Astrum Space - 97,000 Sonic Black Hole Experiments Revealed Something "Impossible"

Episode Date: October 25, 2023

In today’s episode, we discuss escaping the unescapable. Everyone knows that nothing can escape a black hole… but is that actually true? It's time to find out.

In space, there is nothing quite so ominous as a black hole. Perhaps it is the fear of our own mortality, the sure knowledge that these beermoths will almost certainly outlast us. Perhaps it is the unknown. These giants of the cosmos are still so poorly understood by our science and jealously guard their secrets. Or perhaps it is their hunger, and the knowledge that once matter falls into them, it can never leave.

That black event horizon marks a point of inescapable no return, a guarantee of death and destruction under the greatest pressure and gravitational force that can exist within this universe. One so great that not even light can ever be free. But is it really true that nothing can escape a black hole? I'm Alex McColgan and you're listening to the Astrum podcast. Join with me as we attempt to understand the weird science that might be might allow energy and thus mass to escape from the inescapable.

For many years of black hole science, it was a given fact that nothing could ever get free once past the event horizon. That was sort of the point of them. The celestial masses had so much gravity that light itself could not escape past a certain point, and as Einstein laid out that nothing could move faster than the speed of light, then nothing could overcome the crushing acceleration due to gravity. that a black hole produces. Any object that fell into it was doomed to remain there, lost to the rest of the universe for

all of time. However, in 1974, Stephen Hawking came up with a theory that suggested a different outcome. The title of his paper, Exploding Black Holes, was certainly flashy. In it, Hawking hypothesized that Black Holes would release energy slowly over time, in initially tiny quantities. As energy and mass were two expressions of the same thing according to Einstein's famous E equals MC squared equation, this inevitably resulted in a reduction in the black hole's mass. However, as the black hole shrinks, the rate of energy release would speed up, getting faster and faster, until in the very last moments of the black hole's life, it would release a burst

of energy that was truly gargantuan in its scale, before vanishing entirely. But how could both of these things be true? If an event horizon was inescapable, how could radiation ever leave it, and eventually cause such a black hole explosion? The answer is a strange one and relies on unintuitive ideas of quantum theory that completely go against our day-to-day experience. But if it's true, I hope you're prepared for the universe to be a whole lot stranger than you first thought. But to begin understanding Hawking's theory, we need to understand the idea of quantum fields. Let's start with a seemingly strange question.

What is nothing? You might think that nothing is simply the absence of, well, anything else. If you took a patch of space and removed it of every single particle of matter and beam of radiation, nothing is the emptiness that's left. However, in reality, this isn't quite the case. Consider for a moment a photon of light as it passes through such an empty space. It is an electromagnetic wave propagating by rising and falling in a set direction. But that word wave is crucial.

In the ocean, could you have waves if there was no water? If light is a wave, well, then there must be something to be waved, even in the ocean. empty space. Some fundamental fabric from which all reality is woven, a sea on which all matter and energy sails. Scientists call this fundamental fabric of reality a quantum field. In fact, they believe that there are several quantum fields, all overlapping each other, and all covering every single patch of the universe, be it past, present or future. Quantum field defines a particular type of something. One field might define all of the electrons in existence, while another may define quarks that make up an atom. Where nothing can be found, the quantum field is relatively quiet.

Think of it like a guitar string that hasn't been strummed, or a graph that has a zero value. But wherever in time and space, mass or energy can be found, the quantum field is resonating at that point. And when the resonance reaches a certain threat, threshold or quantity, the universe expresses that as, say, an electron or a photon. It's important to note that in this theory, the resonance is not just reacting to a piece of matter. It is the matter. We're not sailing on an ocean. We are the ocean.

An electron is nothing more than a resonating section of the quantum field that defines electrons. This is true for all energy, and all matter too. According to Einstein, energy and matter are two sides of the same coin, after all. All the universe you see around you is resonating quantum fields, and nothing more. In this way, the theory portrays all of the universe as a song being played on these fields, which I think is quite a beautiful image, if nothing else. But why does this matter?

Why is it important to define the universe in this way? Well, due to an idea of quantum physics called Heisenberg's uncertainty principle, sometimes the strings of the universe start strumming themselves. Without going too deeply into this aspect of quantum physics, essentially when we're looking at really tiny objects on the atomic scale, it becomes impossible to know too much about them. You cannot know both the location and the direction of travel of an electron, for instance. Because it is so small, as soon as you try to figure out the location of an electron, it bounces off whatever you are trying to use to measure it, so you can no longer be sure of its

direction of its direction. If you know its direction, according to this principle, you can't know its location. This is not just because our methods of measuring aren't good enough, but because of some fundamental laws about the nature of the universe itself. According to Heisenberg's uncertainty principle, you cannot know everything about particles. on a subatomic level. But when you apply this principle to quantum fields, it gets weird. Quantum fields fluctuate everywhere, and by Heisenberg's uncertainty principle, particle and antiparticle pairs can actually pop in and out of existence. The how and why get

complicated, but basically the universe allows it as long as they only exist for a very short period of time, as ruled by uncertainty relations. You might think this can't possibly be a thing. Matter does not just pop into existence. We would have surely noticed this by now. However, in an experiment done by Hendrik Casimir, evidence was found that suggests that this might actually happen. Casimir took two plates of conductive metal and placed them close enough together so that

only certain sizes of smaller virtual particles could pop into existence between them. This limited the number of such particles that could pop into existence. But because all types of particles could pop into existence on the outside of the plates, this meant that there was a difference in pressure exerted on the two sides of each plate. Theoretically, the larger pressure by the number of virtual particles on the outside of the plate should push the two plates together, and in the test, this proved to be the case. You might think that particles appearing out of nowhere seems to defy the laws of conservation of matter.

would be right. So to balance the scales, whenever a virtual particle appears, a second particle also pops into existence to pair up with the first particle, but while one of the particles is matter, the other is antimatter. A 1 and a minus 1 on our bar chart, thus keeping things overall at 0. The universe is happy. And on top of that, these fluctuations in the quantum field quickly crash into each other and annihilate each other, removing them both from existence again, so we don't normally have to worry about them.

As a side note, there is a theory that antimatter is simply matter that is moving in the opposite direction through time, but that's a level of weirdness that we don't need to get into here. The important part is that the quantum fields are constantly resonating and constantly cancelling each other out. This is why, for the most part, empty space is empty. However, what would happen if you stopped only some of those fields resonating? And that's where black holes come in. Black holes act a bit like putting your thumb on the catastrophe of the universe. Due to their event horizons, certain resonances in the quantum fields are dampened down,

while others are not. Hawking imagines sketching a line through time in a patch of space where a black hole was born. He imagined a quantum field. that resonated along this line, stretching from before the existence of the black hole into the future after it. Before the birth of a black hole, all is normal. Quantum fields are all resonating freely and can cancel each other out. However, the emergence of the black hole's event horizon changed the curvature of space, and outside it, Hawking realized that certain pulses were now missing their opposite numbers. As he looked at the math, he realized

not everything was being cancelled out anymore after the black hole had formed. Indeed, outside the event horizon, travelling away from the black hole, he found resonances that perfectly matched the shape of thermal radiation flying away into space. Radiation is energy, and energy cannot form from nothing. As the black hole was creating this radiation, the black hole would have to pay the price. Every piece of hawking radiation would thus coincide with an equal amount of energy lost from the black hole, which in time would reduce it down to nothing. If it exists, Hawking radiation is kind of like money spontaneously appearing outside of a bank, while inside the bank, the money in the vault vanishes. It's also extremely difficult to prove,

as Hawking predicted this radiation would be colder than the background cosmic radiation that fills the universe, and would have a wavelength as long as the black hole's event horizon itself. As some black holes have event horizons the size of solar systems, we have no way of detecting this kind of radiation. We'd only really see it once the universe had gone cold and dead, so there was nothing else to get in the way, which would probably mean we weren't around anymore to do the detecting. However, in spite of the objections to it, the math behind Hawking radiation seems to be sound, and scientists have recently taken steps to proving it in the lab.

In the Technion-Israel Institute of Technology, researchers looking into Hawking Radiation came up with an idea to get around the difficulty of measuring a real-life black hole. They did this by creating an analog, a sonic black hole, which would mimic the properties of a real one. They relied on the fact that sound moves much slower than light, so it's much easier to create a medium that moves faster than sound. it moves, any sound waves travelling in the same direction as it can never quite escape it. Interestingly, Hawking's math worked for these sonic black holes just as well as it did

for gravity-based ones, and so Hawking radiation ought to be detected from it. After repeating the experiment nine seven thousand times over 124 days of continuous experimentation, the researchers detected multiple instances of Hawking radiation and saw that it matched Hawking's predictions of how his radiation might behave. Although this does not prove that Hawking radiation is definitely real for actual black holes too, the fact that Hawking's math worked for this sonic analogue is a strong implication that he might be onto something. Hawking radiation might just be real. So, to answer our initial question, if you fell into a black hole, could you ever escape it? Still probably not. However, if you waited until almost the end

the universe, the black hole may just radiate hawking radiation until the mass and energy that makes up your existence completely was removed from inside the event horizon, and you would be unwritten from existence. Does that count as escaping? That's probably not so appealing to you. Probably best just not to go in. Well, that's all we have time for today. I hope you've enjoyed listening to this podcast on Black Holes and Hawking Radiation. If you like what you've heard, please feel free to follow us for more podcasts on other fascinating space topics. But for now, I'm Alex McColgan and this has been Astrom. All the best and see you next time.