspersed by under-dense voids.
And may I congratulate the artist responsible for the picture that so brilliantly foreshadows the possible dissolution of dark energy in the development of ideas of curved space?
Editor's pick: Out with obscure dark energy
As a non-physicist, even I could understand this article about the possible banishment of dark energy. I would suggest, though, a better analogy for the “heretics” undermining the “dark side” than comparing them to Copernicus. How about the collapse of the hypothesis that a Planet Vulcan between Mercury and the sun could explain the planet's non-Newtonian orbit? While Copernicus debunked religious dogma with observation and science, Einstein's theory of general relativity explained the orbit and turned good Newtonian science into great science.
Anticipating crimes of the future
Your cartoon of the truncheon-holding bobby peering into the crystal ball presents a funny side of crime anticipation (Feedback, 4 June). But the purpose behind the at University College London is to address the crime and security implications of rapidly emerging technologies and social changes, and to develop pre-emptive measures to address them. Its research will span social, physical, computer and engineering sciences, driven by commitment to real-world impact and scientific rigour.
Society has an unfortunate history of new technologies being followed by “crime harvests” – think of mobile phones, the internet, 3D printers and drones. Getting ahead of criminals is a much-needed strategic extension to the arm of the law.
First class post
Outreach is at the heart of science. Without effective outreach, what we do has no real meaning
David Brockley, amid outrage, (2 July, p 5)
Cannibalism may not be the answer
Archaeologists should consider alternative explanations to their standard interpretation that “cut marks and polishing on bones are hallmarks of cannibalism” (14 May, p 36). As recently as the last century, washing ancestors' bones was normal practice in Okinawa, Japan, so that many generations of remains could be brought together in one tomb.
The dead were interred with appropriate ceremony. One to three years later, to make space for another corpse, remains of flesh were removed from the bones using chopsticks, or, if decomposition wasn't complete, a sickle. When picked clean of all flesh, the bones were washed in water and saki and then placed in an urn. Prayers of apology were offered to the deceased for having disturbed their bones.
A universal meta-simulation game
Geraint Lewis comments on Elon Musk's suggestion that our universe is actually a simulation taking place inside a computer (11 June, p 18). He points out that the laws of physics operating in our universe would be whatever laws the coders decided to bake into their simulation.
However, the computer that runs the simulation must also exist in a universe – a “meta-universe” with its own physical laws, to which its objects and inhabitants are bound. These meta-laws determine the laws the coders can “choose” for us. Of course, the meta-universe could itself be a simulation embedded in a meta-meta-universe. The laws of physics there would trickle down to determine the laws in the two universes beneath.
What if the sequence of meta-universes and simulations continues for a vast number of iterations? Would the laws get more real as we approach the top? If the sequence were infinite, there would be no privileged level at which the laws could be considered more real than at any other level. In this case, the laws we experience around us would be as good as any, and we might as well just get on with them.
Since our attempts to create simulated universes are still extremely primitive, we would be at, or close to, the bottom of any chain that may exist.
A universal meta-simulation game
The theory that our universe may be a simulation was discussed by Nick Bostrom and reported in 快猫短视频 (27 July 2002, p 48).
Not the largest wooden structure
Feedback mentions a at the Creation Museum in Kentucky, which claims it is the “largest timber frame structure in the world” (4 June). Hangar 2 at US Marine Corps Air Station Tustin, in California, has four times the area and eight times the volume, being 327 metres long, 89 m wide and 52 m tall. It is all wood apart from the concrete frames for the sliding wooden doors at each end – these frames don't support the main structure. It was to shelter blimps.
I've seen things you wouldn't believe
You mention that an artificial intelligence has “reinterpreted” parts of the 1982 film Blade Runner (11 June, p 24). Was this the original cinema release with the Harrison Ford voice-over – a thoughtful and thought-provoking discourse on what it means to be human and therefore of some interest to an artificial intelligence? Or was it one of the multitude of “director's cuts” that reduce it to a mindless dystopian shoot-em-up? We wouldn't want to give the AI any wrong ideas.
The trouble with tiny demons
Stephen Battersby uses Maxwell's demon to discuss the physical nature of information (14 May, p 28). But how can the demon “see the motions of air molecules” or operate “a frictionless door” or “slide a partition” without some physical interaction?
Surely, any useful modern analysis has to include the demon's use of photons or the like (which are subject to Heisenberg's Uncertainty Principle) to measure molecules' momentum vectors in order to determine whether they should pass into a hotter location. Similarly, some account is needed of the physical interaction involved in operating the door or inserting a partition.
Battersby mentions Leo Szilard's approach to the thought experiment. Though Szilard estimates the molecule's work of pushing a partition, he appears to me to ignore the physics both of the initial insertion of the partition and of the demon measuring which end the molecule is in.
The trouble with tiny demons
The description of Leo Szilard's 1929 thought experiment really doesn't work. If we have a box with only one molecule in it, and we introduce a movable partition, the molecule has to be on one side or the other. A demon might know which side, but in its absence the partition would still move, though we couldn't predict which way.
Exactly the same amount of work would be done and the molecule would lose just as much energy, thereby getting cooler.
This is classical thermodynamics, since with a molecule on one side and a vacuum on the other we have a pressure difference – or we have used the random position of the molecule to create one where there was none before.
Sydney, New South Wales, Australia
The editor writes:
• To extract work from the molecule, you need to apply some resistance for it to work against, and to do that you need to know which way it will be pushing, and therefore which side of the partition it starts. You could provide bi-directional resistance by making the partition slide against friction, but that's no good, as with friction the motion just gets dissipated as heat. Instead, you need to provide resistance that does something useful, such as winding up a weight against gravity.
The significance of the polygenic score
You report that New Zealanders whose genetic profiles have higher “polygenic scores” have more prestigious occupations, higher incomes and more assets, and being more likeable and friendly (11 June, p 10). But the coefficients of correlation for these traits ranged from 0.10 to 0.13, except that for exams at age 15, which was 0.24. The squares of these numbers tells what fraction of the variance is “explained” by the factor. So between 1 per cent and 2 per cent of the variation is due to these genes, except for the exam results, where it was 6 per cent. So let's not get the wrong idea about the significance of these genetic contributions.
Les Essarts-le-Roi, France
The editor writes:
• The correlations may be small, but they are there, and a tiny percentage across a huge population could potentially have a big impact. It is fascinating that there is a genetic influence on “success” at all.
Pinhead focus presumption flaw
I fear there is a flaw in Brian Pollard's critique of my comment about the inability of a pinhead to cover the sun, as viewed by a wide open pupil at the Oort Cloud (Letters, 11 June). He assumes that the eye's lens can simultaneously focus the distant sun and near pinhead on the retina.
My point is that the wide aperture in that dim light would make this impossible.
Make a human genome at home
You report concern over a meeting to discuss plans to synthesise a complete human genome, from which journalists were excluded (21 May, p 6).
My partner and I have made two novel genomes. We, like the scientists in your article, did not invite any journalists.