Why does the Universe appear so silent after decades spent waiting for a message from elsewhere? Where are the extraterrestrial civilizations? A new, unexpected hypothesis has just emerged, providing, we hope, an explanation for the famous Fermi paradox.
Long perceived as clear, continuous emissions, radio waves encounter barriers and disturbances during their travel. Stellar activity, such as coronal mass ejections, for example, projects charged particles that interfere with the propagation of these waves. These encounters have the potential to disperse a signal over a wide band of frequencies, diminishing its intensity and complicating its reception from Earth.
A narrow signal emitted from a planet (left) can be dispersed in frequency after passing through stellar plasma, reducing its power (right).
Credit: Vishal Gajjar A study led by Vishal Gajjar and Grayce Brown of the SETI Institute quantified this impact by examining signals exchanged between Earth and space probes. Their results, published in
The Astrophysical Journal, have enabled the calibration of the influence of the solar wind and stellar flares on very fine transmissions—precisely the kind astronomers are searching for.
Simulations then extrapolated these measurements to other systems, targeting stars like our Sun and red dwarfs. The latter, modest in size but very turbulent, are particularly likely to cause a pronounced spreading of signals, which can exceed several hundred hertz in some cases.
This advance allows for considering modifications to investigation techniques. By taking local spatial conditions into account, scientists can now develop detection strategies better suited to the signals that actually reach us, rather than those emitted under ideal conditions.
Some wonder if this process provides an element of an answer to the persistent silence. Perhaps the galaxy is not devoid of messages, but we simply need to refine our instruments to discern them through the interference generated by stars.
Future efforts will integrate these new parameters into ongoing research, reviving hope of lifting a corner of the veil on the possible existence of technological civilizations within the Milky Way.