One of the questions underpinning both philosophy and science is “why are we here”? Ask an astrophysicist, and they might answer with an imbalance between matter and antimatter at the beginning of the universe. While that is a (relatively) simple explanation, it then begs the question – why was there an imbalance in the first place? Scientists have been seeking ways to test various theories regarding that imbalance but have come up empty-handed so far. Now, a team of theoretical physicists think they might have found a way to test some of those theories using gravitational waves.
The team, led by Graham White of the Kavli Institute for the Physics and Mathematics of the Universe, focused on a type of phenomenon known as a Q-ball. As with many theoretical physics concepts, Q-balls are relatively difficult to explain. A layman’s explanation from Dr. White uses the relatively well-known Higgs Boson as an analog.
“A Higgs particle exists when the Higgs field is excited. But the Higgs field can do other things, like form a lump. If you have a field that is very like the Higgs field, but it has some sort of charge – not an electric charge, but some sort of charge – then one lump has the charge as one particle. Since charge can’t just disappear, the field has to decide whether to be in particles or lumps. If it is lower energy to be in lumps than particles, then the field will do that. A bunch of lumps coagulating together will make a Q-ball.”
So, essentially, Q-balls are clumps of charged fields that degraded into lumps and stuck together. Once stuck together, they tend to last a long time, outliving the background radiation that came with the universe’s expansion. What’s potentially interesting about them is what happens when the Q-balls decay.
When they do decay, they do so rapidly and violently. Rapidly and violently enough to cause ripples in space-time – gravitational waves. Even more importantly, these decay events are relatively common, and we should have the means to detect them. Gravitational-wave observatories, such as LIGO, have already detected gravitational waves from other sources of comparable strength and frequency to those caused by decaying Q-balls.
So far, there hasn’t been a gravitational wave detection attributed to these decays yet. Still, Dr. White and his colleagues are optimistic that it will happen soon: “It is almost certain that we will soon detect a signal from the beginning of time confirming this theory on why we, and the rest of the world of matter, exist at all.” That is an exciting claim and one that anyone with a vested interest in why matter exists at all (i.e., everyone) should be interested in.
Kavali IMPU – Gravitational waves could be key to answering why more matter was left over after Big Bang
CosmoQuest – Q-balls Knock Matter Into Dominance
UT – Gravitational Waves Reveal Surprising Secrets About Neutron Stars
UT – Gravitational-Wave Observatories Should be Able to Detect Primordial Black Hole Mergers, if They’re out There
Model of how blobs of Q-balls could result in gravitational waves.
Credit – Kavli IPMU