Saverio Spinelli - 13.7 billion years ago with the Big Bang, the Universe was born, which then developed according to the timeline indicated in the image that you can see below, including a few lines on the right. What was the first no one knows exactly. The fact is that at some point something apocalyptic happened: there was a huge explosion that developed tremendous heat and temperatures of billions of degrees (just to get an idea, the surface temperature of the sun is "just" 6,000 ° C).
From that moment, a mix of dense plasma and energy began to expand rapidly; but the force of gravity was so great that it did not allow anything to escape, even to radiation; and then even to photons. For this reason, assuming that a hypothetical human being placed in an equally hypothetical observation position (in fact, even the space, as even time, still existed) would, however, could see that explosion, nor hear. In that immense concentration were only possible interaction processes between particles at the sub atomic strings of energy, and matter as we know it was not yet born.
Expanding the Universe also began to cool.
After 376,000 years the temperature had dropped to "only" 3,000 ° C: this allowed the formation of the first atoms are electrically neutral and with them, then known matter. It was then that the electromagnetic waves and photons, no longer forced to interact only with the free electric charges of the hot plasma, could also begin to propagate in the space that was to be created as the expansion continued.
And it was then that the Universe made his first radiation, the primordial radiation, which began to spread in space in every direction.
So, if we wanted to "listen" to the signal emitted by 'Universe when it became "visible", that is, when he was 376 thousand years, we should first look for a radio telescope with traces of an electromagnetic radiation isotropic (that is detectable in any direction of space points) .
In truth, the way of the discovery of the primordial radiation was traveled exactly the opposite. In fact, in the sixties, some scientists, in the course of radio astronomical measurements, accidentally discovered an electromagnetic radiation at a frequency of 160.2 GHz, detectable in every direction of observation. Found that it was not a trivial interference from the land, as at first it was considered, he deduced later that this was the cosmic background radiation, which was rightly called CMBR (cosmic microwave background radiation). At that frequency corresponds to a temperature of emission of 2.72 ° K (-270.27 ° C). (For a discussion on the concept of emission temperature, please see this article and this further deepening of MeteoWeb already published in the phone book " Journey into the world of electromagnetic waves "). This value very low emission temperature (just above absolute zero) is compatible with the fact that the primordial radiation, with time and with the swell in the space, it could be "cool". The value of the CMBR, related to other cosmological parameters, it also indicates how the radiation is exactly old of 13.7 billion years, so this is the age of the Universe.
After its discovery, further finds made by NASA with the probe WMAP (Wilkinson Microwave Anisotropy Probe) made it possible to draw a very detailed map of the spatial distribution of the radiation and its emission temperature, showing that this presents small deviations in value ( of the order of thousandths of a degree and also smaller) corresponding therefore also at frequencies (even if very slightly) different, as can be seen in the image beside provided by NASA.
In practice, the map of the radiation provides the "registration" of when the universe was an age of 376,000 years. The temperature differences are explained by changes in the concentration of matter; that indicate the presence of compressions and rarefactions of the same, typical phenomena of propagation of a sonic wave.
It so he was able to infer, as it is now it is proved that the early Universe was also path from sound waves!
This, in the first instance, it might seem strange, knowing that the sound propagation can not occur in a vacuum. But in the immediate aftermath of the Big Bang the existing space was mostly empty as it is today, in fact, was particularly dense: this explains precisely the thesis that, after the Big Bang and for a time, you have been able to generate and propagate in 'Universe also sound waves.
Now let's do an example to everyone: if we listened to the roar of an explosion occurred, say, 5 Km away, the noise would not be heard by us in real time: it would take about 15 seconds to reach us (being about 340 meters per second the speed of sound). Listening to the roar, detectable for a certain time, before dissolving, to an observer would understand that something has happened: at a certain distance in space and, even if only slightly, also in time. Naturally the explosion of the example is a phenomenon belonging to a context characterized by spatial dimensions, as well as temporal levels belonging to a very different scale of the cosmic! In any case the noise would be of decreasing intensity in proportion to the distance from the source and, in the absence of the dissipative factors, could be heard even at very large distances, and then a long time after the event occurs. It 'also known to everyone like a double bass, whose strings and the sound box which have dimensions greater than those of a violin, with respect to this play sounds more serious, that is, at a wavelength greater. It is thus easy to understand how, because of the overwhelming size of the entire game in the context in which it is produced, the acoustic waves generated at that stage of the formation of the universe had infinitely low frequencies and therefore a wavelength immense, unimaginable, estimated at several thousand light years! So those sounds were not audible absolutely usual hypothetical human observer and, for the truth even from any creature known to us.
That said, to an American scientist, Prof. John G. Cramer of the Department of Physics of the University of Washington in Seattle, years ago had the idea of trying to reproduce the sound of the Big Bang, so that was also heard by humans, and that in order to meet the request of a teacher who had asked if it was possible to listen to his pupils the noise of the Big Bang. To do this, JG Cramer took the temperature values measured by the probe WMAP (which, as we have seen, rilevavano concentration differences of matter, that is, compressions and rarefactions similar to phenomenology connected to the propagation of an acoustic wave) and elaborated them with software for audio reproductions. First of all assumed that the different sine waves generated to depart all at once at the time of the Big Bang, and that they had a peak of intensity just after 376,000 years and were reduced to 60% of the peak in the 110,000 years before and after, exactly according to the data collected from the WMAP probe. Then corrections brought down in frequency due to the Doppler effect caused by the expansion of the universe, in order to produce the performance of the sound for a certain period, who chose in 760,000 years from the Big Bang (for a depth study on the Doppler effect, please see this article published on MeteoWeb the heading " Journey into the world of electromagnetic waves "). Then he increased the acoustic frequencies detected by a factor of 10 to 26, to make them audible to the human ear. Finally reduced the time scale of 760,000 years from 100 seconds: in fact precisely playback lasts 100 seconds. From his listening you will notice how the sound of the Big Bang is not similar to the detonation of a bomb (as you might expect), but to the sound of a jet flying in the sky, with notes tonal variations due to 'Doppler effect caused by the movement of the source.
Queued article find the video with the sound of the Big Bang: for optimal listening is recommended a sound system of good features.
Enjoy the show!
