Cover photo
Dan Thompson
Lives in Austin, TX
3,547 followers|792,982 views


Dan Thompson

Shared publicly  - 
Today’s #SaturdayScenes   comes from a book I’m editing before handing off to +Karen Conlin for the real edits.  Here, Hell Bent’s protagonist Alice Koufax goes to visit her brother Paul for a little help tracking down some information.

Paul lived on the north side of town near Distraction Gate.  It was a good neighborhood, and it was packed with analysts from the financial markets who commuted daily into Faeburgh.  It was one of the ironies of gate locations that they all commuted through one of the most difficult sections of Faeburgh I had ever visited.  Going through Distraction Gate is a little like being a dog at squeak-toy factory run by squirrels.  If you let it get to you, you will go mad chasing after one thing and the next.  The fact that my brother strolls through it twice a day should give you some insight into why he did so much better in school than I did.

He and Margaret had a nice three bedroom house with a good yard just a few blocks off 279, and their lot backed onto a few acres of wooded hillside.  It was the perfect setting for raising a family, which is exactly what they were planning.  Of course, Mom liked Margaret and had no problems with Paul marrying a full human.  Paul had taken her side in the divorce, and after that, he could do no wrong.  

Unlike me.

I texted him before I left the parking garage at the paper.  “In your neighborhood, stopping by briefly.”  Rush hour had come and gone while I had been talking with Max, so it was only going to take me twenty minutes to get over there.  Technically that was breaking our rule about the sibling drop-in, but it had gotten a little lax on his end after the first year of marriage.  I was still dating, so I stood firm on the thirty-minute rule.  I felt the buzz of his response when I was doing seventy on the highway.  Even if I had wanted to check, it was tucked away in my pocket underneath the coveralls, so I simply assumed it was a yes.

I hit a bit of traffic towards the end, but it was not long before I was ringing his doorbell.  Margaret answered and invited me in.  “We’ve already finished dinner, but I could heat up the leftovers if you’d like.  It’s my pot roast.”

It was very tempting, but I declined.  “If weren’t on my bike, I’d ask to take it home.”  A nasty pothole had once sent her lasagna leftovers flying into a police cruiser’s windshield.  That had been enough to nix any repeat attempt.

She showed me to Paul’s study where he sat at his computer.  “Just a sec, Alice.”  

I slumped down in the easy chair.  From the look of the spreadsheets, he had clearly brought some work home with him.  Finance was big over in Faeburgh, so much so that Pittsburgh was starting to rival Chicago as the nation’s second largest banking hub.  When you have genuine precognition at your disposal, trading on stock futures or commodity markets takes on a completely different flavor.  Of course, when the firm across the street has it too, it gets even messier.  Is that vision of tomorrow’s market accurate, or is it a vision based on the intent of the other guy? And is his intent real, or is that merely a deception meant to throw your analysts off?  Paul calls it an endless game of countermeasure and counter-countermeasure.  I would say throw the whole thing out, but the firms that had not kept up with it were crushed back in the eighties.

Eventually, I saw the tension release from his shoulders, and he pushed back from the desk.  “You know, I got a funny call from Mom today.”

Shit.  “Really?  What about?”

He turned to face me.  “That she got you out of trouble and that I shouldn’t help you get back into it.”

“Gee thanks, Mother.”

He sighed.  “You know she means well.”

“She always does.  It doesn’t mean she’s right.”

“Granted, but she said you got mixed up in some bad magic, something about a cursed box.”

“Yes, but I wasn’t going to keep it.  I’m not that stupid, Paul.”

“I didn’t say you were, and Mom didn’t either.”

Sparring with Paul was not nearly as bad as with Mother, but it could be almost as frustrating.  “So that’s it.  You’re not going to help me?”

“I didn’t say that, Alice.  For starters, I don’t even know what help I can give you.  Mom says she already destroyed this box of yours.”

“It’s not mine,” I protested.  “Never mind, it doesn’t matter who it belongs to at this point.  I just need to know who made it.”

“That would be easy enough if you still had it.  Even Mom might have been able to figure it out if she had the time, but without it, I don’t know where to start.”

I nodded.  “I know, but I had it in a shielded case for a while, and I still have the case.”

“Was that here or over in Evanelle?”  Paul, of course, always used the proper names.

“Here mostly, but it was still in the case over there for maybe half an hour.  Even through the shielding, it should have been drawing at least some power.”

He looked back at his desk for a moment.  “You might have something there.  It’s not much, but it could be worth checking out.”

“Yeah, but who?  It’s not like I can ask Mother.”

“No, I know a guy over in Lumia.  I used to work with him.”

“Used to?”

“He left under something of a cloud.  We had a billion dollar deal go south, and the rumor was he fouled it on purpose.”  He started writing on a post-it note.  “The last I heard he’d started something like a private eye shop.”  He handed me the note: V. Wallace, corner of Remorse and Longing.

“Do you trust him?”

He shrugged.  “I didn’t believed the rumors, but he never refuted them either.”

“That’s not exactly a resounding endorsement.”

“No, but it’s what I have, and it’s certainly more than Mom would have wanted you to get.”

I nodded.  “Okay, thanks.”

“It’s what big brothers are for.”

“I had lunch with Dad yesterday.”

He did a good job of hiding it, but Paul stiffened immediately.  “Good for you.”

“I just know he’s looking forward to having a grandson.  Maybe you could go cigar shopping for the delivery.”

He smiled politely.  “I appreciate what you’re trying to do, Alice, but if Dad really wants to talk to me, he knows how to find me.”

I let it go.  I was not going to solve the feud this week.  I held up Paul’s note.  “Thanks again.”

“You be careful, and let me know if you need anything else.”

I stopped by the nursery to say good night to Margaret.  She was sitting in the rocker listening to some mathematical mix band from Faeburgh.  Mozart for babies had long since been replaced by fae musicians who really knew their numbers.  I leaned in for a quick hug and got under way.  

If you’re a writer and want to play along, post a scene from your own work and tag it with #saturdayscenes    .  Read more about it in the Saturday Scenes community:
walter ngutshane's profile photo
wow wat a beautiful place
Add a comment...

Dan Thompson

Shared publicly  - 
Who enforces the safety regulations?

I've got some comment in a story about whatever state or city organization would enforce safety regulations/codes, e.g. require railings at the edge of an elevation drop-off.  But I can't think of what that organization would be.  I used OSHA in my draft, but that's really about workplace safety.  

Any ideas what this would be?  "Department of Public Safety" tends to be law enforcement, i.e. state police.  I'm thinking more like inspectors and lawyers.

FWIW, the story takes place in #pittsburgh  if anyone there knows the local organization that would enforce it.

#writing   #amediting  
Ronda Reed's profile photoStanley Morris's profile photoShawn Conlin (Wulfric)'s profile photoDan Thompson's profile photo
Thanks all.  For this particular case, I think the "Inspector from the Pittsburgh Public Works Department" is what I'll go with.  It sounds good, and as it turns out, it actually exists:
Add a comment...

Dan Thompson

Shared publicly  - 
It's a major award!

#ChristmasStory   #LegLamp  
CK Wylde's profile photo
OH Good Lord lol
+Maugan Ra 
Add a comment...

Dan Thompson

Shared publicly  - 
Constructing a hexagonal cake knife!

It's a weird one, but I kind of want one.  I just don' have a place to store it.
Add a comment...

Dan Thompson

Shared publicly  - 

Some folks set up a live-action first-person-shooter with a head-mounted camera and a guy walking through the level, and then set it up on chat-roulette to let random people control the POV character.
(h/t +Brooke Johnson )
Jon Porobil (Jon Eric)'s profile photoEll Meadow's profile photoCornelius Windpepper's profile photo
Someone ^^doesnt know fiction from reality.
Go away
Add a comment...
Have him in circles
3,547 people
Kevin Novak's profile photo
JW Arlock's profile photo
Paige E. Roberts's profile photo
ドラえもん For You's profile photo
dhl fernado Muller's profile photo
Michael Robertson's profile photo
M cherubic's profile photo
The Scotia Academy's profile photo
BEATRICE RIGHTON's profile photo

Dan Thompson

Shared publicly  - 
Twin Giants

A supermassive black hole lurks in the center of our galaxy. But two supermassive black holes lurk in some galaxies.

Since most galaxies contain a black hole in their center, and galaxies have been known to collide, it’s thought that supermassive binary black holes could be relatively common in the universe. We know of some that exist, but they are difficult to confirm. But new research in the Astrophysical Journal has found a supermassive binary in the heart of a quasar.

Quasars are extremely bright sources of energy, powered by the superheated material (the accretion disk) near a black hole. They are so luminous that it’s impossible to resolve a supermassive binary directly. But a close binary black hole would clear out the region between the black holes, leaving a gap in the surrounding material. This gap would lower the overall temperature of the accretion disk, and that means less ultraviolet light should be emitted by the quasar. In this work, the team compared the visible and ultraviolet spectrum of a quasar known as Markarian 231. They found a weaker ultraviolet spectrum, just as expected for a supermassive binary.

What’s great about this research is that it allows us to find supermassive binary black holes by looking at the spectra of quasars. So it’s quite likely that the method could be used to find many more of these twin giants.

Paper: Chang-Shuo Yan et al. A Probable Milli-parsec Supermassive Binary Black Hole in the Nearest Quasar Mrk 231. ApJ 809 117 (2015)
A supermassive black hole lurks in the center of our galaxy. But two supermassive black holes lurk in some galaxies.
29 comments on original post
Add a comment...

Dan Thompson

Shared publicly  - 

There's a game called Robocraft where you try to destroy your enemy's "protonium reactors".   These are imaginary devices powered by imaginary "protonium crystals".  But I think reality is cooler than any fantasy, so I'm not interested in that crap.  I'm interested in actual protonium!

Protonium is a blend of matter and antimatter.   It's a kind of exotic atom made of a proton and an antiproton.  A proton is positively charged, so its antiparticle, the antiproton, is negatively charged.  Opposite charges attract, so a proton and an antiproton can orbit each other.  That gives protonium.

A proton and an electron can also orbit each other, and that's called hydrogen.  But there are a few big differences between hydrogen and protonium.

First, hydrogen lasts forever, but protonium does not.  When they meet, the proton and antiproton annihilate each other.  How long does it take for this to happen?  It depends on how they're orbiting each other.  

In both hydrogen and protonium, various orbits are possible.  Particles are really waves, so these orbits are really different wave patterns, like different ways a trampoline can wiggle up and down.   These patterns are called orbitals.

Orbitals are labelled by numbers called quantum numbers.  If a hydrogen atom isn't spinning at all, it will be spherically symmetric.  Then you just need one number, cleverly called n, to say what its wave pattern looks like.  

The picture here shows the orbital with n = 30.   It has 30 wiggles as you go from the center outwards.  It's really 3-dimensional and round, but the picture shows a circular slice.  The height of the wave at some point says how likely you are to find the electron there.  So, the electron is most likely to be in the orange region.  It's very unlikely to be right in the middle, where the proton sits.

The same math works for protonium!  There's another big difference to keep in mind: the proton and antiproton have the same mass, so they both orbit each other.  But we can track just one of them, moving around their shared center of mass.  Then protonium works a lot like hydrogen.  You get spherically symmetric orbitals, one for each choice of that number called n.

So: if you can make protonium in a orbital where n = 30, it's unlikely for the two protons to meet each other.  Gradually your protonium will emit light and jump to orbitals with lower n, which have less energy.  And eventually the proton and antiproton will meet... and annihilate in a flash of light.

How long does this take?  For n = 30, about 1 microsecond.  And if you make protonium with n = 50, it lasts about 10 microseconds.  

That doesn't sound long, but in particle physics it counts as a pretty long time.  Probably not long enough to make protonium crystals, though!

Protonium was first made around 1989.  Around 2006 people made a lot of it using the Antiproton Decelerator at CERN.  This is just one of the many cool gadgets they keep near the Swiss-French border.  

You see, to create antimatter you need to smash particles at each other at almost the speed of light - so the antiparticles usually shoot out really fast.  It takes serious cleverness to slow them down and catch them without letting them bump into matter and annihilate.

Once they managed to do this, they caught the antiprotons in a Penning trap.  This holds charged particles using magnetic and electric fields.  Then they cooled the antiprotons - slowed them even more - by letting them interact with a cold gas of electrons.  Then they mixed in some protons.  And they got protonium - enough to really study it!  

The folks at CERN have also made antihydrogen, which is the antiparticle of an electron orbiting an antiproton.  And they've made antiprotonic helium, which is an antiproton orbiting a helium atom with one electron removed!   The antiproton acts a bit like the missing electron, except that it's 1836 times heavier, so it must orbit much closer to the helium nucleus.  

There are even wackier forms of matter in the works - or at least, in the dreams of theoretical physicists.  But that's another story for another day.

Here's the 2008 paper about protonium:

• N. Zurlo, M. Amoretti, C. Amsler, G. Bonomi, C. Carraro, C. L. Cesar, M. Charlton, M. Doser, A. Fontana, R. Funakoshi, P. Genova, R. S. Hayano, L. V. Jorgensen, A. Kellerbauer, V. Lagomarsino, R. Landua, E. Lodi Rizzini, M. Macri, N. Madsen, G. Manuzio, D. Mitchard, P. Montagna, L. G. Posada, H. Pruys, C. Regenfus, A. Rotondi, G. Testera, D. P. Van der Werf, A. Variola, L. Venturelli and Y. Yamazaki, Production of slow protonium in vacuum, Hyperfine Interactions 172 (2006), 97-105.  Available for free at

The child in me thinks it's really cool that there's an abbreviation for protonium, Pn, just like a normal element.

Puzzle 1: about how big is protonium in its n = 1 orbital, compared to hydrogen in its n = 1 orbital?  I've given you all the numbers you need to estimate this, though not all the necessary background in physics.  

In Puzzle 1 you're supposed to assume protonium in its n = 1 state is held together by the attraction of opposite charges, just like hydrogen.  But is that true?  If the proton and antiproton are too close, they'll interact a lot via the strong force!

Puzzle 2: The radius of hydrogen in its n = 1 state is about 50,000 femtometers, while the radius of a proton is about 1 femtometer.  Using your answer to Puzzle 1, compare the radius of protonium in its n = 1 orbital to the radius of a proton.

If protonium is a lot bigger than a proton, it's probably held together mostly in the same way as hydrogen: by the electromagnetic force.  

#spnetwork #arXiv :0801.3193 #protonium #particlePhysics
78 comments on original post
Jeff Montondon's profile photoDan Thompson's profile photoBill Kemp's profile photo
Indeed, for me, the economy is the draw.  I haven't dug deeply into EVE yet, but before I started backing away from WoW, I reached the gold cap of a million gold, almost entirely via the marketplace.
Add a comment...

Dan Thompson

Shared publicly  - 
A better use for a drone

On the same day I'm seeing articles about taser-armed drones, this seems like a better (and equally shocking) use of a drone: to deliver an AED to a caller anywhere in a 2km radius* in a minute or less.

*(Note: the article says it can deliver "to a patient within 12 square km radius in less than a minute", which doesn't actually make sense, i.e. 12 square km is an area, radius is a distance.  12km radius in one minute would require speeds of about 450mph.  I suspect it's a 2km radius equaling about 12 square km.)
During emergency situation when someone needs medical attention, every second counts. Alec Momont, a Dutch industrial designer, has made an attempt to add drone
Louis Doggett's profile photoBill Kemp's profile photo
Now that is a good idea. 
Add a comment...

Dan Thompson

Shared publicly  - 
Toplessness is great... because the women want it.

My life frequently takes me to places when nudity or partial nudity is allowed.  In fact, my big annual campout allows for this, and while there is some full nudity of both genders, mostly what I see is women enjoying the freedom and safety of going topless outside in welcoming social environment.

I'll admit that the first five or six women I see like this summon that typical male reaction from me, the (hopefully) internal voice that shouts BOOBIES!  After that, it fades quickly.

So by the second or third day, my real enjoyment of these topless ladies is less about getting to see the naughty bits and more about picking up on their happiness at getting to do what they want to be doing!  If there's any way to improve on the beauty of women's breasts, it's by having the women who own them to be happy.  

As I leave the event, I'm always on the lookout for that last topless woman, not to catch one last pair of ta-tas, but to fix in my mind that view of a happy woman free of the rules our male-dominated society has put on her.

So, I'm all for this kind of protest, not for the enjoyable scenery, but because it's one more step towards having my day-to-day world filled with happier women.
New Hampshire beach overrun by topless protesters as gawking men miss the point
Hundreds of bare-breasted women are expected to converge on a popular New Hampshire beach on Sunday to push for greater acceptance of topless sunbathing, much to the consternation of some local residents and officials. The event at Hampton Beach w
1 comment on original post
Penax Purfuver's profile photoIda Barber's profile photo
I could not agree more.  One of the things I enjoy about that particular outdoor event, as well as another that I attend more or less regularly, is people in general, and women in particular, enjoying being free to be as clothed or unclothed as they feel most comfortable.  When a woman is topless or naked around me, I feel very trusted and honored, in a way, and my enjoyment comes much more from that than from the sight of a topless/naked woman.

I'm very much in favor of getting rid of the social taboo against women displaying breasts in public.  If men going topless is socially acceptable, then it's unfair to women to restrict the same freedom for them.

And who knows?  Make it commonplace enough, and the gawking phenomenon could become a thing of the past..
Add a comment...

Dan Thompson

Shared publicly  - 
As is often the case, Yonatun's commentary (on Trump in this case) is more insightful than the article he links to.  Trump's jokes were only ever funny to those who are comfortable with oppression and the side of it that they're on.
This article interests me most for what it misses. 

The body of this article -- which is well-written and worth reading, if you care about the subject -- is about how it's suddenly become evident that Trump's loudly touted and not particularly covert brand of racism, isolationism, and xenophobia isn't just harmless and funny, after two of his followers beat a homeless man into the hospital for being Latino and then praised Trump's speeches while they were being arrested. 

But the interesting thing they miss is hidden in plain sight, right in the headline. For Trump to have stopped being funny, he had to have been funny in the first place. And that joke only ever worked for people with a certain kind of privilege.

Donald Trump has never been subtle about his views. While his hair and his general egomania may be clownish, he was always showing these things off while preaching about how we need to crack down on Latinos, Blacks, immigrants, the Chinese, whoever he's on about on any particular day. He was doing this while calling for mass deportations of tens of millions of people, closing borders, engaging in ludicrously heavy-handed "negotiations" with other countries, and so on. And this has been working: Trump's popularity is because there are people who wonder, "well, why not?" and there is someone out there advocating solutions which sound (a) simple, (b) brutal, and (c) based on beating up people whom they don't see as part of their own society, from whom they can simply "take back" their power. (Although, as these other groups never actually had any such power, what's really meant here is "take")

It is only possible to see that as a joke if you have never had a reason to fear ethnic violence. But the US has just as long and bloody a history of ethnic violence as it has a history. Nothing Trump is suggesting is new; you could have heard it 150 years ago from the Know-Nothing Party, or 100 years ago from the more political branches of the Klan, or 50 years ago from the John Birch Society, each with their own variants.

Nor is it a coincidence that Trump is having these successes in the midst of Black Lives Matter, or in the aftermath of GamerGate; there are powerful movements afoot in our society where groups that were previously excluded are demanding their fair share of the floor, and powerful counter-movements of people who suddenly feel that the one thing they had of their own -- complete dominance of some spaces -- is suddenly being taken away. Trump is a natural mouthpiece for these groups, and he's quite good at it.

(There's some question about whether Trump came out openly in support of GamerGate a few weeks ago, or whether this was just a rogue autoresponder that he let stand, but I would by no means be surprised if he were to say something about it at some point; the complaints of GamerGate align surprisingly well with his rhetoric)

And anyone who watches these issues knows that there is profound violence immediately on deck in all of them. GamerGate was awash in death threats, and a few actual attempts. Black Lives Matter was born in the wake of shootings, and the rate of violence by whites (and especially police) against black youth in this country has hardly decreased. 

You can see another version of this in the part of the Republican press which is highly anti-Trump, not least because Trump is completely disconnected from the party's main political organs. Consider this article by Ben Domenech from The Federalist, which is quite far to the right but unconnected with Trump: The essential meat of the article is that the party has underestimated Trump's appeal, and in order to curb his lunatic candidacy, the Republican Party should find a better way to express his ideas and so pull his followers back into the mainstream.

And what are these ideas? "White identity politics." Note that the article does not fear that these become part of the Republican platform; it fears that they will become such a large part that they overwhelm the rest of the platform, and so these need to be addressed in a careful way. But there's nothing wrong with pulling them in, Domenech says: "'Identity politics for white people' is not the same thing as 'racism,' nor are the people who advocate for it necessarily racist."

Pro tip: "identity politics based on racial categories" is actually the dictionary definition of racism, and "identity politics for white people" is the prototype example of the category. Domenech's article isn't about rejecting Trump's racism: it's about finding more socially acceptable ways to express it, so that it can be folded into the party mainstream without taking it over.

For those wondering about Trump from the outside, I can give a simple explanation of his politics: Trump is a classical European far-right party leader. This is why he seems a bit exotic by recent American standards: especially since the 1980's, the American far right has been dominated by the "theological" far right, a very distinctly American political movement which focuses on making the country explicitly into a Fundamentalist Christian country. Trump, although he speaks to a similar (and overlapping) group of people, isn't talking about religion at all; instead, you'll find his politics very similar to that of European far-right politicians, of the sort who like to put "National" in their party names.

On the European spectrum, Trump falls somewhat to the right of Jean-Marie le Pen, perhaps a shade left of the Golden Dawn, and somewhat more populist than Jobbik. If we were running in a parliamentary, rather than presidential, system, he would currently be at the head of a far-right party that was polling in the high teens, and press coverage would be worried about how many seats he would get and whether he would be able to force a coalition to join him. In the US system, he's instead at the head of a far-right wing of a party, and the question is whether he will be able to force the party to adopt his policies wholesale to avoid electoral defeat next year.

So that's the secret thing which this headline hides: Trump was only ever funny if you had never had a reason to be aware of, or to fear, ethnic or sexual violence tacitly supported by the state. 

If you've ever had to be aware of that before, Trump was never a joke.

h/t to +Lauren Weinstein for pointing out the Federalist article.
Win or lose, Trump's campaign threatens to unleash the Great American Stupid
237 comments on original post
Dan Higdon's profile photoDan Thompson's profile photoBill Kemp's profile photoJeffrey Gipson's profile photo
Yes, I think the closest he got to the F and N words was when he decribed something to the Europeans as the kind of party that likes to put National in their name -- different N word, but it was a short trip to get to 1933 for me.
Add a comment...

Dan Thompson

Shared publicly  - 
An enlightening trip down the black rabbit hole of gravity.
How Does Gravity Escape a Black Hole?

Here’s the deal: nothing can travel faster than light. A black hole traps everything including light. So how does gravity escape a black hole? It’s a great question, and a perfectly reasonable one given most people’s understanding of gravity. The answer is that gravity doesn’t work the way you probably think it does.

The most common way to think of gravity is as a force between two masses. For example, the Earth exerts a gravitational force on the Moon, and the Moon pulls back on the Earth in return. This “force model” of gravity is what Newton used to develop his law of universal gravity, which stood as the definite theory of gravity until the early 1900s, and is still used to this day. But built into this model of gravity are some assumptions that we can explore by playing the “what if?” game.

Suppose we had a universe with a single mass. Imagine empty space extending as far as you like, with a single mass in the center (which we’ll call Bob). Would such a mass have gravity? If gravity is a force of one object on another object, then the answer would be no. There’s no other mass for Bob to pull on, so there’s no gravitational force. If we add another mass to our universe (call this one Alice), then Bob and Alice would each exert a force on each other, and gravity would exist. But gravity would only exist between Bob and Alice, and nowhere else in our empty universe.

One of the problems with this force model is that it requires masses to exert forces on other masses across empty space. This “action at a distance” problem was resolved in part by Pierre-Simon Laplace in the early 1800s. His idea was that a mass must reach out to other masses with some kind of energy, which he called a field. Other masses would sense this field as a force acting upon them. So if we again imagine our Bob mass in a lonely universe, we would say that Bob has a gravitational field surrounding it, even if there were no other masses in the universe. This eliminates the need for action-at-a-distance, because when we put our Alice mass into the universe, it simply detects whatever gravitational field is at its location, and experiences a force. We know the gravitational field is due to Bob some distance away, but Alice simply knows there is a gravitational field at its location.

Both the force model and field model of Newtonian gravity give the same predictions, so experimentally there’s no real way to distinguish one from the other. However fields are often an easier concept to work with mathematically, and fields are also used to describe things like electricity and magnetism, so we generally think of Newtonian gravity as a field.

But this raises another question. Suppose in our Bob and Alice universe we suddenly shift Bob’s position. How long will it take for Alice to recognize the change? In other words, if we change the position of Bob, at what speed does the change propagate through the gravitational field? When Laplace looked at this idea he found that changes in a gravitational field had to happen instantly. The “speed of gravity” would have to be infinite. For example, if gravity travelled at the speed of light, the Earth would try to orbit the point where the Sun was 8.3 minutes ago (the time it takes light to travel from the Sun to Earth). As a result, Earth’s orbit would become unstable over time.

At the time, the idea of gravity acting at infinite speed wasn’t seen as a problem. In fact it was used as an argument against alternative gravity ideas proposed at the time. But in the early 1900s Einstein developed his special theory of relativity, which (among other things) required that nothing could travel faster than light. If that’s the case, then there’s something wrong with our theory of gravity. By 1915 Einstein had developed a new model of gravity known as general relativity, which satisfied both Newton’s gravitational model and special relativity.

Decay of a pulsar orbit compared to general relativity (dotted line).
According to theory, for example, when two large masses such as neutron stars orbit each other, they should produce gravitational waves that radiate away from them. These gravitational waves should travel at the speed of light. There have been experimental attempts to detect such gravitational waves, but they have been unsuccessful so far. We have, however, found indirect evidence of gravitational waves. By observing a binary pulsar, we have observed its orbit decay slightly over time. This orbital decay is due to the fact that gravitational waves carry energy away from the system. The rate of this decay matches the prediction of general relativity perfectly. Since this rate of decay depends crucially on the speed of gravitational waves, this is also indirect confirmation that gravitational waves move at the speed of light.

But if gravity moves at the speed of light, doesn’t that mean that planetary orbits should be unstable? Actually, no. When Laplace studied finite-speed gravity, he considered only the effect of the speed of gravity, which is what leads to his result, but in special and general relativity, the finite speed of light leads to other effects, such as time dilation due to relative motion, and the apparent change of mass due to relative motion. Mathematically these effects arise because of a property known as Poincaré invariance. Because of this invariance, the time delay of gravity and the velocity dependent effects of time and mass cancel out, so that effectively masses are attracted to where a mass is. This canceling effect means that for orbital motion it is as if gravity acts instantly.

But wait a minute, how can a gravitational field have a finite speed and act instantly at the same time? A gravitational field can’t, but in general relativity gravity is not an energy field.

Since long before Newton, it was generally assumed that objects and energy fields interacted in space at particular times. In this way, space and time can be seen as a background against which things happen. Space and time were seen as a cosmic grid against which anything could be measured. In developing special relativity, Einstein found that space and time couldn’t be an absolute background. In Newton’s view, two events seen to occur at the same time will be seen to be simultaneous for all observers. But Einstein found that the constancy of light required this concept of “now” to be relative. Different observers moving at different speeds will disagree on the order of events. Rather than a fixed background, space and time is a relation between events that depends upon where and when the observer is.

This principle carried forward into Einstein’s theory of gravity. In general relativity gravity is not an energy field. Instead, mass distorts the relations between space and time. If we go back to our earlier example, if we place mass Bob in an empty universe, the relations of space and time around it are distorted. When we place mass Alice nearby, the distortion of spacetime around it means that moves toward mass Bob. It looks as if Alice is being pulled toward Bob by a force, but it’s actually due to the fact that spacetime is distorted.

As physicist John Wheeler once said, “Spacetime tells matter how to move; matter tells spacetime how to curve.”

This is how gravity can seem to act instantly while gravitational waves seem to travel at the speed of light. Gravity isn’t something that travels through space and time. Gravity is space and time.

A black hole is an extreme distortion of space and time due to a very dense mass. Such a spacetime distortion can prevent light and matter from ever escaping. But the spacetime distortion is also gravity. It doesn’t need to escape the black hole, because it is the black hole.

That’s the thing about science. Sometimes a simple question will pull you toward an unexpected answer.
Here's the deal: nothing can travel faster than light. A black hole traps everything including light. So how does gravity escape a black hole?
78 comments on original post
Add a comment...
Dan's Collections
Have him in circles
3,547 people
Kevin Novak's profile photo
JW Arlock's profile photo
Paige E. Roberts's profile photo
ドラえもん For You's profile photo
dhl fernado Muller's profile photo
Michael Robertson's profile photo
M cherubic's profile photo
The Scotia Academy's profile photo
BEATRICE RIGHTON's profile photo
I write fiction. I used to program for a living, and I probably still could, but for now I write fiction.
Basic Information
Writer, programmer, artist, dude
Father of three, programmer, writer, etc.  I do weird stuff with my brain for fun and profit. :)

You can see my blog here:

And my books:

For my programming, I did 18 years working on Computer Aided Design programs, everything from add-ons to being on the core graphics team for AutoCAD.  These days I'm still doing a little consulting and some personal explorations with genetic algorithms.

I've been writing off and on since I was eleven, but I've been doing a lot more of it in the last 5 years.

I also have special needs kids, and I've spent a lot of my time on them for the last few years.
Bragging rights
Had a startup, sold it, written a few books, survived twins (so far), have done more strange things than most, but nearly as many as I'd like to.
Map of the places this user has livedMap of the places this user has livedMap of the places this user has lived
Austin, TX