Curious about Black hole information paradox

In summary: What if one is far away and one is just inside of the event horizon? They would not be able to see each other.
  • #1
Akshay_Anti
62
0
Hi!

I am not much of astrophysicist or something but read something about Black hole information paradox in a book. Could anybody please explain me what is the meaning of term and why does it happen?

P.S. Please include Hawking's radiation as well

Thank you in advance
 
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  • #2
You know how before quantum mechanics people used to think that science may allow them to describe the world perfectly - that is, if they could measure all the properties of all the particles in the universe, then they could calculate its exact state both in the past and in the future.
Granted, in its pure form it was more of a popular belief than a scientific one, as any scientist worth his money should be able to recognise the actual impossibility of performing those calculations for anything but the simplest of systems(e.g.easy for two bodies bound gravitationally, insanely hard for three bodies).
Still, in principle it is true: the information a system has at any given moment encodes its past and future interactions.
I'm told that it works even for quantum mechanics, in some way.

Now, if you drop an object into a black hole, of all the information it carried with itself, like mass, chemical and elemental composition, temperature, etc., only mass, electrical charge and angular momentum are retained by the black hole(which is nicely called a "no-hair theorem"). All the rest is irrevocably lost.
So if you measure the properties of a black hole, you are unable to tell e.g.what exactly fell into it, or what kind of star's collapse produced it. All you can say is that it must've had such and such mass, charge and angular momentum.

Note that this is a paradox not in the sense that it produces logically conflicting results, but in the sense of contradicting a widely held belief about something. Here, that the information should be retained.


As for the Hawking Radiation: You know that no radiation can escape black hole, right? There's this boundary called event horizon, which marks the distance from the centre of the black hole under which the escape velocity is higher than the speed of light.
So whatever falls into that boundary should stay there forever, meaning also that black holes should only increase their masses, having no means to lose it.
Hawking came up with a way for black holes to radiate in spite of this. The idea is based on another idea, that the vacuum is full of particle-antiparticle pairs constantly appearing out of nowhere and annihilating an instant later. They pop up, fly a minuscle amount of distance and bump into each other dissapearing again.
Now, imagine these two particles appearing in such a way, that one of them flies just above the event horizon, while the other one just below. The one below is sucked in and cannot escape, while the one above now has no pair to annihilate with, AND is able to fly away from the black hole due to being above the event horizon.
Since the two particles appeared out of nothing, their total energy must be 0. Since the one flying away definitely carries some energy with it(mass, kinetic energy), then the one falling in must have negative energy. Thus it falling in causes the black hole to lose mass, which looks from the outside as if the black hole were radiating like a black body of certain temperature.
 
  • #3
I have a question. Suppose there are two spacecraft s, one near the event horizon and other at quite a distance...

Now, how would they see each other?
 
  • #4
Akshay_Anti said:
I have a question. Suppose there are two spacecraft s, one near the event horizon and other at quite a distance...

Now, how would they see each other?

When you decide to derail a thread, even you own, with a totally unrelated question, you should start a new thread.
 
  • #5
No, I read that this info paradox would have affect on how both see each other, That's why, continued in same thread...
 
  • #6
Akshay_Anti said:
I have a question. Suppose there are two spacecraft s, one near the event horizon and other at quite a distance...

Now, how would they see each other?

As long as the spacecraft hasn't passed the event horizon yet then there is no reason they cannot see each other. You will have to deal with blueshift and redshift, along with other factors thanks to the very high gravity, but if you have the right detectors they can see each other.
 
  • #7
Akshay_Anti said:
No, I read that this info paradox would have affect on how both see each other, That's why, continued in same thread...

That is not correct. As Drakkith said, outside the EH, the info paradox has nothing to do with anything.
 
  • #8
phinds said:
That is not correct. As Drakkith said, outside the EH, the info paradox has nothing to do with anything.

what if one is far away and one is just inside of EH?
 
  • #9
Akshay_Anti said:
what if one is far away and one is just inside of EH?

The one inside the EH is effectively removed from our universe (except for having added to the gravity of the BH). The one outside will see the other as an increasingly red shifted image at the EH but this is NOT part of the information paradox as far as I am aware. The one just inside the EH will continue to see the one outside since the one inside is not aware of the EH.
 

1. What is the Black hole information paradox?

The Black hole information paradox is a theoretical physics problem that arises when trying to reconcile the laws of quantum mechanics with those of general relativity. It refers to the question of what happens to the information that falls into a black hole, as according to the laws of quantum mechanics, information cannot be destroyed.

2. How does the Black hole information paradox challenge our current understanding of physics?

The Black hole information paradox challenges our current understanding of physics by highlighting the discrepancies between the laws of quantum mechanics and general relativity. It suggests that our current theories may not be able to fully explain the behavior of black holes and that a new theory may be needed to fully understand them.

3. What are some proposed solutions to the Black hole information paradox?

There are several proposed solutions to the Black hole information paradox, including the "firewall" hypothesis, which suggests that information is destroyed at the event horizon of a black hole, and the "information is preserved" hypothesis, which suggests that information is somehow encoded on the surface of the black hole.

4. Has the Black hole information paradox been solved?

No, the Black hole information paradox has not been definitively solved. While there are proposed solutions, there is currently no widely accepted explanation that fully resolves the paradox. The search for a solution is ongoing and is an active area of research in theoretical physics.

5. How does the study of the Black hole information paradox contribute to our understanding of the universe?

Studying the Black hole information paradox allows us to explore the boundaries of our current understanding of physics and the universe. It challenges us to think critically and creatively about the fundamental laws that govern our universe, and the search for a solution can lead to new discoveries and advancements in our understanding of the universe.

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