It is fast becoming a testable prediction: the birth rate in a given country should start to rise about two generations after the contraceptive pill becomes widely available there. We are seeing this. Four years ago, Mikko MyrskylÄ and colleagues noted a "puzzling" uptick in some Western countries' birth rates, but speculated that it was due to prosperity passing some critical threshold (Nature, vol 460, p 741).
Believing that educated choice will prevail is like hoping the obesity epidemic can be solved if those who diet successfully are selectively removed from the population every generation.
Causality with care
Reality apparently consists of a small number of basic ingredients, which obey simple relationships with immensely complex consequences. Any given situation gives rise in principle to a simultaneous solution of the relevant relationships. So it is true to say that those ingredients and those relationships are a complete causal explanation of each and every individual solution?– the "reductionist", bottom-up claim.
On the other hand, when the basic ingredients are in a specific context?– when they are arranged in particular structures subject to particular constraints?– the space of possible solutions has certain features and relationships which can properly be described as caused by the nature of the structures and constraints in question. This is consistent with Ellis's persuasive top-down claim.
You report ideas for laser-propelled interstellar craft (24 August, p 8). Almost 10 years ago you reported on a similar idea of spacecraft powered by beams of plasma (newscientist.com/article/dn6543). At the time, I noted that, apart from the issue of maintaining a narrow beam, there were two other problems.
First, all the research was done using ground-mounted lasers, but how would you keep an orbiting projector's extremely narrow beam accurately aligned on a tiny dot a few billion kilometres away for years?
Secondly, this idea was all about getting the spacecraft there much faster than with a conventional rocket. But on arrival, how would it slow down to enter orbit?
The editor writes:
• The proposal is to "phase-lock" the lasers to keep the beam tight?– though no one has yet managed this on a large scale. And yes, you would need a laser at the other end to slow the craft down?– which will make the first trip interesting.
Sign and code
As anyone who has learned sign language or taken a Deaf Awareness course will know, even the best lip-readers can only pick up at most 40 per cent of what is said from lip-reading alone.
To investigate this for yourself, ask your partner to lip-read while you mouth the words "elephant juice". It might just make their day!
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