Scientists want to ‘listen’ to the Big Bang so they can unravel its mysteries
Detecting cosmological gravitational waves could have huge results
High versus low frequency
Current andplannedgravitational wave detectors mostly focus on low frequencies, where astrophysical signals are guaranteed to exist. These can also look for cosmological gravitational waves and will be able to probe signals produced when the universe was extremely young, barthe very first momentsafter inflation.
That’s because the wavelength of a produced wave is proportional to the “size” of the universe (that is expanding). The earlier it was produced, the smaller the corresponding wavelength – and the higher the frequency. The era immediately after the end of inflation is what we are aiming to probe with our new project. This covers times when we could see actual evidence for some of the most fascinating theories of nature, such asstring theory.
There are also other possible sources that would produce high-frequency gravitational waves in the more recent universe. Examples include mysterious objects called boson stars (stars made out of elementary particles called bosons) or “primordial black holes”, whichmight compose dark matter. These are both hypothetical entities thought to exist that have never been observed.
The vast majority of signals at high frequency would immediately point to particles or phenomena that cannot be described within theStandard Model of particle physicsand theStandard Model of cosmology, our best descriptions of nature. So a discovery would shed light on some of the unsolved problems of our universe, such as the composition of dark matter and the origin of inflation.
Tiny machinery
There are a couple of clear advantages of high-frequency detectors. First, as the size of the detector is proportional to the wavelength to be probed, high-frequency gravitational wave detectors would be much smaller (and cheaper) than low-frequency ones. The length of the Ligo arms, for instance, is four kilometers. We dream of listening to the sound of the big bang with a detector that would fit in our kitchen. We are hopeful this could work – at high frequency there are no astrophysical background signals interfering with what we want to measure.
Detecting high-frequency gravitational waves is hard though. An experiment like Ligo looks for the variation of the distance between two mirrors, caused by the passing gravitational wave, equivalent to a fraction of the size of the nucleus of an atom. As high-frequency gravitational waves detectors are smaller, the variation to be detected would be even tinier.
With our currently available technology, we are already able to detect minute variations in the high-frequency range (though we haven’t caught any gravitational waves yet). But we need to improve it a bit more to detect gravitational waves from the early universe. Supporting this technological development is whatour projectis all about.
Ultimately, we are trying to start a challenging journey, much as people did back in the 1970s when they began searching for astrophysical gravitational waves. It took almost 50 years and more than 20 attempts, which ultimately shows that hard work and patience pay off.
Article byFrancesco Muia, Postdoctoral Researcher, Theoretical Physics and Cosmology, Stephen Hawking Fellow,University of Cambridge
This article is republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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