Aliens at the London Science Museum

By Mark Trodden | August 29, 2005 5:13 am

Reporting on a new exhibit at the Science Museum in London, The Guardian has a fun article about the question of extraterrestrial life, its probabilities, its possible forms, and its role in books, film and television.

Amid the historical data, the popular speculations and the observations on Captain Kirk and his penchant for big-haired babes from beyond, are plenty of reasonable comments and a little physics. For example

We don’t know for sure because aliens continue not to visit. One in 100 Americans may believe they have been abducted (cue for a short lecture on sleep paralysis, which manifests itself in pressure on the chest and the experience of being taken away) but if the laws of physics extend beyond Alpha Centauri, then they have not. The distances to the nearest stars are awesome, and the energy costs literally astronomical.

The article ends with a summary of recent work done by people like Clive Trotman, a biologist at the University of Otago in New Zealand.

You can’t just broadcast a message saying, “Is anybody out there?” The signal dissipates as the square of the distance. By the time you get to Pluto, it’s already vanishingly faint.

So you send an ultra-powerful signal as a focused laser beam. How much energy would that take? How long could you afford to transmit? How many directions must you point the transmitter to cover the whole sky? (The answer to that one is 100,000 trillion). And what chance a citizen of an alien civilisation is tuned in when your one-second message whistles by at the speed of light? The arithmetic, says Trotman, predicts one-way communication with both antennae pointing at each other will happen for one second every 10 billion billion years. Assuming, that is, both civilisations are using the same wavelength.

Ah, the inverse square law; cornerstone of physics and astronomy classes everywhere, and a perfect beginning to the first week of my Fall semester.

CATEGORIZED UNDER: Science and the Media
  • Adam

    There’ll be no Big-Haired Babes from Beyond? Damnit.

  • Quantoken


    You neglected to point out the obvious fact that even laser beams, no matter how focused they are, still follows the inverse square law.

    There is simply no possibility of communication between two civilizations, even if they used highly focused laser beams, huge disks that happen to point to each other precisely at the same time, and they are very close to each other: 1000 light years, an impossibly close distance in astronomy terms. Just do some simple numerical estimate, you find whatever few photons that is lucky enough to be received would be completely buried in the background noise, including the CMB and visible light radiation of billions of stars and galaxies.

    Just think how powerful the radiation of the sun is. And that is just one out of a hundred billion stars in the galaxy. You place one such galaxy at ten billion light years away, and using the most powerful Hubble Telescope, you barely receive one or two photons per minutes from that remote galaxy. What kind of civilization is capable of emitting such an enormous amount of energy that out-shines a whole galaxy?

    And even if such extreme power is achieveable technologically, by aliens, I highly doubt that a civilization so intelligent and so advanced, would be so stupid as our human beings, in that they would carelessly waste the resource of a whole galaxy’s energy, just so that they have a one in a 100,000 trillion chance to exchange a simple “hello” message with us.

    If they are so wasteful in utilizing their resources, they would have long destroyed their living space and extinct their little light flash of civilization, long before they could acquire any advanced technology.

    This could well be the case of we the humen on earth. Because in just a few years, we would have depleted our oil and there will be a total collapse of civilization.



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About Mark Trodden

Mark Trodden holds the Fay R. and Eugene L. Langberg Endowed Chair in Physics and is co-director of the Center for Particle Cosmology at the University of Pennsylvania. He is a theoretical physicist working on particle physics and gravity— in particular on the roles they play in the evolution and structure of the universe. When asked for a short phrase to describe his research area, he says he is a particle cosmologist.


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