Black Holes….?
Physics is the study that explains the reasons behind the possible outcomes of experiments.
“Why does the glass break after it falls”? “ Why is the speed of light so high and constant simultaneously?” Even though we are successful at explaining some of these laws, we are still mute to answer many laws - specifically… Quantum Mechanics.
But here we are not discussing the weird laws of Quantum Mechanics we are here to discuss the most significant discovery of mankind which is Black holes. Almost all have heard about black holes and their effects but we are not touching on that part we are going to go deeper and try to truly understand how it changes and breaks some of the laws of classical mechanics.
Here, we will be discussing how black holes supported General Relativity and do we even have an exit point for black holes… possibly another universe??? So, buckle up because this is the whole chapter of black holes.
Spacetime
When Einstein published general relativity, there were lots of issues at first. It completely threw off the Newtonian principle of how space and time are absolute and gave a weird effect (gravity bending light). Years later, when relativity was proven, physicists suggested a hypothetical body known as a black hole. If mass bends space then it is possible for an object(that has an extremely high density) that it can bend the space so deep that nothing can escape its gravitational force including light. However, this hypothetical object was not popular at that time.
As years passed, black holes gained popularity though. Scientists were searching for evidence of black holes- many started writing equations for the gravitational strength. It was sure that black holes must exist but how could we observe them if it doesn’t reflect any light?
Finally, an image appeared proving the existence of black holes. But wait! How is that even possible???
To understand the process of capturing black holes image, we first need to understand some basic features of black holes:
The accretion disk is the orbiting disk where matter moves around with extremely high energy. When black holes attract the body, it doesn’t go right through the center, it goes in a swirling way. All the matters are trapped in the accretion disk and slowly fall into the event horizon. However, the accretion disk is a very stable orbit so if the attracted bodies are exactly at the range of the accretion disk, they don’t fall into the horizon instead they keep swirling around.
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| By Cosmoknowledge |
Any matter that has mass cannot cross the accretion disk and escape the event horizon. The radius of the accretion disk from the center of the black hole is 3 rs(Schwarzschild radius) and if any matter falls after this range of radius, it directly falls into the event horizon. However, light can escape this behavior since it has no mass.
How can light escape from a black hole?
Light doesn’t have any mass so it makes itself unique from other bodies. For any mass object, its limitation boundary is 3rs, but for light, it is actually 1.5rs. This means light can circle the whole black hole if it falls under that range. However, after the light has wholly circled the black hole it either goes inside the horizon or escapes to infinity.
Light escaping to infinity:
If the light travels to the black hole from 2.6rs (from the event horizon), it swirls the black holes and heads to infinity. Likewise, if parallel rays of light fall under 2.6 rs then it circles the black hole but goes to the singularity. To swirl and escape the event horizon, the light must be in the range of 2.6rs.
Isolating the single beam of light that escapes to infinity (light we see from observing the black hole.)
This is the animated version of light escaping the black hole.
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| Remember the radius must be 2.6 rs, then only can light circle the event horizon & escapes |
Black Hole’s Image:
When we see the image of a black hole, we can see a circle (black circle) at the center. We may think that it might be the event horizon that is capturing the light from the source, but it has other components too. The parallel rays of light that fall under 2.6 rs halfway circle the black hole and get pulled into the singularity. The light that falls in this scenario is bent and absorbed which is why we see the black shadow in the black holes. Hence the black shadow is not only the event horizon but also the curved part of the absorbed light.
This is why we see the entirety of the black hole since gravity bends the light. The image we see is from the light (2.6rs) that escapes from the event horizon producing an image 2.6 times the size of the event horizon (since other lights are sucked by gravity).
The light coming from the back of the black hole and the light coming from the front all these lights are bent by the force of gravity and because of that, we see all these lights in a different pattern when we observe a black hole.
Thus the image we see is not just the image of an event horizon of the black hole, instead, it is the combination of all the light that is bent by the gravity of the massive singularities and because of that, they appear different. However, in the real image we only see an event horizon and the accretion disk but as we already discussed the center is not just only the event horizon but it is the combination of all lights...
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Real Image of the black hole (NASA- May 12, 2022)
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Source: NASA image
Quick Note: As we can see that one side of the black hole is brighter than the other side and this is because the brightness of the accretion disk can vary depending on several factors, including the size and mass of the black hole, the rate at which material is falling into the black hole, and the distance between the black hole and the observer. In some cases, the accretion disk may appear more bright on one side due to asymmetries in the distribution of material around the black hole.
The Black Hole Information Paradox:
There are two main pillars in modern physics: Quantum Mechanics and General Relativity. Quantum mechanics is a fundamental theory of physics that describes the behavior of tiny particles on a very small scale, while general relativity is a theory of gravity that describes the behavior of large objects like stars and galaxies.
These two laws, however, never correspond with each other. You can rarely apply the law of quantum physics to the equations of general relativity and vice versa. This is what makes physicists scratch their heads, both of these laws are statistically proven but when mixed together, everything is chaos!
The long search for a unified theory that connects both pillars of modern physics is still in process. String theory is the only leading theory that tries to explain the phenomena of GR(General relativity) connecting with quantum but this is just an idea...
Still, many physicists have tried using some laws in each other, but very few of them have been successful. And even if they are, so many paradoxes occur during this process. String theory may provide some explanations but it has yet to be proven. One of the most popular paradoxes that have tackled physicists for decades is "The Information Paradox."
The black hole information paradox is a puzzle that arises from the combination of two seemingly incompatible theories in physics: quantum mechanics and general relativity.
According to general relativity, once something falls into a black hole, it can never come back out. This means that any information that falls into a black hole is lost forever.
This is known as the "no hair" theorem, which states that black holes have only three properties: mass, charge, and angular momentum. All other information about the objects that have fallen into a black hole is lost.
However, quantum mechanics tells us that
information can never be truly lost. This leads to a paradox because the two theories are in conflict with each other. One possible resolution to this paradox is the idea that the information that falls into a black hole is somehow encoded on the surface of the black hole, in a way that can never be accessed from the outside. This idea is known as the
'holographic principle'.
Hawking's Radiation
When Stephen Hawking introduced his theory of radiation, it was a bomb dropped on physicists. He explained how black holes that attracted everything including light radiates heat and how they gradually lose their mass. But to understand Hawking's Radiation more deeply, first, we must understand the need for the theory and some other topics like Virtual and Real particles.
Virtual Particles
First, let's revise our journey about Real Particles and how quantum field theory completely changes the concept of these particles.
Real particles are the elementary particles that we observe in daily life: photons, electrons, and others. These particles are considered 'real' because their effect can be seen, observed, and they have a long span. This is not the same with the 'virtual' particles, however. The term virtual particle defines itself - it exists hypothetically just for some time.
When Quantum Field Theory was introduced, it claimed that every particle is associated with the energy of the field; if you give energy to the electromagnetic field, you get electrons and photons, and if you give energy to the Higgs field, you get Higgs boson. This made clear that space is not empty, in fact, it must have some sort of field with random energy. If space had 0 energy then it would certainly violate the Heisenberg Uncertainty Principle, we would know the time and energy of a particle. So space must have some energy, which may be deficient but should never be empty.
To give a clear illustration of how particles are formed from the field, here is a quick animation:
This is how particles are supposed to form according to quantum field theory.
Virtual Particles:According to quantum field theory, virtual particles are constantly being created and destroyed in the vacuum of space. These particles are not directly observable and do not have a definite location or mass. However, they can still have an effect on other particles through their interactions, such as the exchange of virtual particles that mediates the electromagnetic force between charged particles.
In this way, quantum fluctuations can be seen as giving rise to virtual particles, which are temporary fluctuations in the fields that make up the universe and are a result of the uncertainty and indeterminacy inherent in quantum systems.
The exchange of virtual photons is a process that occurs when two electrically charged particles, such as electrons, interact with each other through electromagnetic force. According to quantum field theory, the electromagnetic force is carried by particles of light called photons. When two electrically charged particles interact, they can exchange virtual photons, which are temporary fluctuations in the electromagnetic field that can be thought of as "packets" of the force. The exchange of virtual photons can be thought of as a kind of "communication" between the particles, in which they exchange information about their charges and the strength of the force between them. This exchange of information is what allows the particles to interact and feel the force of attraction or repulsion. For example, when two electrons are attracted to each other, they can exchange virtual photons to "mediate" their interaction. In this process, one electron emits a virtual photon, which is then absorbed by the other electron. This exchange of a virtual photon causes the two electrons to feel a force of attraction between them. Similarly, when two protons are attracted to each other, they can also exchange virtual photons to mediate their interaction.
When two electrons are attracted towards each other, they create some effects on the electromagnetic field, this disturbance is said 'Virtual Particles'. In fact, virtual particles are not like particles at all but just a disturbance from the effect of real particles.
Let's say you are to push a swing. If you push the swing very hard you can create a lot of disturbance in the rope of the swing, these disturbances can affect the motion of the swing but it dies at some time. This scenario is exactly like the virtual particles, where the disturbance in the swing's rope corresponds to the disturbance in the field. The disturbance is not necessary but it is an effect of the real particle.
Similarly, when energy is given to the electromagnetic field, electrons are produced and when electrons are traveling they can create some disturbances in the field-virtual particles.
Before we go back to Hawking Radiation, we first need to understand some other things like The Information paradox and the second law of thermodynamics. Let's see how black holes were supposed to violate the second law of thermodynamics and how Hawking's Radiation solved this issue permanently.
The Second Law of Thermodynamics:
This law basically states that the total entropy of the universe never decreases, it must increase all the time. Entropy is the measurement of randomness in the body. One example of the second law of thermodynamics is the way that heat flows from hot objects to cold ones. When two objects at different temperatures are brought into contact, heat will flow from the hotter object to the cooler one, until they reach the same temperature. This is because the molecules in the hotter object have more energy, and they transfer some of that energy to the molecules in the cooler object as they collide.
Another example of the second law of thermodynamics is the way that heat engines, such as steam engines, work. Heat engines convert heat into work by moving a piston or other mechanical device, but they are not 100% efficient. Some of the heat that is put into the engine is always lost to the environment, and this loss is a result of the increase in entropy that occurs as the heat flows from the hot part of the engine to the cold part.
TL;DR the entropy (measurement of randomness) should always increase.
How was Black Hole supposed to violate Second Law:
As we know that black holes attract everything and contract them to singularity. If this is true then we can say that the entropy here is decreasing, and we will be certain about the directions. One way in which black holes were thought to potentially violate the second law of thermodynamics is by "sucking in" matter and energy from their surroundings and increasing their mass, while simultaneously decreasing the total entropy of the system. This would occur if the black hole were able to take in matter and energy without increasing its own entropy, which would violate the second law.
Another way in which black holes were thought to potentially violate the second law is by destroying information. According to the principles of quantum mechanics, information about the properties of particles and systems can never be completely destroyed. However, it was thought that when matter falls into a black hole, it is lost forever, and this seemed to contradict the principles of quantum mechanics. This led to the concept of "information loss" in black holes, which seemed to violate the second law.However, this is not true. Even though black holes suck everything the entropy doesn't decrease. Black holes are not closed systems: When matter falls into a black hole, it increases the mass of the black hole, but it also increases the total entropy of the system. The increase in the mass of the black hole is compensated for by the increase in entropy, so the total entropy of the system remains constant or increases.
Hence, the black hole doesn't violate the second law of thermodynamics, and even to prove this thing a little further Hawking made his theory 'The Hawking Radiation' which gave more clues about non-violation.
Let's talk about Hawking Radiation now that we have some clues about Virtual particles and the Second Law of Thermodynamics. Quantum fluctuations happen all the time in space, it creates a pair of particles and anti-particles which then combines and cancels out.
Imagine boiling water,
when we give heat(energy) to the water, the molecules start vibrating and produce bubbles. If you notice clearly, we can see that the bubbles come out and pop out all the time during the boiling process. This is like quantum fluctuation but instead of bubbles, it is the particles that are simultaneously canceled out.
The boiling of water is because of the energy. When water is heated, the molecules gain energy and move around more quickly. As the temperature of the water increases, the molecules move faster and faster, and the water begins to boil. When the water reaches its boiling point, the molecules have enough energy to break free from the surface of the liquid and form bubbles of steam. This is a simple animation of how quantum fluctuations work in empty space. Here, as you can see that when energy is given to the space it creates disturbance like in a wave and produces a pair of particle and anti-particle which then cancels each other. This happens all the time in every part of space even on the surface of black holes.
So now that we know that Quantum Fluctuation happens all the time in space, it must also happen at the edges of the black hole. We are not consulting this process(Q.F) inside the black hole because we don't even know that the laws of Physics will be inside the singularity.
Ordinarily, when QF happens the particles and anti-particles quickly diminish from their opposite charges but when they are near to the black hole, this changes.
Let's say that some QF is happening at the edge of the black hole and it forms a pair of particles and anti-particle. These two oppositely charged parts quickly try to diminish themselves like normal but this time they are attracted by the force of gravity. Remember when I told you that some matters that are outside of the range of the accretion disk can circle and escape the black hole. Similarly, during QF when a particle and its anti-particle form, one of them is attracted by gravity and while the other just circles the black hole and escapes it.
This might break some laws of Physics because here the energy seems to be created, when two particles are canceled out the net energy is 0, thus we are safe. But when QF happens near the black holes, some particles are attracted to the singularity whereas other anti-particles escape the event horizon, this makes the energy some positive value. This paradox can be solved, however, by Hawking's Radiation.
The idea is that pairs of particles can be created near the event horizon, with one particle falling into the black hole while the other escapes. Since the particle that falls into the black hole has negative energy, the escaping particle will have positive energy. This results in a net loss of energy for the black hole, which causes it to slowly evaporate over time.
Hawking's prediction was made using the principles of quantum mechanics and general relativity, and it has since been supported by several theoretical and observational studies. However, the actual process by which Hawking radiation is produced is not well understood, and it is still an active area of research in theoretical physics.
Let's look at some of these details from animation, I will try to make it as simple as possible.
Here as we can see, due to Quantum Fluctuation happening at the edge of the black holes, we see a pair of particle and an antiparticle. One of the particles is attracted by gravity whereas the other barely skips the accretion disk. This kind of violates the 'Conservation of Energy'. However, it does seem like it breaking the major law of physics, but this is when Hawking's Radiation kicked in.
When one of the particle is absorbed by the black hole and another antiparticle escapes gravity, here the black hole loses its mass. Yes, it is correct, black holes slowly lose their mass. To balance the conservation of energy, Stephen Hawking proved that black holes evaporate slowly. They emit some kind of radiation (probably X-ray) which is considered the particle from the quantum fluctuation.
In short, due to the quantum fluctuations happening at the edge of the black hole, when one of the pairs from QF skips the gravitational force of a black hole, then the black hole loses its mass to balance out the energy/entropy. It's crazy to see how nature works in some cases to balance its laws.
No one in their right mind would have thought about how black holes would lose mass and slowly evaporates or how Space and time are literally another dimensions in which gravity is just an effect of matter and energy. This is why I love Physics because you can think of anything and there is a slight probability that no matter how crazy it sounds, it may yet be proven.
How are we sure about Hawking's Radiation?
While it is still not proven physically yet, Hawking's Radiation still holds ground for its mathematical expressions. It is very difficult to detect the radiations emitted by black holes since they are very far from us. This is not the only issue here, we are not certain about the rate of fluctuations that happen near the black hole plus it attracts so many things from different matter, so the rate at which it loses mass is extremely slow. To prove Hawking's Radiation physically, we need to have advanced technology that can detect X-rays from very far away. However, even though we could measure the X-rays we wouldn't be certain if it is coming from a black hole or not; there are so many stars and matter that produce X-rays, so it is very difficult to predict exactly if Hawking's Radiation is true or not. But this is always the situation in Physics: string theory and quantum gravity are all hypotheses that are not yet proven but the reason that they are thought of as 'reliable theories' is that they are supported mathematically and help to explain other laws and solve some paradoxes.
Who knows The multiverse theory is just a hoax to make physics more interesting. What if this life we're living is just a simulation and every goal we've achieved is worthless since we are just a character in a game. The truth is we don't know yet, but we have to move on, there will be amazing discoveries in the future, AI doing our jobs, humans' journey to Mars, colonizing space, and many more. Even if I am writing this blog, there is happening some innovations; physicists, geologists, doctors, and everyone is creating something for this world to make humans' life reliable. We have come to the stage where AI is writing codes and songs, this is a beautiful journey, my friend. Let us not be afraid of the damn future, and think of the amazing things that will happen tomorrow. Let us raise a glass
"To the Future..."
Happy New Year to each and every one of the Science enthusiasts who is reading this. Whether it is 2023 for you or 2024 or even 2050, it doesn't matter, enjoy each day!
Huge Reference from:
Veristasium - Go check their Youtube Videos about Black Holes
Google.com/NASA - Some of the pics of the black holes are from the NASA official site
Wikipedia
The Theory of Everything by Stephen Hawking
ChatGPT - I may have extracted some information, but this blog is 100% original, not AI-generated
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