Interesting physics article:

[ericthecleric]

Fascinating article.

I haven't studied physics since school, so I have to ask. Is anti-matter the same thing as dark matter, or something else? How can anti-matter exist?

[Sharoth]

Anti-matter is NOT the same as dark matter. We have no real idea what dark matter is, but we have a fairly good understanding of anti-matter. Anti-matter is just matter with an opposite charge than normal matter. Antimatter

[Tacticslion]

Sharoth wrote:

Anti-matter is NOT the same as dark matter. We have no real idea what dark matter is, but we have a fairly good understanding of anti-matter. Anti-matter is just matter with an opposite charge than normal matter. Antimatter

This is correct. To add to this, we are extremely (sort of, kind of, -ish, a bit, maybe) certain that dark matter (and dark energy*) are things that do not react with light, at all, making them very hard to understand, and impossible to study much with our normal methods.

* Which may or may not be an "energy" as we typically understand it - it could be one weird old trick, uh, I mean a weird property of space itself.

I'm about to reveal the limit of my physics to everyone that knows this stuff, but there's a major objection to the idea that information (matter) is eliminated when it hits a black hole; meanwhile black holes create radiation, which, eventually, causes the 'hole to evaporate.

Though I know I'm missing something, it always seems bizarre to me that black holes "couldn't" be, you know, eating the (anti-)matter, and spitting it back out as radiation. The thing is, most of our stuff is guesswork beyond the singularity-point Schwarzschild radius, so... it seems reasonable to me. I'm probably missing something pretty basic, though.

[The Sideromancer]

I mean, its entirely guesswork beyond the singularity, since that's where everything we have just throws their proverbial hands in the air and gives up.

[QuidEst]

Protons are big, positive, and make up part of the nucleus (center) of matter atoms. Electrons are small, negative, and make up the shell (they orbit) matter atoms.

Anti-protons are big, negative, and make up part of the nucleus (center) of antimatter atoms. Positrons (anti-electrons) are small, positive, and make up the shell (they orbit) antimatter atoms.

We know a lot about antimatter. We can even make a few atoms’ worth of it, although just making some of those small positrons is much easier. Put a positron plus an electron together, and they attract, and cancel out, turning 100% into energy. Same for a proton and an anti-proton. So here’s the part that’s weird. As far as we can tell, there’s WAY more matter than antimatter (which is very good for us), but the only ways we know to make one makes an equal amount of the other.

[QuidEst]

Dark matter is a big question mark. We can estimate how much stuff there ought to be in the universe based on the rules of gravity and where things seem to have ended up. We can compare that to how much stuff we can see. The two numbers are nowhere near close to each other, even if we count as much “ordinary matter that’s just hard to see this far away” as we can. That difference is dark matter. Imagine something that was heavy, but not much else- it didn’t get in the way of light, or radio waves, or rocks- it just sat there like like an invisible, incorporeal elephant, having mass and adding to the total gravitational pull of the area. That’s one of our best guesses, loosely put.

[ericthecleric]

Thanks for the replies; that's helpful! :)

[QuidEst]

ericthecleric wrote:

Thanks for the replies; that's helpful! :)

Oh, as for how antimatter can exist, there are a couple ways to make it!

The easiest is a certain kind of radioactive decay producing positrons. (The process converts a proton into a neutron, and also spits out something called an electron neutrino, but neutrinos don't do very much at all.)

Another big one is if you shove a whole bunch of energy into one spot, you can produce matter-antimatter pairs. (That's the energy-to-matter conversion of e=mc^2.)

[Sarzael]

Tacticslion wrote:

I'm about to reveal the limit of my physics to everyone that knows this stuff, but there's a major objection to the idea that information (matter) is eliminated when it hits a black hole; meanwhile black holes create radiation, which, eventually, causes the 'hole to evaporate.

Though I know I'm missing something, it always seems bizarre to me that black holes "couldn't" be, you know, eating the (anti-)matter, and spitting it back out as radiation. The thing is, most of our stuff is guesswork beyond the singularity-point Schwarzschild radius, so... it seems reasonable to me. I'm probably missing something pretty basic, though.

The thing is, those radiation particles are results of particle-antiparticle pairs appearing right next to event horizon, antiparticle sinking into black hole and particle "boosting away" from it. So it is not radiation from black hole itself and it cannot carry any information about anything within gravitational radius of a black hole.

[Tacticslion]

So why does the black hole evaporate?

And why is it only at the poles?

[Tacticslion]

Like, that would seem to mean the 'hole evaporates from the antimatter hitting (and annihilating with) the matter that comprises the 'hole - does that mean that it eventually explodes with radiation when the mass is reduced?

(I'm uncertain if the trapped light would produce enough "effective mass" to maintain the black hole as a singularity, or not.)

[John Napier 698]

Tacticslion wrote:

So why does the black hole evaporate?

And why is it only at the poles?

Black holes evaporate through the release of Hawking Radiation.

[John Woodford]

QuidEst wrote:

Dark matter is a big question mark. We can estimate how much stuff there ought to be in the universe based on the rules of gravity and where things seem to have ended up. We can compare that to how much stuff we can see. The two numbers are nowhere near close to each other, even if we count as much “ordinary matter that’s just hard to see this far away” as we can. That difference is dark matter. Imagine something that was heavy, but not much else- it didn’t get in the way of light, or radio waves, or rocks- it just sat there like like an invisible, incorporeal elephant, having mass and adding to the total gravitational pull of the area. That’s one of our best guesses, loosely put.

IIRC, there was an observation of gravitational lensing from what is believed to be a dark matter halo around a couple of colliding galaxies; anyone know whether that observation has held up?

[Tacticslion]

John Napier 698 wrote:

Tacticslion wrote:

So why does the black hole evaporate?

And why is it only at the poles?

Black holes evaporate through the release of Hawking Radiation.

Yes. I actually already covered that, though.

The hawking radiation must come from somewhere.

My point is: what is the mechanism by which the Hawking radiation works? What is it that causes the thing to evaporate?

We don't know.

There are visualizations, but there's no real understanding of the actual mechanisms (at least according to the article; which, you know, it's Wikipedia - awesome, but not always perfectly clear or dependable).

And that's what I'm getting at. Why does it work that way?

[Tacticslion]

John Woodford wrote:

IIRC, there was an observation of gravitational lensing from what is believed to be a dark matter halo around a couple of colliding galaxies; anyone know whether that observation has held up?

Gravitational Lensing (so, yes)

More about Dark Matter (and what we don't know) - easier to digest, but doesn't talk about lensing much

[John Napier 698]

Tacticslion wrote:

John Napier 698 wrote:

Tacticslion wrote:

So why does the black hole evaporate?

And why is it only at the poles?

Black holes evaporate through the release of Hawking Radiation.

Yes. I actually already covered that, though.

The hawking radiation must come from somewhere.

My point is: what is the mechanism by which the Hawking radiation works? What is it that causes the thing to evaporate?

We don't know.

There are visualizations, but there's no real understanding of the actual mechanisms (at least according to the article; which, you know, it's Wikipedia - awesome, but not always perfectly clear or dependable).

And that's what I'm getting at. Why does it work that way?

Well, last I heard, Hawking radiation involves the creation of pairs of virtual particles at the Event Horizon. Gravity pulls one of those particles into the Event Horizon, and the Conservation of Momentum kicks the other particle away. Thus, the Singularity loses gravitational energy through the creation of virtual particles and the absorption of half of them. So, over time, the radius of the Event Horizon shrinks closer to the Singularity, causing the evaporation to proceed at an even more energetic rate. Eventually, the Singularity loses so much mass that the Event Horizon physically touches the Singularity. Then all remaining mass evaporates in an infinitesimal period of time.

[Gisher]

John Napier 698 wrote:

Tacticslion wrote:

John Napier 698 wrote:

Tacticslion wrote:

So why does the black hole evaporate?

And why is it only at the poles?

Black holes evaporate through the release of Hawking Radiation.

Yes. I actually already covered that, though.

The hawking radiation must come from somewhere.

My point is: what is the mechanism by which the Hawking radiation works? What is it that causes the thing to evaporate?

We don't know.

There are visualizations, but there's no real understanding of the actual mechanisms (at least according to the article; which, you know, it's Wikipedia - awesome, but not always perfectly clear or dependable).

And that's what I'm getting at. Why does it work that way?

Well, last I heard, Hawking radiation involves the creation of pairs of virtual particles at the Event Horizon. Gravity pulls one of those particles into the Event Horizon, and the Conservation of Momentum kicks the other particle away. Thus, the Singularity loses gravitational energy through the creation of virtual particles and the absorption of half of them. So, over time, the radius of the Event Horizon shrinks closer to the Singularity, causing the evaporation to proceed at an even more energetic rate. Eventually, the Singularity loses so much mass that the Event Horizon physically touches the Singularity. Then all remaining mass evaporates in an infinitesimal period of time.

That is the standard interpretation. When I was getting a physics degree at U.C. Berkeley (I think it was in '88) Hawking gave a lecture where he offered an alternative explanation. The virtual particle pair could form inside the event horizon and then one particle could escape by momentarily exceeding the speed of light courtesy of the uncertainty principle. I've never seen this explanation anywhere else so it's possible that this model didn't pan out. I recall the math being very clever, though - as you'd expect.

[John Napier 698]

Could it also be that particles can quantum-mechanically tunnel through the space between the Singularity and the Event Horizon? Especially at a late stage in the evaporation process?

[Drejk]

John Napier 698 wrote:

Could it also be that particles can quantum-mechanically tunnel through the space between the Singularity and the Event Horizon? Especially at a late stage in the evaporation process?

I vaguely recall that the quantum tunneling might be the explanation for the way they escaped the event horizon in that case.

[Rednal]

So, basically, what we're saying is "Black holes are weird". ^^

[Freehold DM]

Can I use this to help destroy math books in their current form?

[I'm Hiding In Your Closet]

Freehold DM wrote:

Can I use this to help destroy math books in their current form?

Well, if it's true that black holes can destroy information, thennnnn....

[John Napier 698]

Rednal wrote:

So, basically, what we're saying is "Black holes are weird". ^^

Anything that involves quantum mechanics is weird.

[The Sideromancer]

John Napier 698 wrote:

Rednal wrote:

So, basically, what we're saying is "Black holes are weird". ^^

Anything that involves quantum mechanics is weird.

As somebody taking a course in quantum, I treat it like game mechanics. Which is to say, **** common sense, if it says it goes through the wall, it goes through the wall.

Black holes are extra weird, since they're a mix of relativity and quantum, and those two don't get along.

[Pink Dragon]

Antimatter is well-known both physically and theoretically, as pointed out above. Antimatter is more of a misnomer, since 'antimatter' particles are the same as corresponding 'matter' particles except for having the opposite charge.

Dark matter is more speculative and is thought to exist only because we see gravitational effects that are unexplainable with our current understanding of the amount of matter in the universe. This is more of a problem with our understanding of the universe than anything else.

Physicist have lots of math to try to explain things. The math and physical observations aren't necessarily coterminous, and are often contradictory. Further, the different maths are often contradictory.

At the forefront of physics, uncertainty rules (and in many cases uncertainty is a physical rule). Even established physics is prone to being overturned, or at least revised, just look at Ptolemy's epicycles or Newtonian physics.

This is how science works in general, not just physics.

[Irontruth]

Tacticslion wrote:

And why is it only at the poles?

No expert, but I would guess it's doe to rotational velocity. The particles have enough velocity to stay beyond the event horizon, but until they reach the pole, they don't have the angular momentum to break orbit. I'm sure someone smarter has the real explanation though.

[John Napier 698]

Think of the force of Gravity as the Hypotenuse of a triangle, and the escape velocity as the base, along the X-axis. As the angle from the Black Hole's equator increases, the Escape velocity decreases according to H X Cos( Theta ). This means that as Theta approaches 90 degrees the Escape Velocity approaches zero ( Cos( Theta ) ).