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How far have our radio/television transmissions reached into the universe?

How far will our first audio and/or visual radio/television transmissions have reached into the universe? Are they likely to have reached an intelligent life form that could intercept and understand that they were transmitted by an intelligent life form (ourselves)? If so if they have replied how long will that reply take to reach us assuming they are transmitting at a similar frequency to our transmissions?
Andrew Hartley from Surrey (Age: 45-54)

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2 Responses

  1. As Carl Sagan states in his novel, Contact, the earliest TV broadcasts didn’t have enough energy to pass through the ionosphere (a layer of charged particles, high in the atmosphere). Radio signals would have a similar problem, since they are essentially the same thing; low frequency electromagnetic radiation.

    Referring to Sagan’s novel again, one of the first TV broadcasts with enough power to be detectable from an extraterrestrial location was, unfortunately, the 1936 Olympics in Berlin. It could be that pictures of Hitler are one of the things an alien lifeform could detect.

    Taking the year 1936 as our start-point, radio signals will have been spreading out through the vacuum of space at the speed of light for the duration of time since then.

    Light travels at around 300,000 km/s, so that’s 18,000,000 km/min, 1,080,000,000 km/hr, 25,920,000,000 km/day, 9,467,280,000,000 km/year.

    So, in the 72 years since the Berlin Olympics the signal would have travelled about 681,644,160,000,000 km (or 423,554,044,000,000 miles or 72 light years). This is far enough to have reached some of the nearest stars, and even some stars that have solar systems around them.

    The only problem is that as the signals spread out, their energy also spreads out in an inverse-squared relationship. Think of ripples in a large pond – they might be quite big near whatever causes the ripples, but as they spread out the height of the ripples gets smaller and smaller. For aliens to detect signals from our planet they would need to be relatively close or have much more sensitive equipment than we currently have available on Earth.

    If an alien was to detect these signals and send a message back it would take just as long for the reply to reach us. For example, if a message was detected by an alien 50 light years away (a very small distance in comparison to the size of the galaxy), then the signal would have taken 50 years to get there and the reply would take another 50 to return, giving a round-trip time of 100 years. Perhaps it would be more sensible to work on some way of travelling faster than light in the intervening time, rather than trying to conduct a centuries-long conversation….

  2. But we are told about particles with instantaneous signaling ability. Looks like we’d need to investigate such particles, and see if they’d mind carrying our signals to distant possible civilizations, so we could hear back like we do across Earth.
    It does seem possible distant civilizations recognize we don’t know how to use spontaneous signaling yet, so don’t bother to mess with us.

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