Parth G | Hawking Paradox FINALLY Resolved? Hairy Black Holes + Information Loss EXPLAINED @ParthGChannel | Uploaded 2 years ago | Updated 9 hours ago
What do hairy black holes have to do with general relativity, quantum mechanics, and information loss?
In this video we start by understanding how black holes behave. They are extremely dense objects, meaning all their mass is packed into a very small region of space. Objects with mass will warp the spacetime around them (according to general relativity), and black holes are dense enough that not even light, the fastest mothing thing in the universe, can escape a black hole once it crosses the event horizon. The spacetime is warped so that anything can only move towards the center of the black hole.
For this reason, we have no way of knowing what happens within a black hole's event horizon. We can only know a small number of basic properties of black holes (mass, charge, angular momentum/spin, radius), but we cannot know things like the mass distribution inside the black hole. This means that from any external observer's perspective, two black holes that were formed of different types of matter, or in different ways, appear identical if they have the same mass, charge, etc. This is known as the no-hair theorem, meaning black holes do not have "hair" on the outside that allows us to know stuff about their insides.
This is problematic because the information about the stuff that made up the black hole, or what is happening inside the black hole, is inaccessible to anyone outside the event horizon. This might not be an issue, as an observer within the event horizon may still be able to access it, so it's there somewhere. However the real problem comes in when we consider Hawking radiation.
Hawking radiation is a quantum mechanical and general relativistic effect, where black holes emit blackbody radiation due to their temperature. Technically speaking, this radiation, in the form of photons, is created a small distance OUTSIDE the event horizon, so nothing is actually leaving the black hole itself. However this Hawking radiation then leaves the black hole, carrying away energy. This results in the black hole losing mass - it effectively becomes smaller.
If Hawking radiation is to exist, this would mean that black holes can eventually disappear once enough Hawking radiation is carried away. And because Hawking radiation only depends on externally known properties of the black hole, this means two black holes with the same initial mass will emit the same Hawking radiation. Thus we cannot know information inside either of the black holes, and if they were to disappear, the information would be lost forever! Where is this information going, and how is it leaving the universe?
This is the Hawking paradox, also known as the Black Hole Information Paradox. For a while scientists suspected we would need some new mysterious physics to explain this, as the answer is not readily apparent in either general relativity or quantum mechanics. However recently some scientists discovered that using a theory of quantum gravity (mixing both quantum mechanics and general relativity), it was possible to actually figure out the internal state of a black hole. This kind of combination is what we expect in the ever-elusive Theory of Everything, or theory of quantum gravity.
This was done by studying the quantum wave function of the black hole, as well as the gravitational field generated by the hole a large distance away. The gravitons (gravity particles) generated by the black hole were shown to be different depending on the wave function of the black hole, which itself depends on the internal properties of the black hole. In other words, it may be possible to measure internal properties of the black hole by measuring its gravitational field far away from it. Or in other words, black holes MIGHT actually have hair, thus resolving the paradox.
In this video, we also look at why we shouldn't get over-excited about this theory yet, as it's just one possible explanation. But it is, at least, a little bit exciting!
Hairy black holes: en.wikipedia.org/wiki/No-hair_theorem
Hawking radiation: en.wikipedia.org/wiki/Hawking_radiation
The research paper in question: journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.111301
Thanks for watching, please do check out my socials here:
Instagram - @parthvlogs
Patreon - patreon.com/parthg
Music Chanel - Parth G's Shenanigans
Merch - https://parth-gs-merch-stand.creator-spring.com/
Here are some affiliate links for things I use! I make a small commission if you make a purchase through these links.
Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL
My Camera: https://amzn.to/2SjZzWq
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Timestamps:
0:00 - Black Hole Basics
2:06 - No-Hair Theorem
4:15 - Hawking Radiation
6:06 - Hawking's Paradox (Black Hole Information Paradox)
6:55 - Cautiously Optimistic
7:45 - Gravitational Fields, Wave Functions, and Gravitons
What do hairy black holes have to do with general relativity, quantum mechanics, and information loss?
In this video we start by understanding how black holes behave. They are extremely dense objects, meaning all their mass is packed into a very small region of space. Objects with mass will warp the spacetime around them (according to general relativity), and black holes are dense enough that not even light, the fastest mothing thing in the universe, can escape a black hole once it crosses the event horizon. The spacetime is warped so that anything can only move towards the center of the black hole.
For this reason, we have no way of knowing what happens within a black hole's event horizon. We can only know a small number of basic properties of black holes (mass, charge, angular momentum/spin, radius), but we cannot know things like the mass distribution inside the black hole. This means that from any external observer's perspective, two black holes that were formed of different types of matter, or in different ways, appear identical if they have the same mass, charge, etc. This is known as the no-hair theorem, meaning black holes do not have "hair" on the outside that allows us to know stuff about their insides.
This is problematic because the information about the stuff that made up the black hole, or what is happening inside the black hole, is inaccessible to anyone outside the event horizon. This might not be an issue, as an observer within the event horizon may still be able to access it, so it's there somewhere. However the real problem comes in when we consider Hawking radiation.
Hawking radiation is a quantum mechanical and general relativistic effect, where black holes emit blackbody radiation due to their temperature. Technically speaking, this radiation, in the form of photons, is created a small distance OUTSIDE the event horizon, so nothing is actually leaving the black hole itself. However this Hawking radiation then leaves the black hole, carrying away energy. This results in the black hole losing mass - it effectively becomes smaller.
If Hawking radiation is to exist, this would mean that black holes can eventually disappear once enough Hawking radiation is carried away. And because Hawking radiation only depends on externally known properties of the black hole, this means two black holes with the same initial mass will emit the same Hawking radiation. Thus we cannot know information inside either of the black holes, and if they were to disappear, the information would be lost forever! Where is this information going, and how is it leaving the universe?
This is the Hawking paradox, also known as the Black Hole Information Paradox. For a while scientists suspected we would need some new mysterious physics to explain this, as the answer is not readily apparent in either general relativity or quantum mechanics. However recently some scientists discovered that using a theory of quantum gravity (mixing both quantum mechanics and general relativity), it was possible to actually figure out the internal state of a black hole. This kind of combination is what we expect in the ever-elusive Theory of Everything, or theory of quantum gravity.
This was done by studying the quantum wave function of the black hole, as well as the gravitational field generated by the hole a large distance away. The gravitons (gravity particles) generated by the black hole were shown to be different depending on the wave function of the black hole, which itself depends on the internal properties of the black hole. In other words, it may be possible to measure internal properties of the black hole by measuring its gravitational field far away from it. Or in other words, black holes MIGHT actually have hair, thus resolving the paradox.
In this video, we also look at why we shouldn't get over-excited about this theory yet, as it's just one possible explanation. But it is, at least, a little bit exciting!
Hairy black holes: en.wikipedia.org/wiki/No-hair_theorem
Hawking radiation: en.wikipedia.org/wiki/Hawking_radiation
The research paper in question: journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.111301
Thanks for watching, please do check out my socials here:
Instagram - @parthvlogs
Patreon - patreon.com/parthg
Music Chanel - Parth G's Shenanigans
Merch - https://parth-gs-merch-stand.creator-spring.com/
Here are some affiliate links for things I use! I make a small commission if you make a purchase through these links.
Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL
My Camera: https://amzn.to/2SjZzWq
ND Filter: https://amzn.to/3qoGwHk
Microphone (Fifine): https://amzn.to/2OwyWvt
Gorillapod: https://amzn.to/3wQ0L2Q
Timestamps:
0:00 - Black Hole Basics
2:06 - No-Hair Theorem
4:15 - Hawking Radiation
6:06 - Hawking's Paradox (Black Hole Information Paradox)
6:55 - Cautiously Optimistic
7:45 - Gravitational Fields, Wave Functions, and Gravitons
