Hi and welcome back! Today, Science News shared a fascinating story about black holes. Way back in the 1970s, Stephen Hawking and Jacob Bekenstein theorized that black holes can’t decrease in size over time. He called this theory the ‘area law.’ Ever since, physicists have been talking about this theory. And recently, someone figured out a way to test it — and the area law held firm. Today, Lord Snow Presides over how people figure out what’s objectively true — and thus, sift true ideas from false ones.
The Area Law of Black Holes.
Entropy refers to the inevitable increase in disorder, randomness, and uncertainty in a system. The system can’t use entropy-affected parts to do its work. It’s like white noise on the radio: too much of it, and you can’t hear the music you want. An outside force can impose more order on the system through what physicists call work. (Or work can reduce the size of the system, which decreases entropy too.) Without work, though, entropy cannot decrease.
Entropy affects pretty much everything: cells in our bodies, waves carrying information, molecules, stars, and yes, black holes. It’s a measurement of the second law of thermodynamics, which says that when energy changes from one form to another in a closed system (meaning a system without any order imposed on it from outside), entropy increases. And entropy will increase until any differences in the system are all evened out, meaning the system is all the same — especially in terms of its temperature.
Back in the 1970s, a pair of theoretical physicists — Stephen Hawking and Jacob Bekenstein — predicted that entropy in black holes doesn’t increase with volume, only with surface area. They called this surprising prediction the area law scaling of entropy. And it was, and is still, a big freaking deal.
See, if a black hole absorbs matter, it gains more mass. That gain increases its surface area. However, that new matter also makes the black hole spin more. And that decreases its surface area. The area law just says that in black holes, those decreases in size due to spin can’t ever overtake gains in size made from absorbing additional matter. It also says that black holes’ size depends on their surface area, not their volume.
Thus, black holes can’t ever decrease in size. They can only get bigger. Their heightened spin will never be able to overtake any additional mass they absorb.
Playing Footsie With Black Holes and Helium Balloons.
There’s also a volume law, and that’s what we normies usually see in the real world. Like if you take a box full of documents, then double the size of the box, you’ll be able to fit twice the amount of documents in it — and thus twice the amount of information. That’s the volume law, and it’s how everyday life works. But black holes and quantum mechanics work very differently, we’ve found. They operate by area law rules instead.
Scientists have been studying this area law prediction for years now. They’ve found that area law plays a lot of footsie with entropy, general relativity, and the second law of thermodynamics, and it extends way past just black holes. However, it was really hard to test the idea in real-world conditions. We were able to test it in simplified or artificial models, but it wasn’t the same.
In 2017, some scientists in Waterloo were able to actually demonstrate area law in “a real quantum fluid” for the first time.
First, they supercooled condensed helium to 2 degrees Kelvin. (That’s -456F, or -271C.) When helium gets that cold, it becomes a superfluid. Its atoms move around with no friction. Then, they measured how those helium atoms interacted with each other. They found that the atoms got entangled with each other across a specific spherical boundary. The size of that sphere and how its atoms behaved depended on area law, like black holes, rather than volume law, like that document box.
One physicist thinks that this 2017 finding could eventually lead toward a quantum theory of gravity and advances in quantum computing (which does a lot with entanglement).
And Now, Black Holes.
In this recent experiment, astrophysicists at MIT studied ripples in spacetime that two black holes stirred up as they began to merge. If area law is true, then the scientists expected to be able to add the respective areas of the two original black holes’ event horizons, and have that at least match the event horizon of the newly-merged black hole (if not be larger).
And that’s what happened.
These astrophysicists got their ripple data from a 2015 experiment done by researchers with LIGO (Advanced Laser Interferometer Gravitational-Wave Observatory). That LIGO experiment was the very first time that we’d ever actually measured and observed gravitational waves. These particular waves were rippling around two black holes that were colliding more than 750 million light-years away from Earth.
These two black holes were so incredibly heavy that their mass pulled them together — and they dented the fabric of spacetime. As that fabric got all churned up, they emitted gravity waves, which don’t travel through space like regular waves do. Rather, what the black holes set off were actual vibrations of spacetime. Those vibrations, once they start, go everywhere, in all directions, at the speed of light.
In 2015, then, LIGO caught sight of those ripples in the fabric of spacetime.
So for the 2021 experiment, scientists examined LIGO’s 2015 data. They measured the surface areas of those two black holes in two different time periods — before and after the merger. And they found that the surface area of the newly-merged black hole was greater than that of the two original black holes.
So they confirmed area law with, they say, a 95% confidence level. That’s huge.
Testing Our Ideas in the Real World.
That writeup in Science News ends by saying that scientists are testing these theories all the time to find out if they’re true or false. They’re clearly okay with either being the case.
If they find quantum mechanics and black holes both play by the rules of general relativity, great: then they can start working on improvements to their theories.
If they find that black holes fail to live up to any of the rules of general relativity, also great: then they can start looking for the theory that better explains how they behave.
In fact, the paper ends with a quote from one of the scientists who worked on this 2021 experiment:
So physicists tend to be grumpy about the enduring success of general relativity, [Will] Farr says. “We’re like, ‘aw, it was right again.’”
They almost want to be wrong, because that means some huge new advances coming up on the horizon.
And the moment I read that quote is the precise moment that this story landed on our dance card for the day.
I found myself thrilling to that whole idea of being wrong as a good thing, an exciting thing, a thing someone might look forward to experiencing.
The Many Glorious and Transcendent Virtues of Being Wrong.
Years ago, I used to be so scared of being proven wrong. In my old (authoritarian) crowd, if someone got discovered to be wrong, that meant they were vulnerable to attack — and inevitably, yes, they got attacked. But in science, it’s okay if something turns out to be wrong. Just be honest about it, then learn and move forward, and keep growing afterward, always.
That’s how it should be.
We should be testing our ideas against what we can observe and measure. Then, we can modify our ideas according to what reality says about them. If we turn out to be flat-out wrong, then fine: we can start looking for the truth.
Indeed, we should want to be proven wrong by reality. At such times, we have a sudden vast potential to grow in the truth, to discard false ideas, to expand our knowledge, and to add to the existing knowledge-base of humanity.
So today, Lord Snow Presides over the glorious excitement of being wrong, and also the exact reason why wingnuts hate and dread the scientific method like they do.
NEXT UP: We begin our examination of what the earliest known Christians thought about Hell — and how the idea quickly evolved. See you tomorrow!
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About Lord Snow Presides (LSP)
Lord Snow Presides is our off-topic weekly chat series. Lord Snow was my very sweet white cat. He actually knew quite a bit. Though he’s passed on, he now presides over a suggested topic for the day. Of course, please feel free to chime in with anything on your mind: there’s no official topic on these days. We especially welcome pet pictures!