Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Thursday, November 17, 2022

A black hole's warm glow

Once again I was sent a link by my buddy Andrew Butters, of the wonderful Potato Chip Math, who is not only a great writer but has a keen eye for a cool science article.

The link was to a story in Science Alert, and was titled, "Scientists Created a Black Hole in the Lab, and Then It Started To Glow," by Michelle Starr.  But before I tell you what the gist is, I have to bring up a peevish complaint about the headline (which may not have been Starr's fault; many times the headlines aren't written by the journalist herself, so I'm not jumping to blaming her for it).  The researchers, as you will see, did not "create a black hole;" what they did was create something that models some of the behavior of a black hole.  Which is cool enough, but doesn't have the cachet that black holes have, so Science Alert apparently thought they needed to jazz things up.  The headline is wildly misleading; no massive stars were destroyed in the course of this experiment.

Of course, this is not going to stop people from reading only the headline and then posting hysterical screeds about how those Mad Scientists Are Trying To Destroy Us All and undoubtedly tying in CERN, HAARP, the Illuminati, and Reptilian Aliens From Zeta Reticuli.

You know how it goes.

Anyhow, back to reality.  What the scientists really did was pretty amazing, and may give us some inroads into figuring out one of the biggest puzzles in physics; why theoretical physicists have been unable to reconcile the equations of quantum mechanics and those of relativity.  When they attempt to accommodate gravitational effects on the scale of the very small, the equations "blow up" -- they result in infinities -- usually a sign that something is very wrong about our understanding.

The reason black holes play into this question is that in the extraordinary gravitational field at the event horizon (the "point of no return," where the space is so strongly curved that even light can't escape), there is a quantum effect that becomes important on the macroscopic scale.  It's called Hawking radiation, after Stephen Hawking (who first proposed it), and deserves some closer attention.

 To start with, empty space isn't empty.  There is an inherent energy in space called zero-point energy or vacuum energy, and it is possible for this energy to be "borrowed" to produce particle-antiparticle pairs (such as an electron and a positron).  There's a catch, though; the pairs always recollide (in a minuscule amount of time, the upper limit of which is determined by the uncertainty principle).  So the pairs pop into existence and right out again, creating continuous tiny, extremely short-lived ripples in the fabric of space.  Not enough for anyone even to notice.

Well, unless you're near the event horizon of a black hole.

[Image is in the Public Domain]

The huge gravitational field at the event horizon means that vacuum energy is much higher, and pair production happens at a much greater rate.  And because of that boundary, sometimes one member of a pair falls into the event horizon, while the other one doesn't.  At that point, the survivor radiates out into space -- taking a little of the black hole's mass/energy along with it.

That's the Hawking radiation.  What it implies is that black holes don't last forever -- eventually they evaporate, finally exploding in a burst of gamma rays.

The problem has been that the Hawking radiation is impossible to study experimentally; we're (fortunately) not near any black holes, at least so far as we know, and the faint signature of the radiation would be lost in the general white noise of the universe.  But now -- and this is where we get to the current research -- a team led by Lotte Mertens of the University of Amsterdam has developed a model that simulates this behavior, and found that just like the real thing, it emits radiation exactly the way Hawking predicted (this is the "it started to glow" in the headline).

What they did was to lock together a chain of atoms that provided a path for electrons to move, and by fine-tuning the rate at which this happened, they created a simulated event horizon that caused some of the electrons' wave-like behavior to vanish completely.  The result was an increase in thermal radiation that matched the Hawking model precisely.

Why this is significant is that it could provide a way to study the quantum effects of gravity in the lab, something that has been impossible before now.  It's not like we can hop a spacecraft and fly to a black hole (which would be inadvisable anyhow).  So this fascinating experiment might be the first step toward one of the prime goals of physicists -- finding a way to unify the quantum and gravitational models.

So even if they didn't "create a black hole in the lab," the whole thing is still pretty freakin' cool.


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