Whatever caused sonic boom, it was not an alien
Your rather sensationalist headline of December 11 ("RAF or ET? 'Sonic Boom is a mystery'") must be challenged. Whatever this phenomenon was due to, it was not ET or alien craft.
To understand why I say this so categorically, we need some understanding of the distances involved, the probability of life-friendly environments and, above all, the absolute barrier of the speed of light.
Light and radio waves are part of the spectrum of electro-magnetic radiation (EMR), and experiment after experiment have confirmed beyond all reasonable doubt Einstein's conclusions that (i) EMR always travels at or very close to a fixed speed of light, which is about 300,000km per second, and (ii), this is the maximum speed of anything in the universe which can convey information.
Having understood this, we can start to address the question could we establish evidence for the existence of extra-terrestrial intelligence (ET) either by receiving their radio signals or by making some sort of contact with them?
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It would help to have some idea how far away they are likely to live, and, from now on, I will express all distances in light units. A light year is the distance travelled by EMR in a year.
In our own system of planets in orbit around the Sun, distances are light minutes or light hours.
A hundred years ago, it was thought conceivable intelligent beings could have built canals on Mars, but our present knowledge tells us that it is as good as certain that extra-terrestrial intelligence is not that local.
So what about the rest of the observable universe, in which there are hundreds of billions of galaxies?
Until about 20 years ago, we had no firm evidence any of these stars had orbiting planets but, from the distribution of the 1,000-plus so far discovered, it looks as if most stars have planets.
Given all that vastness, it is inconceivable Homo sapiens is the only intelligent species anywhere.
We are looking and listening, under the project name Search for Extraterrestrial Intelligence (Seti), but, meanwhile, we have to fall back on probability.
Beyond our own galaxy, the distances become extreme. I am told the energies required to send detectable radio messages across these distances are on massive scales, so would aliens bother?
Probably not, given that any reply would be received at least millions of years into their future.
So we had better stick to our own galaxy.
If the nearest ET was, say, tens of light years away – the nearest star apart from the Sun is about four light years away – I tend to think Seti would probably have picked up their signals by now.
So the optimum likely distance may be hundreds or thousands of light-years. But then we start to run up against the energy problem.
It is difficult enough to communicate by radio over these distances (and conversation becomes meaningless), but physical travel is orders of magnitude even more daunting.
Even if ET, living 100 light years away, could somehow accelerate their spacecraft to say 80 per cent of light speed (the best we can do so far is about 0.01 per cent) their round-trip would still take over 120 years.
They might be very long-lived or cryogenically frozen or something, but, even if ET has the technology to send the spacecraft, it would make no sense to do so without first establishing by radio contact that it is worth going to all that trouble.
Perhaps we are alone in this epoch within our own galaxy.
On the other hand, contact with ET could change the whole human psyche and the course of history.
That is why it is worth spending resources – very moderate compared with what is spent on armed forces and wars – on the effort.
Geoff Gay, Loughborough.