But … but … didn’t these black holes slam into each other long ago, like 3 billion years ago, and the news just hasn’t gotten here yet?
Yes, of course you are correct.
And see here, for two reports on the detection of the oldest galaxy presently known:
It’s about 13.2 billion years old.
Personally, I wonder about 3 significant figures for this difficult measurement.
Indeed, the light which warms us from the Sun left there about 9 minutes ago traveling at a foot per nanosecond.
Not to mention the fact that changes in the gravitational field, that is, in space-time, travel at c.
Thus, the Sun might have vanished a few minutes ago, and the Earth is about to obey Newton’s First Law and head off in a straight line into the Sunless universe.
Here are the introductory paragraphs from that article:
The apocalypse is still on, apparently — at least in a galaxy about 3.5 billion light-years from here.
Last winter, a team of Caltech astronomers reported that two supermassive black holes appeared to be spiraling together toward a cataclysmic collision that could bring down the curtains in that galaxy.
The evidence was a rhythmic flickering from the galaxy’s nucleus, a quasar known as PG 1302-102, which Matthew Graham and his colleagues interpreted as the fatal mating dance of a pair of black holes with a total mass of more than a billion suns. Their merger, the astronomers calculated, could release as much energy as 100 million supernova explosions, mostly in the form of violent ripples in space-time known as gravitational waves that would blow the stars out of that hapless galaxy like leaves off a roof.
Later the astronomers mention the last parsec problem, and I’d like to expand upon this. It has to do with an apparent difficulty getting closer than about a parsec, which is a bit more than 3 light-years. Normally, people wouldn’t use the word close to refer to about as far as the nearest star. But this is astronomy.
Objects interacting through gravitation have a total energy that is the sum of their kinetic energy and their potential energy. KE, of course, is (1/2)mv2, so it is a positive quantity. Physicists consider the PE to be zero when the objects are very far apart. If they are close together, you have to do work on them to get them far apart, if the force between them is attractive. Thus, the PE is negative when they are not infinitely far apart.
If the total energy = KE + PE > 0, then the objects may get back to infinitely far apart. That is, they are not bound together. If the total energy < 0, then the objects cannot make it to infinity without running out of KE. They are bound together.
As the two large galaxies, not bound together, happened to approach one another, their total energy was positive, but in the chaos of the collision they lost energy. Perhaps they tossed millions of stars into inter-galactic space, for example. The massive black holes at their centers also came close together by getting rid of some, immense amounts of energy. The last parsec problem has to do with the fact that it is not obvious to astrophysicists how to get rid of the rest of the energy required for these big guys to splat together.
Well, splat isn’t quite right, since a black hole’s interior is empty except at the center and except for stuff on its way to the center. It’s a splat of space-time itself.
Mighty big picture thinking, and what ever happens has already happened, as you say. The news is on its way, and the researchers guess that we will know in 100,000 years or so.
Another thought: if spooky action at a distance can happen at any scale and distance, is it comforting that we “know” that these black holes gobbled each other up billions of years ago but, no matter how cataclysmic that event was, the universe at large seems pretty much unperturbed by it?>
For one thing, physicists wouldn’t consider this as “spooky action at a distance.” Of course, it is spooky action at a distance, but physicists have two special meanings for that term. It’s original meaning had to do with how objects that were not physically touching could exert forces on each other. It was a criticism of Newton’s universal gravitation that the force acted across empty space. That is, the force was not like, say, billiard balls that influence one another when they touch, but no otherwise. Our modern (a 150 years old) idea is that the partial differential equations describe our force laws. Thus, the laws operate locally. The source of a force influences the space close to it, which influences the space close to it, and so on. These everywhere local influences, however, travel through space-time. Eventually, the local properties of some distant place influence the behavior of an object out there. This is why influences take time to act. These days we would criticize Newton’s Law of Gravitation not for being action at a distance, but for describing instantaneous influences across great distances.
The precise origin of the “spooky” in the famous phrase “spooky action at a distance” is in the Einstein-Podolsky-Rosen paradox, which is a conundrum of quantum mechanics. Proposed as a puzzle for quantum mechanics in the 1930s, the EPR paradox involves pairs of particles created together with certain linked properties, “entangled” is the modern term, that travel apart. Quantum mechanics tells us that certain measurements on one of the particles will influence the results of measurements on the other instantaneously. This would appear to contradict the very strongly supported view that no influence or information can travel faster than the speed of light. Thus, Einstein asserted, there must be a problem with quantum mechanics if it allowed “spooky action at a distance.” As that the EPR paradox and quantum entanglement are not the subjects of this post, I’ll just say that beginning in the 1960s physicists figured out how to transform the EPR paradox from a thought experiment into laboratory tests. Quantum mechanics has, so far, passed all these tests, and the “common sense” ideas of most people, and Einstein’s too, have contradicted the experimental evidence.
I guess that everyone knows that supposedly Einstein didn’t accept quantum mechanics and was left behind by the young new thinkers of the 1920s and 1930s. Actually (in my interpretation of these historical events of which I have no direct knowledge) Einstein made immense contributions to quantum mechanics beginning with the second quantum mechanics paper ever. This was his 1905 photoelectric effect paper. It might have been the second quantum paper, but it was the first in which its author believed his results. Plank, who wrote the first, when he derived his formula for the spectrum of black body radiation, thought, as first, that the chunkiness of the energy he guessed about was just a mathematical fiction. He worked for a time to try to make it smooth again. Einstein also made key contributions to quantum mechanics with papers on low temperature heat capacity (that we’d now call part of solid state physics), particle statistics that differentiate the two great classes of the world’s particles known now as fermions and bosons. The statistics of the latter is known as Bose-Einstein statistics. Also, Einstein made important contributions to the investigation of the interaction of light and matter by calculating the emission and absorption probabilities of light and atoms. These are the Einstein A and B coefficients for spontaneous and stimulated emission, which form the basis for lasers. And other important work that I don’t have at the tip of my fingers at the moment. Any one of these would have been a major life’s work contribution for a normal physicist.
Quantum theory, which we might say is what physicists say when they use words to talk about what the equations are before them, has puzzles, however, because the microscopic world behaves radically differently than the world of ordinary experience. Einstein went to the heart of these puzzles with the EPR paradox, and, in my opinion, it I no shame that 10 or 20 years after his death it turned out that his preferred outcome was not the one that nature chose. I say, “Good work, Albert. Thanks for drawing our attention to this.”
Finally, to your question, I have to contradict your comforting guess that we’d have seen bad effects from the splatting to the two distant super massive black holes, if there had been any. You might just imagine that any bad effects must have occurred after the two black holes merged (or started to merge), so the news of the bad effects would have to arrive here after the news of the merger. The effects travel outward in space no faster than the speed of light, which is also the speed at which disturbances in the gravitational field (that is, in space-time) travel. A gravitational shock wave, say, would travel from the two merging black holes at c. Some of this disturbance is on its way to us. Some, however, blasts a galaxy, a billion light years from the black holes. As that galaxy does who knows what bad thing, the news that this has happened to it will begin traveling in all directions, and some in our direction. I’m afraid that something bad might well be on its way. Well, this sort of thing tends to diminish with distance, at least as fast as 1/r squared, and often faster than this. Thus its not likely to be all that bad for us.