For more than two decades, millions of scientists have been imprisoned by online videos showing grapes that spark and light show when they are microwaves.
Scientists and commentators have published theories explaining why this is happening, but Canadian researchers have now solved the mystery for everyone and reported their findings in the journal PNAS .
The lottery usually involves cutting a grape almost half so the skin is intact on one side and popping it in the microwave. After several seconds, the beam ignites with a hotspot. The grape sparks in the middle and sends a light breath of light or plasma.
A popular theory suggested that the hotspot creates the spark because the skin carries electrons back and forth.
The grape halves were considered to act as a radio "dipole antenna" which converts microwaves into an electrical current across the skin bridge, says co-author Pablo Bianucci of Concordia University, Montreal.
Bianucci and colleagues Hamza Khattak and Aaron Slepkov decided to use thermal imaging and computer simulations to test it and other theories.
They discovered that the effect can occur even without the skin bridge.
"By studying the system further, we find that it is not the skin that is important, but the fact that the grapes are like water balls," says Khattak.
Essentially, this "bulk optical" effect means the entire grape rather than just its surface. And no electric current is needed to create plasma.
"The plasma is created because of an amplification of the electromagnetic field between the grapes," says Bianucci. This is due to the interaction of "captured" microwaves. Having two grapes or two halves is the key.
Following this further, the researchers showed that hot spots were also formed by means of two grape musts, leather-free hydrogel balls made of water.
This revealed that the intact skin only holds the grape halves together. When the two whole beads were microwaved closely, the electromagnetic structure caused the beads to bump against each other.
The researchers are further investigating this oscillating movement. "We are currently studying bouncing behavior if you keep the beads in contact with a gravity potential instead," says Khattak.
Stephen Bosi, Associate Professor of Applied Physics at the University of New England in Armidale, Australia, was among the authors of the original dipole antenna theory. He is still unwilling to give up completely.
The idea rests on the assumption that the symmetrical grape halves resonate, like an incoming radio signal.
Resonance means that when a wave of a certain wavelength hits an object of just the right size, so these waves fit nicely inside or around the object, it causes the waves to swing very intensely, "he explains.
" is like an organ tube – only sounds of the right wavelength (or pitch) can play loud (or intensely) because they fit nicely into the organ tube. "
According to Bosi, the new paper that he was not involved in suggests that resonance is still involved – but is much more subtle than previously guessed.
"They showed by both experiments and a century-old theory of light distribution called" Mie theory "that when two resonant grapes (or two halves of the split trench) come close together, they disturb each other in such a way that they create an extremely intense resonance in the gap between the two halves, "he says.
" The microwave intensity is high enough in the cave to get air the molecules to ionize & # 39; – which means that some of the electrons that normally orbit the atoms in the air molecules are torn off by their parent atoms.
"The electrons (negative charges) are now able to move almo st completely apart from the now positively charged mother atoms (now called ions). Any gas (like air) where this occurs is now called a" plasma & # 39 " ;. "
One of the results of this process is that the plasma lights up.
The Canadian scientists are fascinated by the fact that water can make non-visible wavelengths of microwaves very small, says Bianucci, but it does not have the same effect on visible light.
Khattak explains that the way a material affects light depends on the wavelength of light, why you get rainbows.
"If we could find a material that reduces the wavelength of light, as the water does to the wavelength of microwaves, we could shrink all this to get very small spots of light," he muses.