Sound in Space?
The engines roar as space fighters shoot across the screen from planet to planet, space battleships explode with a tremendous bang – and the nitpickers among the science fiction fans can be seen shaking their heads in disdain: space, they say, has to be silent.
Sound waves are transmitted by air, liquids and solid bodies; on Earth, for example, air is compressed at the source of the sound and then radiates from this point as a pressure wave. In the emptiness of space, however, there is nothing to compress. So does that mean that there
is no sound? Not at all – there’s plenty of sound in space. Actually, the infinite expanses of space are not completely empty. And even the minute density of material particles is sufficient to transport sound waves under certain conditions – sound that is so low and so quiet that it can only be made audible by using the most sophisticated equipment.
In 2003, a group of astronomers using the Chandra X-ray telescope claimed to have measured the lowest sound in the universe. The noise was said to have originated in the galaxy Perseus A. There, two factors come together: a black hole that generates the sound and a particularly high gas density that allows it to propagate. The problem is that this sound, which is caused approximately every 10 million years by the convergence of gases with different densities, is 57 octaves below middle C. Even without their protective and insulating helmets, astronauts wouldn’t hear a thing.
The sun also has its own very special sound. As it was traveling to Saturn, the Cassini space probe recorded the sound of a solar eruption in the same year, the most violent of the past 30 years. The noise is produced by electrons in the solar flare. It starts with a high whistle and ends with the roar of a low-flying jet.
Things were even louder when the universe was created. In the 1920s, the astronomer Edwin Hubble discovered that the universe was constantly expanding, and went on to develop the theory of the Big Bang. But what exactly did the Big Bang sound like 3.7 billion years ago? The scientist Mark Whittle from the University of Virginia believes that it was more of a scream than a bang. In 2004, he recorded and analyzed the waves of the Cosmic Microwave Background radiation, a kind of afterglow of the Big Bang. The pitch of the primordial sound that he calculated is more than 50 octaves too low for human hearing. But thanks to modern recording and digitalization technology, the sound can be converted into a range that we can hear. As a result, we now know that the “primal scream” of the universe was a mixture of a deep roar and a deafening hiss. The lowest two harmonics of the first cosmic chord produce a major third. So the symphony of the universe began majestically with a major chord – at an unimaginably high volume. Even 400,000 years after the Big Bang, the waves of the Cosmic Microwave Background were still producing pressure variations corresponding in human terms to the sound pressure level of a rock concert.
So far, all attempts by mankind to elicit a sound from some intelligent species in space have been unsuccessful. In the 1970s, a golden record with voice samples and music from all countries and cultures of planet Earth was sent off into space on the Voyager space probe. It was meant as an acoustic business card, just in case anyone wanted to respond. As yet, there has been no reply.
The Sounds of Earth
“The Sounds of Earth” is the title of golden records containing images and sounds that have been carried on board the interstellar spacecrafts Voyager 1 and 2 since 1977. The records were produced in the hope of informing intelligent extraterrestrial life forms about mankind and life on Earth. With an estimated lifetime of approximately 500 million years, the records will probably outlive mankind.
The phonograph record is a 12-inch, gold-plated copper disk. On the back, instructions in symbolic language show how the record can be played. The time information required for playing the record are given in a binary code and relate to the fundamental transition of the hydrogen atom, which is also represented. It also includes a diagram defining the location of our sun. The records contain analog images and audio files. These include spoken greetings in 55 different languages – the English version says: “Hello from the children of planet Earth” – as well as sounds such as wind, thunder and animal sounds. These are followed by 90 minutes of selected music, including ethnic sounds and familiar music from artists such as Bach, Mozart and even Chuck Berry.