Top 10 Questions on Leonard Susskind's "The Black Hole War

[PaulMurphy]

1. In Leonard Susskind’s “The Black Hole War,” he says that if radiation has a wavelength larger than the event horizon of a black hole, it will bounce off instead of falling in. I've never read this anywhere else. Can anyone here discuss this topic further?

2. Based on how dense the energy and matter was immediately after the big bang, for how long after the big bang was the escape velocity greater than the speed of light, and thus, the entire Universe was inside the event horizon of a black hole?

3. If gravity was a repulsive force at the singularity of the big bang, why is it not repulsive at the singularity of a black hole?

4. How can a singularity be said to rotate when it has no spatial dimensions?

5. Black holes are described as having a mass, but isn’t 100% of the mass in the singularity itself, which has zero volume? If this is the case, then I think 100% of the volume of the black hole inside the event horizon would have no mass.

6. How does matter ever get to the singularity from the event horizon if time slows to a stop at the singularity?

7. What happens as a string gets close enough to a singularity to experience a time gradient severe enough to distort its vibrational wave pattern?

8. Does the speed of light have any relationship to any process that generates electromagnetic radiation? For instance, does the quantum of energy needed to create the longest wavelength radio wave equal the smallest quantum of energy released to place an electron in the lowest energy orbit?

9. Could the speed of light be a property of spacetime rather than of matter and energy?

10. If all forms of life are entropy engines, taking in low entropy energy and giving off high entropy energy and the arrow of time is the direction pointing toward greater entropy, could a living creature’s perception of time be due to their being entropy engines?

 

[BruceW]

2.There was very high density everywhere, so there was nothing to 'escape from'.
5.The singularity doesn't have zero volume. Its just small.
6.Once the singularity has been established, no more matter goes into the singularity (from our perspective).
9.Both.
10. Could be. Or that could be a coincidence.

 

[Drakkith]

1. In Leonard Susskind’s “The Black Hole War,” he says that if radiation has a wavelength larger than the event horizon of a black hole, it will bounce off instead of falling in. I've never read this anywhere else. Can anyone here discuss this topic further?

I've never heard of this, but it does sound plausible to me. The photon would exist over an area of space greater than the diameter of the BH, so it might not fall in. But that's just a guess.

2. Based on how dense the energy and matter was immediately after the big bang, for how long after the big bang was the escape velocity greater than the speed of light, and thus, the entire Universe was inside the event horizon of a black hole?

I'm not sure this makes any sense. The universe as a whole was compressed, so there was no where for the light to "escape" to at any point. The gravitational force should have been the same everywhere at all points of the universe, unlike a black hole with has a gradiant.

3. If gravity was a repulsive force at the singularity of the big bang, why is it not repulsive at the singularity of a black hole?

Who said gravity was a repulsive force?

4. How can a singularity be said to rotate when it has no spatial dimensions?

I'd guess the same way that a point particle such as an electron can have intrinsic spin. But I really don't know.

5. Black holes are described as having a mass, but isn’t 100% of the mass in the singularity itself, which has zero volume? If this is the case, then I think 100% of the volume of the black hole inside the event horizon would have no mass.

You are correct. The singularity has no size, but infite density. Other than mass that is falling towards the singularity inside the event horizon, the BH would be mostly empty. (I think. I'm not an expert on Black Holes)

6. How does matter ever get to the singularity from the event horizon if time slows to a stop at the singularity?

I'm not sure, but I know that the proper time for the infalling mass is finite, meaning that it takes a finite amount of time to fall in from its own frame.

7. What happens as a string gets close enough to a singularity to experience a time gradient severe enough to distort its vibrational wave pattern?

String? As in string theory?

8. Does the speed of light have any relationship to any process that generates electromagnetic radiation? For instance, does the quantum of energy needed to create the longest wavelength radio wave equal the smallest quantum of energy released to place an electron in the lowest energy orbit?

To my knowledge the amount of energy needed to create a photon has no lower limit.

9. Could the speed of light be a property of spacetime rather than of matter and energy?

Your question doesn't make sense. Everything exists within spacetime, so anything that affects one affects the other somehow. Just like how gravity, which is viewed as spacetime being warped, affects everything within the universe.

10. If all forms of life are entropy engines, taking in low entropy energy and giving off high entropy energy and the arrow of time is the direction pointing toward greater entropy, could a living creature’s perception of time be due to their being entropy engines?

No, as even when you have entropy being lowered in a system time still operates in one direction.

 

[DaveC426913]

...I think 100% of the volume of the black hole inside the event horizon would have no mass.

Why? Your logic does not follow.

 

[Drakkith]

Why? Your logic does not follow.

Really? Why not? If the singularity has no volume, then the volume of the space inside the event horizon should be nearly empty, or so I thought.

 

[DaveC426913]

Really? Why not? If the singularity has no volume, then the volume of the space inside the event horizon should be nearly empty, or so I thought.

But why would that affect the mass?

Oh. I see what he's saying. It's flawed logic: If the mass has zero volume, then a larger volume that contains that mass is 100% mass-free. Therefore ... the mass at the centre ... has no mass.


The flaw is that he first grants that a mass could have zero volume, but then goes on to conclude that, if a volume contains that mass, that the mass can't have mass ... why? because it's zero volume.

 

[Drakkith]

But why would that affect the mass?

The mass would be concentrated in the BH in the singularity. There wouldn't be any mass anywhere else. Is that false?

 

[DaveC426913]

The mass would be concentrated in the BH in the singularity. There wouldn't be any mass anywhere else. Is that false?

Sure. That's OK.

I thought he was putting forth a paradox.

 

[Drakkith]

Sure. That's OK.

I thought he was putting forth a paradox.

Oh, ok lol.

 

[PaulMurphy]

Thanks for all the replies. I learned a few things already. Here is some clarification:

3. Who said gravity was a repulsive force?

I read about inflation theory in Brian Greene's new book, The Hidden Reality. There is a whole section about repulsive gravity, the inflaton field and negative pressure. In summary, he said the force that caused the faster than light expansion of spacetime during inflation was repulsive gravity.



5...I think 100% of the volume of the black hole inside the event horizon would have no mass.
Why? Your logic does not follow.

What I was trying to say is that if a singularity really has zero volume and 100% of the black hole's mass is in the singularity, then 100% of the volume of the black hole within the event horizon would be empty space (except for the background noise of virtual particles caused by quantum uncertainty). I'm creating a contradiction on purpose to show that I don't really believe (yet) that all the mass inside the event horizon truly occupies zero volume yet can still directly interact with exterior spacetime via gravity.


7. String? As in string theory?

Yes, again Brian Greene's books. He says that the strings of string theory vibrate in the extra dimensions and based on the given Calabi-Yau shape they vibrate in, the vibrational pattern gives the particle its properties. A string vibrating in one pattern would be an electron, in another pattern a photon, etc.

I'm wondering if one part of the string is in a slower flow rate of time frame of reference than another part, would that cause distortion to the calabi-yau manifold and change the particle's properties? Say it was vibrating as an up quark and as it gets very close to the singularity, part of it would be vibrating in a different flow rate of time than the rest. Does it become a new type of particle?

 

[DaveC426913]

What I was trying to say is that if a singularity really has zero volume and 100% of the black hole's mass is in the singularity, then 100% of the volume of the black hole within the event horizon would be empty space (except for the background noise of virtual particles caused by quantum uncertainty). I'm creating a contradiction on purpose to show that I don't really believe (yet) that all the mass inside the event horizon truly occupies zero volume yet can still directly interact with exterior spacetime via gravity.

But the argument is circular. If you believe that mass cannot occur in zero volume, you don't need to use the convoluted logic to arrive back at the same conclusion.

 

[jtbell]

Paul, trying to discuss ten questions in a single thread is a surefire route to confusion and madness. Questions on different subjects should be in different threads.

Also, most of these questions really belong in other forums than this one (Quantum Physics), IMO. I suggest:

1, 3, 4, 5, 6: Astrophysics
2: Cosmology
7: Beyond the Standard Model
8: Relativity or Quantum Physics
9: Relativity
10: Classical Physics or maybe Philosophy