Slashdot Mirror
Hawking Radiation Mimicked In the Lab
Annanag writes *Nothing* escapes a black hole, right? Except 40 years ago Stephen Hawking threw a spanner in the works by suggesting that, courtesy of quantum mechanics, some light particles can actually break free of a black hole's massive pull. Then you have the tantalizing question of whether information can also escape, encoded in that so-called 'Hawking radiation'. The only problem being that no one has ever been able to detect Hawking radiation being emitted from a black hole. BUT a physicist has now come closer than ever before to creating an imitation of a black hole event horizon in the lab, opening up a potential avenue for investigating Hawking radiation and exploring how quantum mechanics and general relativity might be brought together.
who?
Larry already had that in his apartment years ago.
This stuff isn't my strong suit at all, but I'm having a hard time grasping how sound waves can behave like subatomic particles in this way.
Pairs of sound waves pop in and out of existence in a laboratory vacuum, mimicking particle-antiparticle pairs in the vacuum of space.
Sound is a wave through some medium, so how can they pop into existence in a vacuum? Are particles of some kind (and what are they? Hydrogen atoms? Helium?) popping into existence long enough for them to physically interact with one another so a physical wave can propagate from one particle to another before they pop back out of existence, and thus "sound waves" are appearing?
All this is pretty amazing to me, but the amount of complexity involved (using dual event horizons to reflect the waves back and forth to amplify the audio signal because its so weak, etc) sure would leave a lot of room to screw something up along the way. Seems the signal to noise ratio would be pretty bad.
Better known as 318230.
Because of the scale of the experimental setup, it is quite obvious that no gravitational effects are involved. Hence, there is no possibility for this experiment to recreate phenomena at the intersection of quantum mechanics and general relativity. What the Steinbauer does is he replicates a particular model of the black hole. If his setup works, fine, but it doesn't prove a single thing about how black holes behave - because he did not create one.
"Long run is a misleading guide to current affairs. In the long run we are all dead." (John Maynard Keynes)
I mimicked Hawkings outside the lab with my keyboard text. Now turn on your text to speech to the robots voice.
Black holes do not exist
Jean-Pierre Petit
04/2014
ABSTRACT We reconsider classical features of Schwarzschild and Kerr metrics, which are the fundamental basis of the black hole model, through new space and time coordinates which transform the object into a space bridge linking two folds of the [...]
Parer available for download
Dear Scientists, Please stop trying to create black holes. I would prefer not waking up in the middle of some random night feeling a tug on my body and seconds later falling into the aforementioned black hole to my death. Thank you.
The reason physicists can't get there head around black holes is because they don't really exist.
There just physicists favorite "what if?" device.
http://science.slashdot.org/story/14/07/24/172221/black-holes-not-black-after-all-theorize-physicists
http://science.slashdot.org/story/14/01/24/1342228/stephen-hawking-there-are-no-black-holes
You mean a Hawking Hole, right?
Get free satoshi (Bitcoin) and Dogecoins
In all my years of reading and thinking about black holes, one question I've got about HR his how it would actually end up causing the decay of a black hole. From what I understand, HR is the spontaneous creation of matter and anti-matter in space that would normally annihilate itself (allowed by QM theory)--the key difference is that this event can happen at the edge of the event horizon. With some positive probability, the anti-matter will be created within the event horizon radius, but the matter will remain outside and escape. When you look at the whole system then, the anti-matter will annihilate matter within the black hole (causing it to "dissolve") and the matter will remain outside the clutches of the black hole.
I'm sure I'm describing it very simplistically, but I believe my question after that should work for all systems that are analogous:
How is the HR process not symmetric? Whatever would cause the dissolution of the black hole--how would the same process happening in reverse (matter falling into the black hole and anti-matter escaping) not cause equilibrium to be maintained?
Didn't we just decide black holes don't have those?
Because the image of pair production just outside the horizon is... inaccurate. I know it's widely used, but it's not actually a good analogy at all.
If while working on all this stuff they manage to create a worm hole to a near by black hole?
One thing is off in your explanation: it is not anti-matter that falls into the black hole. Anti-matter still has positive net energy (âoeweightâ), so throwing antimatter into a black hole will make it more massive, not less massive. The actual idea is that a of a negative-energy particle (the total energy of the virtual pair is zero, so if one particle becomes real, with positive energy, the other had to have negative net energy) falling in, *not* a matter anti-particle (like a positron). Quoth wikipedia:
Antiparticles should not be confused with virtual particles or virtual antiparticles.
The equilibrium is not maintained because if a virtual particle outside the event horizon becomes real, it will always end up having positive net energy: real negative-energy particles do not exist.
I never did get this... Hawking radiation doesn't "Escape" a black hole. In empty space, there is a constant seething foam of particle-antiparticle pairs that get created all the time. Normally these pairs immediately collide with one another, or their neighbors, and obliterate each other so they are mostly undetectable. With a blackhole you have an event horizon. One side of which is inescapable, the other side is escapable. It stands to reason, that along this line these particle-antiparticle pairs would get created with one inside the horizon and the other outside of it. Resulting in a net increase in the number of particles created. Nothing "Escaped" at all.
The theory is, that the trapped particle falls in... and (basically) annihilates its opposite inside the hole. You have to remember that because it's considered to be a singularity it's properties are measured as a "Whole" meaning that all of the properties of everything past the event horizon are combined. The singularity has 1 mass, 1 angular momentum. 1 charge, etc... Once you're past the event horizon you cannot separate the parts from the whole any longer.
I think there is a drastic difference between doing something, and possibly discovering a means to try and do something. The title of this article is misleading.
The phrases "Mimicked In the Lab" and "potential avenue for investigating" are not the same thing.
Another analogy is a particle at the centre of the black hole getting outside the event horizon by quantum tunelling.
I was never sure if that made sense either.
You missed his question entirely, in fact your post is just restating the middle third of his. His question can be boiled down to "why are anti particles more likely to appear inside the horizon than their particle counterparts? "
Thank you, I can't believe I had to scroll all the way down to find this comment. :/
I call it a Hawking hole.
They aren't. You're confusing particles with energy. The particle and anti-particle pair have a net energy of 0. Any one of the 2 particles would have a certain amount of energy and if you're looking at that one particle, the other, because of quantum mechanics, must have negative energy. A strange concept but it's one of those crazy quantum mechanical things that only work if you're not looking directly at it.
So when the pair pops into existence, and one particle is born inside the event horizon... the other particle can be observed and interact with the universe. Because of this, it must have energy... and because it has energy, it's pair inside the Event Horizon must have negative energy. The particle that escaped, be it matter or anti-matter has energy, so therefor it's unlucky partner must have had negative energy. The net effect is the blackhole loses energy which is given off by these particles.
That you not only know the answer to, but also state that answer was discovered 40 years ago in the very post you are asking the question?
The Kruger Dunning explains most post on
Matter and anti-matter annihilating each other produces energy. That energy remains trapped in the hole, so it's mass is unchanged (energy = mass * lightspeed squared). So whether matter or anti-matter fall into the hole, its mass will grow.
What's happening with Hawking radiation is (AFAIK) that particles are actually ripples in a field - for example, a photon is a ripple in the electromagnetic field, and an electron is a ripple in the "electron field". If these ripples are well-formed waves they're said to be "real" and have measurable quantities, such as energy. Otherwise they're "virtual" particles. That's what's meant when they say electromagnetism works by exchanging virtual photons: charged particles cause disturbances in the electromagnetic field, which affect other charged particles.
Now, quantum mehcanics has a number of paired properties, where both members of the pair can't have an exact value at the same time. Position and momentum are perhaps the most famous such pair, but another is the value and rate of change of a field. That means that no field's value can be permanently zero, because then we'd know both the exact value (0) and exact rate of change (also 0). And because they can't be permanently 0 despite having to average to it, they must ripple randomly, a state of affairs often referred to as "quantum foam". Since particles are ripples in these fields, this process is usually depicted as a pair of virtual particles coming from nowhere, living for a while, and then meeting again and canceling each other out.
An interesting property of these virtual particle pairs is that if they receive at least as much energy as corresponds to the pair's rest mass, for example by being accelerated in a black hole's gravity field, they become "real". That is, random ripple turns into a well-defined wave that's not going to disappear, but is going to continue its existence as a real particle. According to current cosmological theories, this is how all matter originated, with the Big Bang acting as a source of energy. This is also how particle accelerators work: smash a stream of particles together hard, so the energy of the collision makes virtual particles materialize.
So what happens is that if a pair of virtual particles is brought to existence near the even horizon of a hole, one might fall in and the other fly away. The one flying outwards loses energy - it's rising against gravity, after all - but the one falling in gains more than enough to offset that, since it gets pulled harder and harder the farther it goes. So, the pair of particles as a whole gain energy, and if that energy exceeds the pair's rest mass the pair turns into real particles. Since energy must be conserved, it must come from somewhere, and the only available source is the black hole's mass, which is diminished as a result. The falling particle is basically carrying a bill with it, which negates some of the black hole's energy. And since it's the direction of gravity that determines which particle gets the bill, it's always the one falling into the hole, making the process asymmetric.
But then again, the actual math is beyond me, so I could be completely wrong here.
Forget magic. Any technology distinguishable from divine power is insufficiently advanced.
They seem to be trying to create a physical analog to the mathematical theory.
What they are doing is remarkably similar to building an analog computer to perform the computations described in the theory. They have physical objects that have properties similar to the mathematical theory of event horizons.
While this is certainly interesting as a technical piece of work, I doubt you can learn much about event horizons with it. At best it will be another way to perform the computations, at worst it will provide misleading results.
I still don't understand why if you had a cable or a rod or something and you stuck one end past the event horizon why you couldn't pull it back over.
X
Usually support scientific research but not particularly conformable with some types of research being performed on earth. There is a very real possibility the reason we haven't found existence of other intelligent life in the world that their technology wipes them at a certain level of advancement. Mimicking black holes is one of those potential red flags.
The assurance is there is no danger. That the black hole would evaporate before posing a threat. Probably true but the problem is we are taking about stakes that threaten the existence of life on this planet. If physicists knew exactly how everything operated then they would have already figured out the perfect experiment to confirm every physics hypothesis. When there is a missing understanding for the vast majority of the universe's mass and conflicting interpretations of QM obviously there are unknowns. Going "oops" after an experiment in producing micro black holes seems like a rather unpleasant prospect. Scientists tend to be a decent lot but much like some tech support types, they sometimes confuse their above average familiarity with the subject material with the idea that they can't make mistakes. Hubris.
Some experiments would be best reserved for space or other planetary bodies. If we keep taking risks in certain types of physics research, eventually one of those risks will come back and bite us.
This is closer to the actual explanation, but your previous post is just wrong. Annihilation wouldn't do anything to decrease the energy in the black hole, as it doesn't increase or decrease energy of the system, especially when the resulting photons couldn't escape anyway. It comes down to the ability to fling a particle out at the expense of one falling in, which just happens to involve a matter-antimatter pair method, not that one particular type falls in.
You can work out the stress in such a rod and you'll get an infinite value at the horizon. Alternatively, you can work out the force needed to keep an object at constant radius above the event horizon, and it becomes infinite as you approach the event horizon. Another way to think of it, is the material within a rod is held together by electromagnetic interactions, and if photons can't get from atom to the next, there would be nothing to actually hold them together.
There is a generalized conservation of stress-energy-momentum in General Relativity ( you can get a glimpse of it here http://www.preposterousunivers... ).
Essentially, the gravitational field around the black hole is constantly swapping energy with the matter fields around the black hole. We do not know what's happening *in* the black hole, at least not at the very centre, but we are pretty confident about what happens at and outside the horizon. (The AMPS firewalls debate offers up the possibility that semiclassical gravity -- which is what we think happens outside the horizon -- is wrong in some limit. However, it's held up very well under observational tests to date.) However knowing exactly what's on and inside the horizon is not necessary to understand the stress-energy-momentum conservation, because we can see it with other observations at many scales (binary stars, galactic clusters, the metric expansion of space).
Energy donated from the gravitational field of the black hole creates a pair of matter particles. If both are drawn into the black hole, the energy is donated back.
It is exactly equivalent in reverse: high energy in the matter field (from, say, collisions with infalling matter, inverse compton scattering, and so forth) can produce a pair. If both are drawn into the black hole, that energy is donated to the gravitational field.
However, if only one half of the pair stays local and the other escapes to infinity, the local gravitiational field is diminished, whether it's the gravity from inside the event horizon, or very near but outside the horizon.
Likewise, both halves could escape to infinity, again reducing the local gravitational field.
We have good reason to believe that any horizon produces a thermal bath of particles -- Fulling–Davies–Unruh radiation. So right on the horizon there are lots of particles bubbling into existence *because* of the horizon itself. And some amount of that will escape to infinity, reducing the local mass-energy, and thus shrinking the black hole. A retreating horizon produces a greater flux of Unruh radiation, so a shrinking black hole in effect heats up *at the horizon*, which shrinks it further, until it evaporates. Hawking elucidated this process.
For an isolated black hole in various theoretical vacuums, the spectrum of the Hawking radiation is the same as blackbody radiation at a temperature that is entirely determined by the mass-energy of the black hole (or equivalently by the surface area of the horizon).
Stellar black holes and supermassive black holes are unlikely to be isolated, which means that radiation will interact with other matter in the accretion disk and nearby. Indeed, other radiation will be produced within the accretion disk itself, producing e.g. gamma or X rays and particle radiation that are possibly detectable by observatories in our solar system (depends on what gas and dust is between the source and us). When we see such radiation, it's because mass-energy was removed from the black hole system, which shrinks the system. Some *small* amount of that energy will have its origin in the black hole's gravity itself via the stress-energy-momentum conservation law.
"the falling in one gains more than enough to offset that, since it gets pulled harder and harder the farther it goes".
No, and this is one of the parts of the AMPS firewalls puzzle. Both particles are in freefall. One follows a geodesic to infinity, another follows a geodesic around and into the black hole. An accelerometer travelling with either of the two will point to no direction in particular.
Certain observers (e.g. a non-accelerating observer at rest with respect to the black hole and at a significant distance from it) *will* see gravitational redshifting and blueshifting of the particles, but that is not what the particles observe locally.
You are right that if the pair is produced because of the gravitational field of the black hole (there are various proposed mechanisms) than if either or both follow a geodseic out of the black hole system (e.g. to infinity), the black hole system's mass-energy will be reduced.
Hawking radiation is a bit more specific about the origin of the pairs -- they occur because of the presence of a horizon (any horizon), they're thermal, they're photons with a spectrum equivalent to a blackbody radiator with a specific temperature, and that temperature relates exactly to the surface area of the horizon. (For black holes the surface area of the horizon is completely determined by the black hole's mass-energy).